cardiomyopathy

Cardiomyopathy

- diseases of the cardiac muscles with an idiopathic cause

Causes

- idiopathic, or primary, disease, but some are secondary to identifiable causes. Hypertrophic cardiomyopathy is almost always inherited as a non–sex-linked autosomal dominant trait.

Pathophysiology

Dilated cardiomyopathy results from extensively damaged myocardial muscle fibers. Consequently, there is reduced contractility in the left ventricle. As systolic function declines, stroke volume, ejection fraction, and cardiac output fall. As end-diastolic volumes rise, pulmonary congestion may occur. The elevated end-diastolic volume is a compensatory response to preserve stroke volume despite a reduced ejection fraction. The sympathetic nervous system is also stimulated to increase heart rate and contractility. The kidneys are stimulated to retain sodium and water to maintain cardiac output, and vasoconstriction also occurs as the renin-angiotensin system is stimulated. When these compensatory mechanisms can no longer maintain cardiac output, the heart begins to fail. Left ventricular dilation occurs as venous return and systemic vascular resistance rise. Eventually, the atria also dilate as more work is required to pump blood into the full ventricles. Cardiomegaly occurs as a consequence of dilation of the atria and ventricles. Blood pooling in the ventricles increases the risk of emboli.

Unlike dilated cardiomyopathy, which affects systolic function, hypertrophic cardiomyopathy primarily affects diastolic function. The features of hypertrophic cardiomyopathy include asymmetrical left ventricular hypertrophy; hypertrophy of the intraventricular septum; rapid, forceful contractions of the left ventricle; impaired relaxation; and obstruction to left ventricular outflow. The hypertrophied ventricle becomes stiff, noncompliant, and unable to relax during ventricular filling. Consequently, ventricular filling is reduced and left ventricular filling pressure rises, causing a rise in left atrial and pulmonary venous pressures and leading to venous congestion and dyspnea. Ventricular filling time is further reduced as a compensatory response to tachycardia. Reduced ventricular filling during diastole and obstruction to ventricular outflow lead to low cardiac output. If papillary muscles become hypertrophied and do not close completely during contraction, mitral regurgitation occurs. Moreover, intramural coronary arteries are abnormally small and may not be sufficient to supply the hypertrophied muscle with enough blood and oxygen to meet the increased needs of the hyperdynamic muscle.

Restrictive cardiomyopathy is characterized by stiffness of the ventricle caused by left ventricular hypertrophy and endocardial fibrosis and thickening, thus reducing the ability of the ventricle to relax and fill during diastole. Moreover, the rigid myocardium fails to contract completely during systole. As a result, cardiac output falls.

Signs and symptoms

Clinical manifestations of dilated cardiomyopathy may include:

Ø shortness of breath, orthopnea, dyspnea on exertion, paroxysmal nocturnal dyspnea, fatigue, and a dry cough at night due to left-sided heart failure

Ø peripheral edema, hepatomegaly, jugular venous distention, and weight gain caused by right-sided heart failure

Ø peripheral cyanosis associated with a low cardiac output

Ø tachycardia as a compensatory response to low cardiac output

Ø pansystolic murmur associated with mitral and tricuspid insufficiency secondary to cardiomegaly and weak papillary muscles

Ø S3 and S4 gallop rhythms associated with heart failure

Ø irregular pulse if atrial fibrillation exists.

Clinical manifestations of hypertrophic cardiomyopathy may include:

Ø angina caused by the inability of the intramural coronary arteries to supply enough blood to meet the increased oxygen demands of the hypertrophied heart

Ø syncope resulting from arrhythmias or reduced ventricular filling leading to a reduced cardiac output

Ø dyspnea due to elevated left ventricular filling pressure

Ø fatigue associated with a reduced cardiac output

Ø systolic ejection murmur along the left sternal border and at the apex caused by mitral regurgitation

Ø peripheral pulse with a characteristic double impulse (pulsus biferiens) caused by powerful left ventricular contractions and rapid ejection of blood during systole

Ø abrupt arterial pulse secondary to vigorous left ventricular contractions

Ø irregular pulse if an enlarged atrium causes atrial fibrillation.

