Morphological and functional evaluation of murine heterotopic cardiac grafts using ultrasound biomicroscopy

This study investigated the use of an ultrasound biomicroscope (UBM) to observe murine heterotopic cardiac transplants. By using an UBM (30 MHz), cardiac isografts in eight mice were studied on days 1, 5, 14 and 50 posttransplantation. The same method was tested in allografts in two mice on days 1, 5, 7 and 9. Two-dimensional imaging delineated the graft structures with high spatial resolution. In isografts, M-mode recording showed gradually decreased left ventricular (LV) wall thickness and chamber dimension, but increased LV fractional shortening. Doppler sampling measured blood velocities from the ascending aorta, left coronary artery (LCA), aortic and mitral orifices of grafts. In isografts, LCA forward flow caused by native circulation to perfuse the graft myocardium increased from day 1 to 5, then moderately decreased by day 14 and stabilized thereafter. In allografts, LCA forward flow sharply decreased to almost zero between day 5-9. Therefore, UBM is a reliable method for following the survival status of cardiac grafts in mice.