ACC 2009: Risk of Sudden Cardiac Death Greater in Triathlons Than Marathons

April 2, 2009 (Orlando, Florida) — The risk of sudden cardiac death appears to be greater in triathlons than marathons, new research shows, and this risk is confined to the swim portion of the event. The risk of sudden cardiac death even exists in the shorter-distance triathlons, those events filled with typical weekend warriors.

"In many of the people doing these events, individuals might come from a running background or another sport," lead investigator Dr Kevin Harris (Minneapolis Heart Institute Foundation, MN) told heartwire . "In Minnesota, where I come from, you can swim outside only a few months of the year, and you get into a condition in a triathlon that's quite different from swimming in a lap pool, where most athletes train."

Presenting the results of the study here at the American College of Cardiology 2009 Scientific Sessions, Harris and colleagues report that the risk of sudden death in the triathlon was 1.5/100 000 participants, a "not-inconsequential" risk that is nearly double the risk of sudden death in marathon runners.

Triathlons Growing in Popularity

Presenting his results to the media during a press conference last week, Harris said that the triathlon, a three-sport event that consists of swimming, cycling, and running, has grown in the past 15 years. USA Triathlon, the governing body of the sport, reported 15 000 registered members in 1993, but this has increased to more than 100 000 members in 2007. Still, despite the growth, little is known about the risks of the sport, said Harris.

In this study, investigators studied the most recent years of participation--from January 2006 to September 2008--to accurately assess the risk to those participating in the events. During this time, there were 2846 triathlons in the US, and these included the shorter sprint distance, the medium-length Olympic distance, and the grueling Ironman race, which involves a 2.4-mile swim, a 112-mile bike ride, and a 26-mile run. In the other events, the swim, bike, and runs are much shorter.

Of the 922 810 participants, there were 14 deaths, with men more likely to die than women (11 males and 3 females died). Of these 14 deaths, 13 occurred during the swim portion of the race, and all were initially attributed to drowning. One triathlete died from a fall off his bike, and none died during the run portion of the race. The average age of those who died was 43 years.

Autopsy reports obtained in six individuals who died during the swim, however, showed that four individuals had associated cardiovascular disease, including three with probable hypertrophic cardiomyopathy and one individual with dilated cardiomyopathy. This translated into a risk of sudden death of 1.5/100 000 participants. Comparatively, a study by Dr Donald Redelmeier (University of Toronto, ON) of more than three million marathon runners showed the rate of sudden cardiac death to be 0.8/100 000 participants [1].

Harris told the media there was no significant difference in the death rates in the different triathlon distances. Also, he said he does not know why triathlons posed a greater risk of sudden death than the marathon or why swimming, in particular, was the riskiest of the three sports. He suspects that the cold water might induce abnormal heart rhythms, such as long-QT syndrome, which can cause sudden death. He pointed out that the swim, with its increased jostling for position and inability to rest when in trouble, likely led to some deaths that were true drowning. Also, many athletes are less experienced in the water.

"Maybe what's going is that you're getting less well-conditioned athletes or more novice athletes, although what's interesting is that we know of only a couple of athletes where this was their first triathlon," he said.

For race directors, it is important to recognize that these events are occurring in the water, and this might involve decreasing the number of athletes in a heat or possibly increasing the number of lifeguards in the water. Often it is difficult for rescue personnel to get to athletes in trouble.

"It's impossible for triathlons to mandate screening," added Harris. "The individual has to decide if he has symptoms that might trigger an investigation, such as a family history, or some other risk factors for heart disease, that might alert this 45-year-old or 50-year-old male to get checked out before participating in a triathlon."

Redelmeier DA, Greenwald JA. Competing risks of mortality with marathons: retrospective analysis. BMJ 2007; 335: 1275-1277. Abstract

The complete contents of Heartwire , a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

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