Vigorous physical activity increases the risk of sudden cardiac death (SCD) and acute myocardial infarction (AMI) but there is no standard definition as to what constitutes an exertion-related cardiac event, specifically the time interval between physical exertion and cardiac event. A systematic review of studies related to exertion-related cardiac events was performed and the time interval between exertion and the event or the symptoms leading to the event was looked for in all the articles selected for inclusion. A total of 12 of 26 articles “suggested” or “defined” exertion-related events as those events whose symptoms started during or within 1 h of exertion. Others used definitions of 0.5 h, 2 h, “during exertion”, “during or immediately post exertion” and “during or within several hours after exertion”. It is suggested, therefore, that the definition of an exertion-related cardiac event be established as a cardiac event in which symptoms started during or within 1 h of physical exertion.
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Physical activity reduces the overall risk of atherosclerotic cardiovascular disease,1 but vigorous physical activity also transiently and acutely increases the risk of cardiac events including sudden cardiac death (SCD)2,–,4 and acute myocardial infarction (AMI).5,–,8 There is no standard definition as to what constitutes an exertion-related cardiac event, and specifically the time interval between physical exertion and cardiac events has not been defined. Consequently, we performed a systematic review of the medical literature to determine the time interval after exertion used to collect exertion-related cardiac events and to propose a standard definition for such exertion-related complications.
We performed a systematic review of studies of exertion-related cardiac events by searching PubMed using combinations of the search terms: “exercise”, “exertion”, “sports” and “athletic” with the terms “acute myocardial infarction”, “myocardial infarction”, “cardiac death”, “cardiac complication” and “sudden cardiac death”. English-language articles published from 1975 to 2008 and included on PubMed were reviewed and additional relevant articles identified from their references. Articles were selected for inclusion and examined in detail if they addressed exertion-related sudden cardiac events and directly or indirectly identified the interval between exertion and the event or the symptoms leading to the event. Single case reports were excluded, as were papers which did not provide data regarding the exact time of the cardiac event in relation to exertion.
We classified the articles as having “defined” exertion-related cardiac events (n = 17) when the hazard period after exercise was stated specifically and as “not defined” (n = 9) when the interval after exertion could only be inferred from the results, case description or discussion. Ten of 17 articles defined exertion-related events as those events whose symptoms started during and within 1 h of exertion. The remainder used definitions of 0.5 h,9 10 2 h,11 “during exertion”,12 “during and immediately post exertion”4 13 and “during and within several hours after exertion”.14 Two of the nine “not defined” articles used a probable definition of during and within 1 h of exertion whereas the remainder probably used during and immediately after exertion.
Two articles examined the risk vs time after exertion more closely. Mittleman et al7 examined the relative risk of myocardial infarction during and after exertion requiring at least six multiples of the resting metabolic rate compared with sedentary activity. There were 54 exertion-related events in this study overall, with 44 having onset during exertion and 10 during the first hour after exertion. The relative risk of myocardial infarction was 5.9 (confidence interval (CI) 4.6 to 7.7) in the hour immediately after exertion, but only 0.6 in the second post-exertion hour. Therefore, only exertion during the hour immediately before the onset of myocardial infarction was associated with an increase in the relative risk, suggesting that the induction time for myocardial infarction is less than 1 h. Hallqvist et al6 calculated the relative risk of myocardial infarction after exertion in 15 minute intervals. Relative risk during exertion in patients without premonitory symptoms was 6.1-fold (95% CI 4.2 to 9) greater than rest, but decreased to 1.9 (95% CI 0.5 to 7.1), 1.9 (95% CI 0.5 to 7.4), and 2.0 (95% CI 0.5 to 7.3) over the subsequent 45 minutes. There was no increase in risk beyond 45 minutes after the end of exertion, and relative risk was 1.8 (CI 0.8 to 3.9) for the full hour after exertion. There were 42 events in this study overall, however, and only four, two, two and two in the 15 minute subsets after exertion, so the power to detect the relative risk after exertion was limited.
Sudden cardiac death (SCD) is generally defined as death from cardiac causes with loss of consciousness occurring within 1 h of a change in cardiovascular status,15 16 but to our knowledge no standard temporal definition of exertion-related cardiac events has been established. The majority of studies identified in this review used symptoms starting during or within 1 h of exertion to define exertion-related events. Mittleman et al7 have documented that the first hour after exertion, but not the second hour after exertion, is associated with an increased risk of myocardial infarction. Hallqvist et al6 have suggested that this risk is actually restricted to the first 45 minutes after exertion, but this study is limited by its small sample size. Given these two studies and the prevalence of using an hour after exertion, we suggest that the definition of an exertion-related cardiac event be established as a cardiac event whose symptoms start during or within 1 h of physical exertion.
Competing interests None.
Provenance and Peer review Commissioned; not externally peer reviewed.
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