(306) - LVAD Weaning Protocol Utilizing Comprehensive Cardiopulmonary Exercise Testing to Define Cardiac Reserve Capacity

Abstract

The optimal protocol for determining whether adequate LV recovery has taken place to permit LVAD explantation is not well established. Peak VO2 (pVO2) is typically the only exercise parameter utilized. We developed a protocol that integrates hemodynamic, imaging, and gas exchange measures at rest, during LVAD speed reduction, and during exercise to characterize cardiac reserve capacity and guide LVAD explant decisions. A 44 year old male with LVEF 14% demonstrated no LV recovery after CABG and required insertion of a BTT Heartware LVAD on post-op day 14. After 6 months, LVAD speed reduction to 2000 rpm led to borderline-acceptable echo parameters (LVEF 49%, LVEDD 58 mm) and a pVO2 of only 14.6 ml/kg/min. We measured VO2, peripheral O2 extraction (Ca-vO2), Fick cardiac output (CO) and pulmonary wedge pressure (PCWP) each minute during an incremental ramp exercise protocol. Exercise CO increased appropriately (7.4 to 14.6 L/min) and PCWP increment was modest (+7mmHg), which prompted us to explant the LVAD. In contrast, a 61 year old patient with a BTT LVAD demonstrated a similar pVO2 (14.1 ml/kg/min). Unlike our first patient, exercise CavO2 was normal, but he was able to augment his CO to only 8.3 L/min with a 15 mmHg increase in PCWP. LVAD explant was therefore not pursued and he underwent cardiac transplantation. Nearly identical pVO2 values in our patients with divergent relative contributions of CO and CavO2 highlight the need to consider both central cardiac and peripheral O2 extraction components of pVO2. Serial measurements of PCWP in relation to CO were particularly informative based on a 2-fold PCWP-CO slope (1.5 vs. 3.1 mmHg/L/min) in the patient not explanted. Our findings suggest that reliance on LVAD explant criteria of a pVO2 > 16 mL kg/min may not adequately reflect reserve capacity and sustained recovery potential of the native heart. Enhanced phenotyping during exercise merits further investigation to refine LVAD explant criteria.