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

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.

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.

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.

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.