The Ventilatory Equivalent for Carbon Dioxide Slope Independently Predicts Perioperative Outcomes in Patients Undergoing Heart Transplantation

Abstract

<h3>Purpose</h3> Cardiopulmonary exercise test (CPET) is commonly used to evaluate patients for heart transplantation (HTX), with the focus being on peak oxygen uptake (VO2). Although the ventilatory equivalent for carbon dioxide (VE/VCO2) slope during exercise predicts survival in patients with advanced heart failure, it has not been shown to predict outcomes from heart transplantation. We aimed to assess its utility in predicting perioperative outcomes following heart transplantation. <h3>Methods</h3> We retrospectively reviewed all patients who underwent CPET within 18 months prior to HTX between January 2002 and August 2021 at our centre. VE/VCO2 slope and peak oxygen consumption (VO2) for each patient was measured and evaluated with recipient and transplant characteristics. The primary outcome was days alive and free of the intensive care unit (ICU) within 30 days of HTX, and the secondary outcome was a composite outcome of postoperative morbidity (defined as either one of respiratory failure, primary graft failure, stroke, bloodstream infection, renal failure, ICU readmission, or mortality). We used a Pearson correlation coefficient and Mann-Whitney U test to respectively assess the association of the continuous variable of VE/VCO2 slope and VE/VCO2slope >35 with ICU-Free days. Multiple regression of VE/VCO2 slope >35 in conjunction with other transplant characteristics was used to assess if VE/VCO2 slope independently predicts ICU-Free days and postoperative morbidity. <h3>Results</h3> 61 patients met the inclusion criteria. There was a correlation between VE/VCO2 slope and ICU free days (R= -.264; p=0.04). VE/VCO2 slope >35 was associated with significantly lower median ICU-free days (23 vs 26.5 days; p<0.01) and a higher odds of postoperative morbidity (OR=5.64, 95% CI=1.75-18.16; p<0.01). Multiple regression analysis showed VE/VCO2 slope >35 is independently associated with lower ICU-free days (p<0.01) and postoperative morbidity (p=0.02) when controlled for age, sex, ethnicity, diagnosis, peak VO2, cardiac index, PVR, and creatinine. No other factor independently predicted ICU-free days or postoperative mortality. <h3>Conclusion</h3> VE/VCO2 slope >35 is independently associated with lower postoperative morbidity following HTX even after controlling for peak VO2 and right heart catheter parameters.