Triggering of acute myocardial infarction by heavy physical exertion. Protection against triggering by regular exertion. Determinants of Myocardial Infarction Onset Study Investigators.
Level 4 - case-series / case-control
Case-crossover observational study
PubMed 8232456 · doi:10.1056/NEJM199312023292301
What was done
Interviews were conducted with 1,228 patients with confirmed acute myocardial infarction (MI) an average of 4 days post-event to record the timing, type, and intensity of exertion in the 26 hours prior to symptom onset and habitual annual physical activity. Using a self-matched case-crossover design, observed frequency of heavy exertion (6 or more metabolic equivalents) in the 1 hour before onset was compared with expected values from control periods and validated against 218 population-based control subjects.
What was found
Heavy physical exertion in the hour prior to MI was reported by 4.4% of patients. Heavy physical exertion was associated with an overall relative risk of MI of 5.9 (95% CI, 4.6 to 7.7) compared to less strenuous activity or rest. Risk varied inversely with habitual physical activity: relative risk was 107 (95% CI, 67 to 171) for people exercising less than once weekly, 19.4 (95% CI, 9.9 to 38.1) for 1–2 times weekly, 8.6 (95% CI, 3.6 to 20.5) for 3–4 times weekly, and 2.4 (95% CI, 1.5 to 3.7) for 5 or more times weekly. Induction time was less than one hour, with symptoms usually starting during exertion.
Why it matters
This study provides quantitative evidence that heavy physical exertion can acutely trigger myocardial infarction and demonstrates that regular physical exercise confers substantial protection against this triggering effect.
Limits
Data rely on retrospective self-reported recall of exertion 4 days after a cardiac event, creating potential recall bias. Only surviving, hospitalized patients were interviewed, excluding fatal out-of-hospital events (survivor bias). Concomitant acute triggers (e.g., emotional stress or dietary factors) were not accounted for in the abstract.
Cited by
- supports The transient risk of a cardiac event during a burst of acute exercise increases up to 100-fold above baseline in unfit individuals, but only 10% to 20% in very fit individuals.