Analysis of the distribution of histologic myocardial lesions during acute cardiac rejection. Experimental study in rodents.

BACKGROUND AND METHOD Asymmetric distribution of histologic lesions have been reported in grafted hearts that could hamper the interpretation of right ventricular endomyocardial biopsy. Heterotopic heart transplantations were performed in rats (n=59) and guinea pigs (n=20). Grafted hearts were examined by a pathologist who established the degree of cardiac rejection in the four cardiac cavities. RESULTS Forty cardiac rejections were diagnosed in rats and ten in guinea pigs. An asymmetric distribution of histologic lesions was observed in 34 (68%) rejected hearts with greater lesions in the auricular myocardium than in the ventricular myocardium (n=25, 50%). One (n=18) or two degrees (n=7) differentiated the severity of rejection between atria and ventricles. Cardiac rejection score was significantly greater in atria than in ventricles (3.12+/-0.18 vs. 2.6+/-0.2 (P<0.01) in rats and 2.35+/-0.37 vs. 1.6+/-0.47 (P<0.001) in guinea pigs. There were histologic lesions of rejection in the auricular myocardium in seven cases, although the ventricular myocardium was completely normal. In nine (18 %) other grafted hearts the degree of rejection was equal in the auricular myocardium and ventricular septum but was greater than the degree of rejection noted in the right and left ventricular free walls. CONCLUSION The distribution of histologic lesions of acute cardiac rejection in rodents was heterogeneous in grafted hearts which exhibited greater lesions in the atria than in ventricles. This should be taken into consideration in the evaluation of new methods of detection of cardiac rejection and in the diagnosis of acute cardiac rejection in humans.