To understand why RCM is so devastating, you need to understand normal diastolic filling:

1. Isovolumetric relaxation: After the aortic valve closes, the ventricle actively relaxes (an energy-dependent process requiring ATP to pump calcium back into the sarcoplasmic reticulum via SERCA2a). Ventricular pressure drops rapidly.
2. Early rapid filling (E wave): When ventricular pressure drops below atrial pressure, the mitral valve opens and blood rushes in passively. This accounts for ~70–80% of filling in young healthy individuals.
3. Diastasis: A period of slow/minimal filling as atrial and ventricular pressures equilibrate.
4. Atrial contraction (A wave): The atrium contracts, pushing in the final ~20–30% of blood.

Normal ventricular compliance means the ventricle can accept this blood at low filling pressures (low left atrial pressure, low pulmonary venous pressure).

In RCM, the ventricular wall is abnormally stiff (↓ compliance). The stiff ventricle cannot expand easily during diastole. To push blood into this stiff chamber, filling pressures must be much higher than normal. This creates:

• Elevated left atrial pressure → transmitted backwards to pulmonary veins → pulmonary congestion
• Elevated right atrial pressure → transmitted backwards to systemic veins → systemic congestion (JVP elevation, hepatomegaly, ascites, peripheral oedema)

Importantly, early diastolic filling may be rapid (the initial rush of blood enters quickly because the pressure gradient is steep) but then filling abruptly stops once the stiff ventricle reaches its compliance limit. This produces the classic "dip-and-plateau" or "square root sign" on ventricular pressure tracings during cardiac catheterisation — a rapid early diastolic pressure drop (dip) followed by a plateau as the stiff ventricle resists further filling.

Normal ventricle: gentle, flat diastolic pressure-volume curve → can accept large volumes at low pressures.

RCM ventricle: steep diastolic pressure-volume curve → even small increases in volume produce large increases in pressure. The ventricle is operating on the steep portion of its compliance curve.

This is one of the most important clinical distinctions in cardiology. Both present with "restrictive physiology" but have fundamentally different causes and, critically, different treatments.

Chronic dyspnoea from cardiovascular disorders includes ^[8]:

From the Heart Failure lecture, after obtaining a diagnosis of HF, the structural DDx includes ^[9]:

• Heart rhythm disorders (bradycardia, tachycardia, loss of AV/VV synchrony)
• Congenital anomalies (volume/pressure overload)
• Pericardial disease (constrictive filling)
• Systemic pressure overload (hypertension)
• Pulmonary pressure overload (pulmonary hypertension)
• Valvular disease (pressure/volume overload)
• Myocardial disease (cardiomyopathies, past MI) — loss of contractile forces (systolic) or impaired relaxation (diastolic) ^[9]

Impaired relaxation → diastolic heart failure / HFpEF. The diastolic phase of the cardiac cycle is ATP-dependent — if the heart fails to relax, the chamber volume remains low and blood from the atrium cannot pass into the ventricle ^[9].

This is the fundamental physiology underlying RCM: the ventricle's wall is so stiff that relaxation is impaired → the chamber cannot fill → filling pressures rise → congestion.

This is the differential that matters most clinically and in exams.

Why it mimics RCM: Both produce impaired ventricular filling → elevated filling pressures → predominantly right-sided congestion (JVP ↑, hepatomegaly, ascites, oedema). Both show "dip-and-plateau" (square root sign) on catheterisation. Both cause Kussmaul sign.

Why distinguishing them matters: Constrictive pericarditis can be successfully treated surgically (pericardiectomy) or with anti-tuberculosis therapy ^[1]. RCM generally cannot be cured surgically — misdiagnosis leads to either unnecessary thoracotomy (if CP is wrongly diagnosed) or missed curative opportunity (if RCM is wrongly diagnosed when the patient actually has CP).

Since constrictive pericarditis will impair ventricular filling, appears as fluid overload in the peripherals (pulmonary oedema would be rare since fluid can't get there easily). Hence, differentiating the two is crucial because constrictive pericarditis is a condition that can be successfully treated surgically / anti-tuberculosis. ^[1]

Why it mimics RCM: HCM also causes diastolic dysfunction (the thickened myocardium is stiff) with preserved or mildly reduced EF. Some patients with HCM develop prominent diastolic filling impairment — so-called "restrictive physiology" on echo.

