Cardiomyopathy

Dilated cardiomyopathy is the most common form. All four chambers, and especially the left ventricle, enlarge while the walls thin, producing systolic dysfunction with a reduced ejection fraction. Many cases are idiopathic; identified causes include chronic alcohol use, viral myocarditis (notably coxsackievirus B), peripartum onset, doxorubicin and other cardiotoxic drugs, thiamine deficiency, hemochromatosis, and inherited mutations. An S3 gallop and mitral regurgitation from a dilated annulus are typical findings.

Hypertrophic cardiomyopathy is usually an autosomal dominant disorder of sarcomere proteins such as beta-myosin heavy chain. The ventricular wall thickens — often asymmetrically at the septum — and myocyte disarray on histology is characteristic. The problem is diastolic: a stiff, poorly compliant ventricle fills badly. When septal hypertrophy obstructs the outflow tract, the murmur intensifies with maneuvers that reduce preload, such as standing or Valsalva, which distinguishes it from aortic stenosis. HCM is a leading cause of sudden cardiac death in young athletes.

Restrictive cardiomyopathy is the least common. Ventricular walls are stiff but not necessarily thick, so filling is limited while systolic function is preserved early. Causes include cardiac amyloidosis, sarcoidosis, hemochromatosis, endomyocardial fibrosis, and radiation. Presentation resembles constrictive pericarditis, and the two must be distinguished before considering intervention.

All three converge on heart failure. Dilated disease produces predominantly systolic failure; hypertrophic and restrictive disease produce heart failure with preserved ejection fraction. Arrhythmia risk is elevated across the group, and mural thrombus with systemic embolization is a recognized complication of dilated cardiomyopathy.

USMLE Step 1 tests the three types side by side with heart failure physiology. CCMA candidates encounter cardiomyopathies among muscular and developmental heart disorders and in rhythm analysis, and the NCLEX approaches them through lifestyle counseling, high-risk behaviors such as alcohol use, and the adverse effects of cardiotoxic medications.