Truncus Arteriosus
Truncus arteriosus is a congenital heart defect, typically diagnosed in newborns, in which a single great vessel arises from the heart instead of a separate aorta and pulmonary artery, resulting in mixed oxygenated and deoxygenated blood entering the systemic and pulmonary circulations.
Truncus Arteriosus in Paediatrics
Truncus arteriosus (TA) — also known as persistent truncus arteriosus or common arterial trunk — is a congenital heart defect in which a single great arterial trunk arises from the base of the heart, overriding the ventricular septum, and gives rise to the systemic, pulmonary, and coronary circulations [1][2][3].
Breaking down the name:
- "Truncus" = trunk (Latin) — referring to the single common arterial trunk
- "Arteriosus" = arterial — referring to the great artery
In normal cardiac development, the embryonic truncus arteriosus divides (via septation of the conotruncal region) into two separate great arteries: the aorta and the pulmonary artery. In this condition, that septation fails to occur, leaving one undivided trunk. A ventricular septal defect (VSD) is almost always present (the truncal valve sits astride the VSD), and the pulmonary arteries arise directly from this common trunk rather than from a separate right ventricular outflow tract [1][2].
Key Conceptual Point
Truncus arteriosus is a common-mixing lesion: oxygenated blood from the pulmonary veins and deoxygenated blood from the systemic veins mix at the ventricular level (through the obligatory VSD) and are ejected into the single trunk. This results in both cyanosis AND congestive heart failure — a hallmark of common-mixing conditions.
- Incidence: 6–10 per 100,000 live births [2]
- Accounts for ~2% of all congenital heart disease (CHD) [2]
- Accounts for ~4% of all critical CHD — i.e., disproportionately represented among life-threatening neonatal heart defects [2]
- No significant sex predilection (roughly equal M:F)
- Without surgical intervention, >80% mortality within the first year of life (most deaths from intractable heart failure and pulmonary hypertension)
Associations
- DiGeorge syndrome (22q11.2 deletion) — truncus arteriosus is one of the hallmark conotruncal anomalies associated with DiGeorge syndrome [2][4][5]
- Up to 35% of infants with truncus arteriosus carry a 22q11.2 microdeletion
- The CATCH-22 mnemonic (see below) captures the spectrum
- C = Cardiac defect (truncus arteriosus, type B interrupted aortic arch, PA with VSD)
- A = Abnormal facies (upslanting/downslanting palpebral fissures, bulbous nose, low-set posteriorly rotated ears, micrognathia)
- T = Thymic hypoplasia / T-cell deficit → immunodeficiency
- C = Cleft palate
- H = Hypocalcaemia due to hypoparathyroidism
- Other associations: right aortic arch (present in ~30% of TA patients), interrupted aortic arch (especially type B — between left carotid and left subclavian arteries, seen in ~10–15% of TA), truncal valve abnormalities (stenosis or regurgitation), aberrant subclavian artery
High Yield – DiGeorge and Conotruncal Defects
Any neonate presenting with a conotruncal cardiac anomaly (truncus arteriosus, interrupted aortic arch type B, tetralogy of Fallot, pulmonary atresia with VSD) should be screened for 22q11.2 deletion with FISH or chromosomal microarray. Also check serum calcium and lymphocyte subsets.
3. Anatomy and Embryological Basis
During weeks 3–8 of embryonic development, the heart develops from a simple tube into a four-chambered structure:
- The conotruncal region is the outflow tract of the primitive heart tube.
- Neural crest cells migrate from the pharyngeal arches (3rd, 4th, 6th) into the conotruncal ridges/swellings.
- These ridges grow and spiral toward each other, eventually fusing to form the aorticopulmonary septum, which divides the single truncus into:
- The aorta (from the left 4th aortic arch)
- The pulmonary artery (from the left 6th aortic arch)
- Simultaneously, the conoventricular septum (infundibular/conal septum) closes, separating the left ventricular outflow tract (LVOT) from the right ventricular outflow tract (RVOT) and contributing to closure of the membranous VSD.
Failure of septation of the conotruncal region — specifically failure of the aorticopulmonary septum to form — results in:
- A single arterial trunk with a single semilunar (truncal) valve that overrides the ventricular septum
- An obligatory VSD (conoventricular type) — because the infundibular septum, which normally contributes to VSD closure, does not form properly
- Pulmonary arteries arising from the common trunk (rather than having their own outflow tract)
The neural crest cell contribution explains the strong association with DiGeorge syndrome — 22q11.2 deletion disrupts neural crest migration and differentiation, leading to defective conotruncal development (as well as thymic/parathyroid hypoplasia from 3rd and 4th pharyngeal pouch maldevelopment) [4][5].
- The truncal valve typically has 3 cusps (in ~60–70% of cases), but can be:
- Bicuspid (~10%)
- Quadricuspid (~20–25%)
- Rarely pentacuspid
- Valve cusps may be thickened, dysplastic, or mal-coapting → leading to truncal valve regurgitation (in ~50%) and/or truncal valve stenosis
- Truncal valve abnormalities are clinically important because they increase perioperative morbidity and mortality [2]
| Aetiological Factor | Details |
|---|---|
| Genetic – 22q11.2 deletion (DiGeorge/VCFS) | Most important association; ~35% of TA cases; screening mandatory; autosomal dominant in familial cases but most are de novo [4][5] |
| Other chromosomal | Rare associations with trisomy 21, trisomy 18 |
| Single-gene disorders | TBX1 gene (within the 22q11.2 region) is the critical gene for conotruncal and pharyngeal arch development |
| Maternal diabetes | Maternal pregestational diabetes mellitus increases risk of conotruncal defects |
| Maternal teratogens | Retinoic acid exposure (isotretinoin), alcohol |
| Multifactorial/sporadic | Many cases have no identifiable genetic syndrome |
In Hong Kong, the incidence of CHD overall is comparable to global figures (~8–10 per 1,000 live births). The relatively high prevalence of consanguinity is not a major factor in Hong Kong, but advanced maternal age and increasing survival of preterm infants make recognition of critical CHD important. Universal pulse oximetry screening for critical CHD in newborns is increasingly adopted.
5. Classification
The most widely used classification is the Van Praagh classification and the historical Collett and Edwards classification:
Based on the origin of the pulmonary arteries from the trunk:
| Type | Description | Frequency |
|---|---|---|
| Type I | A short main pulmonary artery (MPA) segment arises from the trunk and then bifurcates into left and right PAs | ~60% (most common) |
| Type II | Left and right PAs arise separately but adjacently from the posterior aspect of the trunk (no MPA segment) | ~20% |
| Type III | Left and right PAs arise separately and distantly from the lateral aspects of the trunk | ~10% |
| Type IV | No identifiable PAs from the trunk — pulmonary blood supply via major aortopulmonary collateral arteries (MAPCAs) from the descending aorta | Now reclassified as pulmonary atresia with VSD (not true truncus arteriosus) |
| Type | Description |
|---|---|
| Type A1 | MPA segment present, then bifurcates (= Collett & Edwards Type I) |
| Type A2 | Both PAs arise directly from trunk (no MPA) — either close together or separately (= C&E Types II and III combined) |
| Type A3 | One PA absent — that lung supplied by collaterals or a PDA; rare |
| Type A4 | Truncus arteriosus with interrupted aortic arch or coarctation (important surgically) |
- "A" indicates a VSD is present (almost always the case)
- "B" would indicate an intact ventricular septum (exceedingly rare)
Exam High Yield – Classification
For exam purposes, remember that Type I (A1) is the most common (~60%), that Type IV of Collett and Edwards is no longer considered true truncus arteriosus (it is pulmonary atresia with VSD), and that Type A4 (TA with interrupted aortic arch) has special surgical implications and is strongly associated with 22q11.2 deletion.
6. Pathophysiology
Understanding the haemodynamics of truncus arteriosus is critical because it explains every clinical feature.
Both ventricles eject into a single common trunk through the obligatory VSD [1][2][3]:
-
Obligatory mixing at the ventricular/truncal level: Oxygenated blood (from pulmonary veins → LA → LV) and deoxygenated blood (from systemic veins → RA → RV) mix freely through the large VSD and are ejected into the single trunk.
-
Distribution of cardiac output between the pulmonary and systemic circulations depends on the relative vascular resistances:
- Systemic vascular resistance (SVR) vs Pulmonary vascular resistance (PVR)
- In the newborn, PVR is still relatively high → some balance between pulmonary and systemic flow
- As PVR falls postnatally (over the first days to weeks) → pulmonary blood flow increases dramatically (because the PAs are connected directly to the high-pressure trunk at systemic pressure)
-
Result: Torrential pulmonary blood flow (massively increased Qp:Qs ratio) → pulmonary overcirculation
Key pathophysiological consequences:
| Consequence | Mechanism |
|---|---|
| Mild cyanosis | Obligatory mixing of oxygenated and deoxygenated blood at the truncal level; SpO₂ typically 85–93% |
| Congestive heart failure | Torrential pulmonary blood flow (as PVR drops) → massive pulmonary venous return → LV volume overload; RV also exposed to systemic pressure → RV pressure overload |
| Bounding/wide pulse pressure | Diastolic runoff from the trunk into the low-resistance pulmonary vascular bed (similar mechanism to PDA or aortic regurgitation) [2] |
| Pulmonary hypertension | PA directly connected to systemic-pressure trunk → chronic exposure → pulmonary arteriolar remodelling → if untreated, irreversible pulmonary hypertension (Eisenmenger) develops early (by 3–6 months of age) |
| Coronary insufficiency | Diastolic runoff to PA bed lowers diastolic pressure in the trunk → decreased coronary perfusion pressure (coronary "steal") → risk of myocardial ischaemia |
| Truncal valve dysfunction | Dysplastic/abnormal valve → regurgitation adds further volume load; stenosis adds pressure load |
Why Does Truncus Arteriosus Cause Both Cyanosis AND Heart Failure?
This is the defining feature of common-mixing lesions (truncus arteriosus, univentricular hearts without PS, TAPVR without obstruction). The mixing causes cyanosis (desaturation), while the unrestricted pulmonary blood flow causes heart failure. Contrast this with right-to-left shunt lesions like Tetralogy of Fallot, where pulmonary flow is reduced → cyanosis without heart failure. [2]
In truncus arteriosus, the pulmonary arteries are exposed to full systemic pressure from birth (they arise from the trunk at systemic pressure). This is a much higher pressure load than in, say, a moderate VSD (where some of the pressure is dissipated by the restrictive defect). As a result, irreversible pulmonary vascular disease can develop as early as 3–6 months of age — much earlier than in a large VSD (which may take years). This is why early surgical repair (typically by 3 months) is critical.
7. Clinical Features
- Presents within the first days to weeks of life (as PVR falls)
- May be detected antenatally on fetal echocardiography
- Neonates with associated interrupted aortic arch present earlier (with duct-dependent systemic circulation → collapse when duct closes)
| Symptom | Pathophysiological Explanation |
|---|---|
| Mild cyanosis from birth | Obligatory mixing of oxygenated and deoxygenated blood at the truncal level; the degree is usually milder than in conditions with reduced pulmonary flow (e.g., ToF) because there is abundant pulmonary blood flow providing well-oxygenated return to the left heart |
| Tachypnoea / respiratory distress | Pulmonary overcirculation → pulmonary oedema → increased work of breathing |
| Poor feeding / failure to thrive | Heart failure increases metabolic demand and decreases feeding tolerance; pulmonary congestion impairs respiratory mechanics during feeds |
| Diaphoresis (sweating) especially during feeds | Sympathetic activation due to heart failure; increased metabolic demand |
| Recurrent respiratory infections | Pulmonary plethora → congested, oedematous lungs are more susceptible to infection |
| Exercise intolerance (in older unrepaired children — rare in modern practice) | Combination of heart failure and cyanosis |
| Sign | Pathophysiological Explanation |
|---|---|
| Signs of congestive heart failure + mild cyanosis | Common-mixing physiology: mixing causes cyanosis, unrestricted pulmonary flow causes HF [2] |
| Bounding pulses | Diastolic runoff to the pulmonary arteries from the high-pressure trunk causes a wide pulse pressure (similar to PDA or aortic regurgitation) → bounding peripheral pulses [2] |
| Hyperdynamic precordium with biventricular impulse | LV volume overload (from massive pulmonary venous return) + RV pressure overload (RV exposed to systemic pressure through VSD) → both ventricles are overworking → palpable biventricular impulse [2] |
| Loud and single S2 | Only one semilunar valve exists (the truncal valve) — there is no separate aortic and pulmonary valve to produce a split S2; the single closure sound is typically loud [2] |
| Ejection click | Opening snap of the truncal valve — often heard at the apex or LLSB; indicates opening of the large, sometimes dysplastic truncal valve [2] |
| Ejection systolic murmur (ESM) at the left sternal border (LSB) | High flow across the single truncal valve generates a flow murmur; may also reflect truncal valve stenosis if the valve is dysplastic [2] |
| Early diastolic murmur (EDM) at LSB (if truncal valve regurgitation present) | Regurgitation through the incompetent truncal valve produces a high-pitched blowing EDM, similar to aortic regurgitation |
| Mid-diastolic rumble at the apex | Increased flow across the mitral valve (due to massive pulmonary venous return → increased LA to LV flow) — a relative mitral stenosis murmur |
| Hepatomegaly | Right heart failure → systemic venous congestion → hepatic engorgement |
| Tachycardia | Compensatory sympathetic activation in heart failure |
| Failure to thrive / low weight for age | Chronic heart failure increases caloric expenditure while decreasing oral intake |
Auscultation Pearl – The Single S2
A loud, single S2 in a cyanotic neonate with signs of heart failure is a critical clue to truncus arteriosus (or other conditions with a single semilunar valve, such as severe pulmonary atresia). Normal neonates may have a physiologically single S2, but combining it with cyanosis + HF + bounding pulses should immediately raise suspicion for TA.
