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

Background and method: Asymmetric distribution of histologic lesions have b een reported in grafted hearts that could hamper the interpretation of righ t ventricular endomyocardial biopsy. Heterotopic heart transplantations wer e performed in rats (n = 59) and guinea pigs (n = 20). Grafted hearts were examined by a pathologist who established the degree of cardiac rejection i n the four cardiac cavities. Results: Forty cardiac rejections were diagnos ed in rats and ten in guinea pigs. An asymmetric distribution of histologic lesions was observed in 34 (68%) rejected hearts with greater lesions in t he auricular myocardium than in the ventricular myocardium (n = 25, 50%). O ne (n = 18) or two degrees (n = 7) differentiated the severity of rejection between atria and ventricles. Cardiac rejection score was significantly gr eater 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. The re were histologic lesions of rejection in the auricular myocardium in seve n cases, although the ventricular myocardium was completely normal. In nine (18 %) other grafted hearts the degree of rejection was equal in the auric ular myocardium and ventricular septum but was greater than the degree of r ejection noted in the right and left ventricular free walls. Conclusion: Th e 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 ev aluation of new methods of detection of cardiac rejection and in the diagno sis of acute cardiac rejection in humans. (C) 2000 Elsevier Science B.V. Al l rights reserved.