High Right Ventricular Afterload is Associated with Impaired Exercise Tolerance in LVAD Patients

Abstract

Purpose Exercise tolerance, measured by pVO 2 during cardiopulmonary exercise stress test (CPET), is impaired in patients with LVAD. After LVAD, the right heart is more sensitive to afterload. We hypothesize that high RV afterload during exercise is associated with lower pVO 2 . Methods At routine right heart catheterization (RHC), LVAD patients performed supine bicycle exercise to maximal effort. Hemodynamics and echocardiograms at rest and peak exercise were collected. The same patients underwent CPET on different days as part of routine post-operative monitoring. We used effective arterial elastance (Ea = systolic PAP/stroke volume) to measure RV afterload, as it incorporates both pulsatile and resistive loads. Results Between 11/17 and 9/18, 10 patients (median age 54 years) had RHC, 8 of them had CPET. Time between LVAD and RHC was 244 days (IQ 223-299) and between CPET and RHC was 55 days (IQ 35-126). Work achieved (Watts) during CPET and RHC correlated linearly (α=1.1, p=0.003, R²=0.60). Patients had low pVO 2 (13.2 L/kg/min, IQ 11-18) and high VEVCO 2 slope (34, IQ 32-43) despite normal filling pressures and cardiac output (CO) after LVAD. They had no chronotropic incompetence (reaching 89.5% of max predicted heart rate, IQ 66.4-95.4). Compared to resting state, at peak exercise, filling pressures, CO, RV stroke work index, and RV tissue Doppler (S’) increased. Notably, pVO 2 negatively correlated with Ea at peak exercise and the change in Ea from rest to stress, while VEVCO 2 slope had the inverse correlations (Figure). pVO 2 did not correlate with changes in PCWP, CO, or LVAD flow. Moderate-severe baseline RV dysfunction and mild-moderate TR are associated with worse pVO 2 and VEVCO 2 slope. Conclusion This pilot study is the first to suggest that poor baseline RV function and high RV afterload at peak exercise are associated with worse pVO 2 and VEVCO 2 slope in LVAD patients. The practice of increasing pump speed may not be adequate to improve exercise tolerance and may be harmful to RV function.