| Feature | Truncus Arteriosus | TGA with large VSD | TAPVR (unobstructed) |
|---|---|---|---|
| Cyanosis | Mild | Mild | Mild-moderate |
| Heart failure | Yes (prominent) | Yes | Yes |
| Single S2 | Yes (single truncal valve) | Yes (anteriorly positioned aorta) | No (two semilunar valves present) |
| Bounding pulses | Yes (diastolic runoff) | No | No |
| Ejection click | Yes | No | No |
| Pulmonary blood flow | Increased | Increased | Increased |
The bounding (or collapsing) pulses in truncus arteriosus deserve emphasis because they are a distinctive sign:
- In diastole, blood runs from the common trunk (at systemic pressure) into the low-resistance pulmonary vascular bed
- This is essentially a diastolic "steal" from the systemic circulation into the pulmonary circulation
- This lowers diastolic blood pressure while systolic BP remains normal → wide pulse pressure
- The same mechanism explains bounding pulses in:
- Patent ductus arteriosus (diastolic runoff through the duct)
- Aortic regurgitation (diastolic runoff back into the LV)
- Arteriovenous malformations
- In truncus arteriosus, this sign helps distinguish it from other cyanotic lesions (e.g., ToF does NOT have bounding pulses — it has reduced pulmonary flow)
| Feature | Truncus Arteriosus | Tetralogy of Fallot | TGA (intact septum) | Total Anomalous PV Return |
|---|---|---|---|---|
| Cyanosis severity | Mild | Moderate-severe | Severe | Variable |
| Heart failure | Yes (early) | No (unless severe anaemia) | Depends on mixing | Yes |
| Pulmonary blood flow | Increased | Decreased | Increased | Increased |
| S2 | Single, loud | Single (absent P2) | Single, loud | Normal/split |
| Bounding pulses | Yes | No | No | No |
| Duct-dependent? | Usually no (unless a/w IAA) | May be (if severe PS/PA) | Often yes (for mixing) | No |
- Infants with unrepaired truncus arteriosus develop failure to thrive early (within the first 1–2 months) due to the high metabolic demands of heart failure
- Feeding difficulties are often the presenting complaint — the infant tires during breastfeeding/bottle-feeding, takes small volumes, and takes a long time to feed
- Caloric supplementation (high-calorie formula, nasogastric tube feeds) is frequently needed preoperatively
- Developmental delay may occur if there is chronic hypoxaemia, poor nutrition, or prolonged hospitalisation
- In the context of DiGeorge syndrome, additional neurodevelopmental issues (learning difficulties, speech delay) and immune concerns compound the clinical picture
- Parents should be counselled that truncus arteriosus is a critical congenital heart defect requiring surgical repair in the neonatal/early infancy period
- If DiGeorge syndrome is confirmed:
- Genetic counselling (de novo in most cases, but 50% recurrence if parent carries the deletion)
- Multidisciplinary follow-up: cardiology, immunology, endocrinology (hypocalcaemia), speech therapy (cleft palate/velopharyngeal insufficiency), developmental paediatrics
- Live vaccines may be contraindicated if significant T-cell immunodeficiency (thymic hypoplasia)
- Long-term cardiac follow-up is lifelong (conduit replacement, truncal valve surveillance)
- For neonatal surgery: informed consent from parents/legal guardians
- Discussion should include: natural history without surgery (>80% first-year mortality), surgical options, risks of surgery (including need for future re-operations), expected outcomes
- In older children (rare in modern practice for primary repair): assent from the child where age-appropriate (generally from age ~7 years)
| Investigation | Expected Findings |
|---|---|
| CXR | Cardiomegaly and pulmonary plethora (similar to other large L-to-R shunts); LA/LV enlargement [2] |
| ECG | Biventricular overload — RV pressure overload + LV volume overload [2] |
| Echocardiography | Single arterial trunk overriding the ventricular septum; truncal PA origin; assessment of truncal valve stenosis/insufficiency — this is the diagnostic modality [2] |
| Pulse oximetry | SpO₂ typically 85–93% (mild desaturation); pre- and post-ductal difference if interrupted aortic arch |
| Serum calcium | May be low if DiGeorge syndrome |
| FISH / Microarray for 22q11.2 | Screening for DiGeorge in all cases of truncus arteriosus |
| CT angiography / cardiac MRI | Delineation of PA anatomy, aortic arch anatomy (especially if IAA suspected), coronary artery anatomy — may be needed pre-operatively |
| Cardiac catheterisation | Rarely needed in the current era; may be used to assess PVR if late presentation with suspected pulmonary vascular disease |
High Yield Summary
Truncus Arteriosus — Key Points for Exams:
- Definition: Single arterial trunk arising from the heart, overriding a VSD, supplying systemic, pulmonary, and coronary circulations due to failure of conotruncal septation
- Epidemiology: 6–10/100,000 live births; ~2% of all CHD but ~4% of critical CHD
- Association: Strongly associated with DiGeorge syndrome (22q11.2 deletion) — CATCH-22 mnemonic
- Classification: Collett & Edwards (Types I–IV, but Type IV is no longer true TA); Van Praagh (Types A1–A4, where A4 = TA + interrupted aortic arch)
- Pathophysiology: Common-mixing lesion → cyanosis + CHF; PAs at systemic pressure → torrential pulmonary flow as PVR falls; diastolic runoff → bounding pulses; early Eisenmenger risk (by 3–6 months)
- Key Clinical Features:
- Cyanosis + CHF (the hallmark of common-mixing)
- Bounding pulses (diastolic runoff)
- Single loud S2 (only one semilunar valve)
- Ejection click (truncal valve opening)
- ESM at LSB (high flow across truncal valve)
- Biventricular impulse on palpation
- CXR: Cardiomegaly + pulmonary plethora; ECG: Biventricular overload; Echo: Diagnostic
- Surgical repair needed by ~3 months (VSD patch closure + RV-to-PA conduit); without surgery, >80% first-year mortality
- Early Eisenmenger risk due to PAs exposed to systemic pressure from birth
- Screen ALL cases for 22q11.2 deletion, serum calcium, and lymphocyte subsets
Active Recall - Truncus Arteriosus
[1] GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (Truncus Arteriosus slide) [2] Adrian Lui Pediatrics Notes.pdf (Pages 220–221, Section C: Common-Mixing Conditions — Truncus Arteriosus) [3] Block C - Heart failure and cyanosis in children: acyanotic and cyanotic congenital heart disease.pdf [4] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Pages 268, 874 — DiGeorge syndrome / CATCH-22) [5] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Page 581 — DiGeorge syndrome / CATCH-22) [6] Ryan Ho Cardiology.pdf (Pages 189–193 — PDA, CoA, VSD sections for haemodynamic comparison)
Differential Diagnosis of Truncus Arteriosus
The differential diagnosis of truncus arteriosus is fundamentally the differential diagnosis of a neonate presenting with cyanosis AND congestive heart failure (CHF) in the first days to weeks of life. The clinical approach must distinguish truncus arteriosus from other cyanotic congenital heart defects and from non-cardiac causes of neonatal cyanosis.
Truncus arteriosus presents with a characteristic combination of features:
- Mild cyanosis (SpO₂ ~85–93%) — from obligatory mixing
- Congestive heart failure — from unrestricted pulmonary blood flow as PVR falls
- Bounding pulses — from diastolic runoff into the PA bed
- Single loud S2 and ejection click — from the single truncal valve
- Increased pulmonary vascular markings on CXR — pulmonary plethora
The differential therefore centres on conditions that share one or more of these features.
GC High Yield – Categorisation of Cyanotic CHD
Cyanotic CHD can be categorised according to the underlying physiology [1][3][4]:
- ↓ Pulmonary blood flow (RVOT obstruction with R→L shunt)
- ↑ Pulmonary blood flow (common-mixing or parallel circulation — the "3 Ts")
- Severe heart failure (duct-dependent systemic circulation)
Truncus arteriosus falls under "↑ Pulmonary blood flow" — it is one of the "3 Ts" alongside TGA and TAPVR [3][4].
2. Systematic Differential Diagnosis by Physiological Category
These are the closest mimics of truncus arteriosus because they share the combination of cyanosis + heart failure + pulmonary plethora on CXR.
| Condition | Key Distinguishing Features from Truncus Arteriosus | Ductal Dependence |
|---|---|---|
| Transposition of Great Arteries (TGA) | Severe cyanosis (if intact septum) — much worse than TA because of parallel circulation with minimal mixing; "egg on side" CXR appearance (narrow upper mediastinum) [2][5]; no bounding pulses; single S2 (but from anteriorly positioned aortic valve, not truncal valve); usually no murmur unless associated VSD/PS | Yes (duct-dependent for mixing) [3][4] |
| Total Anomalous Pulmonary Venous Return (TAPVR) — unobstructed type | Cyanosis + CHF similar to TA; however, S2 is widely split (two separate semilunar valves exist); no ejection click; no bounding pulses; characteristic "snowman/figure-of-8" CXR in supracardiac type; RV impulse (all pulmonary venous blood returns to RA → RV volume overload, not LV) | No (not ductal-dependent) [3][4] |
| TGA with large VSD | Adequate mixing → milder cyanosis (like TA); CHF develops as PVR falls; but no bounding pulses, no ejection click; "egg on side" CXR may still be seen; PSM of VSD heard | Variable |
Why "3 Ts"? — TGA, Truncus arteriosus, TAPVR. These three conditions share the pattern of cyanosis with increased pulmonary blood flow and plethora. The mnemonic is high-yield for categorisation [3][4].
Key distinction: Truncus arteriosus is NOT ductal-dependent — the PA arteries arise directly from the trunk, so pulmonary blood flow does not depend on the ductus [3][4][6]. In contrast, TGA is ductal-dependent (needs the duct for inter-circulatory mixing).