How to differentiate: HCM has inappropriate LV wall thickness (usually ≥ 15 mm, often asymmetric septal hypertrophy) — in RCM, wall thickness is normal or only mildly increased. HCM often has LVOT obstruction with SAM (systolic anterior motion of the mitral valve), dynamic murmur that increases with Valsalva / standing, and dagger-like Q waves in inferior/lateral leads on ECG ^[2]. Genetic testing shows sarcomere mutations in HCM.

Key conceptual point: HCM and RCM can actually overlap — some sarcomere gene mutations (especially troponin I) can produce either phenotype, reinforcing that cardiomyopathies exist on a spectrum.

Why it mimics RCM: Long-standing hypertension causes concentric LV hypertrophy → diastolic dysfunction → HFpEF. This is actually the most common cause of HFpEF overall.

How to differentiate: History of longstanding hypertension; concentric LVH (uniform wall thickening) on echo; LV wall thickening is appropriate to the degree of hypertension (unlike RCM where thickening is unexplained); responds to antihypertensive therapy with improvement in diastolic function. No infiltrative features on cardiac MRI.

Why it mimics RCM: Impaired filling → elevated filling pressures → low cardiac output.

How to differentiate: Tamponade is acute/subacute; pulsus paradoxus (> 10 mmHg drop in sBP with inspiration) is the hallmark — this is different from Kussmaul sign; echo shows pericardial effusion with diastolic chamber collapse; electrical alternans on ECG. Tamponade does NOT cause Kussmaul sign (because the RV CAN expand into the fluid-filled pericardial space during inspiration, unlike CP/RCM).

Why it mimics RCM: Elevated right-sided pressures → JVP ↑, hepatomegaly, ascites, oedema.

How to differentiate: Auscultatory findings of tricuspid murmur; echo shows valvular pathology rather than myocardial pathology; wall thickness and echotexture are normal.

Why it mimics RCM: Right-sided congestion, reduced exercise capacity, syncope.

How to differentiate: Echo shows elevated RVSP with dilated RV; look for underlying lung disease (COPD, ILD) or thromboembolic disease (CTEPH). RHC confirms elevated mPAP with normal or low PAWP (pre-capillary PH) ^[10]. In RCM, the PAWP is elevated (post-capillary).

Why it mimics RCM: Elevated JVP, facial swelling, upper body oedema.

How to differentiate: SVC obstruction causes non-pulsatile JVP elevation (static congestion, no waveform); restricted to upper body; no hepatomegaly or ascites (lower body venous drainage is normal). CT/MRI shows SVC mass or thrombus.

Why it mimics RCM: Ascites, hepatomegaly, oedema can all occur.

How to differentiate: In hepatic disease, JVP is normal (unless there is co-existing heart disease — "hepatocardiac" syndromes). Ascitic fluid analysis shows high SAAG (> 11 g/L) in portal hypertension but low protein (transudate) in cirrhosis vs. high protein in cardiac ascites. Liver biopsy shows cirrhotic changes rather than centrilobular congestion.

Physical examination findings ^[12]:

• Inspection: Dilated neck veins (elevated JVP) ^[12]
• Presence of Kussmaul's sign ^[12] — Kussmaul's sign = increase in jugular venous distension during inspiration. JVP normally decreases with inspiration due to reduced pressure in expanding thoracic cavity and increased volume afforded to RV expansion during diastole. Impaired filling of RV due to poor compliance of myocardium or pericardium will lead to increased blood flow back into jugular vein causing distension. Classically seen in patients with restrictive cardiomyopathy or constrictive pericarditis ^[12]
• Auscultation: Presence of S3 and rarely S4 ^[12]
• Pan-systolic murmurs (PSM) of MR and TR ^[12] — from annular dilatation secondary to atrial enlargement

JVP waveform in RCM: Look for prominent y descent (rapid early diastolic filling that abruptly halts against the stiff ventricle wall) and prominent a wave (forceful atrial contraction against non-compliant ventricle). If the patient is in AF, the a wave will be absent.

