Life Threatening Events During Endurance Sports: Heat Stroke vs Cardiac Arrhythmia Death

by Paul D. Thompson, MD (Cardiology)

Everyone suddenly seems to be interested in the cardiac problems of athletes. The general rule-of-thumb is that most exercise-related cardiac events in adults are due to coronary artery disease, whereas such events in those under 30 or 35 years of age are primarily due to inherited or congenital cardiac conditions such as hypertrophic cardiomyopathy or anomalous coronary arteries. Yankelson et al remind cardiologists to keep other conditions in the differential, including heat stroke.

These authors reviewed the diagnoses of runners requiring hospitalization after participating in races in Tel Aviv. These races are held twice yearly, one during the day in the spring and once at night during the summer. Races of 10, 21.2, and 42.2 km are run simultaneously with a common finish line, although the marathon (42.2 km) was occasionally cancelled because of the heat. From 2007 to 2013, 23 of the 137,580 participating runners required hospitalization, but only two events, a myocardial infarction and an episode of supraventricular tachycardia, were cardiac-related. Heat stroke accounted for the other 21 serious events; 2 of these were fatal. The authors stress the importance of including heat stroke in the differential for exercise-related collapse and stress; several of these heat stroke events would not have been detected without routine rectal temperatures. These are important lessons, but not new. Heat stroke is a well-known problem in hot and even warm running races, even more so in the shorter events where runners can run faster and generate more body heat per minute.

On the other hand, clinicians should be careful not to over-diagnose heat stroke. Heat stroke in runners rarely occurs in training, when the athlete has enough sense to quit. Heat stroke is usually a condition seen in competition, when competitiveness prevails. The exceptions are football players pushed in training by overzealous coaches and military and law enforcement recruits pushed during basic training.

It is unclear how heat stroke was diagnosed in the present report. The authors stress the importance of rectal temperatures, but rectal temperatures >104°F are often seen in totally asymptomatic runners after intense effort. The authors also fail to discuss exercise-related hyponatremia attributed to inappropriate antidiuretic hormone (IADH). Runners with this condition are often slow runners, spend a lot of time on the course, drink water frequently, and collapse after they finish when gut perfusion is reestablished and the water is absorbed. The sudden hyponatremia produces cerebral edema, which can lead to seizures and death. It is a form of IADH because ADH is detectable despite the hyponatremia.

Despite these caveats, this is a useful study for clinicians interested in exercise medicine because it reminds us to keep a wide differential when caring for the collapsed athlete. It isn’t always the heart.

Reviewed and posted by Dr. Russell

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