Chronotropic Incompetence Limits Aerobic Exercise Capacity in Patients Taking Beta-Blockers

Background Chronotropic incompetence in patients taking beta-blockers is associated with poor prognosis; however, its impact on exercise capacity (EC) remains unclear. Methods We retrospectively analyzed data from consecutive patients taking beta-blockers referred for cardiopulmonary exercise testing. EC was expressed as peak oxygen uptake (peak VO2; mL/kg/min). Chronotropic incompetence was defined as chronotropic index (CI) ≤ 62%. CI was calculated as [(HR at peak–HR at rest) / (maximum predicted HR–HR at rest)] × 100%. Results Among 140 patients all taking beta-blockers (age 61 ± 9.7 years; 73% males), there were 113 (80.7%) patients with chronotropic incompetence. EC was lower in the group with chronotropic incompetence than the group without it, peak VO2 18.3 ± 5.7 vs. 24.0 ± 5.3 mL/kg/min, p < 0.001. In multivariate analysis EC correlated positively with CI (β = 0.14, p < 0.001) and male gender (β = 5.12, p < 0.001), and negatively with age (β = −0.17, p < 0.001) and presence of heart failure (β = −3.35, p < 0.001). Beta-blocker dose was not associated with EC. Partial correlation attributable to CI accounted for more than one-third of the variance in EC explained by the model. Conclusions In patients taking beta-blockers, presence of chronotropic incompetence was associated with lower EC, regardless of the beta-blocker dose. CI accounted for more than one-third of EC variance explained by our model. HIGHLIGHTS Patients on beta blockers with chronotropic incompetence have lower exercise capacity Beta-blocker dose is not associated with exercise capacity We recommend incorporating chronotropic index into exercise stress testing