"If you look at the overall burden of cardiac arrest in middle aged people . . . it turns out only 5 percent had it when they were doing some kind of sporting activity," Chugh said in an interview. "That is very good news and we really didn't know that before."
Sudden cardiac arrest is not the heart attack we typically think of - a blocked artery that cuts off the blood supply to the heart muscle. Many of those myocardial infarctions are survivable. Sudden cardiac arrest is "ventricular fibrillation," a disturbance of the electrical activity that governs the ordered, rhythmic pumping of the heart. The heart's lower chambers lose their synchronization and death occurs in 10 minutes unless someone who knows CPR or has a defibrillator intervenes quickly. About 95 of every 100 victims die, Chugh said.
The triggers of such events are not well known, but risk factors are. They include coronary artery disease, obesity, smoking, a thick-walled heart, a poor "ejection fraction" - the heart's ability to squeeze blood out to the rest of the body - and arterial plaque that can rupture, Chugh said.
His study, published in the journal Circulation, notes that sudden cardiac arrest accounts for nearly half of all cardiovascular-related deaths. The sports-related attacks occurred most often during jogging (27 percent), but also during basketball games (17 percent), while cycling (14 percent), at the gym (11 percent), and while playing golf (8 percent), volleyball, tennis or soccer (3 percent each). The average age at the time of the attack was 51. Surprisingly, 44 of the 63 showed some kind of symptoms that might have indicated heart problems in the week before the attack, including nine with chest pain, the study shows.
Even if someone nearby knows CPR or has a defibrillator, survival is unlikely. "The odds are against you but it depends on your luck " Chugh said. "A marathon is a good place. A basketball court may be."
For that reason Chugh said that even the hint of a symptom should be enough to discourage a middle-aged or older person from undertaking a rigorous bout of exercise until he knows whether he has a problem. "If you don't feel good, you shouldn't do it," he said. "If you have the flu, it's a bad idea."
But the small number of sports-related sudden cardiac arrests clearly indicates that the benefits of a regular, reasonable exercise program outweigh the risks of collapsing during such exertion, even for people with risk factors.
"The findings from this study should in no way discourage patients with cardiovascular risk factors from engaging in regular, appropriate physical exercise within a framework of simple guiding rules from the treating physician," the researchers wrote.