Is VE/VCO2 Slope More Reflective of Isolated Cardiac Performance Compared to Peak VO2: A Comparison of Cardiopulmonary Stress Test Variables before and after Transplantation

Abstract

<h3>Purpose</h3> Peak oxygen consumption (VO2) can be influenced by various cardiac, respiratory, pulmonary vascular, and peripheral extraction limitations. The best prognostic marker for isolated cardiac dysfunction remains unclear. This study aimed to determine whether VO2 or minute ventilation-carbon dioxide production slope (VE/VCO2) is more reflective of isolated cardiac performance by assessing pre- and post-operative outcomes of cardiopulmonary exercise testing (CPX) in heart transplant (HT) patients. <h3>Methods</h3> We conducted a single center, retrospective study of HT patients who underwent pre- and post-operative CPX (N= 16) between 2014 and 2019. CPX after-transplant was part of routine care, and all participants were healthy at the time of assessment. Patients with either discordant (N = 9) or concordant (N= 7) pre-transplant VO2 and VE/VCO2 were categorized. Patients with a ventilatory class (severity of VE/VCO2) that was at least one grade more severe than their Weber class (severity of VO2) were defined as discordant. Pre- and post-operative CPX outcomes were compared between the two groups. <h3>Results</h3> For the entire cohort, peak VO2, VE/VCO2, VO2/HR, METs, and RER were comparable pre- and post-operatively (p > 0.05 for all). Paired comparison of change in peak predicted VO2 was significant for the entire cohort (p= 0.04). It trended towards significance in the discordant group (p= 0.06) and was not significant for the concordant group (p= 0.54). The discordant group had a near normal peak predicted VO2 after HT on average 79% (68,90) while the concordant group had an abnormally low peak predicted VO2 46% (37-59) p=0.09. <h3>Conclusion</h3> Patients with VE/VCO2 values higher and out of proportion to VO2 responded more robustly after transplantation. This difference may be reflective of a more isolated cardiac limitation that is more readily correctible after transplantation.