Neurohormonal activation and exercise tolerance in patients supported with a continuous-flow left ventricular assist device

Determinants of Functional Capacity and Quality of Life After Implantation of a Durable Left Ventricular Assist Device

Continuous-flow left ventricular assist devices (LVAD) are increasingly used as destination therapy in patients with end-stage heart failure and, with recent improvements in pump design, adverse event rates are decreasing. Implanted patients experience improved survival, quality of life (QoL) and functional capacity (FC). However, improvement in FC and QoL after implantation is not unequivocal, and this has implications for patient selection and preimplantation discussions with patients and relatives. This article identifies preimplantation predictors of lack of improvement in FC and QoL after continuous-flow LVAD implantation and discusses potential mechanisms, allowing for the identification of potential factors that can be modified. In particular, the pathophysiology behind insufficient improvement in peak oxygen uptake is discussed. Data are included from 40 studies, resulting in analysis of >700 exercise tests. Mean peak oxygen uptake was 13.4 ml/kg/min (equivalent to 48% of predicted value; 259 days after implantation, range 31–1,017 days) and mean 6-minute walk test distance was 370 m (182 days after implantation, range 43–543 days). Finally, the interplay between improvement in FC and QoL is discussed.

Hemodynamic Response to Exercise in Patients Supported by Continuous Flow Left Ventricular Assist Devices

OBJECTIVES

This study sought to characterize the hemodynamic response to exercise in LVAD-supported patients and identify parameters most strongly associated with peak oxygen consumption (VO₂).

BACKGROUND

Despite improved survival for heart failure patients afforded by continuous flow left ventricular assist devices (LVADs), peak exercise capacity remains impaired. Mechanisms underlying this reduced functional capacity remain poorly understood.

METHODS

Patients referred for post-VAD hemodynamic optimization from December 2017 through June 2019 were enrolled. Swan Ganz catheters were inserted and upright incremental bicycle ergometry with respiratory gas analysis was performed. Hemodynamic measurements, mixed venous saturation, and arterial blood pressure were recorded every 3 min during exercise. Linear correlations were performed between peak VO₂ (ml/min) and peak Fick cardiac output (CO), peak device flow, the assumed intrinsic CO derived as Fick CO-device flow, peak pressure differential across the LVAD (mean arterial pressure-pulmonary capillary wedge pressure), peak pressure differential across right ventricle (mean pulmonary artery pressure - right atrial pressure) and systemic vascular resistance.

RESULTS

Forty-five patients supported by axial flow pumps (n = 12) and centrifugal flow pumps (n = 33) were studied. There were 34 men and 11 women. Age averaged 60 ± 10 years. Peak VO₂ averaged 10.6 ± 3.1 ml/kg/min. Fick CO had the greatest correlation with peak VO₂ with r = 0.73 (p < 0.0001) followed by intrinsic CO (r = 0.67; p < 0.0001). Multivariate model that best predicted peak VO₂ included Fick CO and peak arterial venous oxygen (AVO₂) difference.

CONCLUSIONS

LVAD supported patients have severely impaired peak exercise capacity. The peak Fick cardiac output was the best correlate of peak exercise performance.