Secondary endpoints.

Background
Acute allograft rejection (AAR) is an important cause of morbi mortality in heart transplant (HT) patients, particularly during the first year. Endomyocardial biopsy (EMB) is the “gold standard” to guide post- heart transplantation treatment. However, it is associated with complications that can be potentially serious. The index of microvascular resistance (IMR) is a specific physiological parameter used to assess microvascular function. Invasive coronary assessment has been shown to be both feasible and safe. Detection of coronary microvascular dysfunction (MCD) by IMR may help to identify high risk HT patients. In fact, an increased IMR measured early after HT has been associated with AAR, higher all-cause mortality and adverse cardiac events. A high IMR value early after HT may identify patients at higher risk who require increased surveillance or adjustments in immunosuppressive therapy. Conversely, a low IMR value may support reducing the number of EMBs. Our aim is to evaluate IMR in heart transplant patients within the first year. Changes in management after knowing IMR values and prognostic implications of IMR in a long term follow up will also be assessed.
Study design
The IMR-HT study (NCT 06656065) is a multicenter, prospective study that will include post-HT consecutive stable patients undergoing coronary physiological assessment in the first three months and one year. Cardiac adverse events will be evaluated at one year for up to five years. A clinical management algorithm is proposed: after knowing IMR values the physician will be able to reduce the number of biopsies established in each center protocol or modify immunosuppression therapy.
Conclusions
IMR values may vary within the first year after heart transplant. IMR assessment will be useful to identify high risk heart transplant patients, leading to possible changes in management and prognosis.

背景
急性移植物排斥反应（Acute allograft rejection, AAR）是心脏移植（heart transplant, HT）患者发病与死亡的重要诱因，尤其在术后第一年。心内膜心肌活检（Endomyocardial biopsy, EMB）是指导心脏移植术后治疗的“金标准”，但该操作可能伴随潜在严重并发症。微血管阻力指数（index of microvascular resistance, IMR）是用于评估微血管功能的特异性生理学参数，有创冠状动脉评估已被证实兼具可行性与安全性。通过IMR检测冠状动脉微血管功能障碍（coronary microvascular dysfunction, MCD），或可识别高危心脏移植患者。事实上，心脏移植术后早期测得的IMR升高，与AAR、更高的全因死亡率及不良心脏事件相关。术后早期IMR升高的患者，属于需加强监测或调整免疫抑制治疗的高危人群；反之，IMR偏低则可支持减少心内膜心肌活检的频次。本研究旨在评估心脏移植术后一年内的IMR水平，同时探讨获知IMR结果后临床管理方案的调整情况，以及IMR在长期随访中的预后价值。
研究设计
本研究为IMR-HT研究（临床试验注册号：NCT 06656065），是一项多中心前瞻性研究，纳入术后前3个月及1年时接受冠状动脉生理学评估的连续入组稳定型心脏移植患者。研究将在术后1年起至术后5年期间，对心脏不良事件进行随访评估。本研究提出一套临床管理算法：医师获知IMR结果后，可依据各中心既定方案减少活检次数，或调整免疫抑制治疗方案。
结论
心脏移植术后一年内，IMR水平或存在动态变化。IMR评估有助于识别高危心脏移植患者，进而推动临床管理方案调整并改善预后。