Utility of Stroke Volume Reserve to Evaluate Ventilatory Efficiency in Heart Failure Patients

Abstract

Introduction The use of cardiopulmonary exercise testing (CPET) to evaluate cardiac limitations in heart failure with reduced ejection fraction (HFrEF) patients is well described. Ventilatory inefficiency or increased VE/VCO2 slope > 34 in HFrEF patients has been shown to correlate with poor prognosis. Ventilatory inefficiency in heart failure is often attributed to increased VD/VT during exercise, presumably due to increased filling pressures and resultant pulmonary congestion. Stroke volume reserve is a novel noninvasive parameter, calculated by response in stroke volume at anaerobic threshold (AT) compared to rest. Previous studies have shown an increase in stroke volume at AT compared to resting value to be greater than or equal to 128% in normal patients. In this study, we utilized stroke volume (SV) reserve to evaluate and better understand ventilatory efficiency in HFrEF patients. Objective The study aimed to utilize SV reserve (SV-AT/SV-rest) to evaluate ventilatory efficiency and changes in VD/VT in HFrEF patients. Based on a combinational derivation of Fick's equation [CO=VO2 / Ca - Cv] and the equation for physiological dead space proportion [VD/VT = 1 - (863xVCO2 / VExPaCO2)], we hypothesized that an inappropriate SV reserve (less than 128%) would correlate with decreased carbon dioxide production at anaerobic threshold (VCO2-AT), decreased oxygen consumption at anaerobic threshold, and an increased VE/VCO2 slope. Methods This was a retrospective, cohort analysis of 47 HFrEF patients (EF Results A significant increase in VCO2-AT (0.80 ± 0.32 vs 0.62 ± 0.18, p=0.04) and VO2-AT (11.85 ± 3.22 vs 8.82 ± 1.95, p=0.001) occurred for the appropriate SV reserve cohort compared to the inappropriate SV reserve cohort. VE/VCO2 slope was significantly higher in the inappropriate SV reserve group when compared to the appropriate SV reserve group (34.18 ± 7.86 vs 30.12 ± 4.58, p=0.03). There was an associated increase in VD/VT in the inappropriate SV reserve cohort with exercise. Conclusions In patients with inappropriate stroke volume reserve, the VE/VCO2 slope was elevated above 34 and also correlated with increased VD/VT with exercise. This study is the first to use stroke volume reserve to non-invasively demonstrate inappropriate circulatory response as a potential cause for elevation in VE/VCO2 slope with exercise.