Short-Term Threshold Behavior of Human Ventricular Pacing Electrodes: Noninvasive Monitoring with a Multiprogrammable Pacing System

Twenty-two patients were studied for 8 to 12 weeks following pacemaker implantation. A unipolar multiprogrammable pacing system was used to assess and compensate for early post-implant changes in pulse width threshold (PWT). Changes in PWT were estimated by noninvasive measurements of the lowest pulse width required for 100% capture at constant voltage. All patients showed an early increase in PWT. The magnitude of this change was unpredictable and ranged from 2- to 10-fold. For pacing, we selected an appropriate margin of safety to be a pulse width three times the PWT. During the study period, 4 patients showed critical increases in PWT, requiring reprogramming to an increased pulse width as above, whereas only one patient required lead repositioning. The majority of patients achieved a stable low PWT and were reprogrammed to a reduced pulse width. The programmable pacing system provides a safe accurate technique for monitoring early changes in PWT, defines the need for appropriate alterations in programmable functions, decreases the risk of early pacemaker failure, and offers promise for improved pacemaker longevity in many patients.