Bipolar Intramyocardial Electrogram From an Implanted Telemetric Pacemaker for the Diagnosis of Cardiac Allograft Rejection

Noninvasive detection of acute cardiac allograft rejection remains a challenge. Analysis of the epicardial electrogram transmitted by unipolar telemetric pacemaker can be of help in the detection of rejection with myocytolysis but is hampered by extracardiac factors. Instead, the contribution of a bipolar pacemaker for this purpose was studied. The bipolar peak‐to‐peak amplitude of epicardial electrograms (BPPA) from 25 patients implanted with a bipolar pacemaker at the time of heart transplantation was measured at the time of endomyocardial biopsies. BPPA was expressed as a percent of the baseline value. A voltage drop of more than 10% was considered an indication of rejection. Of 118 biopsies, 80 were free of rejection and 38 showed mild to moderate rejection (Grade 1A = 12; Grade 1B = 17; Grade 2 or 3 = 9). The mean value of BPPA was less for grade 2 biopsies (86.4 ± 17%) than for biopsies with no or mild rejection (101.3 ± 14.3% for Grade 0, 101.4 ± 13.8% for Grade 1A, and 98.6 ± 18% in Grade 1; P < 0.05). Diagnostic concordance between BPPA measurement and biopsy results increased with the histological severity of rejection (Grade 1A = 1/12, Grade 1B = 5/17, Grade > 2 = 7/9). Acute rejection was diagnosed with a sensitivity of 34% for Grade 1A, 46% for Grade 1B, and 78% for rejection episodes with myocytolysis (Grade ≥ 2). Specificity remained approximately 90% for all histologic grades. Overshoot after treatment was regularly observed when rejection was associated with a BPPA decrease of more than 10% (8 of 9), however uncommon, if the corresponding BPPA values were < 10% (2 of 13). These results were obtained with a variability of < 4% with moderate exercise, fever, pericardial effusion, or cytomegalovirus infection. Analysis of the bipolar epicardial electrogram transmitted by the telemetric function of a pacemaker implanted at the time of transplantation allows the detection of Grades 2–3 rejection and the monitoring of treatment efficacy. The limitations encountered in the detection of lower grade rejections might be minimized with the use of multiple bipolar derivations.