A primary disease of the cardiac muscle, hypertrophic cardiomyopathy is characterized by disproportionate, asymmetric thickening of the interventricular septum in relation to the free wall of the left ventricle (3:1 ratio). In hypertrophic cardiomyopathy - previously known as idiopathic hypertrophic subaortic stenosis-cardiac output may be low, normal, or high, depending on whether stenosis is obstructive or nonobstructive.
The natural history of hypertrophic cardiomyopathy is highly variable. Some patients may remain asymptomatic for years. The dyspnea that results is primarily due to markedly impaired diastolic compliance rather than systolic dysfunction. Sudden death, especially during exercise, may be the initial event, as has occurred in athletes.
Although specific causes of hypertrophic cardiomyopathy are not yet fully known, the primary cause seems to be genetic. Nongenetic causes may also influence who will develop this disease.
It has been shown that about 50 percent of patients with hypertrophic cardiomyopathy will have a first-degree relative who also has the diagnosis of hypertrophic cardiomyopathy. This has important implications for screening of relatives as well as planning for families of patients with a diagnosis of hypertrophic cardiomyopathy. Other nongenetic influences may play a part in determining who will and who will not develop hypertrophic cardiomyopathy. Hypertrophic cardiomyopathy appears to occur equally in men and women.
In the majority of cases the condition is inherited. In others there is either no evidence of inheritance or there is insufficient information about the individual's family to assess inheritance. In affected families the condition usually passes from one generation to the next and generations are not skipped. This pattern of inheritance is called dominant, and the condition may be passed on from affected males and females.
Signs and symptoms
Many patients have no symptoms. For those who do, the most common are breathlessness and chest discomfort. Other signs are fainting during physical activity, strong rapid heartbeats that feel like a pounding in the chest, and fatigue, especially with physical exertion. In some cases, the first and only manifestation of hypertrophic cardiomyopathy is sudden death, caused by a chaotic heartbeat. The heart's lower chambers beat so chaotically and fast that no blood is pumped. Instead of beating, the heart quivers. In advanced stages of the disease, patients may have severe heart failure and its associated symptoms, including fluid accumulation or congestion. The most common symptoms are:
Along with typical clinical findings, the diagnosis depends on the following test results:
The goals of treatment are to relax the ventricle and to relieve outflow tract obstruction. Propranolol, a beta-adrenergic blocking agent, slows 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. Atrial fibrillation necessitates cardioversion to treat the arrhythmia and, because of the high risk of systemic embolism, anticoagulant therapy. Calcium channel blockers (such as verapamil) may improve diastolic dysfunction until fibrillation subsides.
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 is digoxin as well as sympathetic stimulators, such as isoproterenol, which enhance cardiac contractility and myocardial demands for oxygen, intensifying the obstruction.
If drug therapy fails, surgery may be indicated. Ventricular myotomy (resection 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, and is experimental.
Dualchamber pacing may prevent progression of hypertrophy and obstruction. Implantable defibrillators may be used in patients with malignant ventricular arrhythmias.
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