ECG shows non-specific findings including ST and T-wave changes, pathologic Q waves, BBB or impaired atrioventricular conduction ^[12].

CXR findings ^[12]:

• Normal ventricular chamber size or cardiomegaly ^[12] — important: the ventricle itself is usually NOT dilated (unlike DCM where cardiomegaly is prominent). Any cardiomegaly may reflect atrial enlargement
• Bilateral atrial enlargement ^[12] — double density sign (enlarged LA overlapping RA on PA view), splaying of the carina
• Pulmonary venous congestion ^[12] — upper lobe pulmonary venous distension (cephalisation), Kerley B lines, pleural effusions
• No pericardial calcification — calcified pericardium on CXR ^[3] favours constrictive pericarditis rather than RCM

• Why: BNP is released from ventricular cardiomyocytes in response to myocardial wall stretch
• In RCM, the myocardium is diseased and stretched by elevated filling pressures → ↑BNP due to myocardial stretching ^[3]
• In constrictive pericarditis, the myocardium itself is normal → BNP is normal or only mildly elevated
• Cut-offs for HF: NT-proBNP > 125 pg/mL (chronic) or > 300 pg/mL (acute) suggests HF; BNP > 35 pg/mL (chronic) or > 100 pg/mL (acute)
• Diagnostic value: Helps distinguish RCM (↑↑ BNP) from CP (normal/mildly ↑ BNP)

Cardiac MRI ^[1] — provides both structural and tissue characterisation information that echo cannot.

Cardiac MRI is increasingly the pivotal investigation because it provides non-invasive tissue characterisation. In many centres, a characteristic MRI pattern (e.g., diffuse subendocardial LGE with abnormal gadolinium kinetics in amyloidosis) may reduce the need for endomyocardial biopsy.

Endomyocardial biopsy ^[1][3] — endomyocardial biopsy is diagnostic ^[3] for RCM.

• Procedure: A bioptome is advanced (usually via the right internal jugular vein or femoral vein) into the RV and small samples of endocardium/myocardium are taken from the RV septum
• Why right ventricle? — thicker septal wall reduces risk of perforation (the RV free wall is thin → higher perforation risk); also, the RV is more accessible from the venous approach
• Risks: Cardiac perforation, pericardial tamponade, arrhythmia, tricuspid valve damage — hence not performed routinely, only when the diagnosis cannot be established non-invasively

What the biopsy shows for each cause:

Indicated if infiltrative processes are suspected ^[12]. Amyloidosis may also do peritoneal biopsy; sarcoidosis lymph node biopsy ^[1] — less invasive tissue sampling options when accessible.

Blood tests; other biopsies ^[1]:

Why they help: Diuretics reduce intravascular volume → ↓ filling pressures → ↓ pulmonary and systemic congestion → symptomatic relief of dyspnoea, oedema, ascites.

Why they are dangerous in RCM: The stiff ventricle is exquisitely preload-sensitive. Stroke volume in RCM depends heavily on adequate filling pressure. If you over-diurese, preload drops → stroke volume falls precipitously → hypotension, organ hypoperfusion, renal failure, syncope. There is a very narrow therapeutic window.

Slowing of HR to increase time for diastolic filling ^[13] is a key management principle in HFpEF/diastolic dysfunction, and this applies to RCM.

The physiology: The stiff ventricle needs as much time as possible during diastole to fill. Tachycardia shortens diastolic filling time disproportionately (diastole is the phase that shortens most as HR increases) → inadequate filling → ↓ stroke volume → ↓ cardiac output → worse symptoms.

Critical contraindications in cardiac amyloidosis: Verapamil/diltiazem and digoxin should be avoided in amyloid cardiomyopathy because amyloid fibrils selectively bind these drugs, increasing their effective tissue concentration and toxicity.

AF is extremely common in RCM (chronically dilated atria → structural remodelling). Loss of the atrial kick is particularly devastating in RCM because the stiff ventricle relies on atrial contraction for the final portion of filling.

