Cardiopulmonary Exercise Metrics Demonstrate that CF-LVAD Patients Suffer from Residual Heart Failure

Abstract

Background Continuous flow left ventricular assist devices (CF-LVADs) improve survival and quality-of-life for patients with heart failure with reduced ejection fraction (HFrEF), but exercise capacity remains reduced. While resting and exertional cardiovascular performance is described in the setting of CF-LVAD support, data on pulmonary performance are limited. The primary objective of this study was to describe changes in metrics of cardiopulmonary performance during exercise among HFrEF patients before and after CF-LVAD implantation. Methods 11 HFrEF patients completed submaximal and symptom-limited cardiopulmonary exercise testing (CPET) on three separate visits. Visit 1 involved CPET testing ∼2-4 weeks prior to CF-LVAD implantation. Visit 2 involved CPET testing ∼3 months post-LVAD at a constant pump speed. Visit 3 involved CPET testing ∼4-5 months post-LVAD with progressive increases in LVAD pump speed during exercise. Exercise involved two levels of submaximal exercise below the ventilatory threshold (steady-states 1-2) and peak exercise on an upright cycle ergometer. Breath-by-breath gas exchange parameters (oxygen uptake [VO2], carbon dioxide production [VCO2], minute ventilation [VE]) were recorded by indirect calorimetry. Results Clinical characteristics are summarized in table 1. There was no improvement in submaximal or peak VO2 following LVAD implantation (figure 1) regardless of whether individuals exercised at constant speed (visit 2) or exercised with progressive pump speed increases (visit 3). Ventilatory efficiency improved modestly on visits 2 and 3, but remained severely impaired. Oxygen uptake efficiency slope (OUES) was largely unchanged post-LVAD. Changes in end-tidal carbon dioxide during exercise were similar on all three visits. Conclusions HFrEF patients suffer from severe impairments in functional capacity as measured by oxygen uptake following CF-LVAD implantation, which does not improve with modulations in pump speed. CF-LVAD patients also suffer from severe impairments in ventilatory efficiency. These data suggest that CF-LVAD patients suffer from residual heart failure that is precipitated by submaximal exercise and not alleviated by modulations in pump speed.