Mixing 1:1 HIIT and MICT in Early to Very Early Phase HTx Recipients : a Retrospective Study From a 510 Patients/12 Years Database

Background: Exercise-based cardiac rehabilitation is recommended early to very early for heart transplant recipients (HTRs), but data on its feasibility and efficacy at this stage are lacking. Primarily, this study reports the results of an intensive program combining moderate-intensity continuous-training (MICT) and high-intensity interval-training (HIIT) in early HTRs. Secondarily, it explores the determinants of VO2peak in this population. Methods: A single-center retrospective study of a prospectively-collected database including patients who were consecutively referred to a cardiac rehabilitation unit immediately after discharge from acute post-transplant care, between December 2012 and December 2024. Patients participated in a tailored program combining MICT and HIIT as soon as they could cycle, and performed a first cardiopulmonary exercise test (CPET1) when possible. The initial prescription included 32 planned 30-minute (±5) aerobic sessions for 4 weeks, on a standard or semi-recumbent cycle-ergometer, twice a day (4 days a week) including one session of MICT (PVT and Borg-RPE 12-14) and one session of HIIT (6-8 x 1':3'/ PAT and Borg-RPE ≥ 15), plus additional sessions (respiratory and strengthening physiotherapy, gymnastics or walking, occupational therapy). The primary outcome was improvement in exercise capacity, measured by maximal oxygen consumption (VO2peak) between CPET1 and discharge (CPET2). Secondary outcomes included feasibility criterions (exercise-related adverse events-AE, and completion rates), then clinical, biological and echocardiographic parameters influencing exercise capacity.