Automatic pace-sense polarity switch as an indicator of early lead corrosion: The usefulness of impedance trend graphing

A rate responsive dual chamber pacemaker system (Medtronic Inc.) was implan ted without complications. At 6-week postimplantation a routine pacemaker c heck showed a spontaneous switch from programmed bipolar pace-sense to unip olar pace-sense on the atrial and ventricular leads. Pacing and sensing thr esholds were not significantly changed from implantation. The atrial and ve ntricular lead impedances increased from 680 and 720 ohms at implantation t o 1,290 and 2,400 ohms, respectively. The device was reprogrammed to bipola r pace-sense and the continuous lead telemetry trend option was programmed On. Evaluation of the system 1 month later revealed a decrease in atrial an d ventricular lead impedances, 680 and 2,100 ohms, without a change in pace -sense polarity. One month later, the lead polarity had again switched from programmed bipolar to unipolar pace-sense. The lead trend data revealed st able atrial impedances with sporadic increases in the ventricular lead impe dance to values > 3,000 ohms. The pacemaker lead system was invasively inve stigated and visible gross corrosion of the ventricular lead distal connect or pin was discovered.