Atlas of pathophysiology, 2 Edition

Part II - Disorders

Cardiovascular disorders

Cardiomyopathy

Cardiomyopathy is classified as dilated, hypertrophic, or restrictive.

Dilated cardiomyopathy results from damage to cardiac muscle fibers; loss of muscle tone grossly dilates all four chambers of the heart, giving the heart a globular shape.

Hypertrophic cardiomyopathy is characterized by disproportionate, asymmetrical thickening of the interventricular septum and left ventricular hypertrophy.

Restrictive cardiomyopathy is characterized by restricted ventricular filling due to decreased ventricular compliance and endocardial fibrosis and thickening. If severe, it's irreversible.

Causes

Most patients with cardiomyopathy have idiopathic disease, but some are secondary to these possible causes:

Dilated cardiomyopathy

·         Viral or bacterial infection

·         Hypertension

·         Peripartum syndrome (related to toxemia)

·         Ischemic heart disease or valvular disease

·         Drug hypersensitivity or chemotherapy

·         Cardiotoxic effects of drugs or alcohol

Hypertrophic cardiomyopathy

·         Autosomal dominant inheritance

·         Hypertension

·         Obstructive valvular disease

·         Thyroid disease

Restrictive cardiomyopathy

·         Amyloidosis or sarcoidosis

·         Hemochromatosis

·         Infiltrative neoplastic disease

Pathophysiology

In dilated cardiomyopathy, extensive damage to cardiac muscle fibers reduces contractility in the left ventricle. As systolic function declines, stroke volume, ejection fraction, and cardiac output fall.

In hypertrophic cardiomyopathy, hypertrophy of the left ventricle and interventricular septum obstruct left ventricular outflow. The heart compensates for the decreased cardiac output (caused by obstructed outflow) by increasing the rate and force of contractions. The hypertrophied ventricle becomes stiff and unable to relax and fill during diastole. As left ventricular volume diminishes and filling pressure rises, pulmonary venous pressure also rises, leading to venous congestion and dyspnea.

In restrictive cardiomyopathy, left ventricular hypertrophy and endocardial fibrosis limit myocardial contraction and emptying during systole as well as ventricular relaxation and filling during diastole. As a result, cardiac output falls.

Signs and symptoms

Dilated cardiomyopathy

·         Shortness of breath, orthopnea, dyspnea on exertion, paroxysmal nocturnal dyspnea, fatigue, and dry cough at night

·         Peripheral edema, hepatomegaly, jugular vein distention, and weight gain

·         Peripheral cyanosis

·         Tachycardia

·         Pansystolic murmur or S3 and S4 gallop rhythms

·         Irregular pulse, if atrial fibrillation is present

Hypertrophic cardiomyopathy

·         Angina, syncope, dyspnea, or fatigue

·         Systolic ejection murmur along the left sternal border and at the apex

·         Pulsus biferiens or abrupt arterial pulse

·         Irregular pulse, if atrial fibrillation is present

Restrictive cardiomyopathy

·         Fatigue, dyspnea, orthopnea, chest pain, peripheral edema, liver engorgement, ascites, and jugular vein distention

·         Peripheral cyanosis, pallor

·         S3 or S4 gallop rhythms or systolic murmurs

Diagnostic test results

·         Chest X-rays show cardiomegaly and increased in heart size.

·         Echocardiography reveals left ventricular dilation and dysfunction or left ventricular hypertrophy and a thick, asymmetrical intraventricular septum.

·         Cardiac catheterization shows left ventricular dilation and dysfunction, elevated left ventricular and, commonly, right ventricular filling pressures, and diminished cardiac output.

·         Thallium scan usually reveals myocardial perfusion defects.

·         Cardiac catheterization reveals elevated left ventricular end-diastolic pressure and, possibly, mitral insufficiency.

·         Electrocardiography usually shows left ventricular hypertrophy, ST-segment and T-wave abnormalities, Q waves in leads II, III, aVF, and in V4 to V6, left anterior hemiblock, left axis deviation, and ventricular and atrial arrhythmias.

Treatment

Dilated cardiomyopathy

·         Treatment of underlying cause

·         Angiotensin-converting enzyme inhibitors, diuretics, digoxin, hydralazine, isosorbide dinitrate, beta-adrenergic blockers, antiarrhythmics, and anticoagulants

·         Cardioversion or pacemaker insertion

·         Revascularization

·         Implantable cardioverter-defibrillator (ICD)

·         Valve repair or replacement

·         Heart transplantation

·         Lifestyle modifications, such as quitting smoking; avoiding alcohol; eating a low-fat, low-salt diet; and restricting fluids

Hypertrophic cardiomyopathy

·         Beta-adrenergic blockers, antiarrhythmics, anticoagulants

·         Cardioversion

·         Ablation and implantation of a dual-chamber pacemaker

·         ICD

·         Ventricular myotomy or myectomy

·         Mitral valve repair or replacement

·         Heart transplantation

Restrictive cardiomyopathy

·         Treatment of underlying cause

·         Beta-adrenergic blockers, digoxin, diuretics, and oral vasodilators

·         Restricted-sodium diet (may ease symptoms of heart failure)

P.45

TYPES OF CARDIOMYOPATHY

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