Cardiac function of transplanted rat hearts using a working heart model assessed by magnetic resonance imaging

Background: A direct correlation between graft rejection and cardiac contra ctile function in small-animal models has been difficult to establish becau se (i) the conventional non-working heart model is greatly different from t he orthotopic heart in terms of left: ventricular work and (ii) it is diffi cult to obtain hemodynamic data in situ. We have used magnetic resonance im aging (MRI) techniques to obtain non-invasive, in-situ quantitation of vent ricular volume after heterotopic cardiac transplantation. Methods: Infra-renal heterotopic cardiac transplantation was performed on r ats using syngeneic and allogeneic untreated donors in both working and non -working left heart models, An occluding balloon catheter in the inferior v ena cava was used to vary the pre-load to the graft. An arteriovenous fistu la was created to raise inferior caval oxygen saturation. Magnetic resonanc e imaging measurements were carried out at day 3, 4, and 5 post-transplanta tion. Left ventricle end-diastolic and end-systolic volumes were calculated using a biplanar ellipsoid model, Results: Stroke volume was significantly increased in the working heart mod el as compared to the non-working model, At day 4 post-transplant, the dias tolic pressure-volume relationship in the allograft group was significantly shifted, indicative of decreased myocardial distensibility, whereas the in dices of systolic function were preserved. Conclusions: We have developed a heterotopic transplant working rat heart m odel and have used it to assess in-situ cardiac function by MRI. Sensitive indices of diastolic contractile function can be obtained in this rodent tr ansplant model that correlate well with histologic evidence of early reject ion.