Use of heart rate for guiding exercise training in patients with atrial fibrillation

BACKGROUND: Heart rate reserve (HRR) is used to guide exercise training in patients with cardiovascular disease, primarily as a surrogate for oxygen uptake reserve (VO₂R) as a marker of metabolic demand. However, the relationship between HRR and VO₂R in patients with atrial fibrillation (AF) is not well described. We aimed to assess the validity of HRR as a surrogate for VO₂R to guide exercise intensity in AF patients. METHODS: One hundred one patients with non-permanent AF undertaking a cardiopulmonary exercise test (CPET) were prospectively enrolled. HR and VO₂ values were recorded throughout exercise to determine HRR and VO₂R at each workload. Linear regression was used to calculate the slope and y-intercept for HRR versus VO₂R with an equivalent slope defined as 1 and y-intercept of 0. The impact of rhythm during exercise, beta blockers and chronotropic incompetence (CI) on the HRR-VO₂R relationship was also assessed. RESULTS: The slope of HRR-VO₂R was 0.79±0.4, indicating a significant difference from an assumed slope of 1.0 (mean difference: -0.21, 95% CI: -0.30 to -0.12, P<0.001). The mean y-intercept slope was 20.1±41.6, differing significantly from 0 (mean difference: 20.1, 95% CI: 11.9-28.3, P<0.001). The presence of AF during CPET, beta-blockers or chronotropic incompetence did not independently alter the association between VO₂R and HRR. CONCLUSIONS: HRR is not equivalent to VO₂R in AF patients. There was no significant effect of rhythm status, chronotropic incompetence or beta-blockers on this relationship. These findings highlight that the HR prescription of exercise intensity in AF patients should be guided by an individualised HRR-VO₂R relationship.