Intensity of physical exertion and triggering of myocardial infarction: a case-crossover study

Acute myocardial infarction (AMI) can be precipitated or triggered by discrete transient exposures including physical exertion. We evaluated whether the risk of having an AMI triggered by physical exertion exhibits an exposure-response relationship, and whether it varies by ambient temperature or by taking place indoors or outdoors.

We conducted a case-crossover study within the Myocardial Infarction Registry in Augsburg, Germany in 1999-2003. One thousand three hundred and one patients reported levels of activity and time spent outdoors on the day of AMI and three preceding days in an interview. The case-crossover analyses showed an association of physical exertion with AMI symptom onset within 2 h, which was strong for strenuous exertion (METs >or= 6) [relative risk (RR) 5.7, 95% confidence interval (CI) 3.6-9.0), and still significant for moderate exertion (METs = 5) (RR 1.6, 95% CI 1.2-2.1) compared to very light or no exertion. Strenuous exertion outside was associated with a four-fold larger RR of AMI symptom onset than exertion performed indoors, which was not explained by temperature.

This study confirms previous results and shows a graded exposure-response relationship between physical exertion intensity and triggering of AMI onset. These findings may have implications for behavioural guidance of people at risk of AMI.