STEPTRACKERCARDIOVASCULAR | PATHOLOGY | HIGH-YIELD REVIEW

Cardiomyopathies & Myocarditis

Primary diseases of heart muscle — too big and weak, too thick, too stiff — and inflammation of the myocardium.

FOCUS ON
Dilated = systolic failure; list its causes (alcohol, doxorubicin, Chagas, myocarditis, peripartum). Hypertrophic = autosomal dominant sarcomere disease, outflow murmur louder with Valsalva, sudden death in athletes. Restrictive = amyloid with thick walls and low ECG voltage. Myocarditis = viral (coxsackie B), lymphocytes.
TYPE
CAUSES
PATHOLOGY · PHYSIOLOGY
CLUE · TREATMENT
Dilated cardiomyopathy
most common
Idiopathic, genetic (titin), alcohol, wet beriberi, post-viral myocarditis, cocaine, Chagas, doxorubicin, peripartum, hemochromatosis, thyrotoxicosis, tachycardia
All chambers dilated; eccentric hypertrophy; ↓ EF (systolic dysfunction)
S3, functional MR/TR · HF therapy, ICD, transplant
Hypertrophic cardiomyopathy
Autosomal dominant sarcomere mutations (β-myosin heavy chain, myosin-binding protein C); Friedreich ataxia
Asymmetric septal hypertrophy, myofiber disarray; diastolic dysfunction; LVOT obstruction from systolic anterior motion of the mitral leaflet
SEM at LLSB ↑ with Valsalva/standing; S4; sudden death in young athletes · β-blocker or verapamil, mavacamten, ICD, myectomy; avoid dehydration and vasodilators
Restrictive cardiomyopathy
Amyloidosis, sarcoidosis, hemochromatosis, Löffler (eosinophilic) endomyocardial fibrosis, radiation, Fabry
Stiff ventricles, normal-size cavities, big atria; diastolic dysfunction
Amyloid: thick walls + low-voltage ECG · sarcoid: heart block · Kussmaul sign
Arrhythmogenic RV cardiomyopathy
Desmosome gene mutations (plakoglobin, desmoplakin)
Fibrofatty replacement of RV myocardium
Ventricular arrhythmias, sudden death in the young; epsilon wave
Takotsubo cardiomyopathy
Emotional or physical stress; postmenopausal women
Catecholamine surge → apical ballooning
Mimics MI with normal coronaries; recovers in weeks
Peripartum cardiomyopathy
Last month of pregnancy to 5 months postpartum
Dilated pattern
New HF around delivery
Viral myocarditis
Coxsackie B, adenovirus, parvovirus B19, HHV-6, SARS-CoV-2
Lymphocytic infiltrate with myocyte necrosis
Young adult after a flu-like illness: chest pain, HF, arrhythmia, ↑ troponin; may lead to DCM
Other myocarditis
Chagas (T cruzi), Lyme (heart block), diphtheria toxin, Toxoplasma, Trichinella, drug hypersensitivity, checkpoint inhibitors, giant cell myocarditis
Eosinophils in drug and parasitic forms; giant cells in the aggressive idiopathic form
Chagas: DCM + megaesophagus/megacolon

Mechanism — three ways muscle fails

Dilated
Weak, big, thin-walled → ↓ EF → systolic HF
Hypertrophic
Thick septum, small cavity → poor filling ± outflow obstruction
Restrictive
Stiff, infiltrated wall → filling stops early → big atria

In HCM, anything that shrinks the LV cavity (less preload, less afterload, more contractility) worsens the outflow obstruction.

Restrictive cardiomyopathy vs constrictive pericarditis

FEATURE
RESTRICTIVE CM
CONSTRICTIVE PERICARDITIS
Pericardium
Normal
Thick, often calcified
Septum
Normal motion
Septal bounce (interdependence)
BNP
Very high
Mildly raised
Extra sound
S3/S4
Pericardial knock
Causes
Amyloid, sarcoid, iron
TB, radiation, surgery, viral

How it's tested

COMMON CONFUSIONHCM and aortic stenosis both make a systolic ejection murmur. Valsalva and standing make HCM louder and AS softer.
THE TRAPA cancer patient develops HF months after chemotherapy. Doxorubicin cardiotoxicity is dose-dependent dilated cardiomyopathy (dexrazoxane protects) — not "deconditioning".
YOUR APPROACHEF and wall thickness → dilated, hypertrophic or restrictive → the exposure, gene or systemic disease behind it.

If you see… think…

Heavy drinker with four dilated chambers and low EF → alcoholic DCM
HF after anthracycline chemotherapy → doxorubicin DCM
Latin American immigrant with DCM and megaesophagus → Chagas disease
Young athlete collapses; septal hypertrophy with myofiber disarray → HCM
Systolic murmur louder on standing → HCM outflow obstruction
Thick ventricles but low-voltage ECG → cardiac amyloidosis
Sarcoidosis with new complete heart block → cardiac sarcoid
Chest pain + ST elevation after bereavement, normal coronaries, apical ballooning → Takotsubo
HF and ↑ troponin a week after a viral illness → coxsackie B myocarditis
Bull's-eye rash then AV block → Lyme carditis