Complications of Hypertrophic Cardiomyopathy

Arrhythmias
A variety of arrhythmias, or irregularities of the heartbeat, are exceedingly common in patients with HCM and are often detected by exercise testing or Holter monitoring. Prolonged arrhythmias known as ventricular tachycardia or atrial fibrillation are particularly important and require treatment in the vast majority of cases. Transient arrhythmias with premature beats from the atria and ventricles occur much more commonly, but usually do not have the same importance to patients, even when present in large numbers.

Ventricular Tachycardia
Ventricular tachycardia is an incessant and repetitive occurrence of abnormal beats arising from the ventricles. This is a potentially serious arrhythmia in HCM since it may lead to ventricular fibrillation and sudden death. Patients prone to this arrhythmia may be treated with an implantable cardioverter-defibrillator.

Congestive heart failure
Any HCM patient with significant shortness of breath during physical exertion is, strictly speaking, experiencing a degree of heart failure. However, this is a different form of heart failure than that which occurs in coronary artery disease, or many other cardiac conditions. In HCM, congestive failure is present in a heart that is ironically not dilated (enlarged) and shows normal contraction of the ventricles. In other diseases heart failure is a profound condition, usually occurring after a heart attack, and producing dilated ventricles that contract poorly. Occasionally, heart failure in HCM may become intractable and fail to respond further to drugs, requiring major therapy and intervention.

Atrial fibrillation and stroke
With atrial fibrillation, the normal regular heart rhythm is altered due to loss of the normal contraction of the atria (the two upper chambers), causing the ventricles to beat in an irregular rhythm. Atrial fibrillation may be episodic or persistent, and occurs in as many as 20 to 25 percent of HCM patients, and is often responsible for important symptoms of heart failure at that time. While some patients are unaware of their atrial fibrillation, most rapidly develop symptoms such as shortness of breath, dizziness, and fainting. Atrial fibrillation increases in frequency with age, but may occur at any time in adulthood (after about 30 to 35 years of age). Although all the potential long-term consequences of atrial fibrillation are not completely resolved, this arrhythmia does not seem to be associated with increased risk for sudden death.

Because the atria "fibrillate" there is also a direct link and risk for clot formation due to the stagnant blood flow. This can result in a stroke if the blood clot travels to the brain. The risk of such an event in HCM is about one percent per year. Anticoagulation, to protect against stroke is important, and the pros and cons of this treatment should be discussed in detail by the patient and cardiologist.

Sometimes atrial fibrillation will revert to normal rhythm spontaneously, but patients often require drug treatment to abolish the abnormal rhythm, or to control and reduce the rapid ventricular rate if the patient must remain in atrial fibrillation. Electrical cardioversion may be used to convert the heart back into its normal rhythm. This treatment requires admission to the hospital and consists of applying a small electrical shock to the chest. Atrial fibrillation occurs in forms of heart disease other than HCM (or even in patients without heart disease), is relatively common in HCM occurring in up to 20 percent of patients, and increases in occurrence with age.

The problem of sudden death
Since the first description of HCM over 40 years ago, the issue of risk for sudden and unexpected death has been a highly visible feature of the disease. In reality, only a small proportion of patients with HCM are at increased risk for sudden premature death due to arrhythmias, which usually occur with little or no warning. The magnitude of this particular problem among all HCM patients has probably been exaggerated over the years due to the disproportionate number of reports from institutions in which there was the preferential referral of high-risk patients.

While the risk for sudden death in young people has been made a highly visible feature of HCM, in reality it is an uncommon occurrence and only a minority of the patients are truly at risk. Therefore, an important aspiration of the HCM evaluation is to identify which patients, among all those with this condition appear to be at particularly high risk.

Nevertheless, sudden unexpected collapse remains a devastating possibility for many patients living with this disease. We know that sudden death occurs most commonly in people who are 30 years of age or younger, but no particular age group is immune as sudden deaths have been reported in mid-life and beyond. The first ten to 12 years of life are generally free of adverse events such as sudden death and heart muscle thickening. However, a very few virulent cases in young children have been reported, with substantial hypertrophy or sudden death.

Sudden death may occur in some patients with HCM because the abnormal heart muscle in HCM can sometimes interfere with normal electrical activity. For example, in those portions of the left ventricular wall with abnormal architecture and myocyte disarray, the electrical signal may become unstable as it crosses areas of scarring and disorganized cells. This can, in turn, lead to distorted electrical impulses that generate fast or erratic heart rhythms, some of which can lead to adverse clinical events

At present, the highest risk for sudden death appears to be most associated with one or more of the following features of the disease (i.e., risk factors):

• prior cardiac arrest (heart stoppage or prolonged ventricular arrhythmia)
• fainting, particularly when repetitive or associated with exertion or when it occurs in young people
• serious arrhythmias (such as ventricular tachycardia) repeatedly detected by Holter monitoring
• family history of HCM-related premature sudden death in one or more close relatives
• extreme increase in the thickness of the left ventricular wall.

While the risk for sudden death in young people has been made a highly visible feature of HCM, in reality it is an uncommon occurrence and only a minority of patients are truly at risk. Therefore, an important aspiration of the HCM evaluation is to identify which patients appear to be at particularly high risk.

While the risk for sudden death in young people has been made a highly visible feature of HCM, in reality it is an uncommon occurrence and only a minority of patients are truly at risk. Therefore, an important aspiration of the HCM evaluation is to identify which patients appear to be at particularly high risk.

The latter disease feature applies to an important ten percent of all HCM patients in whom the maximum thickness of the left ventricular wall is 3.0 centimeters or more, and who may therefore be at increased risk based solely on their particular heart structure.

Relation between the degree to which the left ventricular wall is thickened and the likelihood of sudden death. This analysis shows little risk associated with mild degrees of thickening, but extreme increases in wall thickness (30 millimeters or more) convey a much greater risk.

It is important to emphasize that most patients with HCM are without risk factors for sudden death and are at low risk for premature death, and therefore should receive a large measure of reassurance in this regard.

Adapted from Hypertrophic Cardiomyopathy: For Patients, Their Families, and Interested Physicians, by Barry J. Maron, MD, et al., Copyright 2001, with permission from Futura Media Services, Inc., Armonk, New York