Clinical manifestations of restrictive cardiomyopathy may include:

Ø fatigue, dyspnea, orthopnea, chest pain, edema, liver engorgement, peripheral cyanosis, pallor, and S3 or S4 gallop rhythms due to heart failure

Ø systolic murmurs caused by mitral and tricuspid insufficiency.

Complications

Ø Possible complications of cardiomyopathy include:

Ø heart failure

Ø arrhythmias

Ø systemic or pulmonary embolization

Ø sudden death.

Diagnosis

Ø The following tests help diagnose cardiomyopathy:

Ø Echocardiography confirms dilated cardiomyopathy.

Ø Chest X-ray may reveal cardiomegaly associated with any of the cardiomyopathies.

Ø Cardiac catheterization with possible heart biopsy can be definitive with hypertrophic cardiomyopathy.

Ø Diagnosis requires elimination of other possible causes of heart failure and arrhythmias.

Treatment

Correction of dilated cardiomyopathy may involve:

Ø treatment of the underlying cause, if identifiable

Ø angiotensin-converting enzyme (ACE) inhibitors, as first-line therapy, to reduce afterload through vasodilation

Ø diuretics, taken with ACE inhibitors, to reduce fluid retention

Ø digoxin, for patients not responding to ACE inhibitor and diuretic therapy, to improve myocardial contractility

Ø hydralazine and isosorbide dinitrate, in combination, to produce vasodilation

Ø beta-adrenergic blockers for patients with New York Heart Association class II or III heart failure

Ø antiarrythmics such as amiodarone, used cautiously, to control arrhythmias

Ø cardioversion to convert atrial fibrillation to sinus rhythm

Ø pacemaker insertion to correct arrhythmias

Ø anticoagulants (controversial) to reduce the risk of emboli

Ø revascularization, such as coronary artery bypass graft surgery, if dilated cardiomyopathy is due to ischemia

Ø valvular repair or replacement, if dilated cardiomyopathy is due to valve dysfunction

Ø heart transplantation in patients refractory to medical therapy

Ø lifestyle modifications, such as smoking cessation; low-fat, low-sodium diet; physical activity; and abstinence from alcohol.

Correction of hypertrophic cardiomyopathy may involve:

Ø beta-adrenergic blockers to slow the heart rate, reduce myocardial oxygen demands, and increase ventricular filling by relaxing the obstructing muscle, thereby increasing cardiac output

Ø antiarrhythmic drugs, such as amiodarone, to reduce arrhythmias

Ø cardioversion to treat atrial fibrillation

Ø anticoagulation to reduce risk of systemic embolism with atrial fibrillation

Ø verapamil and diltiazem to reduce ventricular stiffness and elevated diastolic pressures

Ø ablation of the atrioventricular node and implantation of a dual-chamber pacemaker (controversial), in patients with obstructive hypertrophic cardiomyopathy and ventricular tachycardias, to reduce the outflow gradient by altering the pattern of ventricular contraction

Ø implantable cardioverter-defibrillator to treat ventricular arrhythmias

Ø ventricular myotomy or myectomy (resection of the hypertrophied septum) to ease outflow tract obstruction and relieve symptoms

Ø mitral valve replacement to treat mitral regurgitation

Ø cardiac transplantation for intractable symptoms.

Correction of restrictive cardiomyopathy may involve:

Ø treatment of the underlying cause, such as administering deferoxamine to bind iron in restrictive cardiomyopathy due to hemochromatosis

Ø although no therapy exists for restricted ventricular filling, digoxin, diuretics, and a restricted sodium diet may ease the symptoms of heart failure

Ø oral vasodilators may control intractable heart failure.

Nursing Intervention

Ø administer medication as ordered to promote sufficient heart function

Ø assess hemodynamic status at least every 2 hours

Ø Monitor I/O

Ø Continous cardiac monitoring

Ø Assess for side effects of medication

Ø Auscultate heart and breath sounds. HR>100, RR>20, SBP<90>

Ø Give supplemental O2

Ø Assess LOC

Ø Promote periods of rests

Ø Prepare pt if invasive procedure should be done

Sources: Brunner and Suddarth's textbook of Medical-Surgical Nursing, Frizzell- handbook of pathophysiology, Saunder's Manual of Nursing Care, Lippincott's Critical Care Challenges