Echocardiographic diagnosis of cardiac allograft rejection

Current echocardiographic methods are promising for detection of rejection either as an increase in LV mass or a decrease in LV compliance. Both increased mass and decreased compliance during rejection may be mediated by the common mechanism of edema. Edema will appear specifically as increased wall volume in quantitative echocardiograms and, through decreased LV compliance, will be reflected in doppler-derived indices of diastolic filling. Initial difficulties with quantitative echocardiography related to image quality have largely been resolved. These have been replaced by concern for factors independent of rejection that affect LV mass, including hypertrophy due to hypertension or denervation-induced catecholamine hypersensitivity, and secondary effects of the immunosuppressive agents. An additional difficulty with quantitative echocardiography is that convenience for the patient is offset by the labor-intensive nature of planimetry-based analysis that has not yet been supplanted by fully automated methods. Diastolic function abnormalities within the early months following transplantation are indicators of acute rejection. However, their value in the long-term management of transplantation recipients may be diminished by effects of myocardial fibrosis, hypertension-induced hypertrophy, and accelerated coronary atherosclerosis. Analysis of echocardiographically derived indices of diastolic function is also a labor-intensive process that may not be economically feasible in the clinical setting. Echocardiography does have unique advantages for characterizing the functional changes accompanying late-onset chronic rejection. At the present time, echocardiographic techniques cannot replace endomyocardial biopsy; however, echocardiography can be a useful adjunct in the monitoring of patients for acute rejection. Clinical experience has demonstrated that both increased LV mass and abnormalities of doppler-derived indices of diastolic function can herald the onset of acute rejection in some patients that may be missed by standard techniques of immunological surveillance. Experience is insufficient to define whether different sensitivities of echo measurements and endomyocardial biopsy are statistical anomalies or reflect specific differences in the physiology of rejection. Similarly, it is unclear whether poor clinical results frequently seen in such instances reflect a fundamental property of the rejection episode or relatively late detection and treatment. A combined echocardiographic approach that includes measurement of LV mass, ultrasound tissue characterization, and evaluation of diastolic function would lead to further understanding of the interrelationship between the anatomical and physiological changes in the transplanted heart. The applications of echocardiography to the study of the cardiac allograft are multiple, and can be expected to increase as technology continues to improve.