These conditions present with cyanosis WITHOUT heart failure (because pulmonary blood flow is reduced, not increased). They can be distinguished from truncus arteriosus by:
- Oligaemic (dark) lung fields on CXR rather than plethora
- No signs of CHF
- No bounding pulses
| Condition | Key Features | Ductal Dependence |
|---|---|---|
| Tetralogy of Fallot (TOF) | Boot-shaped heart on CXR; oligaemic lung fields; ESM at LUSB (RVOT obstruction); cyanotic spells (tet spells); single S2 (but from absent/soft P2 due to PS, not from a single valve); NO bounding pulses; NO heart failure [7] | √/✗ (only if severe RVOT obstruction) [3][4] |
| TOF with pulmonary atresia (TOF/PA) | Extreme TOF; duct-dependent pulmonary circulation; continuous murmur from PDA or MAPCAs (not from a single truncal valve); severely oligaemic lungs | Yes [3][4] |
| Pulmonary atresia with intact ventricular septum (PA/IVS) | Duct-dependent; severe cyanosis; tiny RV; no VSD; no bounding pulses | Yes [3][4] |
| Critical pulmonary stenosis | Duct-dependent; similar to PA/IVS but RV less hypoplastic; ESM at LUSB with thrill | Yes (in critical PS) [3][4] |
| Tricuspid atresia | Superior axis on ECG (left axis deviation — virtually pathognomonic); small/absent RV; common-mixing in LA; cyanosis depends on presence of PS | √/✗ [3][4][8] |
| Ebstein's anomaly | "Wall-to-wall" cardiomegaly on CXR; massive RA dilatation; TR murmur; WPW on ECG in 10–25% | √/✗ [3][4] |
Distinguishing Truncus Arteriosus from TOF
A common exam mistake is confusing truncus arteriosus with tetralogy of Fallot. Both involve conotruncal maldevelopment and are associated with DiGeorge syndrome. The critical distinction is:
- TOF: ↓ pulmonary blood flow → cyanosis without CHF, oligaemic lungs
- TA: ↑ pulmonary blood flow → cyanosis with CHF, plethoric lungs
- TOF: two great arteries (aorta + hypoplastic PA)
- TA: single great artery (common trunk)
These conditions present primarily with shock and heart failure (± mild cyanosis) as the ductus closes, because systemic circulation is duct-dependent. They differ from truncus arteriosus in that the primary problem is systemic hypoperfusion, not pulmonary overcirculation.
| Condition | Key Features | Ductal Dependence |
|---|---|---|
| Coarctation of aorta (CoA) | Neonatal shock at day 2 (duct closure); weak femoral pulses with radiofemoral delay; differential BP (upper > lower limbs); ESM at LUSB radiating to interscapular area; no significant cyanosis [9] | Yes (critical CoA) [3][4] |
| Interrupted aortic arch (IAA) | Like severe CoA but complete discontinuity; type B (between left carotid and left subclavian) is strongly a/w DiGeorge syndrome (22q11.2 deletion) — like TA [5][7]; neonatal collapse | Yes [3][4] |
| Critical aortic stenosis | Severe AS → LV failure → shock; harsh ESM at RUSB with thrill; ejection click (can overlap with TA's ejection click, but location and context differ) | Yes (critical AS) [3][4] |
| Hypoplastic left heart syndrome (HLHS) | Most common cause of cardiac death in the first week of life; hypoplastic LV, mitral and aortic atresia/stenosis; single RV supports both circulations via PDA; grey, shocked neonate with absent LV impulse | Yes [3][4] |
These conditions share the heart failure component with truncus arteriosus but typically do not present with significant cyanosis (until Eisenmenger develops). They are differential diagnoses in the infant presenting with CHF at 1–3 months.
| Condition | Key Distinguishing Features |
|---|---|
| Large VSD | PSM at LLSB; no ejection click; normal split S2 (two semilunar valves); no bounding pulses; cyanosis only if Eisenmenger develops [10] |
| Large PDA | Continuous ("machinery") murmur at L infraclavicular area; bounding/collapsing pulses (similar to TA! — same diastolic runoff mechanism); normal split S2; no ejection click [11] |
| AVSD (complete) | Common in Down syndrome; superior axis on ECG; fixed split S2; pansystolic murmur of AV valve regurgitation [8] |
| Aortopulmonary window | Very rare; similar haemodynamics to TA (communication between ascending aorta and PA); normal two semilunar valves (S2 is split, not single); no VSD; continuous murmur |
Aortopulmonary (AP) window is the closest mimic of truncus arteriosus haemodynamically — both have systemic-pressure pulmonary blood flow and diastolic runoff. The key distinction is that AP window has two separate semilunar valves (normal S2 splitting) and no VSD, whereas TA has a single truncal valve (single S2) and an obligatory VSD.
Before attributing cyanosis to cardiac disease, non-cardiac causes must be considered:
| Category | Examples | How to Distinguish from TA |
|---|---|---|
| Respiratory | RDS, MAS, pneumonia, pneumothorax, CDH, choanal atresia | Hyperoxia test: PaO₂ rises > 150 mmHg with 100% O₂ in respiratory disease but fails to rise significantly ( < 100 mmHg) in cyanotic CHD; respiratory signs predominate; CXR shows parenchymal disease [12] |
| Persistent pulmonary hypertension of the newborn (PPHN) | Failure of PVR to fall postnatally → R-to-L shunt via PDA/PFO | Pre-/post-ductal SpO₂ difference > 5%; may respond partially to hyperoxia; echo shows structurally normal heart with elevated PA pressures |
| Sepsis / shock | Group B Streptococcus, E. coli | Poor perfusion, temperature instability; positive blood cultures; CXR may show diffuse opacification |
| CNS | Central hypoventilation, birth asphyxia | Irregular respiratory pattern; neurological signs |
| Methaemoglobinaemia | Congenital or toxin-induced (e.g., local anaesthetics, dapsone) | Chocolate-brown blood; does not improve with O₂; methHb level on co-oximetry; SpO₂ reads ~85% and does not change |
GC High Yield – Hyperoxia Test to Differentiate Cardiac vs Respiratory Cyanosis
An oligaemic lung field on CXR supports cyanotic CHD rather than respiratory disease as the cause of cyanosis [12]. However, in truncus arteriosus the lung fields are plethoric (not oligaemic), so the CXR pattern alone may not immediately point to a cardiac cause. The hyperoxia test (failure of PaO₂ to rise > 150 mmHg on 100% FiO₂) remains the bedside tool to differentiate cardiac from pulmonary cyanosis.
When you are presented with a cyanotic neonate with CHF and increased pulmonary blood flow, the following features specifically point toward truncus arteriosus (rather than TGA or TAPVR):
| Feature | Points Toward TA | Points Away from TA |
|---|---|---|
| Bounding pulses | ✓ (diastolic runoff to PA) | Against TOF, TGA, TAPVR |
| Single loud S2 | ✓ (single truncal valve) | Also seen in TGA (but for different reason — anterior aorta); NOT in TAPVR |
| Ejection click | ✓ (truncal valve opening) | Not expected in TGA or TAPVR |
| ESM at LSB | ✓ (flow across truncal valve) | Non-specific |
| Wide pulse pressure | ✓ (diastolic runoff) | Also in large PDA; NOT in TGA, TAPVR |
| DiGeorge features (abnormal facies, hypocalcaemia) | ✓ (strong association) | Also seen in IAA type B, TOF |
| Absent thymic shadow on CXR | ✓ (DiGeorge → thymic hypoplasia) | Also in stressed neonates (but TA + absent thymus is suggestive) |
| CXR: cardiomegaly + plethora | ✓ | Also in TGA with VSD, TAPVR, large VSD, PDA |
| "Egg on side" CXR | ✗ (this is TGA) | Specific for TGA [2] |
| "Snowman" CXR | ✗ (this is supracardiac TAPVR) | Specific for TAPVR |
| Boot-shaped heart on CXR | ✗ (this is TOF) | Specific for TOF |
5. Differential by Presenting Feature
Since bounding pulses are a distinctive feature of truncus arteriosus, consider:
| Condition | Mechanism of Bounding Pulses |
|---|---|
| Truncus arteriosus | Diastolic runoff from trunk into low-resistance PA bed |
| Large PDA | Diastolic runoff through patent ductus into PA |
| Aortopulmonary window | Diastolic runoff through AP communication |
| Arteriovenous malformation (e.g., vein of Galen malformation) | Low-resistance AV shunt → diastolic runoff |
| Severe aortic regurgitation (rare in neonates) | Diastolic regurgitation into LV |
| Condition | Why S2 is Single |
|---|---|
| Truncus arteriosus | Only one semilunar valve (truncal valve) → only one closure sound |
| TGA (d-TGA) | Anteriorly positioned aortic valve is loud; posteriorly positioned pulmonary valve closure is inaudible → single loud S2 [2] |
| Severe TOF / PA with VSD | Absent or severely hypoplastic pulmonary valve → P2 absent → single S2 |
| Severe pulmonary hypertension | P2 fuses with A2 (delay eliminated) → appears single |
The associated syndrome can guide the cardiac differential diagnosis [5][7][9]:
| Syndrome | Associated Cardiac Defects | Key Dysmorphic Features |
|---|---|---|
| DiGeorge syndrome (22q11.2 deletion) | Truncus arteriosus, interrupted aortic arch (type B), TOF, PA with VSD, VSD, ASD | CATCH-22: Cardiac defect, Abnormal facies, Thymic hypoplasia, Cleft palate, Hypocalcaemia [5][7] |
| Down syndrome (Trisomy 21) | AVSD, VSD, ASD, PDA, TOF | Hypotonia, epicanthic folds, upslanting palpebral fissures, single palmar crease [5][9] |
| Turner syndrome (45,X) | CoA, bicuspid AV, AS, HLHS | Short stature, webbed neck, widely spaced nipples [5][9] |
| Williams syndrome (7q11.23 deletion) | Supravalvular AS, peripheral PA stenosis | Elfin facies, hypercalcaemia, intellectual disability [5][9] |
| Noonan syndrome | Dysplastic pulmonary valve stenosis, ASD, HCM | Turner-like but normal karyotype, ptosis, cryptorchidism [5][9] |
Clinical Pearl – DiGeorge as a Diagnostic Clue
If you find hypocalcaemia and/or absent thymic shadow on CXR in a cyanotic neonate with heart failure, this should immediately raise suspicion for a conotruncal anomaly (truncus arteriosus or interrupted aortic arch) in the context of DiGeorge syndrome. Send FISH/microarray for 22q11.2 deletion.
| Condition | Cyanosis | CHF | Pulmonary Flow | S2 | Bounding Pulses | Ductal Dependent | Key CXR Clue |
|---|---|---|---|---|---|---|---|
| Truncus arteriosus | Mild | Yes | ↑↑↑ | Single, loud | Yes | No [3][4] | Cardiomegaly + plethora |
| TGA (intact septum) | Severe | No (initially) | ↑ | Single, loud | No | Yes | "Egg on side" [2] |
| TGA + large VSD | Mild | Yes | ↑↑ | Single, loud | No | Less so | "Egg on side" |
| TAPVR (unobstructed) | Mild-mod | Yes | ↑↑ | Split | No | No | "Snowman" (supracardiac) |
| TOF | Mod-severe | No | ↓ | Single | No | ± | "Boot-shaped", oligaemic |
| Large VSD | No (initially) | Yes | ↑↑ | Normal split | No | No | Cardiomegaly + plethora |
| Large PDA | No (initially) | Yes | ↑↑ | ± loud P2 | Yes | No | Cardiomegaly + plethora |
| AP window | Mild | Yes | ↑↑↑ | Normal split | Yes | No | Cardiomegaly + plethora |
| CoA (critical) | Mild/grey | Yes (shock) | Normal/↑ | Normal | No | Yes | Cardiomegaly ± rib notching (older) |
High Yield Summary – DDx of Truncus Arteriosus
- Truncus arteriosus belongs to the "3 Ts" group of cyanotic CHD with increased pulmonary blood flow: TGA, Truncus arteriosus, TAPVR [3][4]
- NOT ductal-dependent — unlike TGA (which needs the duct for mixing) [3][4]
- The combination of cyanosis + CHF + bounding pulses + single S2 + ejection click is highly suggestive of TA
- Bounding pulses distinguish TA from TGA and TAPVR (diastolic runoff mechanism)
- Single S2 distinguishes TA from TAPVR and large VSD (which have two semilunar valves)
- DiGeorge syndrome (22q11.2 deletion) is a key syndromic clue — check calcium, thymus, immune function
- Aortopulmonary window is the closest haemodynamic mimic but has two separate semilunar valves and no VSD
- Hyperoxia test differentiates cardiac from respiratory cyanosis; CXR pattern (plethoric vs oligaemic) helps subcategorise cyanotic CHD
- Echocardiography is the definitive diagnostic tool to confirm the single arterial trunk and PA origin
Active Recall - DDx of Truncus Arteriosus
References
[1] GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (slide 32 — Truncus Arteriosus heading) [2] Adrian Lui Pediatrics Notes.pdf (Pages 219–220 — TGA; Page 220–221 — Truncus Arteriosus) [3] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 280 — categorisation of cyanotic CHD; Page 287 — Truncus arteriosus DDx) [4] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Pages 593–595 — cyanotic CHD categories and ductal dependence; Page 600 — truncus arteriosus) [5] Adrian Lui Pediatrics Notes.pdf (Page 184 — Syndromal associations table) [6] GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (slide 33 — "cyanosis usually mild, heart failure symptoms predominate as PVR decreases") [7] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 268 — TOF, DiGeorge, CATCH-22) [8] Maksim Paediatric Notes.pdf (Page 59–60 — AVSD, tricuspid atresia, truncus arteriosus) [9] Ryan Ho Cardiology.pdf (Pages 184–185 — CHD classification and syndromal associations) [10] Ryan Ho Cardiology.pdf (Page 193 — VSD) [11] Ryan Ho Cardiology.pdf (Page 189 — PDA) [12] AOS - Paeds.pdf (Question 6 — oligaemic lung field supports cyanotic CHD over respiratory disease)
Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Truncus Arteriosus
Truncus arteriosus (TA) does not have a formal "diagnostic criteria checklist" like, say, Jones criteria for rheumatic fever. Instead, the diagnosis is an anatomical one made by imaging — specifically echocardiography — demonstrating the defining structural features. In practice, the diagnosis requires identification of all of the following:
| Mandatory Anatomical Feature | Explanation |
|---|---|
| A single great arterial trunk arising from the base of the heart, overriding the ventricular septum | This is the defining lesion — the aorticopulmonary septum failed to form, leaving one undivided trunk [2][4] |
| Pulmonary arteries arising from the common trunk | The PAs must originate from the trunk (not from a separate RVOT). The pattern of PA origin determines the type (Van Praagh A1–A4 or Collett & Edwards I–III) [2] |
| A ventricular septal defect (VSD) — almost always present | The conoventricular VSD is obligatory because the infundibular septum (which normally contributes to VSD closure) does not form [2][4] |
| A single semilunar (truncal) valve | Only one set of semilunar valve cusps exists (may be bicuspid, tricuspid, or quadricuspid). There is no separate aortic and pulmonary valve [2] |
Additionally, the following associated features should be systematically assessed at the time of diagnosis:
- Truncal valve morphology — number of cusps, presence of stenosis or regurgitation [2]
- Aortic arch anatomy — right aortic arch (~30%), interrupted aortic arch (Type A4), coarctation
- Coronary artery anatomy — abnormal origins or courses (critical for surgical planning)
- Associated extracardiac features — DiGeorge syndrome (22q11.2 deletion) screening [5][7]
Key Point – Diagnosis is Anatomical, Not Clinical
You do not "diagnose" truncus arteriosus by clinical criteria alone. The clinical presentation (cyanosis + CHF + bounding pulses + single S2 + ejection click) raises suspicion, but the definitive diagnosis is made by echocardiography demonstrating a single arterial trunk with PA origin from the trunk and an obligatory VSD [2].
