Hypertrophic cardiomyopathy
Hypertrophic cardiomyopathy: Excerpt from Professional Guide to Diseases (Eighth Edition)
This primary disease of cardiac muscle, also called idiopathic hypertrophic subaortic stenosis, is characterized by disproportionate, asymmetrical thickening of the interventricular septum, particularly in the left ventricle’s free wall. In hypertrophic cardiomyopathy, cardiac output may be low, normal, or high, depending on whether stenosis is obstructive or nonobstructive. If cardiac output is normal or high, the disorder may go undetected for years; but low cardiac output may lead to potentially fatal heart failure. The disease course varies; some patients progressively deteriorate; others remain stable for years.
Causes and incidence
Despite being designated as idiopathic, in almost all cases, hypertrophic cardiomyopathy may be inherited as a non–sex-linked autosomal dominant trait. Most patients have obstructive disease, resulting from effects of ventricular septal hypertrophy and the movement of the anterior mitral valve leaflet into the outflow tract during systole. Eventually, left ventricular dysfunction, from rigidity and decreased compliance, causes pump failure.
This disorder affects 2 to 5 of every 1,000 people.
Signs and symptoms
Clinical features of the disorder may not appear until it’s well advanced, when atrial dilation and, possibly, atrial fibrillation abruptly reduce blood flow to the left ventricle. Reduced inflow and subsequent low output may produce angina pectoris, arrhythmias, dyspnea, orthopnea, syncope, heart failure, and death. Auscultation reveals a medium-pitched systolic ejection murmur along the left sternal border and at the apex; palpation reveals a peripheral pulse with a characteristic double impulse (pulsus biferiens) and, with atrial fibrillation, an irregular pulse.
Diagnosis
Diagnosis depends on typical clinical findings and these test results:
❑ Echocardiography (most useful) shows increased thickness of the intra-ventricular septum and abnormal motion of the anterior mitral leaflet during systole, occluding left ventricular outflow in obstructive disease.
❑ Cardiac catheterization reveals elevated left ventricular end-diastolic pressure and, possibly, mitral insufficiency.
❑ Electrocardiography usually shows left ventricular hypertrophy, T-wave inversion, left anterior hemiblock, Q waves in precordial and inferior leads, ventricular arrhythmias and, possibly, atrial fibrillation.
❑ Auscultation confirms an early systolic murmur.
Treatment
The goals of treatment are to relax the ventricle and to relieve outflow tract obstruction. Agents such as propranolol, a beta-adrenergic blocker, slow heart rate and increase ventricular filling by relaxing the obstructing muscle, thereby reducing angina, syncope, dyspnea, and arrhythmias. However, propranolol may aggravate symptoms of cardiac decompensation. Atrial fibrillation necessitates cardioversion to treat the arrhythmia and, because of the high risk of systemic embolism, anticoagulant therapy until fibrillation subsides. Because vasodilators such as nitroglycerin reduce venous return by permitting pooling of blood in the periphery, decreasing ventricular volume and chamber size, and may cause further obstruction, they’re contraindicated in patients with hypertrophic cardiomyopathy. Also contraindicated are sympathetic stimulators such as isoproterenol, which enhance cardiac contractility and myocardial demands for oxygen, intensifying the obstruction. Although quinidine is used to suppress ventricular arrhythmia, disopyramide is preferred because of its negative inotropic properties. Patients with potentially lethal arrhythmias may need an implantable-cardioverter defibrillator to prevent sudden death.
If drug therapy fails, surgery is indicated. Ventricular myotomy (resection of the hypertrophied septum) or ventricular myectomy (removal of the hypertrophied septum) alone or combined with mitral valve replacement may ease outflow tract obstruction and relieve symptoms. However, ventricular myotomy may cause complications, such as complete heart block and ventricular septal defect.
Special considerations
❑ Because syncope or sudden death may follow well-tolerated exercise, warn such patients against strenuous physical activity such as running.
❑ Administer medications as prescribed. Caution: Avoid nitroglycerin, digoxin, and diuretics because they can worsen obstruction. Warn the patient not to stop taking propranolol abruptly, because doing so may increase myocardial demands. To determine the patient’s tolerance for an increased dosage of propranolol, take his pulse to check for bradycardia. Also take his blood pressure while he’s supine and standing (a drop in blood pressure [more than 10 mm Hg] when standing may indicate orthostatic hypotension).
❑ Before dental work or surgery, tell the patient to discuss prophylaxis for subacute infective endocarditis with his health care provider.
❑ Provide psychological support. If the patient is hospitalized for a long time, be flexible with visiting hours and encourage occasional weekends away from the hospital, if possible. Refer the patient for psychosocial counseling to help him and his family accept his restricted lifestyle and poor prognosis.
❑ If the patient is a child, have his parents arrange for him to continue his studies in the health care facility.
❑ Because sudden cardiac arrest is possible, urge the patient’s family to learn cardiopulmonary resuscitation.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
» Next page: Restrictive cardiomyopathy (Professional Guide to Diseases (Eighth Edition))
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