Background: Changes in heart rate during exercise and recovery from exercise are mediated by the balance between sympathetic and vagal activity. Since alterations in the neural control of cardiac function contribute to the risk of sudden death, we tested the hypothesis that among apparently healthy persons, sudden death is more likely to occur in the presence of abnormal heart-rate profiles during exercise and recovery.
Methods: A total of 5713 asymptomatic working men (between the ages of 42 and 53 years), none of whom had clinically detectable cardiovascular disease, underwent standardized graded exercise testing between 1967 and 1972. We examined data on the subjects' resting heart rates, the increase in rate from the resting level to the peak exercise level, and the decrease in rate from the peak exercise level to the level one minute after the termination of exercise.
Results: During a 23-year follow-up period, 81 subjects died suddenly. The risk of sudden death from myocardial infarction was increased in subjects with a resting heart rate that was more than 75 beats per minute (relative risk, 3.92; 95 percent confidence interval, 1.91 to 8.00); in subjects with an increase in heart rate during exercise that was less than 89 beats per minute (relative risk, 6.18; 95 percent confidence interval, 2.37 to 16.11); and in subjects with a decrease in heart rate of less than 25 beats per minute after the termination of exercise (relative risk, 2.20; 95 percent confidence interval, 1.02 to 4.74). After adjustment for potential confounding variables, these three factors remained strongly associated with an increased risk of sudden death, with a moderate but significantly increased risk of death from any cause but not of nonsudden death from myocardial infarction.
Conclusions: The heart-rate profile during exercise and recovery is a predictor of sudden death.
Copyright 2005 Massachusetts Medical Society.