There's a good way to prevent cardiac arrest during vigorous exercise, a new study finds: Get plenty of vigorous exercise.
The 12-year study of thousands of male physicians showed that men who exercised at least five times a week had a much lower risk of sudden death — about sevenfold less — than those who only exercised once a week, said Dr. Christine M. Albert, a cardiologist and a researcher at Brigham and Women's Hospital.
Cardiologist Dr. Daniel Shindler called the finding by researchers at three Boston hospitals and the Harvard and University of Miami public health schools very important.
"If you're constantly exercising — not one of those weekend warriors — (the study shows) you have a much better outcome," said Shindler, an associate professor at Robert Wood Johnson Medical School in New Brunswick, N.J.
Sudden cardiac arrest, generally caused by heart attacks or rhythm disturbances, kills an estimated 225,000 Americans each year.
Most, but not all, past studies have found that exercise reduces risk of sudden cardiac death. In the new study, habitual exercise did not cut the doctors' overall risk of sudden cardiac death, just the risk during exertion.
Doctors said any activities that work up a sweat, like brisk walks or gardening, can count as exercise.
Besides protecting the heart, regular, vigorous exercise strengthens bones and muscles, increases flexibility, and reduces blood pressure, cholesterol, body fat, stress and risk of stroke.
The doctors warned that strenuous exercise can still pose short-term danger, at least for sedentary people, and there have been well-publicized deaths of athletes while playing and out-of-shape seniors while shoveling snow. But the risk of fatal cardiac arrest during or right after exertion is still extremely low, they said.
Albert's team found the added risk from exertion was only about one death for every 1.5 million "hazard periods," or the average 30-minute exercise time and the subsequent half-hour.
Shindler said he expects doctors will use the finding to encourage more patients with heart conditions to at least start taking brisk walks regularly. He and Albert stressed that people should ease into a fitness program and should check with a doctor first if they have medical problems.
In the study, which appears in Thursday's edition of the New England Journal of Medicine, researchers analyzed data from the Physicians' Health Study begun in Boston in 1982.
Examining records on 21,481 doctors who started out free of heart disease, Albert and colleagues found that over the next 12 years, sudden cardiac arrest killed 122. Of those, 23 died upon exertion; the rest, during light exertion or rest.
Albert estimated that men exercising less than once a week were 74 times more likely to suffer sudden cardiac death during exertion than at rest. For men who exercised five or more times each week, the risk was 11 times higher during exertion.
Dr. Gerald F. Fletcher, a cardiologist and professor at the Mayo Medical School in Jacksonville, Fla., said this study confirms prior findings that physically conditioned people are less apt to die of heart problems.
Fletcher, an American Heart Association spokesman, said the group will put out new exercise guidelines early next year, calling for 30 to 60 minutes of "fairly vigorous" exercise four to six times per week.
"You don't need to do it all at one time," Fletcher said. "You get credit for leisure-time activity," from racket sports and dancing to house cleaning, on-the-job exercise, even running up and down stairs after toddlers.
Fletcher said that besides staying fit, people should eliminate or better control five other major risk factors for heart disease: smoking, high blood pressure, high cholesterol, obesity and diabetes.
Albert said more research is needed to determine if the findings apply to women.
Dr. Barry J. Maron of the Minneapolis Heart Institute Foundation wrote in an accompanying editorial that two factors might have affected the results. Researchers asked doctors at the start how much they exercised, but didn't measure how that changed over time, and doctors who got moderate but regular exercise were grouped with the occasional exercisers, he wrote.
On the Net: New England Journal of Medicine: www.nejm.org
American Heart Association site on exercise: www.justmove.org