Early cardiac allograft rejection is independent of regional myocardial blood flow.

Noninvasive telemetric monitoring of canine heterotopic cardiac allograft unipolar peak-to-peak amplitude (UPPA) has permitted prospective surveillance for rejection; moreover, this technique is able to reliably detect rejection before the development of histologic evidence of myocyte necrosis. This study was performed to determine whether early cardiac allograft rejection and the accompanying decline in allograft UPPA were associated with alterations in regional myocardial blood flow (RMBF). Seven heterotopic, intrathoracic canine cardiac transplantations were performed using triple-drug immunosuppression. Native hearts and allografts were instrumented with right ventricular and left ventricular epicardial screw-in electrodes connected to subcutaneous telemeters. Daily measurement of native and graft UPPA was performed; using radioactive microspheres, native and graft RMBF were determined during the control period and when UPPA had declined by 15%, 30%, and 45%. Graft histologic status was determined by endomyocardial biopsy at the time of RMBF determination. Mean duration of the study was 19.7 +/- 3.9 days. Rejection was documented in all animals. The UPPA was stable in native hearts; UPPA declined in the allografts after the onset of rejection. A biphasic change in allograft blood flow was seen. Initially RMBF increased as UPPA declined; a 30% to 45% reduction in UPPA was associated with a 41% increase in RMBF (p = 0.028 versus allograft control). Subsequently, a significant decline in blood flow was observed for reductions in UPPA greater than 45% (0.68 +/- 0.44 versus 1.07 +/- 0.47 mL.g-1 x min-1 for a 30% to 45% decline in UPPA; p = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)