Experts Study Heart Rate Before and After Exercise
The way your heart speeds up when you exercise and returns to normal when you stop can predict your risk of sudden death from heart attack, even decades later, according to a report in the New England Journal of Medicine.
Men whose heart rate increased less than 89 beats per minute during a standard exercise test for heart patients - called a stress test - had six times the risk of sudden death over the next two decades.
The study was conducted by physicians in France and Italy, who followed more than 5,700 middle-aged men for an average of 23 years.
Men whose heart rate decreased less than 25 beats in the minute after they stopped the exercise test had more than double the risk of sudden death than those whose rate returned to normal faster.
This is the latest chapter in a series of studies showing a relationship between a higher risk of death from heart disease and the heart's reaction to exercise, says Dr. Michael S. Lauer, a cardiologist at the Cleveland Clinic Foundation who has conducted research on the subject.
A report by his group published in 1999 on a clinical trial of 2,500 men was the first to show the relationship between a slow return to a normal heart rate after exercise and increased risk of death, Dr. Lauer says.
"We have since published a number of papers, and other groups have published as well, all showing the same thing, that failure of the heart rate to decrease quickly after exercise is associated with a higher risk of mortality," explains Dr. Lauer.
"What is unique and new about this paper is that it specifically looked at sudden death, and most mortality in this group is associated with sudden death," he notes.
"The second unique thing [about the new study] is the very long follow-up," Dr. Lauer adds. "It's pretty amazing when you think about it, that a simple measurement on an exercise test can predict what will happen over the next five, 10, 15 years. It's amazing that an old-fashioned, low-tech test has this power."
The new results are "very similar and consistent" with those of a study on men reported in 2003 by researchers at Johns Hopkins University, says Dr. Roger S. Blumenthal, director of the Hopkins Preventive Cardiology Center.
"This really adds to the literature showing that abnormalities on a stress test can show risk," Dr. Blumenthal says. "There is a growing body of information looking at heart rate, not just length of time on the treadmill or EKG changes."
The unanswered question now is how to put this information to use, Dr. Lauer remarks. "We can identify people at increased risk for death, particularly sudden death. Now we have to see how having this information can translate into improved outcomes for patients."
There are two possible strategies that could be followed, he says. One is the already well-known and often-promoted idea of regular exercise, which is recommended for everyone but could have particular value for people with this heart abnormality.
"People who exercise live longer because exercise stabilizes the electrical system of the heart," Dr. Lauer says. "So we could take people with these heart rate problems and enroll them in a formal exercise program that would continue over the long term. My guess is that it would do an enormous amount of good."
A second strategy might be medication therapy aimed at regulating the heart rate, he says. "We have drugs which we used to correct heart rate problems, mainly beta blockers. "They have been shown to improve life expectancy."
A number of studies have shown that "exercise can improve autonomic function and reduce the risk of sudden death," says Dr. William Whang, a cardiac electrophysiology fellow at Massachusetts General Hospital.
Last week at the annual meeting of the Heart Rhythm Society, Dr. Whang presented an analysis of data on more than 70,000 women in the Nurses' Health Study showing that those who did little or no regular exercise had six times the risk of sudden cardiac arrest than those who exercised for more than two hours a week.
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If you - like millions of full-time workers - surf TV channels, play video games, or boot up the computer in what little amount of free time you have, you may be skimping on heart-healthy physical activities, scientists report at the American Heart Association 45th Annual Conference on Cardiovascular Disease Epidemiology and Prevention.
In a study of nearly 4,500 men and women, a subset of full-time workers who spent more of their down time engaged in sedentary activities had significantly less exercise than part-time workers with the same amount of sedentary leisure pursuits.
“Many full-time workers say that one of the biggest barriers to getting enough exercise is that there’s not enough time in the day,” says study author Meghan Warren, a pre-doctoral fellow in the division of epidemiology and community health at the University of Minnesota, Minneapolis. “If they shift their interests, they would have more time for physical activity.”
Many studies found that exercise can help prevent obesity, heart disease, and other health problems.
Warren’s team evaluated the association between sedentary behaviors, physical activity, and fitness using data from the large, population-based 1999-2000 National Health and Nutrition Examination Survey (NHANES) conducted by the National Center for Health Statistics, one of the Centers for Disease Control and Prevention (CDC).
The survey asked the 4,498 adults if they participated in 48 different leisure-time physical activities, including walking, basketball, swimming, and cycling, in the past 30 days. The 2,353 participants who indicated they participated in at least one of these activities were also asked how many minutes, on average, they engaged in each activity per session.
As part of NHANES, participants were also asked about three sedentary activities: watching TV, playing video games. and leisure-time computer use.
“The 1999-2000 survey was one of the first to ask about computer use and video games so that gave our study a more complete assessment of sedentary activities than studies in the past,” Warren says.
When the researchers looked at all 2,353 participants who reported any leisure-time physical activity, the analysis showed no statistically significant association between the amount of time spent in sedentary leisure activities and that spent exercising.
But when they compared two subgroups, 1,573 full-time workers and 508 part-time workers, a different picture emerged for those who spent the most time in sedentary activities.
Full-time workers with five or more hours of sedentary activity per day engaged in about 11 fewer minutes of physical activity such as walking or cycling each day compared to full-time workers who did not spend any time watching TV, playing video games, or using the computer in their off hours, a statistically significant finding.
In contrast, part-time workers who spent five or more hours per day engaging in sedentary activities showed a trend toward engaging in about 11 more minutes of physical activity each day than part-time workers who avoided sedentary activities in their free time.
“Full-time workers have less free time, so the more time spent in sedentary activity, the less time they have to exercise,” Warren says. “Part-time workers have more discretionary time - so it could be that those that watched more TV, exercised more, too.”
Some studies in children reveal a trend similar to that seen in part-time workers, she says. “That makes sense as both have more free time.”
Always consult your physician for more information.
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