Background: There is increasing recognition that heavy exertion can occasionally trigger an acute myocardial infarction (MI), although some uncertainties exist regarding the link. The primary aim of this study was to compare the relative risk (RR) of MI following vigorous exertion between those with confirmed coronary occlusion and those with a non-occluded culprit artery on acute angiography. Secondary aims were to determine if the risk of coronary occlusion is modified by the type of exercise (dynamic or isometric resistance), the frequency of regular exertion or whether the exertion was emotionally charged.

Methods: Seven hundred sixty-two (762) participants with MI (410 with coronary occlusion TIMI 0,1), and 352 (46%) with a non-occluded culprit artery (TIMI 2,3) completed a questionnaire within 4days of admission, detailing episodes of physical exertion in the 28hours prior to symptom onset and the usual frequency of such exertion. Exertion exposures within 1hour prior to symptom onset were compared to subjects' usual yearly exposure, with case-crossover methodology.

Results: The RR of symptom onset following heavy physical exertion level ≥6 (exertion scale 1-8), was higher in those with TIMI 0,1 compared to those with TIMI 2,3 flow (RR 6.30, 95% CI 4.70-8.50 vs 3.93, 2.89-5.30). The increased risk of coronary occlusion following vigorous exertion was observed following both dynamic exertion and isometric resistance, and did not differ between exertion types. The highest risk of coronary occlusion following exertion was observed in those who were sedentary (regular vigorous exertion <1day weekly) (RR=77, 95% CI 46-132), whereas in those who frequently perform regular vigorous physical exertion (>4days weekly), the RR of symptom onset during exertion was significantly lower, RR 2.3 (95% CI 1.5-3.6). There was no significant difference in relative risk based on whether the exertion was reported as emotionally charged.

Conclusions: The relative risk that heavy exertion will trigger a non-fatal MI with an occluded artery is greater than for a non-occluded culprit artery. Both dynamic and isometric exertion increase the relative risk of event, while exposure to regular vigorous exertion reduces the relative risk.