Author + information
- Paolo Angelini, MD∗ ()
- ↵∗Department of Cardiology, Center for Coronary Artery Anomalies, Texas Heart Institute, 6624 Fannin, Suite 2780, Houston, Texas 77030
I read with interest and great concern the report by Yankelson et al. (1) on heat stroke and sudden cardiac arrest (SCA) or death (SCD) during endurance sports. The investigators reported the results of their retrospective study of 137,580 marathon runners in Israel and concluded that: 1) marathon runners who die during competition are more often the victims of fatal heat stroke than of cardiac events, and 2) core body temperature (CBT) should be consistently monitored in endurance athletes as a fundamental risk factor, because a CBT >40°C alone should be considered sufficient to cause sudden death.
The evidence presented in the study does not appear to support either conclusion. The few observed events were superficially described (e.g., no autopsy findings were reported for the 2 runners who died of heat stroke). Although the investigators claimed that measuring CBT is critical to diagnosing heat stroke, adequate CBT data were not reported for a comprehensive group of their cohort of runners. Also, it did not appear that possible alternative causes (primarily cardiovascular-related) of or contributing factors in SCD were ruled out. Strenuous exercise is known to generically increase CBT and is accompanied by the production of inflammatory cytokines (2). This being the case, the absence of control data from runners who had no adverse events (who constituted the majority of the runners, and who were subject to the same conditions of workload and environmental temperature as the runners who had adverse events) seems especially important; without such data, it is difficult to determine whether there is a “critical CBT” above which adverse events are likely to occur. Accurate, routine pre-certification protocols (3) were not required or used in the majority of runners in this cohort, so the prevalence of high-risk cardiovascular conditions (hr-CVC) in the participant runners (and the consequent risk of SCD) was not known.
In contemplating the implications of the findings by Yankelson et al. (1), it is important to consider that although few runners experience SCD, high CBT is essentially related to workload (2) and environmental factors that are common to all runners. Furthermore, runners who have hr-CVC may have a greater-than-normal risk of developing high CBT due to the onset of cardiovascular failure. (Low cardiac output and heart failure, which last for some time after the onset of cardiac decompensation, generally lead to inefficient breathing and heat dispersion.) Athletic competition, by its very nature, encourages participants to perform at their physical limits; among competitors who have hr-CVC, CBT probably becomes substantially higher than that of their peers. In such cases, hr-CVC would be the primary cause of SCA, not a secondarily high CBT.
Although the CBT story is both interesting and puzzling, and although we await more solid data about this parameter in a sizeable sample of endurance runners, we should strive to eliminate the inconvenience and impracticality of using rectal temperature measurements in the usual urban environment of marathons. Acceptable alternative devices other than implantable esophageal or intestinal probes, such as infrared laser earlobe thermometers, already exist and could easily be made available at these races (4,5). Although CBT is higher than cutaneous temperature, the 2 measurements are correlated (and both temperatures increase with exertion [4,5]), and it is likely that a convenient compromise between optimal precision and clinical relevance could be found.
I appreciate the interest of my colleagues in this important aspect of exercise pathophysiology and would encourage them to continue their important study of a potentially easily preventable cause of sudden death during sports. At the same time, the focus on temperature should not distract from the undeniable importance of hr-CVC and the urgent need for effective screening.
- American College of Cardiology Foundation
- Yankelson L.,
- Sadeh B.,
- Gershovitz L.,
- et al.
- Stacey M.,
- Woods D.,
- Ross D.,
- Wilson D.