Impact of right ventricular contractile reserve during low‐load exercise on exercise intolerance in heart failure

AIMS: Traditional criteria for heart transplantation by cardiopulmonary exercise testing (CPX) include peak oxygen uptake (VO(2)) < 14 mL/kg/min. Reaching a sufficient exercise load is challenging for patients with refractory heart failure (HF) because of their exercise intolerance. Recently, a substantial impact of right ventricular (RV) dysfunction was highlighted on urgent heart transplantation and mortality. This study aims to investigate the impact of RV contractile reserve, assessed by low‐load exercise stress echocardiography (ESE), on exercise intolerance defined as peak VO(2) < 14 mL/kg/min, in patients with HF. METHODS AND RESULTS: We prospectively examined 67 consecutive patients hospitalized for HF who underwent ESE and CPX under a stabilized HF condition. Although low‐load ESE was defined as 25 W load exercise, an increment in RV systolic (s′) velocity was regarded as the preservation of RV contractile reserve. All patients completed low‐load ESE. During low‐load ESE, the variation in RV s′ velocity significantly correlated with peak VO(2) (r = 0.787, P < 0.001). The change in RV s′ velocity during low‐load ESE accurately identified patients with peak VO(2) < 14 mL/kg/min (area under the curve, 0.95; sensitivity, 92%; specificity, 85%). The intraclass correlation coefficient for intra‐observer and inter‐observer agreement for the change in RV s′ velocity was 0.96 (95% confidence interval, 0.88–0.99, P < 0.001) and 0.86 (95% confidence interval, 0.64–0.95, P < 0.001), respectively. The RV‐to‐pulmonary circulation (PC) coupling, which was assessed by the slope of the relationship between RV s′ velocity and pulmonary artery systolic pressure at rest and low‐load exercise, was worse in the low‐peak VO(2) group (<14 mL/kg/min) than the preserved‐peak VO(2) group (≥14 mL/kg/min). CONCLUSIONS: The change in RV s′ velocity during low‐load ESE could estimate the exercise capacity in HF patients. The assessments of RV contractile reserve and RV‐to‐PC coupling could be clinically beneficial to distinguish high‐risk HF patients.