Hypertrophic cardiomyopathy (HCM) is a common genetic heart disorder (affecting almost 1 in 500 people) that can cause several varieties of heart problems – not the least of which is sudden death.
What Is HCM and What Causes It?HCM is a form of heart muscle disease in which the muscular walls of the ventricles (lower chambers of the heart) become abnormally thickened.
The thickening of the heart muscle causes the muscle itself to function abnormally. The thickening also can cause the ventricles to become distorted, which can interfere with the function of the aortic valve and the mitral valve, disrupting the flow of blood through the heart.
HCM is caused by a genetic abnormality that produces a disorder in the growth of the heart muscle fibers. In some families, HCM is passed on as an “autosomal dominant” trait, which means that if the gene for HCM is inherited from a single parent, the child will have the disease.
However, in almost half the patients with HCM, the genetic problem is not inherited at all, but occurs as a spontaneous genetic mutation – in which case, parents and siblings of the patient will not be at risk for this condition (but children of the patient can be.)
What Problems Does HCM Cause?
Fortunately, most people with HCM turn out to have a relatively benign form of the disease, and many can live normal or nearly normal lives. However, in some patients with this condition, serious cardiac problems can develop.
There are four kinds of cardiac problems caused by HCM:
1) HCM can cause diastolic dysfunction. "Diastolic dysfunction" refers to the fact that thickened ventricles become stiff, making it more difficult for the ventricles to fill with blood. This stiffness causes the blood to "back up" into the lungs, causing shortness of breath – usually with exertion. The diastolic dysfunction also makes it more difficult for patients with HCM to have arrhythmias, especially atrial fibrillation.
2) HCM can cause systolic dysfunction. "Systolic dysfunction" means that the heart's pumping action is not normal - that is, when the heart beats, an insufficient volume of blood is ejected. In HCM, systolic dysfunction is often caused by an obstruction to the flow of blood through the left ventricle, produced by the thickened heart muscle just below the aortic valve. This condition is referred to as "subvalvular stenosis," which causes the same problems as aortic valve stenosis.
Distortion of the left ventricle caused by abnormally thickened cardiac muscle can also produce mitral regurgitation, which contributes to systolic dysfunction.
3) HCM can cause dilated cardiomyopathy. This condition leads to heart failure, and is caused by an eventual “burning out” of the thickened heart muscle. Dilated cardiomyopathy tends to occur late in the course of HCM, after the disease has been present for many years.
4) Finally, HCM can cause sudden death. The sudden death in HCM is usually due to ventricular tachycardia or ventricular fibrillation - extremely rapid cardiac rhythm disturbances. While many of these sudden deaths occur during vigorous exertion, it can also occur during minimal exertion or at rest, with no warning whatsoever. The risk of sudden death has been estimated being as high as 5% per year in patients with HCM who are in their teens and 20s, though it drops off somewhat after that.
How Is HCM Diagnosed?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.
How Is HCM Treated?HCM cannot be cured, but it can be managed. Beta blockers and calcium blockers can help reduce the "stiffness" in the thickened heart muscle. In some patients - especially those who have significant heart valve dysfunction - surgery to remove portions of the thickened heart muscle is necessary. Atrial fibrillation, if it occurs, often causes severe symptoms and needs to be managed more aggressively in patients with HCM than in the general population.
How Can Sudden Death Be Prevented?Sudden death in HCM is often seen in younger patients – often before symptoms have occurred, or even before a diagnosis has been made. While sudden death is always a devastating problem, it is particularly so when it occurs in young people.
Many methods have been tried for reducing the risk of sudden death in patients with HCM - including avoiding exercise, using beta blockers and calcium blockers, and using antiarrhythmic drugs - these methods unfortunately have met with mixed results. In recent years it has become apparent that in patients whose risk of sudden death appears high, an implantable defibrillator should be used. The implantable defibrillator is a pacemaker-like device that is implanted under the skin, monitors the heart rhythm continuously, and automatically delivers a shock to the heart to restore a normal rhythm should a dangerous ventricular arrhythmia occur. While it sometimes seems a drastic step, it is much less drastic than allowing a young individual to die suddenly.
Massie, BM "Heart Failure" in: Goldman L and Ausiello D (Eds). Cecil Textbook of Medicine, WB Saunders, 2003