Heat Stroke vs. Arrhythmic Death: Life-Threatening Events During Endurance Sports

The article “Life-Threatening Events During Endurance Sports: Is Heat Stroke More Prevalent Than Arrhythmic Death?” by Yankelson and colleagues makes several important points that are often overlooked in the discussion of adverse outcomes in endurance racing and highlights the risk of death from heat stroke.1 Cardiac arrest is a complication of heat stroke and as underscored in this article, exertional heat stroke (EHS) will be missed if a rectal temperature is not measured at the time of collapse.1,2 Cardiac sudden death (SCD) on the race course is a public event that usually makes headlines and can be tracked using press and internet publications, and 3% of the cardiac arrests in the Associated Cardiac Arrest Event Registry (RACER) study using this method were attributed to hyperthermia.3 Sudden cardiac arrest (SCA) with successful resuscitation and EHS with or without a fatal outcome is not as public and requires access to race medical records and medical outcomes to truly understand the incidence.4

The results published by Yankelson, et al reflect the outcomes that have been accumulated over the last 30 plus years at the Twin Cities Marathon; that is, the rate of EHS is greater, especially in warm conditions than the rate of SCA, and medical encounters, including EHS, rise dramatically in conditions that are hot for the season.5 In a longitudinal study from the Twin Cities and Marine Corps Marathons, the rate of SCA was 2.6 per 100,000 finishers with an SCD rate of 1.3 per 100,000 finishers.4 In contrast, the rate of EHS in hot conditions (WBGT >70 °F) is ≈150 per 100,000 finishers, warm condition (WBGT 60-70 °F) is ≈50 per 100,000 finishers, and cooler conditions is ≤10 per 100,000 finishers (Roberts – unpublished data). In the TC 10-mile race run on the same day as the marathon, there have been two SCA with no deaths (2.73 per 100,000 finishers), and the rate of EHS is about the same as the marathon in the same WBGT ranges (Roberts – unpublished data). EHS is a function of race environment, acclimatization, and exercise intensity, not necessarily race distance. While there have been no deaths from EHS at Twin Cities Marathon or 10-mile races, there have been some near misses that resulted in hospitalizations of four to 10 days, fortunately with no long-term sequelae (Roberts – unpublished data).5-10 The cases identified on site and cooled immediately went home the same day, either directly from the finish area or from the emergency department after observation. The key to optimum outcomes is early recognition with a rectal temperature measurement and immediate, rapid cooling to preserve tissues and organ systems.

The issue of electrocardiogram (ECG) pre-participation screening is interesting. A comparison of the decade pre- and post-required ECG screening in Israel showed no change in athlete SCD outcomes.11 The rate of SCD during training or competition (like the above road racing SCD statistics) in Minnesota State High School League athletes screened every three years with a standardized pre-participation physical examination (PPE) and no ECG is 0.24 per 100,000 athlete-seasons over a 19-year time span and 0.11 per 100,000 over the last decade.12 Deaths during sports activity for college age athletes are also comparatively low at 1.37 per 100,000 athlete-seasons.13 Endurance runs often involve an older age group than is usually addressed with formal PPE screening in the U.S., and also attracts people who were not involved in formal sports programs as teenagers and young adults. The required ECG screening in Israel provides an opportunity to look at the effectiveness of previous screening in this set of events. It is likely that many who were “disqualified” from participation by previous ECG screening were not in this participant pool, but it is also possible that some entered into this activity because the screening license was not required. It does not appear that previous ECG screening influenced the outcomes in this survey cohort and SCA occurred in at least one previously screened runner. There is no required PPE for the entry into the Twin Cities or Marine Corps Marathons, and the incidence of SCA is low; however, like this study, some of the runners with SCA had “passed” EGC and exercise stress testing within weeks of their marathon related SCA. ECG screening for this group of asymptomatic runners is not very effective and has false-negative results.

The study by Kim looking at SCD in nearly four million road race finishers across a decade showed that coronary artery disease was not the only cause of cardiac arrest in endurance runners, with about half of the 59 deaths related to hypertrophic cardiomyopathy (HCM).3 How frequently this cohort of runners would need to be screened with ECGs to reduce the number of HCM deaths and how many runners would be affected either by false-positive ECG readings (restricted activity, expensive workups, insurability, etc.) or false-negative readings is an unanswered question. The data from the Yankelson study does not seem to support the effectiveness of prior ECG screening for the road race population, and the SCA rates are similar to the Kim and other studies with no ECG screening.1,3,4,10

The take-away messages from this endurance running study are five-fold: 1) potentially fatal heat stroke is more common than SCA, especially in unexpectedly hot conditions; 2) heat stroke can trigger a potentially fatal cardiac arrest; 3) race medical teams must be schooled in rectal temperature measurement and immediate management of EHS, as well as SCA management; 4) prior ECG screening does not seem to influence SCD rates in this population; and 5) there is no discernable difference in SCA risk between previously ECG screened and unscreened runners.


  1. Yankelson L, Sadeh B, Gershovitz L, et al. Life-threatening events during endurance sports: Is heat stroke more prevalent than arrhythmic death? J Am Coll Cardiol 2014;64:463-9.
  2. Ronneberg K, Roberts WO, McBean AD, Center BA. Temporal Artery and Rectal Temperature Measurements in Collapsed Marathon Runners. Med Sci Sports Exerc 2008;40:1373-5.
  3. Kim JH, Malhotra R, Chiampas G, et al. Cardiac arrests during long-distance running races. N Eng J Med 2012; 366:132-42.
  4. Roberts WO, Roberts DM, Lunos S. Marathon related cardiac arrest risk differences in men and women. Brit J Sports Med 2012;47:168-71.
  5. Roberts WO. Determining a “do not start” temperature for a marathon based on adverse outcomes. Med Sci Sports Exerc 2010;42:226-32.
  6. Roberts WO. A 12-yr profile of medical injury and illness for the Twin Cities Marathon. Med Sci Sports Exerc 2000;32:1549-55.
  7. Roberts WO. Exertional heat stroke during a cool weather marathon: a case study. Med Sci Sports Exerc 2006;38:1197-202.
  8. Roberts WO. Exertional heat stroke in the marathon. Sports Med 2007;37:440-3.
  9. Roberts WO. Heat and cold: what does the environment do to marathon injury? Sports Med 2007;37:400-3.
  10. Schabe K, Schwellnus M, Derman W, et al. Medical complications and deaths in 21 and 56 km road race runners: a 4-year prospective study in 65 865 runners—SAFER study I. Br J Sports Med 2014;48:912-8.
  11. Steinvil A, Chundadze T, Zeltser D, et al. Mandatory electrocardiographic screening of athletes to reduce their risk for sudden death: proven fact or wishful thinking? J Am Coll Cardiol 2011;57:1291-6.
  12. Roberts WO, Stovitz S. Incidence of sudden cardiac death in Minnesota high school athletes 1993-2012 screened with a standardized pre-participation evaluation. J Am Coll Cardiol 2013;62:1298-1301.
  13. 13.  Harmon KG, Asif IM, Klossner D, et al. Incidence of sudden cardiac death in national collegiate athletic association athletes. Circulation 2011;123:1594-600.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Sports and Exercise Cardiology, SCD/Ventricular Arrhythmias, Sports & Exercise and ECG & Stress Testing

Keywords: Acclimatization, Athletes, Cardiomyopathy, Hypertrophic, Coronary Artery Disease, Death, Sudden, Cardiac, Electrocardiography, Exercise Test, Heat Stroke, Hospitalization, Israel, Medical Records, Minnesota, Physical Examination, Resuscitation, Seasons, Temperature

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