Exercise And Sudden Death
by Karin van Hoek, M.D.
Cardiology Department
Sansum Medical Clinic
Santa Barbara CAHeart disease is the number one cause of death in the United States. Approximately 50% of cardiac deaths are sudden, accounting for more than 300,000 deaths in this country each year. Most cardiac deaths are due to ventricular fibrillation, an abnormal heart rhythm that interferes with the heart muscle's ability to effectively generate a blood pressure. Ventricular fibrillation can cause death if not immediately treated.
Almost all victims of sudden cardiac death have some form of structural heart disease. Studies of younger athletes who died during exercise have shown some form of congenital heart disease, usually either a disease of heart muscle called hypertrophic cardiomyopathy or a defect in blood vessels supplying the heart.
Hypertrophic cardiomyopathy is characterized by an abnormally thick heart muscle. Since it is often genetically transmitted, the disorder is often found in multiple family members. Symptoms may include chest pain, shortness of breath, or syncope (loss of consciousness). Unfortunately, these young people may present with sudden cardiac death as their first symptom. The disorder is easily diagnosed, however, by a painless echocardiogram (ultrasound exam).
Coronary blood vessel anomalies result from an abnormally located artery. This malformation can interfere with blood flow to the heart muscle.
In contrast to younger victims, sudden cardiac death in those over age 35 is most often caused by blockage of cardiac blood vessels by fatty deposits, or coronary atherosclerosis. Although many of these individuals have had prior myocardial infarctions (heart attacks), most cases of sudden cardiac death do not result from heart attacks. Instead, ischemia, or lack of blood supply to the heart muscle, is thought to be the chief factor when sudden cardiac death occurs while engaged in physical activity. The reason ischemia is important is that it predisposes the heart muscle to abnormal rhythms including ventricular fibrillation.
Most cases of sudden death do not occur during strenuous physical exercise, but rather during rest or usual daily activities. This is because a relatively small portion of one's time is spent in vigorous activity. However, strenuous physical activity does increase the risk of sudden death and cardiovascular mortality
But despite this short term risk associated with exercise, there is a significant long term benefit. The risk/benefit ratio comes out in favor of habitual vigorous exercise. The greatest risk, in fact, is found in the sedentary individual who rarely engages in physical activity.
Before beginning a vigorous exercise program, consult your physician, since certain tests may be appropriate. In those over age 40 who have been sedentary or with risk factors for coronary artery disease (smoking, elevated cholesterol, hypertension, diabetes, strong family history of heart disease) an exercise study may be advisable. These are usually performed on a treadmill with continuous EKG (electrocardiographic) monitoring.
Dr. van Hoek received her M.D. degree from Dartmouth and completed both her Internship and Residency in Internal Medicine at the Dartmouth-Hitchcock Medical Center. After completing a Cardiology fellowship at Dartmouth, she returned to her alma mater as Instructor of Clinical Medicine. Fellow of the American College of Cardiology and a member of the American Heart Association's Council on Clinical Cardiology, she is the author of numerous papers on cardiovascular research.