Comparison of methods to evaluate acute rejection in heterotopic heart transplantation in rats

We compared palpation and electrocardiograms (ECG) as methods of evaluation of acute rejections, and also studied the mode of expression of rejection from histological findings by means of a cervical heart transplantation model in LEW strain rats with (LEW x BN) F1 rats as donors. Evaluation by palpation mainly involved changes in the intensity of the beat of the transplanted heart. With this method, it was also possible to observe changes in the size of the graft, and to investigate these changes over time. Unlike with abdominal heart transplants, the time of cardiac arrest can be clearly determined without any influence from the heart rate of the recipient. But with the ECG evaluation method, it was possible to distinguish clearly between the waveforms of the graft and the recipient waveforms unlike with the conventional lead method. In histological findings, the time of transfer of infiltrating cells into the graft and the time of appearance of CD8 positive cells matched the times when changes occur in the intensity of the beat and in the heart rate seen with palpation. Unlike the palpation and ECG methods, however, these findings are not suitable for evaluation of the time of cardiac arrest of the graft. The graft survival time was 6.1 +/- 0.6 days (n = 73) by palpation and 8.5 +/- 1.8 days (n = 73) by ECG. Since the graft survival time was significantly longer in the ECG evaluation than in the evaluation by palpation (P < 0.001), it appeared better to use these methods independently rather than concurrently in consideration of their features. Histological examination appeared to be useful in experimental systems for clarification of the mode of expression of the acute rejection after its has occurred.