PHYSICAL EXERTION AS A TRIGGER OF ACUTE MYOCARDIAL-INFARCTION

Background. It is controversial whether the onset of myocardial infarc tion occurs randomly or is precipitated by identifiable stimuli. Previ ous studies have suggested a higher risk of cardiac events in associat ion with exertion. Methods. Consecutive patients with acute myocardial infarction were identified by recording all admissions to our hospita l in Berlin and by monitoring a general population of 330,000 resident s in Augsburg, Germany. Information on the circumstances of each infar ction was obtained by means of standardized interviews. The data analy sis included a comparison of patients with matched controls and a case -crossover comparison (one in which each patient serves as his or her own control) of the patient's usual frequency of exertion with the las t episode of exertion before the onset of myocardial infarction. Resul ts. From January 1989 through December 1991, 1194 patients (74 percent of whom were men; mean age [+/-SD], 61+/-9 years) completed the inter view 13+/-6 days after infarction. We found that 7.1 percent of the ca se patients had engaged in physical exertion (greater-than-or-equal-to 6 metabolic equivalents) at the onset of infarction, as compared with 3.9 percent of the controls at the onset of the control event. For th e patients as compared with the matched controls, the adjusted relativ e risk of having engaged in strenuous physical activity at the onset o f infarction or the control event was 2.1 (95 percent confidence inter val, 1.1 to 3.6). The case-crossover comparison yielded a similar rela tive risk of 2.1 (95 percent confidence interval, 1.6 to 3.1) for havi ng engaged in strenuous physical activity within one hour before myoca rdial infarction. Patients whose frequency of regular exercise was les s than four and four or more times per week had relative risks of 6.9 and 1.3, respectively (P<0.01). Conclusions. A period of strenuous phy sical activity is associated with a temporary increase in the risk of having a myocardial infarction, particularly among patients who exerci se infrequently. These findings should aid in the identification of th e triggering mechanisms for myocardial infarction and improve preventi on of this common and serious disorder.