# Cardiomyopathies Pathology > Cardiomyopathies in MBBS Pathology: dilated, hypertrophic, restrictive and ARVC genetics, myofibre disarray and endomyocardial fibrosis. - Canonical URL: https://prepelephant.com/topics/mbbs/pathology/cardiomyopathies-pathology - Exam / course: MBBS · Subject: Pathology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Cardiomyopathies Pathology", PrepElephant, https://prepelephant.com/topics/mbbs/pathology/cardiomyopathies-pathology ## Direct answer A primary disorder of heart muscle — dilated, hypertrophic, restrictive or arrhythmogenic — defines the cardiomyopathies: myocardial disease occurring without coronary, valvular, hypertensive or congenital cause. Dilated cardiomyopathy, the commonest form, produces eccentric hypertrophy with a globular, poorly contracting ventricle; hypertrophic cardiomyopathy is an autosomal-dominant sarcomere disease with asymmetrical septal hypertrophy, myofibre disarray and a risk of sudden death; restrictive disease stiffens the ventricle through infiltrates such as amyloid or through endomyocardial fibrosis; arrhythmogenic right ventricular cardiomyopathy replaces right ventricular muscle with fibrofatty tissue. Each carries a gene list, a gross appearance and a treatment logic that examinations reward. ## What you must remember - **Dilated cardiomyopathy:** commonest form; causes include familial titin (TTN) mutations, alcohol, viral myocarditis, doxorubicin, thiamine deficiency (beriberi) and the peripartum period; all four chambers dilate, the wall thins, mural thrombi line the apex. - **Hypertrophic cardiomyopathy genetics:** autosomal dominant with variable penetrance; MYH7 and MYBPC3 sarcomere genes account for most genotype-positive cases; septum exceeds 15 mm asymmetrically. - **HCM histology:** disordered whorls of myofibre disarray, interstitial fibrosis and thickened intramural coronary arterioles — the microscopic triad. - **HCM mechanics and risk:** systolic anterior motion of the mitral leaflet creates dynamic outflow obstruction; sudden-death markers include wall thickness over 30 mm, family history of sudden death, non-sustained ventricular tachycardia, unexplained syncope and a flat blood-pressure response to exercise. - **Treatment logic:** beta-blockers and disopyramide reduce the gradient; digoxin, vasodilators and vigorous dehydration worsen it — a contraindication question in every series. - **Restrictive causes:** cardiac amyloidosis leads in the West; endomyocardial fibrosis — endemic in Kerala and tropical Africa — plaques the ventricular apex and inflow tract; Loeffler eosinophilic endocarditis is its temperate counterpart. - **Arrhythmogenic right ventricular cardiomyopathy:** desmosomal mutations (plakophilin-2 classical), fibrofatty replacement, exercise-triggered arrhythmia in the young; competitive sport is prohibited. ## The athlete with a thick septum A 22-year-old cricketer collapses briefly during training; echocardiography shows a 16 mm septum. Is this athlete's heart or hypertrophic cardiomyopathy? Reason it through. Athlete's heart gives a modest, symmetrical septum (rarely beyond 12-14 mm) with a large cavity, normal diastolic filling, a physiologically slow heart rate and a bland electrocardiogram that deconditions within weeks of stopping training. Hypertrophic cardiomyopathy gives asymmetrical thickening, a small hyperdynamic cavity, left atrial enlargement, diastolic dysfunction, bizarre electrocardiographic voltages, and — the decisive step — a first-degree relative with the same picture or a documented sudden death. Where the numbers straddle the grey zone, a period of detraining and family screening resolves more cases than any single test, and a positive genetic panel settles the rest. Missing the diagnosis kills a young person; overcalling it ends a career for no reason. ## Restrictive versus constrictive The classic bedside trap is the wet, stiff patient: restrictive cardiomyopathy or constrictive pericarditis? Both equalise diastolic pressures and both raise the jugular venous pulse. Constriction, the commonest cause of which is tuberculosis in India, adds a pericardial knock, a Kussmaul sign, septal bounce on imaging and often visible pericardial calcification on the lateral chest film; brain natriuretic peptide tends to be lower than in myocardial disease. Amyloid restriction gives a thick, speckled, grainy ventricular wall on echocardiography and a telling mismatch between a small-voltage electrocardiogram and a thick wall on imaging. The distinction matters because constrictive pericarditis is cured by pericardiectomy, while restrictive cardiomyopathy is treated medically — operating on the wrong patient is catastrophic. ## Frequently asked questions ### Which genes are most often mutated in hypertrophic cardiomyopathy? MYH7 (beta-myosin heavy chain) and MYBPC3 (myosin-binding protein C), inherited as autosomal dominant with variable penetrance. ### Why is digoxin contraindicated in hypertrophic cardiomyopathy? Increased contractility enlarges the dynamic left ventricular outflow gradient generated by systolic anterior motion of the mitral leaflet; vasodilators and dehydration act in the same wrong direction. ### What is the histological hallmark of hypertrophic cardiomyopathy? Myofibre disarray — obliquely cut, whorled, hypertrophied myocytes in disordered bundles — accompanied by interstitial fibrosis and thickened intramural arterioles. ### Where is endomyocardial fibrosis endemic? Kerala and tropical Africa; fibrous endocardial plaques obliterate the ventricular apex and inflow tract, producing a restrictive picture with atrioventricular regurgitation. ### Which structural protein is most often mutated in familial dilated cardiomyopathy? Titin (TTN), the giant sarcomeric scaffold protein; other causes include alcohol, viral myocarditis, doxorubicin and the peripartum period.