Time Course of Transvenous Pacemaker Stimulation Impedance, Capture Threshold, and Electrogram Amplitude

To examine the time course of atrial and ventricular stimulation impedance, capture threshold, and electrogram amplitude, we obtained noninvasive telemetric data in 63 patients who underwent implantation of unipolar, endocardial pacing leads and a second‐generation dual chamber pacemaker with expanded bidirectional telemetry, including stimulation impedance, endocardial electrograms, and automatic capture threshold determination. On follow‐up of 9–20 months [mean, 15 months], all but six patients continued to pace in the DDD mode. To validate measurements made with telemetry, invasive measurements made directly with a pacing system analyzer at time of implant were compared with immediate postimplant telemetric measurements. Significant correlation of acute stimulation impedance was noted in both atrial (r = .7, p < .001) and ventricular (r = .8, p < .001) lead systems. The atrial stimulation impedance decreased from 538 ohms at implant to 471 ohms at 13 months (p < .01); the ventricular stimulation impedance similarly declined from 545 ohms to 485 ohms at 13 months (p < .0l). Capture thresholds peaked at one month, then declined: atrial, 1.2 V at implant vs 2.2 V at 1 month (p < .008) and 1.4 V at 13 months; ventricular, 1.1 V at implant vs 1.9 V at 1 month (p < .001) and 1.3 V at 13 months. There were no significant changes noted in atrial or ventricular electrogram amplitude following implantation. We conclude that there is close correlation of invasive recordings with those made telemefrically with this pacemaker at time of implant. Chronic atrial and ventricular stimulation impedances gradually decline for at least one year following implant, while electrogram amplitude in both chambers remains unchanged. Atrial and ventricular capture thresholds increase within one month after implant and thereafter decline for at least one year, but not to implant levels. Expanded bidirectional telemetry with such second‐generation units allows more precise and efficacious long‐term appraisal of the pacemaker‐myocardium interface.