Exercise heart rate gradient: A novel index to predict all-cause mortality

Abstract

Although substantial evidence relates reduced exercise heart rate (HR) reserve and recovery to a higher risk of all-cause mortality, a combined indicator of these variables has not been explored. Our aim was to combine HR reserve and recovery into a single index and to assess its utility to predict all-cause mortality. Retrospective cohort analysis. Participants were 1476 subjects (937 males) aged between 41 and 79 years who completed a maximal cycle cardiopulmonary exercise test while not using medication with negative chronotropic effects or having an implantable cardiac pacemaker. HR reserve (HR maximum - HR resting) and recovery (HR maximum - HR at 1-min post exercise) were calculated and divided into quintiles. Quintile rankings were summed yielding an exercise HR gradient (EHRG) ranging from 2 to 10, reflecting the magnitude of on- and off-HR transients to exercise. Survival analyses were undertaken using EHRG scores and HR reserve and recovery in the lowest quintiles (Q1). During a mean follow up of 7.3 years, 44 participants died (3.1%). There was an inverse trend for EHRG scores and death rate (p < 0.05) that increased from 1.2% to 13.5%, respectively, for scores 10 and 2. An EHRG score of 2 was a better predictor of all-cause mortality than either Q1 for HR reserve (<80 bpm) or HR recovery alone (<27 bpm): age-adjusted hazard ratios: 3.53 (p = 0.011), 2.52 (p < 0.05), and 2.57 (p < 0.05), respectively. EHRG, a novel index combining HR reserve and HR recovery, is a better indicator of mortality risk than either response alone.