Write a short note on the cardiomyopathies.

Definition and Classification

Cardiomyopathies are diseases of the myocardium associated with mechanical and/or electrical dysfunction, in the absence of coronary artery disease, hypertension, valvular disease or congenital heart disease sufficient to explain the abnormality.

Dilated Cardiomyopathy

The commonest cardiomyopathy. Characterised by dilatation and impaired contraction of one or both ventricles.

Causes:

• Idiopathic — a substantial proportion, many now recognised as genetic
• Genetic/familial — 30–50%; titin, lamin A/C and other mutations
• Toxic — ALCOHOL (a major and reversible cause), anthracyclines (doxorubicin — dose-dependent), trastuzumab, cocaine, amphetamines
• Infective — viral myocarditis (coxsackie, adenovirus, parvovirus B19), HIV, Chagas disease, diphtheritic myocarditis
• Metabolic and nutritional — thiamine deficiency (wet beriberi), selenium deficiency, hypocalcaemia, hypophosphataemia, thyroid disease
• PERIPARTUM CARDIOMYOPATHY — in the last month of pregnancy or the first 5 months postpartum; an important cause in India, with a risk of recurrence in subsequent pregnancies
• Tachycardia-mediated — from persistent uncontrolled tachyarrhythmia; reversible with rate control
• Autoimmune, sarcoidosis, haemochromatosis, muscular dystrophies

Clinical features: progressive heart failure (dyspnoea, orthopnoea, PND, oedema), fatigue, arrhythmias including atrial fibrillation and ventricular arrhythmias, thromboembolism from mural thrombus, and sudden cardiac death. Examination: displaced diffuse apex, S3 gallop, functional mitral and tricuspid regurgitation, raised JVP.

Investigations:

• ECG (non-specific — LBBB, arrhythmia, poor R wave progression), chest X-ray (cardiomegaly, pulmonary congestion), echocardiography (dilated ventricle with globally reduced EF), cardiac MRI for aetiology and scar, natriuretic peptides, and screening bloods (thyroid, iron studies, HIV, autoimmune).
• Coronary angiography to exclude ischaemic cardiomyopathy — an essential distinction.
• Genetic testing and family screening where familial disease is suspected.

Management:

• standard heart failure therapy — the four pillars (ARNI/ACE inhibitor, beta-blocker, MRA, SGLT2 inhibitor) with diuretics
• anticoagulation for AF or mural thrombus
• treat the cause — abstinence from alcohol (which can produce dramatic recovery), thiamine, rate control, stopping the offending drug
• ICD for primary prevention of sudden death
• CRT for broad QRS
• transplantation or mechanical support in end-stage disease.

Hypertrophic Cardiomyopathy

Definition: left ventricular hypertrophy (usually asymmetric, involving the interventricular septum) in the absence of a haemodynamic cause. It is the commonest inherited cardiac disorder (about 1 in 500) and the leading cause of sudden cardiac death in young people and athletes.

Genetics: AUTOSOMAL DOMINANT with variable penetrance, caused by mutations in sarcomeric proteins — beta-myosin heavy chain and myosin-binding protein C most commonly.

Pathophysiology: hypertrophy with myocyte disarray and interstitial fibrosis (the substrate for arrhythmia) causes:

• Diastolic dysfunction — a stiff, poorly relaxing ventricle
• LV OUTFLOW TRACT OBSTRUCTION in about a third (HOCM), caused by septal hypertrophy plus systolic anterior motion (SAM) of the mitral valve, which also produces mitral regurgitation
• Myocardial ischaemia — from increased demand, reduced capillary density and small vessel disease
• Arrhythmias — atrial fibrillation and ventricular arrhythmias

Clinical features: frequently asymptomatic and detected on screening or a murmur; exertional dyspnoea (the commonest symptom), angina, exertional syncope or presyncope — an ominous symptom, palpitations, and sudden cardiac death, characteristically during or just after exertion.

