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Cardiomyopathies & Myocarditis (Clinical)

Name: Cardiomyopathies & Myocarditis (Clinical)
Creator: Veli Bakalov, MD

Dilated, thick, or stiff — plus the stress, viral, and postpartum hearts

Cardiology·Heart Failure & Cardiomyopathy·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Dilated cardiomyopathy = systolic HFrEF (dilated LV, S3); idiopathic is most common, then alcohol, coxsackie B myocarditis, doxorubicin, cocaine, Chagas, peripartum, and thyroid disease.
Primary-prevention ICD: EF ≤35% after at least 3 months of GDMT with NYHA II–III symptoms; secondary prevention after cardiac arrest or sustained VT; a wearable defibrillator bridges the waiting period.
HCM: autosomal dominant sarcomere mutations (MYH7, MYBPC3); SAM of the mitral valve causes a systolic murmur that gets louder with Valsalva or standing, the opposite of aortic stenosis.
Treat HCM with β-blockers or verapamil (mavacamten newer); avoid dehydration, extreme exertion, diuretics, and vasodilators; myectomy or alcohol septal ablation for refractory obstruction.
Screen first-degree relatives of HCM patients with ECG and echo; ICD for prior arrest or high-risk features (unexplained syncope, family sudden death, wall ≥30 mm, NSVT).
Restrictive cardiomyopathy = infiltration (amyloidosis most common, sarcoidosis, hemochromatosis, endomyocardial fibrosis); amyloid shows thick walls with low ECG voltage and apical sparing.
Viral myocarditis: young patient after a URI with HF, troponin rise, and diffuse ST changes; biopsy shows lymphocytic infiltrate; supportive care and avoid exercise.
Takotsubo: postmenopausal woman after acute stress, STEMI mimic with apical ballooning and clean coronaries; catecholamine-driven and usually reversible within weeks.
Peripartum cardiomyopathy: new HFrEF from the last month of pregnancy to 5 months postpartum; avoid ACEi/ARB/ARNI while pregnant (hydralazine-nitrates plus β-blocker); may recur in later pregnancies.

Three patterns of cardiomyopathy

Systolic vs diastolic. Dilated cardiomyopathy is a systolic problem: a weak, dilated pump with a low ejection fraction. Hypertrophic (thick septum) and restrictive (stiff, infiltrated walls) cardiomyopathies are diastolic problems: the ventricle cannot fill, so the EF is preserved.

Dilated, hypertrophic, and restrictive cardiomyopathy

Feature	Dilated	Hypertrophic	Restrictive
Failure type	Systolic (HFrEF), low EF	Diastolic, EF preserved	Diastolic, EF preserved
Structure	Big cavity, eccentric dilation	Asymmetric septal hypertrophy	Stiff, infiltrated walls
Classic clue	S3, cardiomegaly	Systolic murmur louder with Valsalva or standing	Thick walls but low ECG voltage (amyloid)
Leading cause	Idiopathic	Autosomal dominant sarcomere mutations	Amyloidosis
Mainstay	HFrEF GDMT; ICD if EF ≤35%	β-blocker or verapamil; avoid low preload	Cautious diuresis; treat the infiltrative cause

Workup. Echocardiography is the first-line test for every cardiomyopathy. Cardiac MRI with late gadolinium enhancement characterizes myocarditis, sarcoidosis, amyloidosis, and HCM. BNP and troponin support the diagnosis, and genetic testing with family screening applies to HCM.

Dilated cardiomyopathy and sudden-death prevention

Causes. Idiopathic is most common. Identifiable causes include alcohol (may improve with abstinence), viral myocarditis (coxsackie B), doxorubicin (dose-dependent), cocaine, Chagas disease, peripartum cardiomyopathy, and thyroid disease.

Treatment. Full guideline-directed therapy for HFrEF: an ARNI, ACE inhibitor, or ARB; an evidence-based β-blocker; a mineralocorticoid receptor antagonist; and an SGLT2 inhibitor, with diuretics for congestion.

ICD indications.

Primary prevention: EF ≤35% (ischemic or non-ischemic) despite at least 3 months of GDMT, with NYHA class II–III symptoms.
Secondary prevention: survived cardiac arrest or sustained VT.
A wearable defibrillator can bridge patients through the waiting period, such as the first 40 days after MI.

