Heart-rate profile during exercise as a predictor of sudden death.

Background - The heart rate changes during exercise and recovery are mediated by the balance between sympathetic and vagal activity. As alterations in the neural control of cardiac function contribute to the risk for sudden death, we tested the hypothesis that among apparently healthy individuals sudden death is more likely to occur in the presence of abnormal heart rate profiles during exercise and recovery. Methods - A total of 6101 asymptomatic working men (age 42 to 53), free of clinically detectable cardiovascular disease, underwent a standardized graded exercise test between 1967 and 1972. We focused on resting heart rate, heart rate increase (from rest to peak exercise), and heart rate decrease (from peak exercise to one minute after). Results – During a 23-year follow-up period, the risk of sudden death (n=81) was strongly increased in subjects with a resting heart rate higher than 75 beats/min [relative risk = 3.92 (95% C.I. 1.91-8.00)], in subjects with an attenuated heart rate increase, lower than 89 beats/min [relative risk = 6.18 (95% C.I. 2.37-16.11)], and in subjects with an attenuated heart rate decrease lower than 25 beats/min [relative risk = 2.20 (95% C.I. 1.02-4.74)]. After adjustment for potential confounding variables, these three factors remained strongly associated with an increased risk for sudden death with a modest albeit statistically significant higher risk for total mortality but not with the occurrence of non-sudden coronary death. Conclusions : Heart rate profile during exercise and recovery is a powerful predictor of sudden death.