Coronary Microcirculatory Dysfunction and Acute Cellular Rejection After Heart Transplantation.

Background: Acute cellular rejection is a major determinant of mortality and re-transplantation after heart transplantation. We sought to evaluate prognostic implications of coronary microcirculatory dysfunction assessed by index of microcirculatory resistance (IMR) for risk of acute cellular rejection after heart transplantation. Methods: The current study prospectively enrolled 154 heart transplant recipients who underwent scheduled coronary angiography and invasive coronary physiologic assessment 1 month after transplantation. IMR is microcirculatory resistance under maximal hyperemia. By measuring hyperemic mean transit time using 3 injections (4 mL each) of room-temperature saline under maximal hyperemia, IMR was calculated as hyperemic distal coronary pressure × hyperemic mean transit time. The primary endpoint was biopsy-proven acute cellular rejection of grade ≥2R during 2 years of follow-up after transplantation and was compared using multivariable Cox proportional hazard regression according to IMR. The incremental prognostic value of IMR, in addition to the model with clinical factors, was evaluated by comparison of c-index, net reclassification index (NRI), and integrated discrimination index (IDI). Results: Mean age of recipients was 51.2±13.1 years (81.2% male), and cumulative incidence of acute cellular rejection was 19.0% at 2 years. Patients with acute cellular rejection had significantly higher IMR values at 1 month than those without acute cellular rejection (23.1±8.6 vs. 16.8±11.1, P=0.002). IMR was significantly associated with the risk of acute cellular rejection (per 5-unit increase: adjusted HR 1.18, 95% CI 1.04-1.34, P=0.011) and the optimal cut-off value of IMR to predict acute cellular rejection was 15. Patients with IMR≥15 showed significantly higher risk of acute cellular rejection than those with IMR<15 (34.4% vs. 3.8%, adjusted HR 15.3, 95% CI 3.6-65.7, P<0.001). Addition of IMR to clinical variables showed significantly higher discriminant and reclassification ability for risk of acute cellular rejection (C-index 0.87 vs. 0.74, P<0.001; NRI 1.05, P<0.001, IDI 0.20, P<0.001). Conclusions: Coronary microcirculatory dysfunction assessed by IMR measured early after heart transplantation showed significant association with the risk of acute cellular rejection. In addition to surveillance endomyocardial biopsy, early stratification using IMR could be a clinically useful tool to identify patients at higher risk of future acute cellular rejection after heart transplantation. Clinical Trial Registration: URL: https://clinicaltrials.gov Unique Identifier: NCT02798731.