Chronotropism in CPET - Is incompetence limiting functional capacity?

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Chronotropic incompetence (CI) is defined as the inability to reach 80% of the expected reserve frequency for age during exertion, and it is frequently observed in stress tests of patients undergoing cardiac rehabilitation programs due to a combination of factors, that include the use of betablockers. Despite the theoretical basis for suggesting that a lower peak heart rate is related to a lower tolerance to exertion, we lack data correlating the CI to the maximal functional capacity, measured in cardiopulmonary tests as the maximal oxygen volume consumption (peak VO2). Purpose To correlate the impact of CI on functional capacity in patients (pts) undergoing a cardiac rehabilitation program and try to find the best value of chronotropic incompetence that could predict a worse prognosis. Methods Prospective cohort study which included consecutive pts who were submitted to cardiopulmonary exercise test (CPET) during 5 years in a tertiary hospital. Demographic data were analyzed and medication with beta blocker was registered. CI and chronotropic index were calculated using the equation (220-age) for estimating maximum HR. ROC curve method and Kaplan-Meier survival analysis were used to evaluate the cut-off efficacy. Results We analyzed 358 CPET and 74,1% patients (n=206) were under beta blocker therapy (7,6% high dose). The majority of the patients had CI (83.5%); CI was more frequent in pts under BB therapy although it didn’t reach statistical significance (p=0.12). A low maximum predicted heart rate (mpHR) was associated with low peak VO2 (p=0.02) and a mpHR < 61% was the best value to predict peak VO2< 12mL/(kg.min) (AUC=0.746, S=72; E=65), despite not showing association with cardiovascular events. Regarding the chronotropism, 96.9% of the pts were categorized as having a low chronotropic index . A CI < 0.38 was the best cut-off to predict a peak VO2<12 mL/(kg.min) (AUC=0.81, S=72, E 76) and it was predictor of all-cause hospitalizations (p=0.015). Conclusion This study shows a high percentage of pts with CI. A low cronotropic index was associatated with low peak VO2 and was a predictor of all-cause hospitalizations.