MYOCARDIAL ACOUSTICS IN PEDIATRIC ALLOGRAFT-REJECTION

Background: Ultrasonographic tissue characterization is the assessment of physical properties of biologic tissue on the basis of quantitativ e analysis of its acoustic characteristics. Abnormalities in microscop ic structure that occur with cardiac allograft rejection may result in characteristic alterations in myocardial acoustics. Ultrasonographic tissue characterization may allow noninvasive detection of rejection. Methods: Findings in 22 pediatric heart transplant patients undergoing routine surveillance for rejection by endomyocardial biopsy were pros pectively evaluated. Off-line ultrasonographic tissue characterization analysis was done on transthoracic echocardiograms obtained at each b iopsy. Within patients, tissue characterization texture measures deriv ed from the ultrasonographic image data were compared with histologic findings. Univariate multiple regression analysis was used to identify texture measures associated with acute allograft rejection in a subgr oup (n = 8) with at least one biopsy-proven episode of moderate reject ion. Results: Measures of homogeneity (co-occurrence matrix correlatio n and heterogeneity (run-length nonuniformity) decreased with moderate rejection (p < 0.03). Homogeneity measures decreased if the patient h ad a previous episode of rejection. Several measures of heterogeneity (gray level difference and run-length statistics) were affected by the presence of edema. Run-length nonuniformity was the only measure that differentiated moderate rejection from edema. Discriminant analysis o n all 22 patients correctly identified 96% of first rejection episodes (sensitivity 80%, specificity 64%), 93% of moderate and severe reject ion episodes (sensitivity 71%; specificity 62%), and 69% of all reject ion episodes (sensitivity 51%, specificity 91%). Conclusions: Histolog ic changes associated with moderate and severe pediatric allograft rej ection as reflected by characteristic alterations in myocardial acoust ics can be assessed with ultrasonographic tissue characterization. His tologic changes associated with transplantation itself (resolution of rejection and edema) also affect myocardial acoustics and must be take n into account in rejection surveillance.