Lvad pump speed increase is associated with increased peak exercise cardiac output and vo2, postponed anaerobic threshold and improved ventilatory efficiency

Abstract

Backgrounds: Peak exercise cardiac output (CO) increase is associated with an increase of peak oxygen uptake (VO₂), provided that arteriovenous O₂ difference [Δ(Ca-Cv)O₂] does not decrease. At anaerobic threshold, VO₂, is related to CO. We tested the hypothesis that, in heart failure (HF) patients with left ventricular assistance device (LVAD), an acute increase of CO obtained through changes in LVAD pump speed is associated with peak exercise and anaerobic threshold VO₂ increase.

Methods: Fifteen of 20 patients bearing LVAD (Jarvik 2000) enrolled in the study successfully performed peak exercise evaluation. All patients had severe HF as shown by clinical evaluation, laboratory tests, echocardiography, spirometry with alveolar-capillary diffusion, and maximal cardiopulmonary exercise testing (CPET). CPETs with non-invasive CO measurements at rest and peak exercise were done on 2days at LVAD pump speed set randomly at 2 and 4.

Results: Increasing LVAD pump speed from 2 to 4 increased CO from 3.4±0.9 to 3.8±1.0L/min (ΔCO 0.4±0.6L/min, p=0.04) and from 5.3±1.3 to 5.9±1.4L/min (ΔCO 0.6±0.7L/min, p<0.01) at rest and peak exercise, respectively. Similarly, VO₂ increased from 788±169 to 841±152mL/min (ΔVO₂ 52±76mL/min, p=0.01) and from 568±116 to 619±124mL/min (ΔVO₂ 69±96mL/min, p=0.02) at peak exercise and at anaerobic threshold, respectively. Δ(Ca-Cv)O₂ did not change significantly, while ventilatory efficiency improved (VE/VCO₂ slope from 39.9±5.4 to 34.9±8.3, ΔVE/VCO₂ -5.0±6.4, p<0.01).

Conclusions: In HF, an increase in CO with a higher LVAD pump speed is associated with increased peak VO₂, postponed anaerobic threshold, and improved ventilatory efficiency.

Keywords: Cardiac output; Exercise testing; Heart failure; LVAD.