Improved Fitness Lowers Mortality Risk of Male Heart-Attack Survivors

ORLANDO -- Increasing fitness, not merely enrolling in an exercise program, appears to help men live longer following a heart attack, the first long-term follow-up study of participants in the National Exercise and Heart Disease Project (NEHDP) has shown.

Results of the research were presented here today (March 24, 1999) at the 39th Conference on Cardiovascular Disease Epidemiology & Prevention by Joan Dorn, Ph.D., assistant professor in the Department of Social and Preventive Medicine in the University at Buffalo School of Medicine and Biomedical Sciences.

The NEHDP was a three-year, multi-center, randomized, clinical trial conducted in the U.S. from 1976-79 to determine if participation in a structured exercise program improved long-term survival of men who had suffered a heart attack. John P. Naughton, M.D., UB professor of medicine and former dean of the UB medical school, directed the initial study.

Twenty years ago, prescribing exercise after a heart attack was considered risky because the prevailing wisdom called for rest. The NEHDP was designed to answer the exercise-or-no-exercise question. Dorn completed the follow-up analysis in 1998.

"If you just compare the men who were assigned to an exercise program with men who weren't, there was no difference in long-term survival at the 19-year follow-up," Dorn said. "But the men who improved their fitness during the three-year study did live longer, and the most likely way to improve fitness is through exercise."

The explanation for this finding probably is due to contamination between study groups, Dorn said. The men were assigned randomly to a structured exercise group or to a control group whose members were told to maintain their normal routines and not to take part in a regular exercise program during the trial. However, by the end of two years, 23 percent of the members of the exercise group reported they had stopped exercising, while 31 percent of the controls said they had begun exercising regularly, Dorn said.

"The observed increases in fitness probably reflect the men who were most diligent in actually performing regular exercise," she noted. "Although we have no measures of fitness after the three-year study period, the thought is that the men who actually exercised after a heart attack probably became more fit, were likely to stay with it and, consequently, lived longer."

The original trial involved 651 men between the ages of 30 and 64 who had suffered a heart attack within eight weeks to three years of the trial's start in 1976. Before being enrolled and at every six months of the trial, participants received a physical examination and performed a multi-stage graded exercise test on a treadmill to estimate oxygen uptake, an indication of fitness, at different levels or stages of exertion. The highest stage completed and oxygen uptake at the end of the trial were designated as the participant's maximal physical work capacity.

Dorn and colleagues assessed mortality rates of all participants until their death, or at three, five, 10, 15 and 19 years after the trial's completion. Results showed that at three years, exercisers had approximately a 30 percent lower risk of death than non-exercisers, but the benefit did not reach statistical significance. This small, early benefit derived from a structured exercise program dissipated over time and had disappeared at 10 years.

On the other hand, those who increased their capacity to do work during the study period lowered their risk of death at every time period. Results showed that each increase of one stage in work capacity reduced the risk of death by about 10 percent, regardless of which study group the men were assigned to or their initial level of fitness.

"The increased capacity to do physical work most likely reflects the actual exercise performed during the trial," Dorn said. "If this is the case, our results indicate that exercise performed at a level sufficient to increase physical work capacity as measured by our testing method may have long-term survival benefits for heart-attack survivors."

The follow-up study was supported by a First Independent Research Support in Transition Award from the National Heart, Lung and Blood Institute. The original trial was funded by the Rehabilitation Services Administration of the then Department of Health, Education and Welfare.

Additional researchers on the follow-up study were Naughton, Dai Imamura and Maurizio Trevisan, M.D., all of the Department of Social and Preventive Medicine in the UB medical school.