Serial measurement of integrated ultrasonic backscatter in human cardiac allografts for the recognition of acute rejection.

Cyclic variation of integrated ultrasonic backscatter (IB) was noninvasively measured in the septum and left ventricular posterior wall using a quantitative IB imaging system to assess the alterations in the acoustic properties of myocardium associated with acute cardiac allograft rejection. The study population consisted of 23 cardiac allograft recipients and 18 normal subjects. In each cardiac allograft recipient, one to eight (mean, four) IB studies were performed, each within 24 hours of right ventricular endomyocardial biopsy performed for rejection surveillance. The magnitude of the cyclic variation of IB in the posterior wall was 5.9 +/- 0.9 dB in normal subjects and 6.2 +/- 1.3 dB in the cardiac allograft recipients without previous or current histological evidence of acute rejection (n = 17, p = NS vs. normal subjects). The magnitude of cyclic variation of IB in the septum was 4.8 +/- 1.1 dB in normal subjects and 3.8 +/- 2.0 dB in the cardiac allograft recipients (n = 15, p = NS vs. normal subjects). A significant decrease in the septal IB measure was observed in cardiac allograft recipients with left ventricular hypertrophy (wall thickness of at least 13 mm) (2.6 +/- 1.7 dB, n = 8, p less than 0.05 vs. normal subjects). IB studies were done before and during moderate acute rejection in 11 recipients (14 episodes). During moderate acute cardiac rejection, the magnitude of the cyclic variation in IB decreased from 6.7 +/- 1.3 to 5.1 +/- 1.4 dB in the posterior wall (n = 14, p less than 0.05) and from 4.2 +/- 2.1 dB to 2.9 +/- 1.8 dB in the septum (n = 12, p less than 0.05). These data suggest 1) the magnitude of the cyclic variation in IB of the septum is different in cardiac allografts with cardiac hypertrophy and normal subjects, possibly reflecting regionally depressed myocardial contractile performance and 2) acute cardiac rejection in humans is accompanied by an alteration in the acoustic properties of the myocardium. This change is detectable by serial measurement of the magnitude of the cyclic variation in IB, both in the septum and in the posterior wall.