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

Abstract

Aims: Traditional criteria for heart transplantation by cardiopulmonary exercise testing (CPX) include peak oxygen uptake (VO₂ ) < 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 VO₂ < 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 VO₂ (r = 0.787, P < 0.001). The change in RV s' velocity during low-load ESE accurately identified patients with peak VO₂ < 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 VO₂ group (<14 mL/kg/min) than the preserved-peak VO₂ 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.

Keywords: cardiopulmonary exercise testing; exercise stress echocardiography; heart failure; low-load exercise; right ventricular contractile reserve; right ventricular-to-pulmonary circulation coupling.

Figure 1

Correlation between peak VO₂ and RV function during low‐load exercise. (A) Correlation between the change in RV s′ velocity and peak VO₂ during low‐load exercise (r = 0.787; P < 0.001). (B) Correlation between the change in RV strain and peak VO₂ during low‐load exercise (r = 0.244; P < 0.001). RV s′ velocity, right ventricular systolic velocity; RV strain, right ventricular strain; VO₂, oxygen uptake.

Figure 2

Representative cases of a patient in the low‐peak VO₂ group and a patient in the preserved‐peak VO₂ group. (A) Representative case in a low‐peak VO₂ group (peak VO₂, 12.9 mL/kg/min). (B) Representative case in a preserved‐peak VO₂ group (peak VO₂, 21.0 mL/kg/min). RV s′ velocity did not increase in a patient with low‐peak VO₂ compared with a patient with preserved‐peak VO₂. PASP was higher in a patient with low‐peak VO₂ than a patient with preserved‐peak VO₂. PASP, pulmonary artery systolic pressure; RV s′ velocity, right ventricular systolic velocity; VO₂, oxygen uptake.

Figure 3

Receiver‐operating characteristic curve analysis of echocardiographic parameters during low‐load exercise to predict low‐peak VO₂. The change in RV s′ velocity during low‐load exercise had higher AUC (0.95; P < 0.001) than the change in RV strain. AUC, area under the curve; RV s′ velocity, right ventricular systolic velocity; RV strain, right ventricular strain; TAPSE, tricuspid annular plane systolic excursion; VO₂, oxygen uptake.

Figure 4

Relationship between right ventricular systolic function and pulmonary artery systolic pressure during low‐load exercise. (A) Relationship between RV s′ velocity and PASP at rest and low‐load exercise. (B) Relationship between TAPSE and PASP at rest and low‐load exercise. Red symbols, low‐peak VO₂ group; blue symbols, preserved‐peak VO₂ group. The slopes in the low‐peak VO₂ group were steeper than that in the preserved‐peak VO₂ group. PASP, pulmonary artery systolic pressure; RV s′ velocity, right ventricular systolic velocity; TAPSE, tricuspid annular plane systolic excursion; VO₂, oxygen uptake.

Figure 5

Correlation between RV dP/dt/P max and change in RV s′ velocity during low‐load exercise. The change in RV s′ velocity during low‐load exercise significantly correlated with RV dP/dt/P max (r = 0.706; P < 0.001). RV s′ velocity, right ventricular systolic velocity; RV, right ventricular.