Intramyocardial electrogram variability in the monitoring of graft rejection after heart transplantation.

The ventricular evoked response is a well-standardized electrophysiological signal that can be used for noninvasive, long-term cardiac transplant monitoring. Rejection-sensitive and infection-specific parameters extracted from intramyocardial electrograms correlate with clinical results. The influences of pacing rate, transition from intrinsic to paced rhythm and positional changes on the diagnostic parameters were studied. Increasing the pacing rate shortened the ventricular evoked response and directly influenced the infection specific parameter. The rejection-sensitive parameter remained stable at pacing rates between 100 and 120 beats/min. Measurements made immediately after the patient assumed a supine position and after switching to paced rhythm showed a decrease in the rejection-sensitive parameter. A change in position from supine to upright did not influence the rejection-sensitive parameter, but higher values were measured after returning to the supine position. In conclusion, noninvasive recordings of the ventricular evoked response for monitoring of cardiac allograft should be done at the same time of day, at the same pacing rate, and with the patient resting for at least 5 minutes before measurements are made.