Predictors of cardiorespiratory fitness improvement in phase II cardiac rehabilitation

Background: Cardiac rehabilitation (CR) improves cardiorespiratory fitness (CRF) and has been shown to reduce cardiovascular events and death. However, data about predictors of fitness improvement during CR are limited and conflicting. The objective of this study was to determine predictors of improvement in metabolic equivalents of task (METs) based on formal exercise testing throughout phase II CR. Methods: We retrospectively reviewed 20 671 patients enrolled in phase II CR at our center from 2006 to 2016. Patients who completed 36 sessions and had entry and exit exercise stress tests were included for study. The short form-36 (SF-36) questionnaire was used to assess quality-of-life. Univariate and multivariate regression analyses were performed to determine independent predictors of METs improvement. Results: Of the full cohort, 827 patients completed 36 sessions and had entry/exit stress test data. The majority of patients (N = 647, 78.2%) had improvement in METs (mean Δ 2.0 ± 1.2 METs), including patients ≥65 and < 65 years old (77% vs 79%, P = 0.46 for difference). METs improvement was negatively associated with body mass index, diabetes, left ventricular dysfunction, and poor baseline fitness; and positively associated with SF-36 score (P < 0.05 for all). After multivariable adjustment, improvement was no longer affected by age, ejection fraction, or baseline fitness. Patients with poor fitness (≤5 METS) and adequate fitness (> 5 METS) both had improvement, with no statistical difference between the groups (P = 0.36). Conclusions: In a large cohort of phase II CR patients, improvement in CRF was seen in the majority of patients across all ages, genders, and levels of baseline fitness.