Sudden cardiac death due to physical exertion is extremely rare in women, and the small increase in risk can be minimized through regular exercise, reported Dr. William Whang of Massachusetts General Hospital, Boston, and his colleagues.
They used prospective data from the Nurses' Health Study cohort of female nurses (mean age 53 years in 1986) to analyze cases of sudden cardiac death.
Starting in 1986, study questionnaires asked participants about the average time spent per week doing such activities as walking briskly, jogging, running, biking, swimming, playing tennis or squash, and participating in aerobics or other sports, as well as yard work and housework. In 1992, information was also gathered on average time spent doing lower-intensity exercises, such as yoga. Exercise intensity was based on self-assessments of time spent doing moderate to vigorous exercise (JAMA 2006;295:1399–403).
There were 288 sudden cardiac deaths among the 84,888 women who completed the 1980 questionnaire. “Of these, only nine deaths (3.1%) occurred during an episode of moderate to vigorous exertion, and only three of these occurred during activities that would be considered exercise,” the researchers wrote.
These nine deaths happened during yard work, swimming, physical therapy, housework, and shoveling snow, among participants who reported exercising at moderate to vigorous intensity at least 4 hours per week.
Among participants who did not report any moderate to vigorous exercise on a weekly basis, there were 74 sudden cardiac deaths. There were 46 deaths among those exercising at this intensity for 0–1.9 hr/week, and 28 deaths among participants exercising 2–3.9 hr/week.
The relative risk (RR) of exertion-related sudden cardiac death during moderate to vigorous exertion was calculated to be “modestly elevated” at 2.38. However, this “transient” elevation in risk was no longer significant for women reporting 2 or more hours per week of moderate to vigorous exertion—they had an RR of 1.49. Women with 2 or fewer hours per week of exertion had an RR of 8.98, and women who exercised 4 or more hours per week had an RR of 0.41.
Even after controlling for factors such as age, smoking status, body mass index, and menopausal status, the researchers said this trend persisted.
Data from the Physician's Health Study (N. Engl. J. Med. 2000;343:1355–61) showed that the relative risk for men during an episode of vigorous exertion was about 19-fold higher, at 44.9, compared with the risk observed during moderate to vigorous exertion in the Nurses' Health Study cohort (RR, 2.38).
“Part of this difference could be due to the inclusion of moderate exertion in our exercise measure,” Dr. Whang and colleagues wrote. They noted, however, that a similar gender difference was found in previous, smaller studies.