Daily simultaneous recordings of an electrocardiogram and an external thorax phonocardiogram and abdominal phonocardiogram were obtained in 24 rats with abdominal heart grafts so that rejection could be studied. The sounds recorded above the heterotopic heart are the result of a pressure differential between host and graft ventricle competing with one another. As soon as the contractility of the graft ventricle decreases below the contractility of the host ventricle, characteristic and specific changes occur in the abdominal phonocardiogram: the amplitude of the first sound becomes smaller while the timing of the second heart sound (aortic valve closure) is subsequently controlled by the host ventricle. These observations coincide with clinical and histological symptoms of rejection and are, therefore, of diagnostic value. In addition, a rough quantitative record of graft function is obtained by abdominal phonocardiography using the host's own cardiac function as a reference parameter.SUMMARY
In the heterotopic heart transplanted to the abdominal great vessels of the rat, graft function is examined usually by direct palpation. Postoperatively, a vigorous beat can be felt reflecting good contractility of the myocardium. With the onset of graft rejection, the heartbeat becomes weaker and finally ceases whereas the host continues to thrive supported by his own heart. As a result of the heterotopic position of the graft, no quantitative information is obtained about its actual working capacity. Specifically, in the case of prolonged graft survival, one would like to know if the heterotopic heart really would be capable of sustaining life. Although the electrocardiogram may record qualitative changes (1), we have found that the phonocardiogram allows a more quantitative assessment of graft function. The host's own heart thereby serves as the standard for comparison.