Signs:

• jerky, bisferiens carotid pulse
• double or triple apical impulse
• fourth heart sound
• EJECTION SYSTOLIC MURMUR at the left sternal edge, NOT radiating to the carotids
• pansystolic murmur of mitral regurgitation at the apex.

The dynamic murmur — a defining feature and a favourite examination question:

This is the opposite of aortic stenosis, where the murmur decreases with Valsalva — the key bedside discriminator.

Investigations:

• ECG is abnormal in over 90% — LVH, deep narrow Q waves in the inferolateral leads, T inversion (giant negative T waves in apical HCM)
• echocardiography — asymmetric septal hypertrophy, SAM, outflow gradient
• cardiac MRI for apical variants and fibrosis
• Holter monitoring for arrhythmia
• exercise testing for blood pressure response
• genetic testing and cascade screening of first-degree relatives.

Management:

• Avoid dehydration, and avoid drugs that reduce preload or afterload — nitrates, diuretics in excess, ACE inhibitors and digoxin — all of which worsen outflow obstruction.
• Beta-blockers first-line; verapamil as an alternative; disopyramide for refractory obstruction.
• Mavacamten — a cardiac myosin inhibitor and the first disease-specific therapy for obstructive HCM.
• Septal reduction therapy for drug-refractory obstruction — surgical myectomy or alcohol septal ablation.
• ICD for primary prevention in those at high risk (family history of sudden death, unexplained syncope, massive hypertrophy, non-sustained VT, abnormal blood pressure response to exercise, extensive fibrosis on MRI).
• AVOID COMPETITIVE SPORTS AND INTENSE EXERTION; treat atrial fibrillation with anticoagulation and rate or rhythm control.
• Screen all first-degree relatives — clinically, by ECG and echocardiography, and by genetic testing where the mutation is known.

Restrictive Cardiomyopathy

Definition: restrictive ventricular filling with normal or reduced diastolic volume, normal or near-normal systolic function and wall thickness — the ventricle is stiff and cannot fill.

Causes:

• Infiltrative — AMYLOIDOSIS (the commonest), sarcoidosis
• Storage — haemochromatosis, Fabry disease, glycogen storage disease
• Endomyocardial — ENDOMYOCARDIAL FIBROSIS (of major importance in tropical regions including parts of India and Africa), Löffler's endocarditis (hypereosinophilic), carcinoid, radiation, anthracyclines
• Idiopathic and familial

Clinical features:

• predominantly RIGHT heart failure — markedly raised JVP with prominent x and y descents, KUSSMAUL'S SIGN (a paradoxical rise in JVP on inspiration), hepatomegaly, ascites (often out of proportion to peripheral oedema), and oedema
• exercise intolerance and dyspnoea
• atrial fibrillation from biatrial enlargement
• thromboembolism.

RESTRICTIVE CARDIOMYOPATHY versus CONSTRICTIVE PERICARDITIS — a critical distinction, because constriction is surgically curable:

Investigations:

• ECG (low voltage complexes — classic in amyloidosis, conduction disease, arrhythmia)
• echocardiography (thickened ventricles with a "granular sparkling" myocardium in amyloid; biatrial enlargement; restrictive filling pattern)
• cardiac MRI
• endomyocardial biopsy where the diagnosis is uncertain
• investigation for the underlying systemic disease (serum free light chains and immunofixation for AL amyloidosis; bone scintigraphy for transthyretin amyloidosis; ferritin and transferrin saturation for haemochromatosis; serum ACE for sarcoidosis).

Management:

• treat the underlying cause (chemotherapy or transthyretin stabilisers such as tafamidis for amyloidosis, venesection for haemochromatosis, steroids for sarcoidosis and Löffler's)
• diuretics cautiously — these patients are preload-dependent and over-diuresis causes hypotension
• rate control and anticoagulation for atrial fibrillation
• avoid digoxin in amyloidosis (increased toxicity)
• surgical resection for endomyocardial fibrosis
• transplantation in selected cases.
• Prognosis is generally poor.