The diagnostic approach to a neonate with suspected truncus arteriosus follows the general approach to a cyanotic neonate, narrowing down to the specific anatomical diagnosis.
3. Investigation Modalities — Detailed Findings and Interpretation
3.1 Bedside Investigations
- What it shows: SpO₂ typically 85–93% in truncus arteriosus — mild desaturation from obligatory mixing
- Pre- vs post-ductal difference:
- Usually minimal or absent in isolated TA (because the TA itself is not ductal-dependent — PAs arise from the trunk, not via a duct) [4]
- If associated with interrupted aortic arch (Type A4), there may be a significant pre-/post-ductal SpO₂ difference (post-ductal SpO₂ lower than pre-ductal if there is R→L ductal shunting to supply the descending aorta)
- Why it matters: Universal neonatal pulse oximetry screening (increasingly standard in Hong Kong) can detect critical CHD including TA before clinical deterioration
- Principle: The neonate is placed on 100% FiO₂ for 10–15 minutes, and a right radial arterial blood gas (pre-ductal) is obtained
- Interpretation:
- PaO₂ > 150 mmHg → suggests respiratory cause of cyanosis (healthy alveolar gas exchange can correct hypoxaemia when given supplemental O₂)
- PaO₂ < 100 mmHg → suggests cyanotic CHD (the intracardiac mixing/shunting bypasses the lungs, so supplemental O₂ cannot correct the desaturation)
- In truncus arteriosus, the PaO₂ typically rises modestly (to ~60–90 mmHg) because there IS increased pulmonary blood flow (well-oxygenated pulmonary venous blood returns and mixes), but it does NOT reach > 150 mmHg because of obligatory mixing with deoxygenated blood at the truncal level
Why Does the Hyperoxia Test Partially Improve PaO₂ in TA?
In TA, pulmonary blood flow is increased (not decreased). So giving 100% O₂ does effectively oxygenate the blood passing through the lungs. However, this well-oxygenated blood then mixes with deoxygenated systemic venous blood in the single trunk — so the final systemic PaO₂ is better than in conditions with reduced pulmonary flow (like TOF) but still cannot reach normal levels. This is why TA gives an "intermediate" hyperoxia test result.
- Useful to detect interrupted aortic arch (Type A4) or coarctation — lower limb BP significantly lower than upper limb BP
- In isolated TA without arch abnormality: four-limb BP is usually similar
CXR in truncus arteriosus shows cardiomegaly and pulmonary plethora, similar to other large L-to-R shunts, with LA/LV enlargement [2]
| CXR Feature | Explanation | Why This Occurs |
|---|---|---|
| Cardiomegaly | Enlarged cardiac silhouette (cardiothoracic ratio > 0.6 in neonates, > 0.55 in infants) | LV volume overload from massive pulmonary venous return + RV pressure overload from exposure to systemic pressure through the VSD [2] |
| Pulmonary plethora (increased pulmonary vascular markings) | Prominent, engorged pulmonary vasculature extending to the lung periphery | PAs arise from the trunk at systemic pressure → unrestricted pulmonary blood flow → pulmonary overcirculation [2] |
| LA and LV enlargement | Dominant left heart enlargement on the lateral view (posterior displacement of barium-filled oesophagus by LA — rarely done now) | Torrential pulmonary venous return overloads the LA and LV [2] |
| Absent thymic shadow | The thymic silhouette may be absent or diminished | DiGeorge syndrome → thymic hypoplasia/aplasia (seen in ~35% of TA cases) [5][7] |
| Right aortic arch | The aortic knuckle is seen on the right side rather than the left | Present in ~30% of TA; should raise suspicion for a conotruncal anomaly |
| High origin of pulmonary arteries | The PA branches may appear to arise unusually high, coming directly off the trunk | Because the PAs arise from the common trunk rather than from a separate main PA |
| Narrow or absent main PA segment | The normal concavity of the left heart border at the main PA region may be absent | There is no separate main PA — the PA branches come off the trunk |
CXR Comparison – TA vs Other Cyanotic CHD
| Condition | Classic CXR Appearance |
|---|---|
| Truncus arteriosus | Cardiomegaly + plethora + absent thymic shadow ± right aortic arch |
| TGA | "Egg on side" (narrow upper mediastinum) + plethora |
| TOF | "Boot-shaped" heart (coeur en sabot) + oligaemic lung fields |
| TAPVR (supracardiac) | "Snowman / figure-of-8" + plethora |
| Ebstein anomaly | "Wall-to-wall" massive cardiomegaly |
ECG shows biventricular overload: RV pressure overload and LV volume overload [2]
| ECG Feature | Explanation |
|---|---|
| Biventricular hypertrophy (BVH) | RV pressure overload: RV ejects into the systemic-pressure trunk through the VSD → high afterload on RV. LV volume overload: massive pulmonary venous return → increased preload on LV [2] |
| Right axis deviation (RAD) | RV hypertrophy shifts the axis rightward; however, RAD is normal in neonates, so must be interpreted in context of age-specific normal ranges |
| Tall R waves in V1 with deep S waves in V5–V6 | RV hypertrophy pattern |
| Tall R waves in V5–V6 with deep Q waves | LV volume overload pattern |
| LA enlargement (bifid P wave in lead II, > 0.08s) | Increased pulmonary venous return overloads LA |
| Normal sinus rhythm | Arrhythmias are uncommon in unoperated neonatal TA |
Important paediatric ECG interpretation caveat: In the neonate, RV dominance is physiologically normal (in utero, the RV is the "systemic" ventricle). Normal neonatal ECG shows right axis deviation and dominant R wave in V1. Therefore, RVH may be difficult to identify in the first few days of life. LVH is more informative in this age group because it is always abnormal in the neonate.
Echocardiography demonstrates: a single arterial trunk that overrides the ventricular septum, truncal PA origin, and assessment of truncal valve stenosis/insufficiency [2]
Echocardiography is the gold standard for diagnosing truncus arteriosus. It is non-invasive, readily available, and provides comprehensive anatomical and functional assessment.
| Echo Feature | What to Look For | Clinical Significance |
|---|---|---|
| Single great arterial trunk overriding the ventricular septum | In parasternal long-axis (PLAX) and subcostal views: one large vessel is seen arising from the heart, straddling the VSD | Confirms the diagnosis — distinguishes TA from TOF (which has two great arteries) and from TGA (which has discordant ventriculoarterial connections) [2] |
| Origin of pulmonary arteries from the trunk | Identify where PA branches arise from the trunk — MPA segment (Type A1), separate origins (Type A2), one PA absent (Type A3) | Determines the Van Praagh type — critical for surgical planning [2] |
| VSD (conoventricular type) | Large, non-restrictive VSD immediately beneath the truncal valve; the truncal valve overrides this defect | Obligatory in TA — if absent, diagnosis is exceedingly unlikely |
| Truncal valve morphology | Number of cusps (bicuspid, tricuspid, quadricuspid); leaflet thickness; calcification | Truncal valve stenosis → increases afterload and perioperative risk. Truncal valve regurgitation → adds volume load; severe regurgitation increases perioperative mortality significantly [2] |
| Truncal valve regurgitation (colour Doppler) | Regurgitant jet from trunk into ventricular cavity; grade severity | Severe regurgitation is a major determinant of surgical risk and may require concomitant valve repair or replacement |
| Aortic arch anatomy | Right vs left aortic arch; presence of interrupted aortic arch (Type A4); coarctation | Interrupted aortic arch (Type A4) is present in ~10–15% and is strongly a/w 22q11.2 deletion; changes surgical approach |
| Coronary artery anatomy | Origins and proximal courses of coronary arteries | Abnormal coronary patterns must be identified pre-operatively (similar importance as in TGA/ASO — inadvertent injury to coronary → catastrophic) |
| PA pressures (estimated by Doppler) | Velocity of TR jet → estimate RV systolic pressure (≈ PA systolic pressure in TA since RV communicates freely with trunk) | PA pressure is at systemic levels in TA — this is expected. If presentation is late, PVR assessment is critical to determine operability |
| Ventricular function | LV and RV systolic function (fractional shortening, ejection fraction) | Impaired function may reflect severe volume overload, truncal valve regurgitation, or coronary insufficiency |
| Additional anomalies | ASD, additional VSDs, anomalous pulmonary venous return | Important for complete surgical planning |
GC High Yield – Echo is Diagnostic
Echocardiography is the primary diagnostic tool for truncus arteriosus. It demonstrates the single arterial trunk overriding the ventricular septum, the truncal PA origin, and allows assessment of truncal valve stenosis/insufficiency [1][2]. In the vast majority of cases, echo alone is sufficient for diagnosis and surgical planning.
These are second-line imaging modalities, used when echocardiography provides incomplete information:
| Modality | Indications | Key Findings |
|---|---|---|
| CT Angiography | Delineation of PA branch anatomy (especially if small or stenotic); aortic arch anatomy (right arch, IAA, coarctation); coronary artery anatomy; assessment of airway compression | High spatial resolution with rapid acquisition → ideal for critically ill neonates (fast scan, minimal sedation needed with modern scanners). Radiation exposure is a consideration in paediatrics — use low-dose paediatric protocols |
| Cardiac MRI | Assessment of ventricular volumes and function; PA anatomy and flow quantification; PVR estimation (in late presenters) | Superior soft-tissue contrast without radiation. However, longer scan times requiring sedation/GA in neonates; less available in acute settings. More commonly used for post-operative follow-up |
What CT/MRI Adds Beyond Echo:
- Aortopulmonary collaterals (MAPCAs): In Type A3 (one PA absent), the absent lung is supplied by collaterals from the descending aorta — CT/MRI maps these
- Airway assessment: The common trunk or aberrant vessels may compress the trachea/bronchi — important pre-operatively
- Arch anomalies: CT is excellent for demonstrating the precise anatomy of interrupted aortic arch or right aortic arch with vascular ring
| Role | Details |
|---|---|
| Rarely needed in the current era | Echocardiography ± CT/MRI provides sufficient anatomical detail for surgical planning in neonates and young infants |
| Main indication: late presentation with suspected elevated PVR | If a child presents late (> 3–6 months), pulmonary vascular disease may already be developing. Cardiac catheterisation allows direct measurement of PVR and assessment of pulmonary vasoreactivity (response to inhaled NO or 100% O₂) to determine operability |
| Additional haemodynamic data | Measurement of Qp:Qs ratio; assessment of truncal valve gradient; coronary angiography if echo is inconclusive |
| Interventional catheterisation | Generally not applicable for primary TA — catheter interventions are used post-operatively (e.g., balloon dilatation of conduit stenosis, stenting of PA branches) |
Why Is Cardiac Catheterisation Reserved for Late Presenters?
In a typical neonate with TA diagnosed by echo, surgery should proceed promptly (by ~2–3 months of age at latest). Catheterisation adds risk (vascular access in a small neonate, sedation, contrast) without changing management. However, if a child presents late (e.g., from a resource-limited setting) and you suspect the PVR has risen irreversibly, catheterisation is the only way to directly measure PVR and test vasoreactivity — this determines whether the child is still operable or has developed Eisenmenger physiology.