Drug choice: Warfarin has the most evidence in cardiomyopathy-associated thrombus. DOACs (dabigatran, rivarelbaxaban, apixaban, edoxaban) may be used for AF but evidence in intracavitary thrombus is limited.

General measures ^[14]:

• Lifestyle: weight reduction, exercise, stop smoking, avoid alcohol/other cardiotoxins, low-Na diet ^[14]
• Treat exacerbating factors: HTN (to 130/80), hyperlipidaemia, DM, arrhythmia, anaemia, OSA ^[14]
• Other prophylactic: anticoagulation, immunisation, daily weights, close OP monitoring ^[14]
• Fluid restriction: Usually 1.5–2 L/day in symptomatic congestion
• Salt restriction: < 2 g sodium per day
• Exercise: Gentle, regular aerobic exercise is generally encouraged in stable HF. Avoid competitive/strenuous exercise

Prognosis if untreated: Median survival ~6 months with cardiac involvement → early recognition and treatment is critical.

TTR amyloidosis actually quite common, 10% of patients with HFpEF have this → have to know since there are treatments ^[1].

Key point: Cardiac iron overload is reversible with adequate chelation — one of the few causes of RCM where the myocardial disease can genuinely be reversed if treated early.

• Primarily supportive — there is no way to reverse established radiation fibrosis
• Manage as HFpEF with cautious diuretics
• Address co-existing radiation damage: coronary artery disease (PCI/CABG), valvular disease (surgery), pericardial disease (pericardiectomy if constrictive)

Intractable ventricular arrhythmias / heart failure → LVAD / heart transplant ^[1][5].

Prevalence: AF occurs in up to 60–70% of patients with RCM, making it the most common arrhythmia in this condition.

Pathophysiology: Chronically elevated atrial filling pressures → progressive atrial dilatation → structural remodelling of atrial myocardium (fibrosis, myocyte hypertrophy) → altered electrical conduction properties → development of re-entrant circuits → AF. Once AF develops, it tends to be permanent because the atrial substrate is irreversibly remodelled.

Clinical impact: Loss of the atrial kick is particularly devastating in RCM. In a normal heart, atrial contraction contributes ~20–30% of ventricular filling. In RCM, the stiff ventricle depends heavily on this "atrial kick" because passive early filling is severely limited. When AF eliminates this contribution:

• Cardiac output drops acutely (up to 25–30%)
• Filling pressures rise further
• Symptoms worsen dramatically — patients may present with acute decompensation or even cardiogenic shock upon development of AF

Thromboembolic risk: AF in the setting of dilated atria and low cardiac output creates conditions of severe blood stasis → very high risk of intracavitary thrombus formation → systemic embolism (see below).

Pathophysiology: Myocardial fibrosis (any cause), myocyte disarray, and infiltrative deposits create areas of abnormal conduction → re-entrant circuits within the ventricle → monomorphic VT. The heterogeneous myocardial substrate also increases dispersion of refractoriness → predisposes to VF.

Specific risks by cause:

• Cardiac sarcoidosis: VT is very common (~25–30% of patients) and is a leading cause of death. Granulomatous inflammation creates patchy scar → ideal substrate for re-entry
• Cardiac amyloidosis: VT less common than in sarcoidosis but can occur; more often the terminal arrhythmia is electromechanical dissociation (PEA) rather than VT/VF
• Haemochromatosis: VT can occur from iron-mediated myocyte damage

ICD for primary prevention in patients with low LVEF ^[13], though in RCM the EF is typically preserved, so the standard ICD implantation criteria (LVEF ≤ 35%) may not apply. ICD decisions in RCM are individualised based on specific aetiology and arrhythmia burden.

Pathophysiology: Infiltrative material (amyloid fibrils, sarcoid granulomas, iron) deposits within the cardiac conduction system — the sinoatrial (SA) node, atrioventricular (AV) node, and His-Purkinje fibres.

Sarcoidosis note: AV block is the most common cardiac manifestation of sarcoidosis — may be the presenting feature even before heart failure symptoms. Should prompt screening for cardiac sarcoidosis in young patients with unexplained AV block.