Exercise heart rate reserve and recovery as risk factors for sudden cardiac death

Little is known if heart rate responses during and after exercise test may be associated with the risk of sudden cardiac death (SCD). Our aim was to determine if exercise heart rate reserve and recovery, providing non-invasive indices, may predict SCD risk in general male population.We evaluated the impact of delayed heart rate reserve and slow heart rate recovery and the risk of SCD in the Kuopio Ischemic Heart Disease prospective cohort study of randomly selected 1967 men aged 42-61 years at recruitment. Heart rate reserve was calculated as the difference between the maximal attained heart rate and resting heart rate, whereas heart rate recovery was defined as maximal heart rate minus the heart rate measured at 2 min of recovery, on a symptom-limited cardiopulmonary exercise testing.During a median follow-up interval of 25 years, 209 events of SCD occurred. The age and examination adjusted relative hazards of SCD were in the lowest third of heart rate reserve 3.86 (95% confidence interval (CI) 2.56-5.80, p 0.001) and the lowest third of heart rate recovery 2.86 (95% CI 1.95-4.20, p 0.001) as compared to men in the highest third of heart rate reserve and heart rate recovery, respectively. After adjusting for potential confounders, the respective relative hazards were 1.96 (95% CI 1.24-3.12) and 1.75 (95% CI 1.16-2.64). Each unit increment (1 beat/min) in heart rate reserve and heart rate recovery decreased the incidence of SCD by 1-2%.Delayed exercise heart rate reserve and slow heart rate recovery predicted the risk of SCD, suggesting that heart rate responses may be associated with an increased risk for SCD in general population.