These are not diagnostic for TA itself but are essential parts of the workup, especially for associated conditions and pre-operative planning:
| Investigation | Rationale | Expected Findings in TA |
|---|---|---|
| Serum calcium | Screen for hypoparathyroidism in DiGeorge syndrome | May be low — neonatal hypocalcaemia can cause seizures, jitteriness, QTc prolongation [5][7] |
| Lymphocyte subsets (CD3, CD4, CD8, CD19, CD16/56) | Screen for T-cell immunodeficiency from thymic hypoplasia (DiGeorge) | May show low T-cell counts with preserved B-cells; important for vaccine planning (live vaccines contraindicated if significant T-cell deficiency) [5][7] |
| FISH or chromosomal microarray for 22q11.2 deletion | Screen for DiGeorge syndrome — present in ~35% of TA cases | Positive in ~35%; even if negative for 22q11.2, consider other genetic testing (whole exome sequencing) [5][7] |
| Arterial blood gas (ABG) | Assess degree of hypoxaemia and acid-base status | Mild hypoxaemia (PaO₂ ~45–70 mmHg on room air); metabolic acidosis if poor cardiac output/shock |
| Complete blood count (CBC) | Baseline; polycythaemia may develop with chronic hypoxaemia | Usually normal in neonates; polycythaemia is rare because the degree of cyanosis in TA is usually mild |
| Renal function, liver function | Pre-operative baseline; assess end-organ perfusion | May be deranged if cardiac output is compromised (especially if IAA with duct closure → shock) |
| Blood group and crossmatch | Pre-operative preparation for surgery | Standard pre-cardiac surgery workup |
| NT-proBNP / BNP | Marker of heart failure severity | Elevated in the setting of significant CHF; useful for monitoring response to medical therapy |
- Fetal echocardiography at 18–22 weeks gestation can identify TA:
- Single arterial trunk with PA branches arising from it
- Overriding truncal valve
- VSD
- Associated arch anomalies
- Antenatal diagnosis allows:
- Delivery planning at a centre with paediatric cardiology and cardiac surgery
- Parental counselling and preparation
- Genetic testing (amniocentesis for 22q11.2 deletion if conotruncal anomaly identified)
- Immediate neonatal echo confirmation and stabilisation after birth
Universal neonatal pulse oximetry screening is increasingly adopted in Hong Kong nurseries and is relevant to TA:
- Protocol: SpO₂ measured on the right hand (pre-ductal) and either foot (post-ductal) at > 24 hours of age
- Positive screen: SpO₂ < 95% in either extremity, or > 3% difference between pre- and post-ductal readings
- Sensitivity for TA: TA typically shows mild desaturation (SpO₂ ~85–93%) → will usually be picked up by screening
- Important limitation: If the infant is in severe heart failure and being ventilated, the SpO₂ may be higher due to supplemental O₂, potentially masking the cyanotic component
| Investigation | Key Finding | Interpretation |
|---|---|---|
| SpO₂ | 85–93% | Mild desaturation from obligatory mixing |
| Hyperoxia test | PaO₂ < 100 mmHg on 100% O₂ | Confirms cyanotic CHD (intracardiac mixing) |
| CXR | Cardiomegaly + pulmonary plethora + LA/LV enlargement ± absent thymic shadow ± right aortic arch | Consistent with a large L-to-R shunt; absent thymus → DiGeorge [2] |
| ECG | Biventricular overload | RV pressure overload + LV volume overload [2] |
| Echo | Single arterial trunk overriding VSD; truncal PA origin; truncal valve assessment | Diagnostic [2] |
| CT/MRI | PA branch anatomy; arch anatomy; coronary anatomy | Pre-operative planning; second-line |
| Cath | Direct PVR measurement; vasoreactivity testing | Only for late presenters with suspected pulmonary vascular disease |
| Serum Ca²⁺ | May be low | DiGeorge → hypoparathyroidism [5][7] |
| 22q11.2 FISH/microarray | Positive in ~35% | Confirms DiGeorge syndrome [5][7] |
| Lymphocyte subsets | Low T-cells | DiGeorge → thymic hypoplasia [5][7] |
High Yield Summary – Diagnosis and Investigations for Truncus Arteriosus
- No formal diagnostic criteria — diagnosis is anatomical, made by echocardiography
- Echo is the gold standard: shows single arterial trunk overriding VSD, truncal PA origin, truncal valve morphology [2]
- CXR: cardiomegaly + pulmonary plethora (similar to large L-to-R shunts) ± absent thymic shadow (DiGeorge) [2]
- ECG: biventricular overload (RV pressure + LV volume overload) [2]
- Hyperoxia test: PaO₂ fails to rise > 150 mmHg but may reach ~60–90 mmHg (intermediate, because pulmonary flow IS increased)
- CT angiography: for PA branch anatomy, aortic arch, coronary arteries — second-line
- Cardiac catheterisation: reserved for late presenters to assess PVR and operability
- Screen ALL cases for DiGeorge (22q11.2 deletion): FISH/microarray, serum calcium, lymphocyte subsets [5][7]
- Fetal echo can detect TA antenatally → allows delivery planning and immediate neonatal stabilisation
- Neonatal pulse oximetry screening will usually detect TA (SpO₂ 85–93%)
Active Recall - Diagnosis and Investigations for Truncus Arteriosus
References
[1] GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (slides 31–33 — Truncus Arteriosus) [2] Adrian Lui Pediatrics Notes.pdf (Pages 220–221 — Truncus Arteriosus investigations and management) [3] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 280 — categorisation of cyanotic CHD) [4] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 287 — Truncus arteriosus physiology and embryology) [5] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 268 — DiGeorge syndrome, CATCH-22) [6] Ryan Ho Cardiology.pdf (Pages 184–185 — CHD classification and syndromal associations) [7] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Page 581 — DiGeorge syndrome, CATCH-22)
Management of Truncus Arteriosus
The management of truncus arteriosus is fundamentally a two-phase strategy: initial medical stabilisation of heart failure, followed by early definitive surgical repair. Without surgery, the natural history is dismal — > 80% mortality in the first year from intractable heart failure and/or irreversible pulmonary vascular disease. The goal is to operate before irreversible pulmonary hypertension develops.
2. Phase 1: Initial Stabilisation and Medical Management
When truncus arteriosus is diagnosed (prenatally or postnatally), the neonate should be admitted to a neonatal intensive care unit (NICU) at a centre with paediatric cardiology and cardiac surgery:
| Action | Rationale |
|---|---|
| Monitoring: Continuous SpO₂, ECG, BP, urine output | Standard critical CHD monitoring; detect deterioration early |
| IV access | For medication administration; central line if inotropes needed |
| Avoid excessive supplemental O₂ | Caution with O₂ in large L-to-R shunts: supplemental O₂ → ↑PaO₂ → pulmonary vasodilation → ↓PVR → ↑pulmonary blood flow → worsens heart failure and pulmonary overcirculation [8]. Target SpO₂ ~75–85% may be acceptable |
| Correct hypocalcaemia | If DiGeorge syndrome suspected/confirmed — neonatal hypocalcaemia can cause seizures, QTc prolongation, cardiac dysfunction. IV calcium gluconate 10% (0.5–1 mL/kg slowly) [5][7] |
| Screen for DiGeorge | FISH/microarray for 22q11.2; serum calcium; lymphocyte subsets [5][7] |
| PGE1 infusion (prostaglandin E1, alprostadil) | Only if associated interrupted aortic arch (Type A4) — to maintain ductal patency for systemic circulation [2][4]. In isolated TA, PGE1 is generally not indicated because TA is not ductal-dependent [3][4] |
Why Is PGE1 NOT Routinely Used in Truncus Arteriosus?
A common misconception is that all cyanotic CHD needs PGE1. Truncus arteriosus is NOT ductal-dependent — the PAs arise directly from the trunk at systemic pressure, so pulmonary blood flow does not depend on the ductus [3][4]. Giving PGE1 in isolated TA can actually worsen heart failure by further lowering PVR and increasing pulmonary overcirculation. However, if the TA is associated with interrupted aortic arch (Type A4), then PGE1 IS needed to maintain systemic circulation to the lower body via the ductus.
Stabilisation and management of heart failure before surgery: e.g. diuretics, inotropes, ACEI [2]
Heart failure develops as PVR falls in the first days to weeks of life. Medical therapy is a bridge to surgery, not definitive treatment.
| Drug Class | Specific Agent | Dose (Paediatric) | Mechanism | Why Used in TA |
|---|---|---|---|---|
| Diuretics | Furosemide (frusemide) | 1–2 mg/kg/dose PO/IV BD-TDS | Loop diuretic → inhibits Na⁺/K⁺/2Cl⁻ cotransporter in thick ascending limb → reduces fluid reabsorption → decreases preload and pulmonary congestion | Directly addresses pulmonary oedema and fluid overload from pulmonary overcirculation [2][8] |
| Spironolactone | 1–3 mg/kg/day PO in 1–2 divided doses | Aldosterone antagonist → K⁺-sparing diuretic; also anti-fibrotic effects on the myocardium | Synergistic with furosemide; prevents hypokalaemia; long-term benefit on cardiac remodelling [8] | |
| ACE inhibitors | Captopril | 0.1–0.5 mg/kg/dose PO TDS (neonates: start 0.01–0.05 mg/kg) | Inhibits ACE → ↓angiotensin II → ↓afterload (systemic vasodilation) + ↓aldosterone → ↓fluid retention | Reduces systemic vascular resistance → more balanced distribution of cardiac output between systemic and pulmonary circulations (lowering SVR diverts some flow systemically, partially reducing the L-to-R shunt) [2][8] |
| Enalapril | 0.1 mg/kg/day PO in 1–2 doses | Same mechanism as captopril; longer acting | Alternative to captopril; fewer doses needed | |
| Inotropes (if decompensated) | Dobutamine | 5–20 µg/kg/min IV infusion | β₁ agonist → ↑contractility + mild ↓afterload (β₂) | For acute decompensation with poor cardiac output [2][8] |
| Milrinone | 0.25–0.75 µg/kg/min IV infusion (± loading dose 50 µg/kg over 15 min) | PDE-3 inhibitor → "inodilator" → ↑contractility + ↓afterload + ↓PVR | Particularly useful in TA because it reduces both systemic and pulmonary vascular resistance while augmenting contractility; used peri-operatively [8] | |
| Digoxin | 5–10 µg/kg/day PO maintenance (after loading) | Inhibits Na⁺/K⁺-ATPase → ↑intracellular Ca²⁺ → ↑contractility; also vagotonic (slows HR) | Seldom used in modern paediatric practice due to narrow therapeutic index; risk of toxicity is high especially with electrolyte disturbances (hypokalaemia, hypercalcaemia) [8] |
Nutritional Support — A Critical and Often Underestimated Component
| Strategy | Details |
|---|---|
| High-calorie feeds | Infants with TA have increased metabolic demand from heart failure + poor feeding tolerance → caloric requirement may be 120–150 kcal/kg/day (vs normal ~100–120 kcal/kg/day) |
| Concentrated formula | High-calorie formula (e.g., 1 kcal/mL formula) to deliver more calories in smaller volumes — important because these infants cannot tolerate large-volume feeds |
| Nasogastric (NG) tube feeds | If the infant tires during oral feeds or has poor weight gain despite optimised HF therapy → continuous or bolus NG feeds to ensure adequate caloric intake |
| Fluid restriction | Mild fluid restriction (120–150 mL/kg/day rather than 150–180 mL/kg/day) to reduce volume overload; balance with caloric needs by using concentrated feeds |
| Breast milk fortification | Human milk fortifier (HMF) can be added to expressed breast milk to increase caloric density |
Why Is Nutritional Support So Important?
Failure to thrive is one of the earliest and most common manifestations of TA. These infants are "running a marathon at rest" — their hearts are working at maximum capacity to handle the volume and pressure overload. If caloric intake does not meet this demand, weight loss and wasting develop rapidly, increasing surgical risk. Optimising nutrition pre-operatively directly improves surgical outcomes.
