A new study that analyzes 10 years of data finds that contrary to what many people may believe, taking part in marathons and half-marathons is not linked to higher risk of cardiac arrest compared to other forms of athletics. The study, published online on 12 January in the New England Journal of Medicine, reveals that most of the participants who did experience cardiac arrest during such long-distance races had undiagnosed, pre-existing heart problems.

The researchers, who sourced their data from a US registry of cardiac arrests during marathons and half-marathons, also found that a key factor in saving the lives of such victims was the ability of bystanders to start CPR.

Senior author Dr Aaron Baggish, director of the Cardiovascular Performance Program in the Cardiology division of Massachusetts General Hospital (MGH), and colleagues found that the rate of cardiac arrest in marathons and half-marathons was the same as or lower than that for other strenuous physical activities, that male contestants accounted for most of them and appear to be at most risk. Their analysis also revealed that the most common cause was hypertrophic cardiomyopathy or coronary artery disease.

Baggish said in a statement there appears to be a general consensus, stimulated by intense media coverage, that the risk of cardiac arrest during long-distance running races like marathons is high, throwing into question their safety.

“But we found that the risk of cardiac arrest for marathon and half-marathon runners is equal to or less than the risk for other athletes – including triathletes, college athletes and casual joggers,” said Baggish.

He said their study gives the “first accurate, comprehensive characterization of cardiac arrest and sudden cardiac death risk in this population”, and the “finding provides important reassurance” that marathon-running is a “generally safe and well tolerated activity”.

Previous studies have tended to focus on sudden cardiac deaths in young, competitive athletes. However, people who take part in marathons are often older, and may have unknown, underlying health problems.

For their study, Baggish and colleagues assessed the incidence and outcomes of cardiac arrests occuring during or at the finish line of marathons or half-marathons in the United States between 2000 and mid-2010.

To compile data on the clinical backgrounds of the arrests, they interviewed survivors and next of kin of non-survivors, reviewed medical records, and analyzed post-mortem records.

The interviews were extensive and helped them obtain demographic data, family and medical history, cardiac risk factors, previous diagnoses, and information surrounding the cardiac event itself.

The results showed that:

  • Out of nearly 11 million registered runners, there were 59 cardiac arrests: 40 at marathons and 19 at half marathons (an incidence rate of 0.54 per 100,000 participants).
  • More than 85% of the cardiac arrests were in men.
  • Cardiovascular disease was the main reason for the arrests.
  • The incidence rate was significantly higher for marathons than half-marathons (1.01 versus 0.27 per 100,000)
  • .

  • The incidence rate among male runners (the highest risk group) was higher in the second half of the study decade than in the first (0.71 per 100,000 for 2000-2004, 2.03 per 100,000 for 2005-2010).
  • Of the 59 cases of cardiac arrest 42 (71%) were fatal.
  • Of these, the researchers were able to get complete clinical data for 31 of them, and this showed that the strongest predictors of survival were initiation of CPR by a bystander or having an underlying diagnosis that was not hypertrophic cardiomyopathy.

The authors conclude:

“Marathons and half-marathons are associated with a low overall risk of cardiac arrest and sudden death. Cardiac arrest, most commonly attributable to hypertrophic cardiomyopathy or atherosclerotic coronary disease, occurs primarily among male marathon participants; the incidence rate in this group increased during the past decade.”

Hypertrophic cardiomyopathy is an abnormal thickening of the heart muscle: the most common cause of sudden cardiac death in young athletes. This is the first study to show it could be an issue for older runners.

The authors also point out that 71% mortality is considerably better than the usual 92% rate for cardiac arrests occuring outside of hospital environments. They suggest this is probably because of the presence of on-site medical teams and spectators at marathons, making it more likely that victims of collapse receive help quickly.

None of the participants with coronary disease had any evidence of acute coronary plaque rupture, something Baggish commented on:

“The lack of plaque rupture – a critical event in many heart attacks – was an intriguing and surprising finding.”

“”It suggests that the kind of underlying disease that causes cardiac arrest in distance runners may be detectable by a simple stress test prior to race day,” he added.

The team now intend to investigate how best to educate runners, screen them for heart disease, and to examine specific risk factors in more detail.

The study also highlights how bystander CPR, a simple skill that anyone can learn, can be the difference between life and death for marathon runners.

“Recognition of this important finding calls us all to action, and we will be offering the first-ever CPR education session for runners, family members and spectators at this year’s Boston Marathon,”said Baggish.

Written by Catharine Paddock PhD