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Exercise and Acute Cardiovascular Events: Placing the Risks into Perspective

Habitual physical activity reduces coronary heart disease events, but vigorous activity can also acutely and transiently increase the risk of sudden cardiac death and acute myocardial infarction in susceptible persons. This scientific statement discusses the potential cardiovascular complications of exercise, their pathological substrate, and their incidence and suggests strategies to reduce these complications. Exercise-associated acute cardiac events generally occur in individuals with structural cardiac disease. Hereditary or congenital cardiovascular abnormalities are predominantly responsible for cardiac events among young individuals, whereas atherosclerotic disease is primarily responsible for these events in adults. The absolute rate of exercise-related sudden cardiac death varies with the prevalence of disease in the study population. The incidence of both acute myocardial infarction and sudden death is greatest in the habitually least physically active individuals. No strategies have been adequately studied to evaluate their ability to reduce exercise-related acute cardiovascular events. Maintaining physical fitness through regular physical activity may help to reduce events because a disproportionate number of events occur in least physically active subjects performing unaccustomed physical activity. Other strategies, such as screening patients before participation in exercise, excluding high-risk patients from certain activities, promptly evaluating possible prodromal symptoms, training fitness personnel for emergencies, and encouraging patients to avoid high-risk activities, appear prudent but have not been systematically evaluated.

Regular physical activity is widely advocated by the medical community in part because substantial epidemiological, clinical, and basic science evidence suggests that physical activity and exercise training delay the development of atherosclerosis and reduce the incidence of coronary heart disease (CHD) events. Nevertheless, vigorous physical activity can also acutely and transiently increase the risk of acute myocardial infarction (AMI) and sudden cardiac death (SCD) in susceptible individuals. This scientific statement presents the cardiovascular complications of vigorous exercise, their pathophysiological substrate, and their incidence in specific patient groups and evaluates strategies directed at reducing these complications. The goal is to provide healthcare professionals with the information they need to advise patients more accurately about the benefits and risks of physical activity.

Most studies of exercise-related cardiovascular events have examined events associated with sports participation in young subjects and with vigorous exercise in adults. Vigorous exercise is usually defined as an absolute exercise work rate of at least 6 metabolic equivalents (METs), which is historically assumed to equal an oxygen uptake (V˙O2) of 21 mL·kg-1·min-1. Six METs approximates the energy requirements of activities such as jogging. Six METs is an arbitrary threshold and does not account for the fact that the myocardial oxygen demands of any physical activity are more closely related to the V˙O2 requirements relative to maximal exercise capacity than to the absolute work rate per se. Consequently, exercise work rates < 6 METs may still place considerable stress on the cardiovascular systems of unfit and older individuals.

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