Development And Validation Of The Regression Equations For Cardiorespiratory Fitness In Patients With Heart Failure With Preserved Ejection Fraction

Abstract

Background Cardiorespiratory fitness (CRF), measured by maximal oxygen consumption (VO2max), is an important independent predictive factor for cardiovascular outcome in heart failure (HF) patients. However, it is unclear whether the conventional equations for estimating CRF could be applicable to HF with preserved ejection fraction (HFpEF) patients. Methods Current study, three conventional equations for estimating VO2max were compared with directly measured VO2max in HFpEF patients. In addition, we developed and internally validated the Kor-HFpEF equation to estimate VO2max in HFpEF patients. This study included 421 HFpEF (EF≥50%) patients whose CRF was directly measured by cardiopulmonary exercise test using a treadmill. Participants were divided into two randomly assigned groups: control (n=220) and validation (n=201) groups. Data from the control group were used to create the Kor-HFpEF equation, while data from the validation group were used to validate the estimated VO2max using the Kor-HFpEF. The accuracy of the Kor-HFpEF equation was compared with that of the other equations in the validation group. Results In the total HFpEF cohort, the directly measured VO2max was significantly overestimated by the conventional FRIEND and ACSM equations (p <0.001) and underestimated by the FRIEND-HF equation (p <0.001) (direct 21.7±5.9 mL/kg/min; FRIEND 23.1±7.1 mL/kg/min; ACSM 25.8±8.0 mL/kg/min; FRIEND-HF 11.6±2.9 mL/kg/min). However, the VO2max estimated by the Kor-HFpEF equation (21.9±6.1 mL/kg/min) was similar to the directly measured VO2max (21.9±6.1 mL/kg/min, p=0.407), whereas the VO2max estimated by the other three equations was still significantly different from the directly measured VO2max in the validation group (all p<0.001). Conclusions Traditional equations used to estimate VO2max were not applicable to HFpEF patients in this study. We developed and validated a new Kor-HFpEF equation for these patients and achieved high accuracy. Interestingly, the results suggest that the specific phenotype of HFpEF differs from that of HFrEF or healthy adults, and different CRFs based on race and/or ethnicity may also have influenced the results. The Kor-HFpEF equation should be externally validated in other HFpEF cohorts.