January 11, 2012 9:01 pm
The New England Journal of Medicine has just published the biggest and most informative medical research yet on cardiac arrests and deaths in marathons (and half-marathons). It's titled "Cardiac Arrests during Long-Distance Running Races," and it appears in the Jan. 12, 2012, edition of the historic medical journal. The article, from the RACER study (Race Associated Cardiac Arrest Registry), concludes: “Long distance running races are associated with low overall risk of cardiac arrest and sudden death.”
Indeed, the authors present evidence that cardiac-arrest rates in distance races are lower than those in college sports (18-to-22-year-olds!) and triathlons, and comparable to rates among healthy joggers and avid recreational exercisers. Thus: “The risk associated with long distance running events is equivalent to or lower than the risk experienced in other vigorous physical activity.” (See Tables below for key statistical data from RACER.)
Of course, hundreds of other medical studies have shown that individuals who regularly perform aerobic exercise have lower heart-attack and death risks than those who do not exercise. That's why many scientific groups, including the American Heart Association, the American College of Sports Medicine, and the Institute of Medicine, recommend that Americans engage in roughly 150 minutes of moderate aerobic exercise per week. (AHA guidelines here.) The NEJM article was not intended to investigate public-health issues related to regular running. It looked only at cardiac arrest and deaths during actual marathon and half marathon races.
The principal author of the study, cardiologist Aaron Baggish, M.D., directs the Cardiovascular Performance Program at Massachusetts General Hospital in Boston, advising many runners about their heart health. Baggish is himself a running devotee who has completed more than 30 marathons with a PR of 2:49. His NEJM study tracked 10,900,000 runners who participated in marathons and half marathons from January 2000 to May 2010. In this group, Baggish and colleagues uncovered 59 "cardiac arrests," defined as a fallen, unconscious runner with no discernible pulse. Seventeen of these runners were subsequently resuscitated and survived, while 42 died. [For a separate Runner's World interview with Baggish, click here.]
This is the first major study of runner-cardiac-arrests to include half-marathon races along with marathon races. The rate of cardiac arrests in marathons was found to be roughly four times that in half marathons. There were 40 cardiac arrests among slightly fewer than 4 million marathon runners, and 19 among slightly fewer than 7 million half marathoners. The researchers believe that the marathon distance probably fatigues the heart more. "Longer races involve more physiological stress and thus a higher likelihood of precipitating an adverse event," they wrote.
The risk of having a heart attack in a marathon is 1.01 per 100,000 participants, and the death risk is .63/100,000. This means big marathons might expect to see one heart attack for every 99,000 runners, and one death for every 158,000 runners. The highest-risk group, men in marathons, has a cardiac-arrest incidence of 1.41/100,000, or one per 70,900 runners. Men have about a five-times higher risk than women for both heart attacks and death.
RACER also notes that hyponatremia and heat stroke are “uncommon causes” of heart attack and death, that aspirin probably doesn’t reduce heart attacks in runners, and that the vast majority of cardiac arrests occur in the last 6 miles of the marathon and last 3 miles of the half-marathon.
The 71% death rate among the cardiac-arrest runners is considerably lower than the 92% death rate for similar out-of-hospital events. This has led some marathon medical experts to quip that a marathon is the second-best place to have a heart attack (given medical teams along the course and at the finish) after a hospital itself.
RACER breaks new ground in becoming the first study to investigate "clinical information" about many of the stricken runners. Previous studies only looked at the number of cardiac arrests and deaths. But the RACER researchers were able to secure deep medical information, including autopsy results, for 31 (23 fatalities, 8 survivors) of the 59 stricken runners. A look at this clinical information yielded a surprise. Until now, almost all exercise-heart experts have believed that middle-aged men suffered exercise heart attacks when a chunk of cholesterol plaque broke free from an artery and lodged elsewhere. However, RACER found “no evidence of acute plaque rupture” in autopsies of those who had cardiac arrests.
Instead, it found signs for “demand ischemia” resulting from an "imbalance of oxygen supply and demand." This could explain the high percent of cardiac-arrest cases that occur near the finish of marathons, if runners with fatigued hearts suddenly break into a sprint that requires more oxygen supply. Some medical experts have begun recommending that marathoners relax and take it easy in the last mile.
The demand ischemia finding led Baggish and colleagues to suggest that "preparticipation exercise testing, by virtue of its ability to accurately detect physiologically significant coronary-artery stenosis, may be useful for identifying some persons at high-risk, including middle-aged and older men." However, they acknowledge that this advice remains "speculation," and it continues to be an area of hot debate among other exercise cardiologists. (See our Baggish interview for more on this topic.)
From autopsy results, RACER found that the biggest cause of cardiac arrests and deaths was “definite/probable hypertrophic cardiomyopathy.” This is the largely genetic condition believed to provoke many heart deaths among young athletes (under age 35) in all sports. Because of the age-factor involved with HCM, the age of deceased runners in the clinical-information group was 34 years, while survivors averaged 53 years. In other words, if you are younger (<35) and suffer a heart attack while running, you are more likely to have a tough-to-resuscitate cardiomyopathy than the slightly less serious ischemic heart disease.
Importantly, CPR provided by spectators, other runners or medical personnel can be a key factor in survival of heart-attack runners. Eight out of 8 survivors (100 percent) in the clinical-information subgroup received CPR on the course. Among nonsurvivors, only 43 percent received CPR.
RACER also uncovered an increasing risk of male heart attacks in the last five years (2005-2010) vs 2000-2004. Baggish and colleagues termed this "troubling," and suggested it could result because "long-distance racing has recently been attracting more high-risk men with occult cardiac disease who seek the health benefits of routine physical exercise."
From web site : http://peakperformance.runnersworld.com/2012/01/new-study-on-heart-deaths-in-distance-runners-from-new-england-journal-of-medicine/
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