Triggering of sudden death from cardiac causes by vigorous exertion

Background Retrospective and cross-sectional data suggest that vigorous exe rtion can trigger cardiac arrest or sudden death and that habitual exercise may diminish this risk. However, the role of physical activity in precipit ating or preventing sudden death from cardiac causes has not been assessed prospectively in a large number of subjects. Methods We used a prospective, nested case crossover design within the Phys icians Health Study to compare the risk of sudden death during and up to 30 minutes after an episode of vigorous exertion with that during periods of lighter exertion or none. We then evaluated whether habitual vigorous exerc ise modified the risk of sudden death that was associated with vigorous exe rtion. In addition, the relation of vigorous exercise to the overall risk o f sudden death and nonsudden death from coronary heart disease was assessed . Results During 12 years of follow-up, 122 sudden deaths were confirmed amon g the 21,481 male physicians who were initially free of self-reported cardi ovascular disease and who provided information on their habitual level of e xercise at base line. The relative risk of sudden death during and up to 30 minutes after vigorous exertion was 16.9 (95 percent confidence interval, 10.5 to 27.0; P < 0.001). However, the absolute risk of sudden death during any particular episode of vigorous exertion was extremely low (1 sudden de ath per 1.51 million episodes of exertion). Habitual vigorous exercise atte nuated the relative risk of sudden death that was associated with an episod e of vigorous exertion (P value for trend = 0.006). The base-line level of exercise was not associated with the overall risk of subsequent sudden deat h. Conclusions These prospective data from a study of U.S. male physicians sug gest that habitual vigorous exercise diminishes the risk of sudden death du ring vigorous exertion. (N Engl J Med 2000; 343:1355-61.) (C) 2000, Massach usetts Medical Society.