Registration of thoracic electrical bioimpedance for early diagnosis of rejection after heart transplantation.

In this study, registration of thoracic electrical bioimpedance was used for early detection of acute rejection after heart transplantation. Thirty-five heart transplant recipients were monitored by registration of thoracic electrical bioimpedance signals during the immediate postoperative period and during the outpatient follow-up. At the same time, endomyocardial biopsy specimens were taken. In addition to cardiac stroke volume index and ejection fraction, the acceleration index (seconds -2) was calculated. This acceleration index describes the acceleration of blood volume and represents a function parameter of the myocardial inotropy. Seventeen acute rejection episodes were diagnosed during the follow-up period. The average acceleration index value during the 17 rejection episodes was 92.5 +/- 11.7 sec-2 and thus significantly lower when compared with the nonrejection levels (p < 0.05). The acceleration index values decreased during acute rejections by an average of 36.4 +/- 19.3 sec-2 (28%). The sensitivity of this diagnostic parameter in the examined patients was 71%, and the specificity was 100%. Thus registration of thoracic electrical bioimpedance and calculation of the acceleration index represents a quick and noninvasive monitoring technique and can ideally be used in the outpatient clinic as a supplement to invasive endomyocardial biopsies.