3. Phase 2: Definitive Surgical Repair
Definitive surgical repair: usually at ~3 months of age [2]
- In current practice (2024–2026), many centres aim for repair at 4–12 weeks of age (some as early as the neonatal period if the infant is deteriorating despite medical therapy)
- Why not immediately after birth? In the first days of life, PVR is still relatively high, so the haemodynamic burden is manageable. Surgery is technically easier and outcomes better if the infant has a few weeks of growth. However, delay beyond 3 months risks irreversible pulmonary vascular disease
- Why not delay further? The PAs are exposed to full systemic pressure from birth → irreversible pulmonary vascular remodelling (Eisenmenger physiology) can develop as early as 3–6 months [2]
- If interrupted aortic arch (Type A4) is present → repair is urgent/emergent (neonatal period) because the systemic circulation is duct-dependent
The definitive operation for truncus arteriosus is a complete biventricular repair involving three key steps [2]:
| Surgical Step | Details | Why This Step Is Needed |
|---|---|---|
| 1. VSD closure with a prosthetic patch | The conoventricular VSD is closed with a patch (Dacron or Gore-Tex), directing LV outflow exclusively into the truncal root (which becomes the neo-aorta) | Without VSD closure, mixing would continue → persistent cyanosis. The patch separates the LV from the RV, so the LV supports the systemic circulation through the trunk [2] |
| 2. PA mobilisation from the trunk and RV-to-PA valved conduit | The pulmonary arteries are detached (mobilised) from the common trunk. A valved conduit (homograft — typically a cryopreserved pulmonary or aortic homograft, or a bovine jugular vein graft / Contegra conduit) is placed to connect the RV to the detached PA confluence | This creates a separate RV outflow tract, establishing two-ventricle physiology. The valve within the conduit prevents pulmonary regurgitation. Without this step, there would be no pathway for RV blood to reach the lungs [2] |
| 3. Repair of the trunk (neo-aorta) with a patch | The defect in the trunk (where the PAs were detached) is repaired with a patch of pulmonary homograft tissue or autologous pericardium | Prevents bleeding and maintains the structural integrity of the neo-aorta [2] |
| 4. Truncal valve repair (if needed) | If significant truncal valve regurgitation is present, the valve may undergo repair (leaflet plication, commissuroplasty) or, rarely, replacement | Truncal valve abnormalities are associated with increased perioperative morbidity and mortality [2] |
| 5. Interrupted aortic arch repair (if Type A4) | Direct anastomosis of the aortic arch segments or interposition graft | Restores aortic continuity for systemic perfusion |
| Conduit Type | Details | Advantages | Disadvantages |
|---|---|---|---|
| Pulmonary homograft | Cryopreserved cadaveric pulmonary artery with valve | Excellent haemodynamics; good valve function initially | Calcification and degeneration over time; limited availability; will be outgrown requiring replacement |
| Aortic homograft | Cryopreserved cadaveric aortic root with valve | Good structural integrity | Same limitations as pulmonary homograft; less ideal for RV-PA position |
| Bovine jugular vein graft (Contegra) | Bovine jugular vein with intact venous valve | Off-the-shelf availability in small sizes suitable for neonates/infants; good early results | Risk of conduit stenosis (especially at distal anastomosis); endocarditis risk; also degenerates over time |
| Mechanical valved conduit | Dacron conduit with mechanical valve | Durable valve function | Lifelong anticoagulation → extremely problematic in paediatrics (growth, compliance, bleeding risk); rarely used in infants |
The Inevitability of Re-Operation
All children who undergo TA repair will need conduit replacement at least once (often multiple times) during childhood and adolescence. The conduit does not grow with the child. As the child grows, the conduit becomes relatively stenotic, and biological conduits degenerate. Families must be counselled about this at the time of initial surgery.
Associated with increased perioperative morbidity/mortality due to truncal valve abnormalities and liability to develop severe pulmonary hypertension [2]
| Factor | Impact on Outcome |
|---|---|
| Truncal valve regurgitation | Severe regurgitation at the time of repair is the strongest predictor of perioperative mortality; increases volume load on the heart intra- and post-operatively [2] |
| Truncal valve stenosis | Adds pressure load; may complicate VSD patch placement |
| Interrupted aortic arch | Increases surgical complexity and CPB time; a/w higher mortality |
| Age at repair | Repair beyond 3–6 months → higher risk due to developing pulmonary vascular disease |
| Low birth weight / prematurity | Smaller vessels, higher perioperative risk |
| DiGeorge syndrome | Immune deficiency → post-operative infection risk; hypocalcaemia → arrhythmia risk; irradiated blood products may be needed if T-cell deficiency is severe [5][7] |
| Coronary anomalies | Aberrant coronary artery courses may be injured during surgery |
Modern surgical mortality: In experienced centres, operative mortality for TA repair is approximately 5–10% (higher if severe truncal valve regurgitation or IAA is present).
4. Phase 3: Post-Operative Care and Lifelong Follow-Up
| Aspect | Details |
|---|---|
| Ventilation | Mechanical ventilation weaned as tolerated; avoid hyperventilation (which lowers PaCO₂ → pulmonary vasodilation → can unmask residual conduit issues) |
| Haemodynamic monitoring | Invasive BP, CVP, LA line (if placed); watch for low cardiac output syndrome |
| Milrinone infusion | Standard post-CPB inodilator; reduces afterload, supports contractility, and lowers PVR |
| Pulmonary hypertensive crises | Risk especially in late repairs; managed with inhaled nitric oxide (iNO) at 20 ppm → selective pulmonary vasodilator; IV sildenafil as adjunct |
| Pacing wires | Temporary epicardial pacing wires placed intra-operatively; used if post-operative heart block (from VSD patch closure near the conduction system) |
| Blood products | Irradiated blood products if DiGeorge syndrome with significant T-cell deficiency (to prevent transfusion-associated graft-versus-host disease) [5] |
| Calcium monitoring | Essential if DiGeorge — hypocalcaemia exacerbated by CPB, citrate in blood products |
| Antibiotic prophylaxis | Perioperative antibiotics; continued as per local protocol |
AV (truncal valve) replacement with chronic truncal valve insufficiency [2]
| Issue | Timeline | Management |
|---|---|---|
| Conduit stenosis / regurgitation | Progressive; first re-intervention often needed by 5–10 years post-repair (earlier if small conduit placed in infancy) | Catheter-based: Balloon dilation of conduit stenosis ± stenting; percutaneous pulmonary valve implantation (e.g., Melody valve or Edwards SAPIEN) now standard for suitable anatomy. Surgical: Conduit replacement with a larger homograft or bioprosthetic conduit when catheter options are exhausted |
| PA branch stenosis | May develop at the site of PA mobilisation or at conduit-PA anastomosis | Catheter balloon dilation ± stenting |
| Truncal valve (neo-aortic valve) regurgitation | Progressive in those with abnormal truncal valve morphology | Valve repair if feasible; valve replacement (mechanical or bioprosthetic) if severe and irreparable [2] |
| Residual VSD leak | Usually small and haemodynamically insignificant; may close spontaneously | Surgical or catheter closure if haemodynamically significant |
| Arrhythmias | Late complication from scar tissue, VSD patch proximity to conduction system | Electrophysiology assessment; antiarrhythmic therapy or ablation |
| Pulmonary hypertension | If repair was late or if residual PA issues persist | Pulmonary vasodilator therapy (sildenafil, bosentan); monitoring with echo and cath |
| Endocarditis prophylaxis | Lifelong — prosthetic material (conduit, VSD patch, prosthetic valve) | Antibiotic prophylaxis before dental and certain surgical procedures (amoxicillin 50 mg/kg PO 1 hour before procedure) |
| Exercise counselling | Individualised based on residual haemodynamic burden | Most can participate in moderate recreational activity; competitive sports restriction if significant residual lesions [8] |
5. Special Considerations
If a child with TA presents late (beyond 6–12 months) and has developed irreversible pulmonary vascular disease (Eisenmenger physiology), surgical repair is contraindicated:
- Why? Closing the VSD and establishing two-ventricle physiology in the setting of fixed elevated PVR would cause acute RV failure (the RV cannot pump against the high PVR without the "pop-off" of the VSD)
- Assessment: Cardiac catheterisation to measure PVR and test vasoreactivity
- If PVR > 8 Wood units·m² or PVR index > 6–8 with no vasoreactivity → inoperable
- Management of inoperable patients: Pulmonary vasodilator therapy (sildenafil, bosentan, epoprostenol/treprostinil); palliative care; eventual consideration of heart-lung transplantation (very limited availability)
| Issue | Management |
|---|---|
| Immunodeficiency | Avoid live vaccines (BCG, MMR, varicella, rotavirus) if severe T-cell deficiency; irradiated blood products; CMV-negative blood; Pneumocystis prophylaxis (cotrimoxazole) if CD4 count severely low; thymic transplant in complete DiGeorge (very rare) [5][7] |
| Hypocalcaemia | Oral calcium and calcitriol (1,25-dihydroxyvitamin D₃) supplementation; monitor closely peri-operatively |
| Speech/feeding | Cleft palate → speech therapy, surgical repair; velopharyngeal insufficiency → speech bulb or pharyngoplasty |
| Neurodevelopment | Learning difficulties and behavioural issues common; early intervention with developmental paediatrician |
| Genetic counselling | De novo in ~90%; 50% recurrence risk if parent carries deletion; offer testing to parents |
| Contraindication | Rationale |
|---|---|
| Irreversible pulmonary vascular disease (Eisenmenger) | Fixed PVR → RV failure post-repair → death |
| Active uncontrolled sepsis | Increased perioperative mortality; need to stabilise first |
| Severe associated anomalies incompatible with life | Palliative approach may be more appropriate |
| Drug | Paediatric Formulation | Key Monitoring | Cautions |
|---|---|---|---|
| Furosemide | Oral solution 10 mg/mL; IV 10 mg/mL | Electrolytes (K⁺, Na⁺, Ca²⁺), renal function, fluid balance | Ototoxicity with rapid IV push; hypokalaemia |
| Spironolactone | Oral suspension (extemporaneous — "special") 5–10 mg/mL | K⁺ (risk of hyperkalaemia with ACEI) | Gynecomastia (long-term) |
| Captopril | Oral solution 1 mg/mL (special preparation) | BP (first-dose hypotension), renal function, K⁺ | Start with very low dose in neonates (0.01 mg/kg); titrate cautiously |
| Milrinone | IV only; 1 mg/mL | Continuous BP and HR monitoring; arrhythmia risk | Thrombocytopenia; hypotension if volume depleted |
| PGE1 (Alprostadil) | IV infusion 0.01–0.05 µg/kg/min | Apnoea (10–12%), temperature, BP | Only for Type A4 with IAA; intubation equipment must be at bedside; causes apnoea → may need ventilatory support |
High Yield Summary – Management of Truncus Arteriosus
- Medical stabilisation of heart failure before surgery: diuretics (furosemide + spironolactone), ACEI (captopril/enalapril), inotropes if decompensated (dobutamine/milrinone), nutritional support [2]
- PGE1 is NOT routinely indicated — TA is not ductal-dependent [3][4]. Only use if Type A4 (associated interrupted aortic arch)
- Caution with supplemental O₂ — ↓PVR → worsens pulmonary overcirculation and heart failure [8]
- Definitive surgical repair at ~2–3 months (some centres: 4–12 weeks) [2]:
- VSD closure with prosthetic patch
- RV-to-PA valved conduit (PA mobilised from trunk)
- Truncus repair with homograft/pericardial patch
- Truncal valve abnormalities increase perioperative morbidity/mortality [2]
- Early Eisenmenger risk (by 3–6 months) mandates early repair
- Conduit replacement is inevitable — all children will need re-intervention (catheter-based or surgical) as they grow
- Truncal valve replacement for chronic truncal valve insufficiency [2]
- Lifelong endocarditis prophylaxis required (prosthetic material)
- DiGeorge syndrome management: screen and manage hypocalcaemia, immunodeficiency (irradiated blood products, avoid live vaccines), speech/feeding issues, neurodevelopment [5][7]
Active Recall - Management of Truncus Arteriosus
References
[1] GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (slides 31–33 — Truncus Arteriosus) [2] Adrian Lui Pediatrics Notes.pdf (Pages 220–221, 233 — Truncus Arteriosus management, surgical repair, truncal valve replacement) [3] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 280 — ductal dependence table; Page 287 — TA physiology: NOT ductal-dependent) [4] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Pages 593–595 — ductal dependence; Page 600 — TA physiology) [5] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 268 — DiGeorge syndrome, CATCH-22) [7] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Page 581 — DiGeorge syndrome, CATCH-22) [8] Adrian Lui Pediatrics Notes.pdf (Page 200 — HF management in paediatrics: diuretics, ACEI, inotropes, O₂ caution, nutritional support)
Complications of Truncus Arteriosus
Complications of truncus arteriosus can be divided into those arising from the natural history of the unrepaired lesion, those occurring in the perioperative period, and those that develop as late sequelae after surgical repair. Understanding each complication requires tracing it back to the underlying anatomy and physiology.
