Objective.

—To determine the relative risks of nonfatal myocardial infarction (MI) triggered by sexual activity among the general population and in patients with prior coronary heart disease.

Design.

—Relative risks and effect modification were calculated by the case-crossover method, a new epidemiologic technique designed to quantify the transient change in risk following exposure to a potential disease trigger.

Setting/Participants.

—A total of 1774 patients with MI were interviewed in 45 hospitals throughout the United States. Data were gathered on potential triggers of MI occurring immediately prior to the event and during the previous year. Results are presented for the 858 patients who were sexually active in the year prior to the Ml, with attention to the 273 patients who had coronary artery disease prior to their index Ml, and the effect of regular exertion on risk.

Main Outcome Measure.

—The relative risk of nonfatal MI following sexual activity.

Results.

—Of the 858 patients, 79 (9%) reported sexual activity in the 24 hours preceding Ml, and 27 (3%) reported sexual activity in the 2 hours preceding onset of symptoms of MI. The relative risk of MI occurring in the 2 hours after sexual activity was 2.5 (95% confidence interval [CI], 1.7-3.7). The relative risk of triggering onset of Ml among patients with a history of prior angina (2.1 [95% CI, 0.8-5.8]) or prior Ml (2.9 [95% CI, 1.3-6.5) was not greater than that observed in those without prior cardiac disease. Sexual activity was a likely contributor to the onset of Ml in only 0.9% of cases and regular exertion was associated with decreasing risk.

Conclusions.

—Sexual activity can trigger the onset of MI. However, the relative risk is low, and since the absolute hourly risk of MI is extremely low, the absolute risk increase caused by sexual activity also is extremely low (1 chance in a million for a healthy individual). Moreover, the relative risk is not increased in patients with a prior history of cardiac disease and regular exercise appears to prevent triggering. These findings should be useful for counseling patients and decreasing the fear of sexual activity that often prevents complete rehabilitation from cardiovascular disease. (JAMA. 1996;275:1405-1409)

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