Evaluation de la fonction microvasculaire myocardique par résonance magnétique cardiaque sensible à l'oxygène chez des transplantés cardiaques

BACKGROUND: Cardiac allograft vasculopathy (CAV) is one of the leading cause of long-term mortality after heart transplantation. This multifactorial pathology is characterized by diffuse and concentric thickening of the graft vessels and induces microvascular damages to the myocardium. Due to the lack of angina symptomatology of cardiac transplant patients and the difficult detection of diffuse involvement by conventional coronary angiography, CAV progresses insidiously and is often diagnosed at an advanced stage. Our aim was to test a new method of assessment of microvascular function by oxygen-sensitive cardiac magnetic resonance (OS-CMR) in a population of cardiac transplant (CT) recipients with varying degrees of CAV at coronary angiography.  METHODS: We compared in OS-CMR the change in signal intensity induced by vaso-modulatory breathing maneuvers (hyperventilation followed by breath hold) in 46 CT, 23 of whom had an angiographic CAV and compared to 25 healthy volunteers (HV). The feasibility of breathing maneuvers and the quality of OS-CMR images were also evaluated. Finally, we looked for potential predictors of microvascular response after cardiac transplantation.  RESULTS: The myocardial microvascular response represented by the signal intensity change during breathing maneuvers is significantly attenuated in CT compared to HV (2.63 ± 4.16 versus 6.40 ± 5.96 p=0.0099) for SI change at 30 seconds breath hold; (4.91 ± 3.74 versus 8.86 ± 6.15 p=0.0063) for the maximum SI change measured during breath hold. The maximal response is significantly lower in grades 2-3 combined (1.02±2.03) compare to grades 0 (5.09±4.20) and to grade 1 (5.88±2.73), whilst there is no difference between these last 2 groups (p=0.45). The maximal response is lower in CT without any angiographically CAV compare to the HV (5.09±4.20 versus 8.86±6.15 p<0.05). The aforementionned comparisons at 30 seconds breath hold lead to the same conclusion. The breathing maneuvers of hyperventilation and breath hold are feasible in cardiac transplant recipients (0% total disability to perform maneuvers, 9% inability to maintain at least 30sec breath hold). Due to the good quality of the OS-CMR images, 94% of the myocardial segments could be analyzed (3074/3264). Finally, there is an inverse correlation between microvascular response and donor age, ventricular volumes and regional or diffuse fibrosis, while there is a positive linear correlation between the microvascular response and the presence of dyslipidemia.  CONCLUSION: OS-CMR combined with breathing maneuvers is a clinically drug-free, non-invasive and innovative imaging technique allowing the detection of abnormal microvascular response in cardiac transplant recipients at a stage where conventional angiography doesn’t diagnose any degree of CAV.

Keyphrases: circulation coronaire, cardiac transplantation, heart transplantation, cardiac allograft vasculopathy, oxygen sensitive cardiac magnetic resonance, chronic rejection, coronary circulation, microcirculation, breathing maneuvers, oxygenation