Introduction: Impaired chronotropic response (ICR) has been reported as a risk factor of reduced exercise tolerance, and often relates to the future prognosis. The purpose of the present study is to assess the clinical impact of ICR persistent at the completion of phase II cardiac rehabilitation (RH) on a long-term cardiovascular prognosis.
Methods: We enrolled 247 consecutive patients (68 y.o. on average, 165 male) who participated in phase II cardiac rehabilitation program at least for 3 months (8.5 month on average). All underwent cardiopulmonary exercise test (CPX) at the initial and completion period of rehabilitation. Using CPX data, following 2 parameters were assessed: 1) Heart rate (HR) reserve (HRR) from CPX data, calculated as the following formula: HRR = (peak HR - resting HR) / (220 - age - resting HR). Using the established criteria, HRR <0.80, or <0.62 on beta-blocker (BB) regimen, was regarded as "impaired". 2) HR recovery: defined as HR difference between at the peak exercise and 1-minute after the peak in CPX: less than 15 minutes (the median) was regarded as “impaired”. We compared each parameter whether they showed change during RH. Impaired HRR cases at completion were divided in 2 groups by the median (defined as “severe” and “mild”). A Kaplan-Meier analysis was done to compare the incidence of future cardiovascular events according to the persistence of severe HRR.
Results: ICR was detected in 182 cases (74%) at the beginning of rehabilitation, and persisted in 128 (52%) at the completion. Both parameters significantly improved at completion of RH compared to the initial phase (HRR: from 0.632 to 0.762 with no BB and from 0.509 to 0.609 with BB, HR recovery: from 13 to 16 /min with no BB and from 10 to 12 with BB, respectively (all p < 0.001)). Kaplan-Meier analysis showed significantly lower event-free survival rate in “severe HRR persisted” (p = 0.004).
Conclusion: Persistence of severe ICR after phase II cardiac rehabilitation may lead to the future adverse events.