Chronotropic efficiency: heart rate/oxygen uptake relation at VO2 peak in health and disease

Purpose: The exercise heart rate (HR)/oxygen uptake (VO2) relationship, expressed as beats/metabolic equivalent (MET), represents chronotropic efficiency (CE), a widely cited “normal value” ~10 beats/MET. This analysis examined the range of beats/MET values observed at peak oxygen uptake (VO2peak) in patients with and without heart failure and the impact of superimposed atrial fibrillation (AF) versus sinus rhythm (SR). Methods: From Medline and Google Scholar searches, a database of 100 studies for SR and 46 for AF was identified. Study requirements included: 1. HRrest, 2. HRpeak and 3. Measured peak oxygen uptake i.e. VO2peak. From these data, the following were determined: (a) HR reserve (HRR) [HRpeak – HRrest], (b) For VO2peak, beats/MET equalled HRR/(peak METs -1) and (c) HR index (HRI) [HRpeak/HRrest]. Results: VO2peak, expressed as METs, was grouped from 14 METs. For SR, beats/MET ranged from 14.9 ± 3.8 for VO2peak 14 METs. For AF, beats/MET ranged from 20.5 ± 5.9 for VO2peak20 beats/MET, compared with