Heart rate response and recovery in cycle exercise testing - normal values and association with mortality.

Chronotropic incompetence and impaired heart rate (HR) recovery are related to mortality. Guidelines lack specific reference values for HR recovery. We defined normal values and studied blunted HR response and recovery, and mortality risk. We included 9,917 subjects (45% females) aged 18-85 years who performed a cycle exercise test. We defined normal values for peak HR, HR reserve, and HR recovery at 1 and 2 minutes (HRR1 and HRR2) based on individuals apparently healthy (N=2,242). Associations between blunted HR indices (<5th percentile) and mortality over a median follow-up of 8.6 years were analysed using Cox regression and competing risk analysis. All HR indices were age-dependent and independent predictors of all-cause and CV mortality. The 5th percentiles of HR reserve, HRR1, and HRR2 correlated weakly with existing reference values. HR recovery variables were the strongest predictors of all-cause mortality (HRR1, hazard ratio 1.70 [95% confidence interval, 1.49-1.94] and HRR2, 1.57 [1.37-1.79]), including in subjects with normal exercise capacity (HRR1, 1.96 [1.61-2.39] and HRR2, 1.76 [1.46-2.12]). Combining HR indices appeared to increase the risk of all-cause (HRR1 and HRR2, 1.96 [1.68-2.29] and peak HR and HRR1, 1.87 [1.56-2.23]) and CV mortality, although no specific combination was superior for predicting CV mortality. All HR variables were age-dependent and associated with all-cause and CV mortality. Blunted HR recovery variables were the strongest predictors of all-cause mortality, even in subjects with normal exercise capacity. Combined blunted HR indices appeared to add prognostic value. We provide a detailed description on the physiologic HR response and recovery kinetics in a population apparently CV risk-free referred for cycle exercise testing. When assessed in a larger population, blunted HR response and recovery were associated with increased mortality. HR response and recovery are age-dependent. We provide novel reference values.All blunted HR indices (peak HR, HR reserve, HRR1 and HRR2) are strong predictors of all-cause and CV mortality, and combined HR indices appeared to add prognostic value in all the analyses.Blunted HRR1 followed by HRR2 are the strongest predictor of all-cause mortality even in subjects with normal exercise capacity, highlighting the importance of their assessment in standard exercise testing.

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