Cardiomyopathy Types

Three hearts in one sentence

Three morphologies, three problems. Dilated cardiomyopathy — the chamber is too big to squeeze. Hypertrophic cardiomyopathy — the wall is too thick to relax. Restrictive cardiomyopathy — the muscle is too stiff to fill. The visual cue is decisive: at first glance on an echo, DCM looks like a balloon, HCM looks like a wedge with one fat side, and restrictive looks like a normal heart with monstrously dilated atria.

Dilated cardiomyopathy (DCM)

All four chambers enlarge, especially the LV. Ejection fraction drops — often well below 30% by the time symptoms present. Mitral and tricuspid regurgitation appear as the annuli stretch. Wall thickness is preserved relative to volume, so LV mass is increased but in an eccentric pattern.

Causes split into ischemic (the largest category — multiple prior MIs and chronic CAD) and non-ischemic. Familial DCM is increasingly recognized; titin (TTN) truncating variants alone account for roughly 25% of familial cases. Other inherited contributors: LMNA (lamin A/C), FLNC (filamin C), BAG3, RBM20, DSP. Acquired drivers include alcohol, anthracycline chemotherapy, peripartum, viral myocarditis, sarcoidosis, hemochromatosis, and tachycardia-induced (which can fully reverse with rate control).

Hypertrophic cardiomyopathy (HCM)

The most common monogenic heart disease — roughly 1 in 500 people. Sarcomere protein mutations cause myocyte hypertrophy and disarray. Two genes — MYH7 (beta-myosin heavy chain) and MYBPC3 (myosin-binding protein C) — account for most identified mutations. Autosomal dominant inheritance with variable penetrance and expressivity.

Morphology: asymmetric septal thickening (typically much more than the posterior wall), septum often 15-30 mm and occasionally beyond. Systolic function is preserved or hyperdynamic. About 60-70% develop dynamic LV outflow tract obstruction during systole as the mitral leaflet drifts into a Venturi-effect jet (systolic anterior motion, SAM). The feared complication is sudden cardiac death, especially in young athletes. Risk markers include prior arrest or sustained VT, family history of SCD, syncope, wall thickness > 30 mm, non-sustained VT on Holter, and abnormal BP response to exercise. Mavacamten — a cardiac myosin inhibitor — is the first disease-modifying drug approved for obstructive HCM.

Restrictive cardiomyopathy

The chambers stay normal-sized, but the muscle becomes infiltrated or fibrotic and cannot stretch to fill. Filling pressures rise sharply with small volume changes. The atria, working against stiff ventricles, dilate massively — biatrial enlargement is the visual clue.

Causes: cardiac amyloidosis (AL from plasma cell dyscrasia, ATTR from transthyretin — wild-type or hereditary), sarcoidosis, hemochromatosis (iron deposition), endomyocardial fibrosis (especially in tropical regions), radiation, and post-transplant. Amyloid is increasingly diagnosed — clues are thick walls but paradoxically low ECG voltage, conduction system disease, and bilateral carpal tunnel syndrome predating cardiac symptoms by years. ATTR has a disease-modifying treatment: tafamidis.

Worked clinical example

A 24-year-old college basketball player collapses during practice and is resuscitated from VF. On hospital echo: LVEF 70%, septal thickness 28 mm, posterior wall 11 mm, dynamic LVOT gradient 70 mmHg, systolic anterior motion of the mitral valve. Family history: paternal uncle died suddenly at age 28.

• Diagnosis: Hypertrophic cardiomyopathy, obstructive variant, presenting with aborted SCD.
• Risk markers met: Survived SCD, family history of SCD, septum > 30 mm (close), LVOT obstruction. ICD indicated for secondary prevention.
• Symptom management: Beta blocker first-line. If obstructive symptoms persist, add disopyramide or mavacamten (cardiac myosin inhibitor — reduces gradient and symptoms). Septal myectomy or alcohol septal ablation if refractory.
• Genetic testing: Send sarcomere gene panel (MYH7, MYBPC3 likely culprits). If a pathogenic variant identified, cascade screen first-degree relatives.
• Lifestyle: Avoid competitive athletics; recent guidelines allow individualized shared decision-making for moderate exercise.

Three cardiomyopathies — the side-by-side

Side-by-side comparison of DCM, HCM, and restrictive cardiomyopathy

Feature	DCM	HCM	Restrictive
Chamber size	Massively enlarged	Normal or small	Normal
Wall thickness	Normal / mildly thin	Thick, often asymmetric	Normal or mildly thick
Ejection fraction	Reduced (< 40%)	Preserved or hyperdynamic	Preserved (until end-stage)
Primary problem	Systolic failure	Diastolic + outflow	Diastolic, infiltration
Atria	Dilated (from MR/TR)	Often enlarged (LA)	Severely dilated (both)
Genetics	TTN, LMNA, FLNC, BAG3	MYH7, MYBPC3 (~1 in 500)	Amyloid: TTR; hemochromatosis: HFE
Treatment focus	GDMT: ARNI, BB, MRA, SGLT2i	BB, disopyramide, mavacamten, ICD	Etiology-specific (tafamidis, chelation)
SCD risk	Elevated, ICD if EF ≤ 35%	High in risk subgroups	Variable; arrhythmia substrate

Common mistakes

• Calling HCM "thick LV from hypertension." Hypertensive LVH is usually symmetric and rarely > 15 mm; asymmetric septum > 15 mm without obvious load is HCM until disproven.
• Treating obstructive HCM with vasodilators. Nitrates, ACE inhibitors, and high-dose diuretics drop preload, worsen LVOT obstruction, and can cause syncope. Use beta blockers, disopyramide, or mavacamten.
• Missing cardiac amyloid. Disproportionately thick walls + low ECG voltage + bilateral carpal tunnel = consider amyloid; ATTR is treatable with tafamidis.
• Skipping family screening in HCM. First-degree relatives need cascade echo and consideration of genetic testing — sudden death in young athletes is often the first family event.
• Calling tachycardia-induced cardiomyopathy "irreversible DCM." Sustained tachycardia (chronic AF with rapid rate, frequent PVCs) can reduce EF; rate control or PVC ablation reverses it in months.