Last Sunday, an experienced marathon runner in his mid-50’s collapsed a few yards from the finish line during the Road2Hope half-marathon in Hamilton, Ontario.  Regrettably, the paramedics were unable to resuscitate him.  This unfortunate story illustrates the rare but tragic phenomenon of exercise-induced sudden cardiac arrest.

We’ve known since the 1970’s that sudden cardiac arrest can strike runners during marathon races.  Until recently, little was known about how frequently the problem occurs.  However, a study published in 2012 in the New England Journal of Medicine has given us important information about various aspects of the problem.

By systematically searching online databases, the investigators identified all cases of sudden cardiac arrest that occurred during marathons and half-marathons races between January 2000 and May 2010.   They then divided the number of incidents by the total number of participants in those races to get the “rate” of sudden cardiac arrest.  They also tried to obtain any additional available information about the victims, e.g., age, gender, timing of collapse during the race, resuscitation outcomes, and autopsy findings.

Note that the study could not take into account the number of marathon runners who ran in more than one race during that 10-year period.  For example, if a runner participated in three races, he or she would be counted as three participants.  So the incidence rate obtained (the number of cases of cardiac arrest divided by the number of participants) likely underestimates the true rate (number of cases divided by number of individual participants).  In other words, cardiac arrest during marathons and half-marathons is more frequent than reported in the study.

Here are 10 important factors to consider:

1.  Frequency:  The overall rate of cardiac arrest during the 10-year period was very low (1 per 184,000 total participants), but as noted above, the rate per individual participant is likely higher.  The rate in men has risen over time, and is  now about double what it was 10 years ago.  The authors suspect that endurance events may be attracting more athletes with hidden, unsuspected heart disease than in the past (particularly more middle-aged and older men).

2. Length of race: Cardiac arrest is more frequent during marathons than half-marathons.  In both types of races, cardiac arrest is much more frequent toward the end of the race than at the beginning or in the middle.  This strongly suggests that strain or exhaustion may be an important contributing factor.

3.  Gender:  The vast majority (86 percent) of cardiac arrests occur in men, but women may be affected as well.

4.  Age:  The average age of a cardiac arrest victim was 43 years, but the age range was wide.  Among the cases about which age information was available, the youngest was 22 and the oldest 65.

5.  Causes:  In most cases, an underlying cardiovascular condition, previously unsuspected, was present.  The most common conditions were coronary artery disease and hypertrophic cardiomyopathy (thickening of the heart muscle).  Both of these conditions can be detected by non-invasive testing.

6.  Screening and aspirin:  In all cases of coronary artery disease identified at autopsy, there was severe obstruction of the artery by plaque, but no evidence of clot or acute “plaque rupture.”  This was an unexpected finding and, as a result, the authors timidly suggested that screening adults with a stress test might be of value.  (Of course, at AHSF we strongly endorse the screening approach!).  The absence of clots also suggests that taking aspirin before the race might not be an effective way to reduce the risk of cardiac arrest.

7.  Non-cardiac factors:  In the rare cases where no abnormality of the heart was discovered, the suspected cause of the cardiac arrest was hyponatremia (low blood sodium level) or hyperthermia (severe heat stroke).  Hyponatremia is an increasingly recognized problem in endurance races and probably results from excessive intake of fluid.

8.  Benefit of CPR:  The success of CPR and resuscitation was 29 percent, which means that less than a third of cardiac arrest victims survived the event.  This is a paltry number, but it is better than the survival rate in the general population, where only about 10 percent of cardiac arrest victims survive.  The reason for the better outcomes is that marathon races are generally well organized and equipped to respond promptly to medical emergencies.

9.  Survival:  Older victims of cardiac arrest had a better chance of survival than younger ones.  For those age 40 and above, the survival rate was almost 50 percent, whereas for those under age 40 it was just 7 percent.  This is explained by the fact that cardiomyopathies are the more common causes of cardiac arrest in young people, and CPR is less successful in patients with cardiomyopathy than in those with coronary artery disease.

10.  Take home message:  Athletes and prospective runners should not be alarmed by these reports and statistics.  The overall benefits of exercise far outweighs the risks.  However, we believe  it is prudent and justifiable to undergo non-invasive cardiac screening to detect an unsuspected problem and, if one is found, to implement appropriate proactive measures to reduce the risk of cardiac arrest.

I hope you have found this useful.  If you enjoy reading what we right, sign-up for our free monthly newsletter at the bottom of this page.  It covers the latest on heart health and sports cardiology.

I wish all marathoners safe, enjoyable running!

Dr. Accad