Intramyocardial impedance measurements for diagnosis of acute cardiac allograft rejection

Background. Measurements of intramyocardial impedance at high frequencies c an indicate alterations in cell membranes and intracellular spaces during a cute cardiac allograft rejection. Methods. Fifteen beagle dogs underwent heterotopic heart transplantation an d were immunosuppressed with cyclosporine and methyl prednisolone (MP). Imp edance was determined twice daily by means of four screw-in electrodes in t he right and left ventricle. Transmyocardial biopsies and the intramyocardi al electrogram (IMEG) were performed as reference methods. A total of 23 re jection episodes were induced. When acute rejection was recognized histolog ically and through IMEG readings, the animals were treated with a bolus of 125 mg of methyl prednisolone over 5 consecutive days. Treatment of rejecti on was controlled by biopsy and IMEG. Results. All hearts showed a uniform decrease in impedance of about 28.3% /- 5.5% immediately after transplantation, which subsequently reached a sta ble plateau after 7 to 8 days. Impedance values then remained unchanged as long as rejection was absent. Biopsy findings of grades 1A to 1B (ISHLT) we re accompanied by a statistically significant increase in impedance of 12.2 % +/- 2.5%; of grades 2 to 3A of 19.2% +/- 3.2% and of grades 3B to 4 of 27 .0% +/- 2.9%. Sensitivity was 96%, specificity 91%. Successful treatment of rejection led to a decrease of impedance to the initial levels. Conclusions. The amount of increase in impedance of high frequencies is a m ethod to stratify acute cardiac allograft rejection into grades like histol ogically grading. The effectiveness of rejection treatment can also be moni tored through impedance measurement. The method is also applicable for tele metric rejection monitoring by means of an implantable device. (C) 2000 by The Society of Thoracic Surgeons.