July 28th, 2014

Death by Running: It’s the Heat and Not the Heart

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.”

4 Responses to “Death by Running: It’s the Heat and Not the Heart”

  1. Leon Hyman, Ms M.D. says:

    Too many people wait till they are thirsty to drink, which is probably another factor leading to heat stroke or exhaustion. The average person is at least a liter and one have depleted in water before they begin to perceive thirst. then it is very difficult to catch up they continue to maintain the same degree of activity.

  2. Thierry Legendre, MD says:

    Remember that excessive fluid intake can induce hyponatremia and also be deleterious as shown in this paper : Excessive Fluid Intake Among Runners In The Boston Marathon . New England Journal of Medecine 2005;352:1550.

  3. Enrique Guadiana, Cardiology says:

    Most of the runners don’t drink many fluids for the fear of discomfort after doing that. With the heat the organism has to divert circulation to skin to cool so the heart work increases considerably but a very important factor is the relative humidity, in Tel Aviv the dew point in summer is between 55 – 72 F so it is very muggy, with high relative humidity the body can’t use sweat to lower the core temperature and if it is too low you loose fluids more quickly. So don’t excercice in extreme weather conditions.

  4. Jean-Pierre Usdin, MD says:

    I agree with Enrique.
    And remember, by heart …this aphorism:
    “Too much heat makes you hit the road!”