CardioExchange Archive

The growing popularity of marathons and other extreme sports has sparked worries about the potential dangers of these activities. The press and medical research have both focused on the risk for arrhythmias. But that concern may be misdirected. A new study from Israel published in the Journal of the American College of Cardiology finds that a much more serious danger may be heat stroke, which is defined as a core body temperature above 104-105 degrees associated with multiorgan dysfunction.

Researchers retrospectively reviewed data from more than 137,000 runners who participated in endurance races in Tel Aviv. They found only two serious cardiac cases: one myocardial infarction and one hypotensive supraventricular tachycardia. Serious cases of heat stroke, however, occurred in 21 runners; two were fatal, and 12 were life threatening.

The Israeli researchers said that the diagnosis of heat stroke can be missed and mistaken for a cardiac disorder unless the core temperature — which can only be reliably obtained with a rectal measurement — is taken immediately. They raise the possibility that many cases that have been thought to be cardiac in nature may actually be caused by heat stroke:

…social-cultural conceptions and logistic issues may prevent the implementation of immediate rectal temperature assessment following collapse in a race, especially in urban areas. Unheralded collapse with documented ventricular fibrillation may be the mode of presentation of heat stroke. In this setting, the correct diagnosis will be missed if, as often happens, the rectal temperature is not measured promptly.

They further note that “the risk of heat stroke is not limited to endurance races,” and is “an important cause of death among high school and college football players, who train and compete wearing heavy protective equipment.”

The study may also have important implications for the ongoing debate over whether student athletes should be screened before participating in sports, the authors say. In an accompanying editorial, Brian Olshansky and David Cannom write that “heat stroke has no predictive clinical profile that a screening examination may uncover and can only be diagnosed at the onset of the episode.”