Consistent, Moderate Exercise Reduces Women's Risk of Sudden Cardiac Death

May 09, 2005

Linda Little

May 9, 2005 (New Orleans) — Women should exercise more regularly for longer periods of time to reduce the risk of sudden cardiac death (SCD) both overall as well as during exertion, Boston researchers reported here at the Heart Rhythm Society (HRS) 26th annual scientific sessions.

Although they saw a short-term increase in the risk of SCD in women during moderate to vigorous physical activity, the risk lessened in women who reported more weekly exercise, the researchers said.

"Women who exercised regularly had a lower transient risk of [SCD]," said William Whang, MD, a cardiologist at Massachusetts General Hospital and Brigham and Women's Hospital in Boston, Massachusetts, told Medscape. "For women who exercise, the transient risk was lower in women who exercised two or more hours a week."

The study was the first to assess both the short- and long-term risks of SCD conferred by exercise among women.

"The important point of this study is that regular exercise can substantially reduce the risk of [SCD]," commented Dwight Reynolds, MD, HRS program chairman and chief of cardiology at the University of Oklahoma Health Science Center in Oklahoma City. "Even if the overall risk is low, if you don't exercise, then the risk is increased."

The researchers examined the relationship between self-reported physical activity and SCD in 70,000 women from the Nurses' Health Study. Information on moderate to vigorous exertion in hours per week were collected during six different years starting in 1986 and ending in 2000. The information was collected via questionnaires and at the time of SCD by reviewing medical records and talking with the next-of-kin.

Women were queried on hours of such exercise as walking, jogging, running, bicycling, lap swimming, and aerobics performed in a week.

Of the almost 70,000 women with no cardiovascular disease or history of stroke, the relative risk for SCD within one hour of moderate to vigorous exertion was 6.2 times that of no exercise in a case crossover analysis, Dr. Whang noted.

Women who exercised fewer than two hours per week had 21 times the risk of SCD during the one-hour period after exercise compared with when they did not exercise. That risk was dramatically reduced in women who exercised regularly, Dr. Whang said. Women who exercised more than two hours a week had three times the risk for SCD in the time period after moderate to vigorous exertion compared with when they did not exercise.

Case crossover analysis estimated the odds ratios for exposure to moderate to vigorous exertion in the hour before SCD. The researchers then determined estimated hazard ratios for the long-term risk of SCD with increasing amount of exertion after adjusting for comorbidities and cardiovascular risk factors.

In a multivariate analysis that adjusted for biologic factors such as body mass index, hypertension, diabetes, and high cholesterol there was a consistent reduction in the risk of SCD with increased hours of exercise per week.

"Increasing amount of regular moderate to vigorous exercise was associated with a lower overall risk of SCD," Dr. Whang told attendees.

With each increase in the number of hours of moderate to vigorous exercise, there was a relative risk reduction in SCD. For example, women who exercised more than four hours per week had about a 50% reduced risk of SCD. Those who exercised more than seven hours per week had a 66% reduced risk of SCD compared with women who exercised less than one hour.

The relative risk was under one for women exercising more than four hours per week, said Dr. Whang. "It's consistent with common sense that exercise is associated with benefits in [SCD]; while a transient risk is present, it is very low," he said. "Women should start off an exercise program slowly and build up. Regular exercise is beneficial."

The study was independently funded. The authors report no pertinent financial conflicts of interest.

HRS 26th Annual Scientific Sessions: Abstract 12. Presented May 5, 2005.

Reviewed by Gary D. Vogin, MD

Linda Little is a freelance writer for Medscape.

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