Association Of Changes In Measured And Estimated Cardiorespiratory Fitness With Cardiovascular Events In Cardiac Rehabilitation

PURPOSE: Cardiorespiratory fitness (CRF) is a strong predictor of major adverse cardiovascular events (MACE), whether directly measured (gas exchange) as peak oxygen uptake (peak VO2) or estimated from maximal exercise test workload. However, limited data compares the association of estimated CRF (CRFe) and the gold standard measured CRF (CRFm) with MACE. We hypothesized CRFm would be a stronger predictor of MACE compared with CRFe in exercise-based cardiac rehabilitation (CR) patients. METHODS: Adults who attended CR for an eligible indication between 1999-2017 and had a cardiopulmonary exercise test (CPET) pre- and post-CR with VO2 data (peak respiratory exchange ratio ≥ 1.0) were included and followed-up until January 2020. CRFm was obtained and CRFe calculated (using FRIEND equation) from CPET pre- and post-CR; and changes in CRFm and CRFe determined. Cox proportional hazard models were used to test the associations with MACE. RESULTS: 701 patients (age:60.8 ± 12.1; 24% female) met inclusion criteria. Mean follow-up was 6.1 ± 3.2 yrs, with a total of 137 (20%) events. The majority of CPETs were performed on treadmill (96%) using an institutionally derived protocol. CRFm was significantly lower than CRFe at pre- and post-CR CPET, however delta change in CRFm and CRFe was not different (Table 1a). All CRFm and CRFe variables (except pre-CR CRFe) were significantly associated with MACE, with delta change in CRFm and CRFe showing the greatest association per 1 ml/kg/min (Table 1b). As hypothesized, association with MACE was of a greater magnitude for delta change in CRFm than CRFe (9% vs 7% risk reduction per 1 ml/kg/min increase). CONCLUSIONS: Both CRFm and CRFe are strong predictors of MACE in CR patients. For programs without resources to measure peak VO2, CRFe appears to be an effective alternative for predicting MACE risk reduction from exercise training. As CRFe is influenced by test protocol, future studies should also compare CRFm and CRFe using generalized protocols.