1. Complications of the Unrepaired Lesion (Natural History)
Without surgical intervention, truncus arteriosus carries > 80% mortality in the first year of life. The complications arise directly from the pathophysiology of common mixing and unrestricted pulmonary blood flow.
| Mechanism | Details |
|---|---|
| Why it occurs | As PVR falls postnatally (over the first days to weeks), the PAs — arising from the trunk at systemic pressure — receive torrential blood flow. This creates massive pulmonary venous return → LV volume overload. Simultaneously, the RV is exposed to systemic pressure through the obligatory VSD → RV pressure overload. The combined biventricular burden leads to progressive heart failure [1][2] |
| Timeline | Heart failure symptoms predominate as pulmonary vascular resistance decreases after birth [1] — typically manifesting at 1–4 weeks of age |
| Clinical manifestation | Tachypnoea, feeding difficulty, diaphoresis, hepatomegaly, failure to thrive, recurrent respiratory infections |
| Why it is the leading cause of death | Without surgical repair, the heart cannot sustain the volume and pressure overload → progressive biventricular failure → death, typically within the first 6 months |
This is the most feared long-term complication if repair is delayed.
| Mechanism | Details |
|---|---|
| Why it occurs | The PAs are exposed to full systemic pressure from birth (they arise directly from the trunk). This is a much more severe haemodynamic insult than in a large VSD (where the defect offers some resistance). Chronic exposure of the pulmonary vasculature to high pressure and high flow triggers medial hypertrophy → intimal proliferation → plexiform lesions in the pulmonary arterioles — these changes become irreversible [6] |
| Timeline | Can develop as early as 3–6 months of age in TA — much earlier than in VSD or PDA (which may take years). This is why surgical repair must be completed by ~2–3 months [2] |
| Consequence | Once PVR is fixed and elevated, the shunt reverses (R→L) → Eisenmenger syndrome: progressive cyanosis, exercise intolerance, erythrocytosis, haemoptysis, right heart failure, paradoxical embolism (stroke, brain abscess), and ultimately death [6] |
| Inoperability | Surgical repair becomes contraindicated because closing the VSD in the setting of fixed elevated PVR would cause acute RV failure (the RV cannot pump against the high resistance without the VSD acting as a "pop-off") |
Why Does Eisenmenger Develop So Early in TA?
In truncus arteriosus, the PAs arise directly from the systemic-pressure trunk — there is no intervening obstruction to buffer the pressure. Compare this with a large VSD, where some pressure is dissipated across the defect itself. The unprotected pulmonary vasculature in TA is exposed to the full force of systemic pressure from the moment of birth, driving accelerated and irreversible pulmonary arteriolar remodelling. This is why TA has one of the shortest windows for operability among all CHD [2][6].
| Mechanism | Details |
|---|---|
| Why it occurs | Diastolic runoff: Blood runs from the high-pressure trunk into the low-resistance PA bed during diastole → lowers diastolic pressure in the trunk → decreases coronary perfusion pressure (coronary arteries fill predominantly in diastole). This "coronary steal" phenomenon can lead to subendocardial ischaemia, particularly under conditions of increased myocardial oxygen demand (tachycardia, heart failure) [2] |
| Clinical significance | May manifest as unexplained myocardial dysfunction, ventricular arrhythmias, or sudden cardiac death in the unrepaired infant. Often subclinical but contributes to overall cardiac decompensation |
| Mechanism | Details |
|---|---|
| Why it occurs | The truncal valve is frequently abnormal (bicuspid, quadricuspid, dysplastic cusps) → progressive regurgitation over time. The regurgitant volume adds to the already massive volume load on the LV (from pulmonary overcirculation) |
| Consequence | Accelerates heart failure; increases surgical risk when repair is eventually performed [2] |
| Mechanism | Details |
|---|---|
| Why it occurs | Heart failure → ↑metabolic demand (the overworking heart + increased respiratory effort consume enormous calories) + ↓oral intake (infants tire during feeds due to tachypnoea and respiratory distress) + ↓absorption (gut oedema from venous congestion reduces nutrient absorption) |
| Timeline | Weight falls first, then length, head circumference usually spared (growth failure pattern of chronic heart failure) [9] |
| Impact | Poor nutritional status increases surgical risk; catch-up growth usually occurs after successful repair |
| Mechanism | Details |
|---|---|
| Why it occurs | Pulmonary overcirculation → pulmonary congestion and oedema → oedematous, engorged lungs are a perfect medium for bacterial proliferation; impaired mucociliary clearance; ↓cough effectiveness from respiratory muscle fatigue |
| Consequence | Pneumonia, bronchiolitis episodes more frequent and more severe; each infection episode further destabilises the infant and may precipitate acute heart failure decompensation |
2. Perioperative Complications
Associated with increased perioperative morbidity/mortality due to truncal valve abnormalities and liability to develop severe pulmonary hypertension [2]
| Mechanism | Details |
|---|---|
| Why it occurs | The pulmonary vasculature has been exposed to systemic pressure preoperatively. Even after successful repair, the pulmonary arterioles remain reactive and prone to acute spasm. Stimuli such as suctioning, pain, hypoxia, acidosis, or hypothermia can trigger acute severe pulmonary vasoconstriction → sudden ↑PVR → ↑RV afterload → acute RV failure → cardiovascular collapse |
| Timeline | Most common in the first 24–72 hours post-operatively |
| Management | Inhaled nitric oxide (iNO, 20 ppm) — selective pulmonary vasodilator; IV sildenafil; deep sedation and paralysis to minimise stimulation; avoid hypoxia, acidosis, and hypothermia; gentle ventilation strategy |
| Risk factors | Late repair (older age at surgery → more advanced pulmonary vascular changes); pre-operative elevated PVR |
| Mechanism | Details |
|---|---|
| Why it occurs | Cardiopulmonary bypass (CPB) causes myocardial stunning (ischaemia-reperfusion injury); aortic cross-clamp time → myocardial ischaemia; hypothermia; post-operative volume shifts. In TA specifically, the chronically volume-overloaded LV and pressure-overloaded RV are particularly vulnerable |
| Timeline | Typically nadir at 8–12 hours post-CPB |
| Clinical features | Tachycardia, cool peripheries, poor urine output, rising lactate, narrow pulse pressure |
| Management | Milrinone (inodilator), volume optimisation, vasopressin if vasodilatory shock, ECMO if refractory |
| Mechanism | Details |
|---|---|
| Why it occurs | The VSD in TA is conoventricular — located close to the His bundle and bundle branches (conduction system). Suturing the VSD patch in this area can damage the conduction system → complete heart block (CHB) or right bundle branch block (RBBB) |
| Incidence | ~5–10% transient; ~2–3% require permanent pacemaker |
| Management | Temporary epicardial pacing wires (placed intraoperatively); if CHB persists > 7–10 days post-operatively → permanent pacemaker implantation |
| Lesion | Mechanism | Consequence |
|---|---|---|
| Residual VSD | Incomplete patch closure or suture dehiscence | Continued L→R shunt → persistent volume overload; may require re-operation if haemodynamically significant |
| Residual truncal valve regurgitation | Inadequate valve repair; progressive degeneration | Continued volume overload → LV dilation and failure |
| Conduit obstruction | Kinking, thrombosis, or technical issues at anastomosis | Acute RV pressure overload → RV failure; may need emergent revision |
| PA branch stenosis | Distortion from mobilisation of PAs from the trunk or tension at anastomotic site | RV pressure overload; unequal lung perfusion |
| Mechanism | Details |
|---|---|
| Why it occurs | Complex surgery with CPB → coagulopathy (dilutional, consumptive); multiple suture lines (VSD patch, conduit anastomoses, trunk repair patch); heparinisation during CPB. DiGeorge syndrome may compound coagulation issues (chronic liver congestion, poor nutrition) |
| Management | Meticulous surgical haemostasis; protamine for heparin reversal; blood products (platelets, FFP, cryoprecipitate); tranexamic acid |
| Mechanism | Details |
|---|---|
| Why it occurs | ~35% of TA patients have DiGeorge syndrome → thymic hypoplasia → T-cell immunodeficiency. Post-operative stress, CPB-related immunomodulation, and central lines create an environment of high infection risk. Opportunistic infections (Pneumocystis jirovecii, CMV) may occur if T-cell deficiency is severe [5][7] |
| Prevention | Irradiated, CMV-negative blood products; Pneumocystis prophylaxis (cotrimoxazole) if significant T-cell deficiency; aseptic technique; broad-spectrum perioperative antibiotics |
3. Late / Long-Term Complications (Post-Repair)
These are the complications that require lifelong surveillance and often multiple re-interventions.
| Mechanism | Details |
|---|---|
| Why it occurs | The RV-to-PA conduit (biological homograft or xenograft) does not grow with the child. Additionally, biological conduits undergo progressive calcification, fibrosis, and degeneration over time. The combination of somatic growth and conduit degeneration results in progressive obstruction |
| Timeline | First conduit replacement typically needed by 5–10 years post-initial repair; many patients require 2–4 conduit replacements during childhood and adolescence |
| Clinical features | Exercise intolerance, new ESM at LUSB (conduit stenosis), signs of RV failure (hepatomegaly, peripheral oedema, elevated JVP in older children) |
| Detection | Serial echocardiography (RV pressure estimation, conduit gradient); cardiac MRI (RV volumes, conduit flow); cardiac catheterisation if intervention planned |
| Management | Catheter-based: Balloon dilation of conduit stenosis ± stenting; percutaneous pulmonary valve implantation (e.g., Melody valve, Edwards SAPIEN) — an increasingly used strategy that delays the need for open surgical conduit replacement. Surgical: Conduit replacement with a larger conduit when catheter options are exhausted |
Why Is Conduit Replacement Inevitable?
All biological conduits placed in infancy will eventually fail. A conduit that is appropriate for a 3-month-old infant (typically 10–12 mm diameter) will become severely stenotic as the child grows to 20–30 kg. Additionally, immune-mediated rejection of allograft tissue, calcification, and intimal peel formation progressively narrow the conduit lumen. This is the single most common reason for re-operation in repaired TA.
