124. Cardiomyopathies - classification, etiology, pathogenesis, clinical manifestations.

Cardiomyopathies – classification, etiology, pathogenesis, and clinical manifestations.

Cardiomyopathies are a group of primary diseases of the heart muscle, characterized by structural and functional abnormalities that are not due to coronary artery disease, hypertension, valvular disease, or congenital heart defects.

Classification

1. 1 Dilated cardiomyopathy (DCM)

• Most common type (~90% of cases).

1. 2 Hypertrophic cardiomyopathy (HCM)

• Usually genetic.

1. 3 Restrictive cardiomyopathy (RCM)

• Least common.

Etiology

Dilated cardiomyopathy

• Genetic (about 30–50%): mutations affecting cytoskeletal proteins (e.g., dystrophin).
• Infectious: viral myocarditis (Coxsackievirus B).
• Toxic: alcohol, chemotherapeutic agents (doxorubicin), chronic cocaine use.
• Peripartum cardiomyopathy.
• Nutritional deficiencies: thiamine deficiency (beriberi).

Hypertrophic cardiomyopathy

• Genetic (autosomal dominant): mutations in sarcomeric proteins (e.g., β-myosin heavy chain, myosin- binding protein C).

Restrictive cardiomyopathy

• Infiltrative diseases: amyloidosis, sarcoidosis.
• Endomyocardial fibrosis.
• Hemochromatosis.

Pathogenesis

Dilated cardiomyopathy

1. Myocyte injury → impaired contractility.
2. Ventricular dilation → reduced systolic function (EF <40%).
3. Secondary mitral/ tricuspid regurgitation, mural thrombi formation.

Hypertrophic cardiomyopathy

1. Myocyte hypertrophy and disarray → thickened ventricular walls, especially septum.
2. Reduced compliance → impaired diastolic filling.
3. Possible dynamic left ventricular outflow tract obstruction (due to septal bulge and systolic anterior motion of mitral valve).

Restrictive cardiomyopathy

1. Stiffened myocardium due to infiltration or fibrosis.
2. Impaired diastolic relaxation and filling.
3. Relatively preserved systolic function early on.