Cardiomyopathy

– Any structural or functional abnormality of the ventricular myocardium that results in enlargement or ventricular dysfunction and is not attributable to pressure or volume overload or to segmental loss of muscle function secondary to ischemia. The three major classifications are dilated (congestive) cardiomyopathy, hypertrophic cardiomyopathy, and restrictive cardiomyopathy.

Causes and Incidence

Cardiomyopathy is idiopathic in origin. However, underlying disease processes and factors may produce symptoms of cardiac involvement that simulate cardiomyopathy and as such are important to consider. These processes include coronary artery disease; infections of all types (bacterial, viral, parasitic, fungal, rickettsial, spirochetal, helminthic); granulomatous diseases (sarcoidosis, giant cell myocarditis, granulomatosis); metabolic disorders (beriberi, kwashiorkor, thyrotoxicosis, myxedema); neoplasms; connective tissue disorders; hereditary autosomal dominant disorders, pheochromocytoma, acromegaly, neurofibromatosis; amyloidosis, fibroelastosis, Gaucher’s or Loffler’s disease; and toxins or drugs (alcohol, cocaine, cobalt, catecholamines, cyclophosphamide, psychotherapeutics, radiation, carbon monoxide, arsenic, immunosuppressive drugs).

Disease Process

Dilated cardiomyopathies are characterized by abnormal systolic pump function, gross dilation of the heart, and damage to the myofibrils. The cardiac valves and coronary arteries remain grossly normal. Hypertrophic cardiomyopathies are characterized by disordered diastolic function and reduced distensibility, as well as a marked pattern of distinctive hypertrophy involving thickening of the interventricular septum and a reduction in the size of the ventricular cavities. The ventricular walls become rigid and increase the resistance to blood flow from the left atrium. Ventricular outflow is obstructed, impeding ventricular ejection during systole. Restrictive cardiomyopathy is marked by abnormal diastolic filling and excessively rigid ventricular walls. Contractility is relatively unimpaired, and systolic emptying is normal.

Symptoms

Dilated type
Exertional dyspnea, fatigue, peripheral edema, neck vein distension, rapid pulse, narrowed pulse pressure, and crackles (symptoms usually are chronic).

Hypertrophic type
Chest pain, syncope, palpitations, exertional dyspnea, fatigue.

Restrictive type
Exertional dyspnea, fatigue, edema, narrowed pulse pressure, distended neck veins.

Potential Complications

Complications include mural thrombus formation, pulmonary embolus, severe heart failure, and sudden death. The prognosis is poor in all categories of disease.

Diagnostic Tests

Chest x-ray
Dilated: enlarged cardiac silhouette, prominent left ventricle, pleural effusions Hypertrophic: enlarged cardiac silhouette Restrictive: mild cardiac enlargement.

Electrocardiography
Dilated: left ventricular (LV) hypertrophy, sinus tachycardia, atrial and ventricular dysrhythmias, ST segment and T-wave changes, conduction disturbances Hypertrophic: LV hypertrophy, ST segment and T-wave changes, Q waves in inferior and precordial leads, atrial and ventricular dysrhythmias Restrictive: lowvoltage; conduction disturbances.

Echocardiography
Dilated: LV dilation, abnormal diastolic mitral valve motion, decreased ejection fraction Hypertrophic: narrow LV outflow tract, thickened septum, systolic anterior motion of mitral valve, decreased LV chamber Restrictive: increased LV thickness and mass, pericardial effusion.

Radionuclide studies
Dilated: LV dilation, hypokinesis, reduced ejection fraction Hypertrophic: hyperdynamic systolic function, reduced LV volume, increased muscle mass, ischemia Restrictive: myocardial infiltration.

Cardiac catheterization
Dilated: LV enlargement and dysfunction, mitral and tricuspid regurgitation, elevated diastolic filling pressures, reduced cardiac output Hypertrophic: decreased LV compliance, mitral regurgitation, hyperdynamic systolic function, LV outflow obstruction Restrictive: decreased LV compliance, elevated diastolic filling pressures, normal systolic function.

Treatments

Surgery
Dilated: cardiac transplantation Hypertrophic: with septal myopathy, myectomy Restrictive: excision of fibrotic endocardium.

Drugs
Dilated: symptoms direct intervention (e.g., diuretics or digitalis with congestive heart failure, anticoagulants to prevent mural thrombus formation, antidysrhythmics for dysrhythmias) Hypertrophic: betaadrenergic blockers and calcium antagonists to decrease ventricular contractility and increase ventricular volume and outflow; with mitral valve regurgitation, antiinfectives as prophylaxis against endocarditis Restrictive: drugs to treat underlying disorders.

General
Hemodynamic monitoring; cardiac monitoring; cardioversion for atrial fibrillation; intraaortic balloon pump to sustain severely depressed ventricular function; restriction of fluid and sodium intake; oxygen therapy; rest; exercise restrictions.

_____________________________________