European Heart Journal Advance Access published online on January 10, 2009
European Heart Journal, doi:10.1093/eurheartj/ehn550
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Physical exertion and triggering of myocardial infarction
uli
Division of Cardiology
Department of Medicine
University Hospital Split 
oltanska 1, 21000 Split
Croatia
E-mail: viktor.culic{at}st.t-com.hr
von Klot et al.1 reported that the risk of having myocardial infarction triggered by physical exertion exhibits an exposure–response relationship. This is the first study showing the increased risk of infarction associated with moderate exertion defined as five metabolic equivalents (METs). One previous case–crossover study2 found no increase in relative risk for mild-to-moderate exertion of three to five METs. Accordingly, in contrast to relatively safe activities of up to four METs, more vigorous activities may bring proportional cardiovascular risk. As, in observational studies on triggering circumstances, mild-to-moderate activities precede in average 29% of the infarction onsets in the general population,3 the significance of moderate exertion in the triggering may be greater than thought before.
One of the most interesting findings of the present study is that among elderly, exercise was associated with a four-times greater risk of myocardial infarction when performed outdoors than indoors, which could not be explained by air temperature.
Indoor activities are usually performed in more controlled and predictable conditions than outdoor activities. Outdoors, a person is more directly exposed to the influence of all weather elements, including wind and rain. Outside activities could also be more associated with unexpected situational factors or distractions that may act as bouts of additional emotional stress.
Exertion is probably a much powerful trigger and outweighs the effect of environmental factors.4 However, the major confounding may come from the fact that the temperature is not an isolated variable. Change in only one meteorologic factor practically does not occur; it is unseparately interrelated with other factors. Multiple confounding cannot be adequately controlled for, which may cause an incorrect estimation of the effect of a single factor. While one recent study observed modifying effect of atmospheric pressure but not temperature on the risk of cardiac incident associated with soccer matches as a possible emotional trigger,5 other studies showed clear associations of incidents with the atmospheric pressure, temperature, and wind activity.4,6,7
Within environmental confounding, the association between higher anthropogenic air pollution and acute myocardial infarction should also be considered.8,9 In addition to air pollutant emissions and transmission, the concentration of overall gaseous and particulate pollutants is also subjected to the meteorologic and atmospheric chemical processes, and strong correlation has been suggested with wind speed, rainfall, air pressure, temperature, and relative humidity.10–12
Not only intensity, but also the activity type may determine cardiovascular risk. Blood pressure increase is one of the principal hemodynamic internal triggering mechanism responsible for the initiation of plaque injury and acute coronary syndrome, larger the increase greater the risk.4 Perhaps, static activities are associated with a greater triggering risk since they generally increase arterial blood pressure to a greater extent than dynamic activities.13,14
The issue of environmental confounding requires development of new investigation designs, more extensive data gathering, and factors considering. Cardiovascular risk associated with a variety of activity profiles in different environmental settings must be further explored to provide recommendation for a safer physical activity in asymptomatic individuals, including coronary patients.
References
- von Klot S, Mittleman MA, Dockery DW, Heier M, Meisinger C, Hörmann A, Wichmann H-E, Peters A. Intensity of physical exertion and triggering of myocardial infarction: a case-crossover study. Eur Heart J (2008) 29:1881–1888.
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- Goerre S, Egli C, Gerber S, Defila C, Minder C, Richner H, Meier B. Impact of weather and climate on the incidence of acute coronary syndromes. Int J Cardiol (2007) 118:36–40.[Medline]
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- Peters A, Dockery DW, Muller JE, Mittleman MA. Increased particulate air pollution and the triggering of myocardial infarction. Circulation (2001) 103:2810–2815.
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- Palatini P, Mos L, Di Marco A, Mormino P, Munari L, Del Torre M, Valle F, Pessina AC, Dal Palu C. Intra-arterial blood pressure recording during sports activities. J Hypertens (1987) 5:479–481.
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- Physical exertion and triggering of myocardial infarction: reply
- Stephanie von Klot, Murray A. Mittleman, and Annette Peters
EHJ 2009 30: 251-252.[Extract] [Full Text]
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