THE MEASUREMENT OF THE BIOELECTRICAL MYOC ARDIAL IMPEDANCE AS A NONINVASIVE METHOD FOR REJECTION MONITORING AFTER HEART-TRANSPLANTATION

12 beagle dogs underwent neck-heart transplantation and were immunosup pressed with cyclosporine and methylprednisolone. Intramyocardial impe dance was determined twice daily with our screw-in electrodes in the r ight and lek ventricle. Transmyocardial biopsies and the intramyocardi al electrogram (IMEG) were performed as reference methods. 19 rejectio n episodes were induced. When acute rejection was seen in histology th e animals were treated with pulsed 125 mg methylprednisolone over 5 co nsecutive days and immunosuppression was raised to sufficient levels. Successful treatment of rejection was controlled by biopsy. All hearts showed a uniform decrease of impedance of about 28.3 % +/- 5.5 % imme diately after implantation then reaching a stable plateau after 7 to 8 days. Impedance values then remained unchanged as long as rejection w as absent. Biopsy findings of grade 1A to 1B (ISHLT) were accompanied by a statistically significant increase of impedance of 12.2 % +/- 2.5 %, of grade 2 to 3A of 19.2 % +/- 3.2%, and of grade 3B to 4 of 27.0 % +/- 2.9 %. Sensitivity was 95 %, specificity 91 %. Successful treatm ent of rejection led to a uniform decrease of impedance to initial lev els. Measurements of intramyocardial impedance for high frequencies ca n reliably indicate alterations of the cell membrane and the intracell ular space during acute cardiac allograft I-ejection. The amount of in crease of impedance is a reliable noninvasive parameter to graduate ac ute cardiac allograft rejection. The success of treatment of rejection tan also be monitored by impedance. This noninvasive method is applic able for telemetric rejection monitoring via an implantable device, wh ich would allow continuous rejection surveillance of a patient at home without hospital admission.