Heart disease is the number one cause of death among Americans. Many types of heart disease can cause the heart to abruptly stop beating, a condition known as cardiac arrest .

The American Heart Association estimates that sudden death accounts for close to half of all deaths from heart disease, affecting nearly 340,000 Americans each year. Death occurs within minutes after symptoms appear—which may account for why nearly half of all people who die from heart disease do so without being hospitalized or admitted to an emergency room. Victims may have been diagnosed with heart disease, but for many, sudden death by a heart attack is the first indication of a problem.

Until recently, research into causes of sudden death has focused on patients with known heart disease. Studies have shown that imbalances or abnormalities in heart-rate profiles in these patients can indicate an increased risk for sudden death. In the May 12, 2005 issue of the New England Journal of Medicine , researchers interested in identifying apparently healthy people with abnormal heart-rate profiles published the results of their study. The researchers concluded that an abnormal heart-rate profile during exercise and recovery is a predictor of sudden death.

About the Study

Researchers from centers in France and Italy analyzed heart-rate profiles on more than 5,700 middle-aged men, using data from the Paris Prospective Study I. This study followed apparently healthy French men from 1967 to 1972 to determine risk factors for cardiovascular disease. Participants, who were all age 43-52, underwent a battery of tests, including a standardized bicycle exercise test.

Participants were followed to determine whether heart-rate profile was a predictor of sudden death. Researchers examined three components of the profile: resting heart rate; how much the heart rate increased during exercise; and how quickly the heart rate recovered after exercise. During the 23-year follow-up period, 400 men died from cardiac causes, 81 of them suddenly.

The Findings

The researchers concluded that an abnormal heart-rate profile during exercise and recovery is in fact a predictor of sudden death. Among the three components of the profile, lower heart rate during exercise was the strongest risk factor for sudden death. The other components were also predictors: the higher a person’s resting heart rate the higher risk they carried, and those whose heart rate recovered slowly after exercise were at increased risk as well.

There are several limitations to the study, and the results may not apply to the general population. The study included men only, and the follow-up data didn’t assess the development of disease or the results of treatment, only those who died. In addition, changes in the incidence of heart disease today, and variations in exercise protocols might produce different results.

How Does This Affect You?

This study suggests that an abnormal heart-rate profile may be an indicator of future cardiovascular disease, even in apparently healthy adults. Researchers hope to use this information to identify people at high risk for sudden death by observing changes in their heart rate during exercise. This is not to say that an unfavorable heart-rate profile alone causes sudden death. The results of this test, therefore, should not be construed as a diagnosis of heart disease.

Where the test may be helpful is in the identification of individuals who, in the presence of other risk factors for heart disease (e.g., tobacco use, calorie-rich, high fat diet, high cholesterol, uncontrolled hypertension and diabetes) may benefit from earlier and more aggressive intervention. Results from other studies, for example, indicate that regular exercise may improve the balance in the heart-rate profile as well as decrease the overall risk of heart disease. If you think you are at risk, however, it unwise to start an exercise program without first consulting your physician.