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

BackgroundChronotropic incompetence in patients taking beta-blockers is associated with poor prognosis; however, its impact on exercise capacity (EC) remains unclear. MethodsWe 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) [&le;] 62%. CI was calculated as [(HR at peak-HR at rest) / (maximum predicted HR-HR at rest)] x 100%. ResultsAmong 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 ({beta} = 0.14, p < 0.001) and male gender ({beta} = 5.12, p < 0.001), and negatively with age ({beta} = -0.17, p < 0.001) and presence of heart failure ({beta} = -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. ConclusionsIn 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. HIGHLIGHTSO_LIPatients on beta blockers with chronotropic incompetence have lower exercise capacity C_LIO_LIBeta-blocker dose is not associated with exercise capacity C_LIO_LIWe recommend incorporating chronotropic index into exercise stress testing C_LI