Cardiac rehabilitation and improvement of chronotropic incompetence: Is it the exercise or just the beta blockers?

Introduction: Clinical use of chronotropic response has been limited due to lack of consensus on the appropriate formula for chronotropic index (Ci) calculation and the definition of chronotropic incompetence.
Objectives: To assess the effects of cardiac rehabilitation programs (CRP) on Ci, irrespective of betablockers (BB) use and dosage. Assess the relative contribution of change in Ci on improvement in functional capacity.
Methods: Retrospective analysis of a sample of patients admitted to a CRP after acute coronary syndrome, with at least 12 months of follow-up. Ci was calculated using the conventional (CCi) and the Brawner formula (BCi) for age-predicted maximum heart rate. Ci and functional capacity were estimated at three time points: T1 and T2, before and at the end of the CRP, and T3, at 12 months. The sample was categorized according to BB dosage modification between T1 and T3: G1 - reduced; G2 - no change; G3 - increased.
Results: In G1, CCi increased from 63.5% in T1 to 77.9% in T3; in G2, from 67.3% to 77.9%; in G3, from 71.2% to 75.4%. In G1, BCi increased from 110.4% to 140.0%; in G2, from 122.8% to 140.1%; in G3, from 133.3% to 139.2%. An average increase in 1.0% in CCi was associated with an average increase in functional capacity of 0.37 METS.
Conclusions: Chronotropic index significantly improves with CRP, irrespective of BB dose changes. CCi is more closely related with improvement in functional capacity than BCi. Improvement of Ci is an important predictor of functional capacity and prognosis in cardiovascular disease patients.
(Copyright © 2021 Sociedade Portuguesa de Cardiologia. Published by Elsevier España, S.L.U. All rights reserved.)