AV replacement with chronic truncal valve insufficiency [2]
| Mechanism | Details |
|---|---|
| Why it occurs | The truncal valve is inherently abnormal (dysplastic cusps, abnormal number of cusps). Even after successful initial repair, progressive cusp degeneration, annular dilatation, or leaflet prolapse can worsen regurgitation over years. The trunk (now the neo-aorta) is exposed to full systemic pressure, accelerating wear [2] |
| Consequence | Chronic volume overload of the LV → progressive LV dilation and dysfunction |
| Management | Valve repair if anatomy is favourable (leaflet plication, commissuroplasty); valve replacement (mechanical → lifelong warfarin anticoagulation, or bioprosthetic → limited durability) if repair not feasible [2]. In children, the Ross procedure may occasionally be considered but is complex in the setting of a previously repaired trunk |
| Mechanism | Details |
|---|---|
| Why it occurs | The PAs were mobilised from the trunk during initial surgery — the sites of detachment and re-anastomosis to the conduit can develop scar tissue and narrowing. Extrinsic compression by the conduit may also contribute |
| Consequence | Unequal lung perfusion; ↑RV pressure (pressure overload) → RV dysfunction |
| Management | Catheter balloon dilation ± stenting of PA branches; surgical patch augmentation if diffuse or proximal |
| Mechanism | Details |
|---|---|
| Why it occurs | The trunk (neo-aorta) receives the entire cardiac output at systemic pressure. Over decades, the wall may progressively dilate, especially if the truncal valve is regurgitant (volume overload accelerates root dilatation) |
| Consequence | Worsening truncal valve regurgitation (annular dilatation prevents coaptation); risk of dissection (very rare); aortic rupture (extremely rare) |
| Surveillance | Serial echo and/or MRI to measure neo-aortic root dimensions |
| Mechanism | Details |
|---|---|
| Why it occurs | Surgical scarring from VSD patch, conduit placement, and ventriculotomy (incision in the RV free wall for conduit placement) creates substrates for re-entrant circuits. Additionally, chronic RV pressure overload (from conduit stenosis) causes RV dilation and fibrosis → arrhythmogenic substrate |
| Types | Ventricular tachycardia (VT) — most dangerous; atrial tachycardia/flutter (from atrial dilation); complete heart block (if conduction system was damaged at initial repair) |
| Clinical significance | Risk of sudden cardiac death (SCD) — estimated at 1–2% per decade in repaired complex CHD |
| Management | Holter monitoring; electrophysiology study; antiarrhythmic drugs (amiodarone, sotalol); catheter ablation; ICD implantation if sustained VT or high risk |
| Mechanism | Details |
|---|---|
| Why it occurs | Prosthetic material (VSD patch, conduit, conduit valve, any prosthetic truncal valve) creates a nidus for bacterial adhesion and biofilm formation. Turbulent flow across residual gradients damages endothelium → platelet-fibrin deposition → susceptible to bacterial seeding during bacteraemia |
| Organisms | Viridans group streptococci (post-dental); Staphylococcus aureus; coagulase-negative staphylococci (prosthetic material) |
| Prevention | Lifelong endocarditis prophylaxis before dental procedures and certain other procedures: Amoxicillin 50 mg/kg PO (max 2 g) 1 hour before procedure (or clindamycin 20 mg/kg PO if penicillin-allergic) |
| Importance | All repaired TA patients have residual prosthetic material and remain at high risk for IE for life |
| Mechanism | Details |
|---|---|
| Why it occurs | Even after timely repair, some degree of pulmonary vascular remodelling may have already occurred. Additionally, PA branch stenosis or conduit obstruction can elevate RV and PA pressures |
| Consequence | Limits exercise capacity; contributes to RV failure; may eventually progress |
| Management | Pulmonary vasodilators (sildenafil, bosentan); address any anatomical cause (conduit stenosis, PA stenosis) |
| Mechanism | Details |
|---|---|
| Cardiac surgery-related | CPB with hypothermia and circulatory arrest in the neonatal/infant period → risk of white matter injury, periventricular leukomalacia; intraoperative hypoxia or low cardiac output → neuronal injury |
| DiGeorge syndrome-related | 22q11.2 deletion independently associated with learning difficulties, attention deficit, speech and language delay, behavioural problems, psychiatric disorders (anxiety, ADHD, schizophrenia spectrum in adolescence/adulthood) [5][7] |
| Chronic cyanosis | Pre-operative chronic hypoxaemia (mild in TA, but still present) → may affect neurocognitive development |
| Management | Early developmental assessment; neurodevelopmental follow-up; speech and language therapy; educational support; psychological services |
These persist throughout life in the ~35% of TA patients with 22q11.2 deletion [5][7]:
| Complication | Mechanism | Management |
|---|---|---|
| Recurrent infections | T-cell immunodeficiency from thymic hypoplasia | Prophylactic antibiotics (cotrimoxazole if severe); avoid live vaccines; IVIG if hypogammaglobulinaemia develops |
| Hypocalcaemia | Hypoparathyroidism from parathyroid hypoplasia | Calcium and calcitriol supplementation; monitoring at times of stress (illness, surgery) |
| Speech and feeding difficulties | Cleft palate; velopharyngeal insufficiency | Surgical cleft repair; speech therapy; feeding support |
| Psychiatric disorders | Intrinsic to 22q11.2 deletion | Screening for anxiety, ADHD; psychiatric referral in adolescence |
| Phase | Key Complications |
|---|---|
| Unrepaired (natural history) | CHF (weeks), failure to thrive, recurrent respiratory infections, coronary insufficiency, progressive truncal valve regurgitation, Eisenmenger syndrome (3–6 months) |
| Perioperative | Pulmonary hypertensive crises, low cardiac output syndrome, heart block, bleeding, infection (especially DiGeorge), residual lesions |
| Late post-repair | Conduit stenosis/degeneration (inevitable), truncal valve regurgitation (need for valve replacement) [2], PA branch stenosis, neo-aortic root dilatation, arrhythmias, infective endocarditis, residual pulmonary hypertension, neurodevelopmental issues |
High Yield Summary – Complications of Truncus Arteriosus
- Without repair: > 80% first-year mortality from CHF (as PVR falls) and Eisenmenger syndrome (as early as 3–6 months)
- Heart failure symptoms predominate as PVR decreases after birth [1] — this is the primary mode of deterioration
- Increased perioperative morbidity/mortality due to truncal valve abnormalities and liability to develop severe pulmonary hypertension [2]
- Pulmonary hypertensive crises are the most dangerous perioperative complication — managed with inhaled NO
- Heart block from VSD patch closure near the conduction system (~2–3% need permanent pacemaker)
- Conduit replacement is inevitable — the RV-to-PA conduit does not grow and biological conduits degenerate; most need re-intervention by 5–10 years
- Truncal valve (neo-aortic valve) replacement for chronic truncal valve insufficiency [2]
- Infective endocarditis — lifelong prophylaxis required (prosthetic material)
- DiGeorge-related complications in ~35%: immunodeficiency (irradiated blood products, avoid live vaccines), hypocalcaemia, speech/feeding issues, neurodevelopmental/psychiatric concerns [5][7]
- Arrhythmias — risk of VT and sudden cardiac death from surgical scarring and chronic RV pressure overload
- Lifelong follow-up is mandatory — these patients are never "cured"
Active Recall - Complications of Truncus Arteriosus
References
[1] GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 2.pdf (slides 31–33 — Truncus Arteriosus: "cyanosis usually mild; heart failure symptoms predominate as PVR decreases after birth"; common mixing conditions classification) [2] Adrian Lui Pediatrics Notes.pdf (Pages 220–221, 233 — Truncus Arteriosus: increased perioperative morbidity/mortality due to truncal valve abnormalities and liability to develop severe pHT; AV replacement with chronic truncal valve insufficiency; biventricular repair details) [3] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 280 — categorisation of cyanotic CHD; Page 287 — TA physiology: NOT ductal-dependent) [4] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Page 600 — Truncus arteriosus physiology) [5] MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (Page 268 — DiGeorge syndrome, CATCH-22) [6] Ryan Ho Cardiology.pdf (Page 186 — Eisenmenger syndrome: mechanism, symptoms, signs, complications, management) [7] MBBS Final MB (Medicine) (Felix PY Lai).pdf (Page 581 — DiGeorge syndrome, CATCH-22) [9] Adrian Lui Pediatrics Notes.pdf (Page 184 — Congestive HF: weight drops before height and HC)
High Yield Summary
Truncus Arteriosus — Key Points for Exams:
- Definition: Single arterial trunk arising from the heart, overriding a VSD, supplying systemic, pulmonary, and coronary circulations due to failure of conotruncal septation
- Epidemiology: 6–10/100,000 live births; ~2% of all CHD but ~4% of critical CHD
- Association: Strongly associated with DiGeorge syndrome (22q11.2 deletion) — CATCH-22 mnemonic
- Classification: Collett & Edwards (Types I–IV, but Type IV is no longer true TA); Van Praagh (Types A1–A4, where A4 = TA + interrupted aortic arch)
- Pathophysiology: Common-mixing lesion → cyanosis + CHF; PAs at systemic pressure → torrential pulmonary flow as PVR falls; diastolic runoff → bounding pulses; early Eisenmenger risk (by 3–6 months)
- Key Clinical Features:
- Cyanosis + CHF (the hallmark of common-mixing)
- Bounding pulses (diastolic runoff)
- Single loud S2 (only one semilunar valve)
- Ejection click (truncal valve opening)
- ESM at LSB (high flow across truncal valve)
- Biventricular impulse on palpation
- CXR: Cardiomegaly + pulmonary plethora; ECG: Biventricular overload; Echo: Diagnostic
- Surgical repair needed by ~3 months (VSD patch closure + RV-to-PA conduit); without surgery, >80% first-year mortality
- Early Eisenmenger risk due to PAs exposed to systemic pressure from birth
- Screen ALL cases for 22q11.2 deletion, serum calcium, and lymphocyte subsets
High Yield Summary – DDx of Truncus Arteriosus
- Truncus arteriosus belongs to the "3 Ts" group of cyanotic CHD with increased pulmonary blood flow: TGA, Truncus arteriosus, TAPVR [3][4]
- NOT ductal-dependent — unlike TGA (which needs the duct for mixing) [3][4]
- The combination of cyanosis + CHF + bounding pulses + single S2 + ejection click is highly suggestive of TA
- Bounding pulses distinguish TA from TGA and TAPVR (diastolic runoff mechanism)
- Single S2 distinguishes TA from TAPVR and large VSD (which have two semilunar valves)
- DiGeorge syndrome (22q11.2 deletion) is a key syndromic clue — check calcium, thymus, immune function
- Aortopulmonary window is the closest haemodynamic mimic but has two separate semilunar valves and no VSD
- Hyperoxia test differentiates cardiac from respiratory cyanosis; CXR pattern (plethoric vs oligaemic) helps subcategorise cyanotic CHD
- Echocardiography is the definitive diagnostic tool to confirm the single arterial trunk and PA origin
High Yield Summary – Diagnosis and Investigations for Truncus Arteriosus
- No formal diagnostic criteria — diagnosis is anatomical, made by echocardiography
- Echo is the gold standard: shows single arterial trunk overriding VSD, truncal PA origin, truncal valve morphology [2]
- CXR: cardiomegaly + pulmonary plethora (similar to large L-to-R shunts) ± absent thymic shadow (DiGeorge) [2]
- ECG: biventricular overload (RV pressure + LV volume overload) [2]
- Hyperoxia test: PaO₂ fails to rise > 150 mmHg but may reach ~60–90 mmHg (intermediate, because pulmonary flow IS increased)
- CT angiography: for PA branch anatomy, aortic arch, coronary arteries — second-line
- Cardiac catheterisation: reserved for late presenters to assess PVR and operability
- Screen ALL cases for DiGeorge (22q11.2 deletion): FISH/microarray, serum calcium, lymphocyte subsets [5][7]
- Fetal echo can detect TA antenatally → allows delivery planning and immediate neonatal stabilisation
- Neonatal pulse oximetry screening will usually detect TA (SpO₂ 85–93%)
High Yield Summary – Management of Truncus Arteriosus
- Medical stabilisation of heart failure before surgery: diuretics (furosemide + spironolactone), ACEI (captopril/enalapril), inotropes if decompensated (dobutamine/milrinone), nutritional support [2]
- PGE1 is NOT routinely indicated — TA is not ductal-dependent [3][4]. Only use if Type A4 (associated interrupted aortic arch)
- Caution with supplemental O₂ — ↓PVR → worsens pulmonary overcirculation and heart failure [8]
- Definitive surgical repair at ~2–3 months (some centres: 4–12 weeks) [2]:
- VSD closure with prosthetic patch
- RV-to-PA valved conduit (PA mobilised from trunk)
- Truncus repair with homograft/pericardial patch
- Truncal valve abnormalities increase perioperative morbidity/mortality [2]
- Early Eisenmenger risk (by 3–6 months) mandates early repair
- Conduit replacement is inevitable — all children will need re-intervention (catheter-based or surgical) as they grow
- Truncal valve replacement for chronic truncal valve insufficiency [2]
- Lifelong endocarditis prophylaxis required (prosthetic material)
- DiGeorge syndrome management: screen and manage hypocalcaemia, immunodeficiency (irradiated blood products, avoid live vaccines), speech/feeding issues, neurodevelopment [5][7]
High Yield Summary – Complications of Truncus Arteriosus
- Without repair: > 80% first-year mortality from CHF (as PVR falls) and Eisenmenger syndrome (as early as 3–6 months)
- Heart failure symptoms predominate as PVR decreases after birth [1] — this is the primary mode of deterioration
- Increased perioperative morbidity/mortality due to truncal valve abnormalities and liability to develop severe pulmonary hypertension [2]
- Pulmonary hypertensive crises are the most dangerous perioperative complication — managed with inhaled NO
- Heart block from VSD patch closure near the conduction system (~2–3% need permanent pacemaker)
- Conduit replacement is inevitable — the RV-to-PA conduit does not grow and biological conduits degenerate; most need re-intervention by 5–10 years
- Truncal valve (neo-aortic valve) replacement for chronic truncal valve insufficiency [2]
- Infective endocarditis — lifelong prophylaxis required (prosthetic material)
- DiGeorge-related complications in ~35%: immunodeficiency (irradiated blood products, avoid live vaccines), hypocalcaemia, speech/feeding issues, neurodevelopmental/psychiatric concerns [5][7]
- Arrhythmias — risk of VT and sudden cardiac death from surgical scarring and chronic RV pressure overload
- Lifelong follow-up is mandatory — these patients are never "cured"
Tricuspid Atresia
Tricuspid atresia is a congenital heart defect present at birth in which the tricuspid valve between the right atrium and right ventricle fails to form, preventing normal blood flow to the lungs and requiring mixing of oxygenated and deoxygenated blood through associated septal defects, typically presenting with cyanosis in the neonatal period.
Total Anomalous Pulmonary Venous Return
Total anomalous pulmonary venous return is a congenital heart defect, typically presenting in the neonatal period, in which all four pulmonary veins fail to connect to the left atrium and instead drain anomalously into the systemic venous circulation, necessitating an atrial septal defect or patent foramen ovale to sustain systemic blood flow.