≤35%EF for a primary-prevention ICD

≥3 monthsof GDMT before deciding

Hypertrophic cardiomyopathy

Genetics. Autosomal dominant mutations in sarcomere proteins, most often β-myosin heavy chain (MYH7) and myosin-binding protein C (MYBPC3). HCM is a leading cause of sudden death in young athletes. Symptoms are dyspnea, angina, syncope (often exertional), and sudden death; an S4 is common.

Dynamic obstruction. Systolic anterior motion (SAM) of the mitral valve against the thick septum obstructs the LV outflow tract and produces the systolic murmur. Anything that shrinks the LV cavity worsens obstruction:

Less preloadValsalva, standing, dehydration, diuretics, vasodilators.
Smaller LV cavityThe septum sits closer to the mitral valve.
More SAMWorse outflow tract obstruction.
ResultLouder murmur, presyncope or syncope.

Unlike aortic stenosis, the HCM murmur gets louder with Valsalva and standing and softer with squatting; handgrip softens both.

Treatment: fill the tank. β-blockers (or verapamil) slow the heart and lengthen filling; mavacamten, a cardiac myosin inhibitor, is a newer option. Avoid dehydration, extreme exertion, diuretics, and vasodilators. Septal myectomy or alcohol septal ablation is for obstruction that stays symptomatic despite drugs. AF in HCM warrants anticoagulation regardless of the CHA₂DS₂-VASc score.

Screening and sudden death. Screen first-degree relatives with ECG and echocardiography. Competitive athletics have traditionally been restricted; current guidelines individualize this after expert evaluation. An ICD is indicated after cardiac arrest and considered for high-risk features:

Unexplained syncope
Family history of sudden cardiac death
Massive LV hypertrophy (wall ≥30 mm)
Non-sustained VT
Blunted blood-pressure response to exercise

Restrictive cardiomyopathy

Infiltrated walls. Amyloidosis (most common), sarcoidosis, hemochromatosis, and endomyocardial fibrosis stiffen the ventricle, causing diastolic heart failure with preserved EF and prominent right-sided congestion. Standard heart-failure drugs help little; treat congestion cautiously and target the underlying disease.

Cardiac amyloid clue: thick walls on echo but low QRS voltage on ECG (voltage–mass discordance), with apical sparing of longitudinal strain. True hypertrophy from hypertension or HCM shows high voltage.

Sarcoidosis infiltrates the conduction system, so heart block or ventricular arrhythmia in a younger patient should raise the question. Restrictive cardiomyopathy must also be distinguished from constrictive pericarditis, which has a thickened pericardium and is cured by pericardiectomy.

Myocarditis, takotsubo, and peripartum cardiomyopathy

Acquired cardiomyopathies with a story

Feature	Viral myocarditis	Takotsubo (stress)	Peripartum
Typical patient	Young adult after a URI	Postmenopausal woman after acute emotional or physical stress	Last month of pregnancy to 5 months postpartum
Mechanism	Viral injury with lymphocytic infiltrate (coxsackie B, parvovirus B19, HHV-6, adenovirus)	Catecholamine surge	New systolic HF with no other cause
Findings	New HF or chest pain, S3, elevated troponin, diffuse ST changes, normal coronaries	ST elevation and troponin rise mimicking anterior MI; apical ballooning; clean coronaries	Dilated LV with low EF
Management	Supportive HF therapy; avoid exercise	Supportive; usually reverses within weeks	HF therapy adapted to pregnancy

Myocarditis. Endomyocardial biopsy showing a lymphocytic infiltrate is the gold standard, although cardiac MRI usually suffices. Restrict competitive exercise for several months, because arrhythmias and sudden death can occur during recovery.

Takotsubo. The name comes from a Japanese octopus-trap pot, whose round bottom and narrow neck resemble the ballooned apex. Because it mimics an anterior STEMI, coronary angiography is needed to show that the arteries are clean.

Peripartum cardiomyopathy. Risk factors are multiparity, age over 30, twin pregnancy, and preeclampsia. ACE inhibitors, ARBs, and ARNIs are teratogenic, so while the patient is pregnant use hydralazine with nitrates and a β-blocker (and avoid MRAs), switching to an ACE inhibitor after delivery; enalapril or captopril is compatible with breastfeeding. It may recur in later pregnancies, particularly if the EF has not recovered.