An analysis of previous studies that examined whether episodic physical activity and sexual activity can act as a trigger for cardiac events found an association between these activities and a short-term increased risk of heart attack and sudden cardiac death, although the absolute risk was small and lessened among persons with high levels of regular physical activity, according to an article in the March 23/30 issue of JAMA.

Acute cardiac events are a major cause of illness and death, with as many as a million acute myocardial infarctions (MIs; heart attacks) and 300,000 cardiac arrests occurring in the United States each year. "Regular physical activity has been identified as strongly associated with a decreased risk of cardiovascular disease and related mortality. Despite the well-established benefits of regular physical activity, anecdotal evidence has suggested that physical activity, as well as other acute exposures, such as sexual activity and psychological stress, can act as triggers of acute cardiac events," the authors write.

Issa J. Dahabreh, M.D., of Tufts Medical Center, Boston, and Jessica K. Paulus, Sc.D., of Tufts University, Medford, Mass., and the Harvard School of Public Health, Boston, conducted a systematic review and meta-analysis to examine the association between episodic physical activity and sexual activity and acute cardiac events and also the interaction of regular physical activity levels with the triggering effect of these exposures. The researchers identified 14 studies that met criteria for inclusion in the analysis.

The researchers found that overall, the studies suggested an association (3.5 times increased risk) between episodic physical activity and heart attack. Also, there was evidence of an increase in the risk of sudden cardiac death (SCD) triggered by episodic physical exertion. Overall, episodic sexual activity was associated with a 2.7 times increased risk of heart attack. The authors also found that because these exposures of episodic physical exertion and sexual activity are infrequent, the absolute risk of these activities triggering an event is small.

Subgroups of patients with higher habitual activity levels tended to be less susceptible to the triggering effect of episodic physical activity. Analysis indicated that the relative risk of heart attack triggered by episodic physical activity was decreased by approximately 45 percent, and SCD 30 percent, for each additional time per week a person was habitually exposed to physical activity.

"Habitual activity levels significantly affected the association of episodic physical activity and MI, episodic physical activity and SCD, and sexual activity and MI; in all cases, individuals with lower habitual activity levels had an increased relative risk for the triggering effect," the authors write.

"In conclusion, based on our review of 14 case-crossover studies of acute cardiac events, we found a significant association between episodic physical and sexual activity and MI and suggestive evidence of an association between episodic physical activity and SCD. Most importantly, these associations appear to be strongly modified by habitual physical activity, with individuals with higher habitual activity levels experiencing much smaller increases in risk compared with individuals with low activity levels. In view of this, as well as the small absolute magnitude of the risk associated with acute exposure to episodic physical or sexual activity, our findings should not be misinterpreted as indicating a net harm of physical or sexual activity; instead they demonstrate that these exposures are associated with a temporary short-term increase in the risk of acute cardiac events."

JAMA. 2011;305[12]1225-1233.