Myocardial External Efficiency and Energetic Adaptation After Heart Transplantation: An Exploratory Study

Background. Mitochondrial dysfunction and impaired myocardial energetics may contribute to graft dysfunction after heart transplantation (HTX). We aimed to characterize early posttransplant myocardial external efficiency (MEE) and its relationship with mitochondrial capacity. Methods. In this prospective single-center study, 22 HTX recipients underwent [ 11 C]acetate positron emission tomography, echocardiography, biomarker testing, and high-resolution respirometry of endomyocardial biopsies once between week 1 and 3 and at 6 mo post-HTX. Temporal changes in positron emission tomography–derived MEE, cardiac output, and myocardial oxygen consumption were evaluated within patients and compared with those of 20 control participants. Mitochondrial capacity was assessed only in HTX recipients. Results. MEE increased from 18 ± 5% to 21 ± 5% at 6 mo post-HTX ( P = 0.003) but remained lower than in control participants (26 ± 6%, P < 0.0001). Cardiac output, myocardial oxygen consumption, and mitochondrial oxidative capacity did not change significantly over time. At 6 mo, both MEE and mitochondrial oxidative capacity correlated with left-ventricular global longitudinal strain ( r = –0.49, P = 0.002; r = –0.58, P = 0.010, respectively). Furthermore, MEE was inversely associated with troponin I ( r = –0.49, P = 0.030) and N-terminal pro-brain natriuretic peptide ( r = –0.35, P = 0.029). Conclusions. MEE improved significantly from 1–3 wk to 6 mo after HTX. Both MEE and mitochondrial respiratory function were associated with left-ventricular contractile performance. Overall, these findings suggest alterations in myocardial energetics during early graft recovery and support a link between oxidative metabolism and graft performance.