restrictive cardiomyopathy

Pathophysiology: RCM results from infiltrative, fibrotic, or storage processes that increase myocardial stiffness, impairing ventricular relaxation and filling during diastole. Unlike dilated cardiomyopathy, ventricular volume and wall thickness are usually normal or mildly increased, and systolic function (ejection fraction) is preserved until late in the disease. The impaired diastolic filling causes elevated atrial and ventricular end-diastolic pressures, leading to atrial enlargement and symptoms of both left- and right-sided heart failure (dyspnea, fatigue, peripheral edema, ascites, hepatomegaly, jugular venous distension).

Etiologies: - Infiltrative: Amyloidosis (most common cause in adults), sarcoidosis - Storage diseases: Hemochromatosis (iron), Fabry disease (glycolipids), glycogen storage diseases - Endomyocardial: Loeffler endocarditis (hypereosinophilic syndrome), endomyocardial fibrosis (tropical regions), carcinoid heart disease - Post-radiation fibrosis - Idiopathic

Clinical Presentation: Signs of right heart failure often predominate (JVD, hepatomegaly, ascites, edema) due to biventricular diastolic dysfunction. Kussmaul sign (JVD increases with inspiration) may be present. S3 or S4 gallop can be heard. Patients may have preserved EF but significant exercise intolerance.

Diagnostic Workup: - Echocardiogram: Normal or near-normal EF, biatrial enlargement, restrictive filling pattern (E/A ratio elevated), speckled myocardium in amyloidosis - ECG: Low voltage (especially in amyloidosis), arrhythmias - Cardiac MRI: Late gadolinium enhancement pattern helps distinguish etiology (e.g., subendocardial in amyloidosis) - Endomyocardial biopsy: Definitive diagnosis, especially for amyloidosis (apple-green birefringence with Congo red stain) or sarcoidosis (granulomas) - BNP/NT-proBNP: Often elevated

Key Differentiation: Must distinguish from constrictive pericarditis, which has similar hemodynamic profile but involves the pericardium rather than myocardium. Cardiac MRI and biopsy help differentiate; constrictive pericarditis often shows pericardial thickening and calcification, and may be treated surgically (pericardiectomy), whereas RCM treatment is limited to managing underlying cause and heart failure symptoms.

Management: Treat underlying cause (e.g., chemotherapy for AL amyloidosis, chelation for hemochromatosis, corticosteroids for sarcoidosis). Diuretics for volume overload, though must be used cautiously since these patients depend on elevated filling pressures for cardiac output. Cardiac transplantation may be considered in severe cases.

Board Relevance: High-yield associations include amyloidosis as classic amyloid cardiomyopathy cause with low-voltage ECG despite increased wall thickness on echo (discordance is a key testable point), Loeffler endocarditis with eosinophilia, and differentiating RCM from constrictive pericarditis using imaging and hemodynamic findings.