Hypertrophic Cardiomyopathy (HCM)

What is Hypertrophic Cardiomyopathy?

Hypertrophic cardiomyopathy (HCM) - also known as idiopathic hypertrophic subaortic stenosis. hypertrophic obstructive cardiomyopathy, and muscular aortic stenosis is a primary disease of cardiac muscle. It's characterized by left ventricular hypertrophy and disproportionate. asymmetrical thickening of the intraventricular septum and free wall of the left ventricle. It's also distinguished by a dynamic left ventricular outflow tract pressure gradient related to subaortic narrowing caused by septal hypertrophy in the mitral valve area. The obstruction produced may change between examinations and even from beat to beat.

In HCM, cardiac output may be low, normal. or high. depending on whether the stenosis is obstructive or nonobstructive. Eventually, left ventricular dysfunction resulting from rigidity and decreased compliance causes pump failure. If cardiac output is normal or high, the stenosis may go undetected for years, but low cardiac output may lead to potentially fatal heart failure.

The course of this disorder varies. Some patients demonstrate progressive deterioration; others remain stable for several years.

Causes of Hypertrophic Cardiomyopathy

About half of all cases of HCM are transmitted as an autosomal dominant trait. Other causes aren't known.

Signs & Symptoms of Hypertrophic Cardiomyopathy

Symptoms of hypertrophic cardiomyopathy may occur at any time of life. However, in some cases people do not develop any symptoms even though the condition may have been present for some time.

The most common symptoms are shortness of breath and fatigue. Other common symptoms are chest pain (angina), heart palpitations, and fainting or near-fainting (syncope), especially with physical activity. Sometimes life-threatening abnormal heartbeats (arrhythmias) cause fainting and heart palpitations—these are symptoms that you should always report to your doctor because of your increased risk of sudden death.

Diagnostic Tests

In general, the echocardiogram is the best method of diagnosing HCM. The echocardiogram allows accurate measurement of the thickness of the ventricular walls, and can detect abnormal heart valve function as well. The electrocardiogram (ECG) also can give important clues as to the presence of HCM.

Both an ECG and echocardiogram should be performed in close relatives of a patient diagnosed with HCM, and an echocardiogram should be performed in any person in whom the ECG or the physical examination suggests ventricular hypertrophy.

Unfortunately, the first symptom of HCM among many young patients is sudden death, caused by severe arrhythmias. HCM is a major cause of death in young athletes who seem completely healthy but die during heavy exercise.

Treatment

The goals of treatment are to relax the ventricle and to relieve outflow tract obstruction. Propranolol, a betaadrenergic blocking agent, is the drug of choice. It slows the heart rate and increases ventricular filling by relaxing the obstructing muscle, thereby reducing angina, syncope, dyspnea, and arrhythmias. However, propranolol may aggravate symptoms of cardiac decompensation.

Calcium channel blockers may reduce elevated diastolic pressures and severity of outflow tract gradients and increase exercise tolerance. Disopyramide can be used to reduce left ventricular contractility and the outflow gradient.

Atrial fibrillation, a medical emergency with HC, necessitates cardioversion. It also calls for heparin administration before cardioversion and continuing until fibrillation subsides because of the high risk of systemic embolism.

If heart failure occurs, amiodarone may be used, unless an atrioventricular block exists. This drug seems to be effective in reducing ventricular and supraventricular arrhythmias, as well. Vasodilators (such as nitroglycerin), diuretics, and sympathetic stimulators (such as isoproterenol) are contraindicated.

Prevention Tips

Identify, by family history, which people are at high risk for the genetic form of the disease. Some patients with mild forms of hypertrophic cardiomyopathy are only diagnosed by screening echocardiograms because of their known family history. Treat known high blood pressure.