Metabolic and Hemodynamic Determinants of Exercise with the HeartMate 3 LVAD

Abstract

<h3>Purpose</h3> Several studies have reported that peak oxygen consumption (pVO2) is diminished after continuous flow (CF) LVAD support and recent data shows that pVO2 post LVAD predicts outcomes. It has been suggested that augmentation of native cardiac output (NCO) and not LVAD flow supports exercise. Using simultaneous metabolic and hemodynamic measures, we further studied the determinants of maximal exercise with the Heartmate 3 (HM3) LVAD. <h3>Methods</h3> Subjects underwent maximal upright bicycle exercise testing utilizing a 10-15 W ramp protocol with hemodynamic measurements from a right heart and radial arterial catheter, and CPET testing with a metabolic cart (Metalyzer 3B, Cortex, Germany). Mid-point hemodynamics were acquired to plot pressure/flow relationships. NCO was calculated by subtracting LVAD flow from Fick cardiac output (FCO). Arterial lactate and regional tissue oxygenation (rSO2) with the NIRS SenSmart™ were also measured. <h3>Results</h3> Six HM3 subjects (43-76 yrs) were studied at least 12 weeks post implant, all were on at least 2 neurohormonal agents. All patients performed maximal exercise (RER 1.10-1.34). Most did not demonstrate chronotropic incompetence; achieving median 80.8 (63.5- 90.9) % of predicted heart rate. We saw robust oxygen extraction, with median peak A-VO2 difference 14.2 (10.5-15.8) mL/100mL with no change in rSO2 and median peak lactate 6.5 (3.5-9.9) mmol/L. However, 5/6 subjects achieved pVO2 ≤14 ml/kg/min. During exercise, there was minimal augmentation of LVAD flow (0.4-1.6 L/min) while NCO increased by 2.0-7.1 L/min. Mean pulmonary artery (mPA)/FCO relationships were available for 5 subjects (Fig.1), demonstrating abnormal rate of rise of mPA in all patients (slope 3.7-7.0, normal < 3). <h3>Conclusion</h3> Neither chronotropic response nor peripheral extraction appeared to limit exercise. Steep rise in mPA suggests either impaired pulmonary vasoreactivity and or cardiac reserve may be the key determinants of exercise capacity during HM3 support. Further study will clarify these factors.