Impact of Chronotropic Incompetence and Correlation with Exercise Tolerance in Patients with Implantable Cardiac Devices Undergoing a Phase II Cardiac Rehabilitation Program

Objective: Since patients with implantable cardiac devices tend to develop chronotropic incompetence (CI) associated with the effect of the device itself or the pharmacological effect of the underlying disease, CI could act as a limiting factor in improving exercise tolerance in patients undergoing cardiac rehabilitation program, since an increase in HR is a crucial part in improving cardiac output as a central component of oxygen consumption (VO2). However, it has been observed that there could be other factors contributing to the improvement in exercise tolerance in these patients regardless of the presence of CI. The aim of this research is to clarify the effect of chronotropic incompetence on the improvement in exercise capacity in patients with implantable cardiac devices after a phase II cardiac rehabilitation program (CRP). Methods: Quasi-experimental study applied to patients with implantable cardiac devices (ICDs, CRT, pacemakers) undergoing a supervised concurrent CRP, lasting 4-6 weeks, at an intensity between 65-80% of heart rate reserve (HRR), associated with kinesiotherapy sessions (with strength and endurance training and other biomotor qualities) and interdisciplinary intervention, education, and counseling. CI was calculated using the chronotropic response index, and METs-load measurement was performed at the beginning and at the end of the intervention. Results: Forty patients with a mean age of 61.4 years were included, mostly male (29) 72.5%, (23) 57.5% diagnosed with heart failure, and regarding the type of device, pacemakers (20) 50%, implantable cardioverter-defibrillator (ICD) (12) 30%, and cardiac resynchronization therapy with defibrillator (CRT-D) (20) 8%, of the total patients (35) 87.5% presented chronotropic incompetence and only (5) 12.5% with normal chronotropic response at the end of the intervention. A significant decrease in the chronotropic response index from 0.70 to 0.47 (p <0.001) and a significant increase in METs-load from 5.47 to 9.35 (p <0.001) were found. The value of the differential between initial and final METs (delta-METs) was obtained for both groups, observing a significant increase between initial and final METs in favor of patients with CI (3.8 Vs 3.5, p<0.012) at the end of the intervention. A significant moderate negative correlation (r=-0.395, Spearman, p<0.012) was determined between the degree of CI and final METs-load. Conclusions: It was observed that patients with implantable cardiac devices undergoing a CRP show an increase in exercise tolerance measured in METs, with an inversely proportional correlation to chronotropic incompetence.