Initial experience with 1.5-mm2 high impedance, steroid-eluting pacing electrodes

In this human study, 21 atrial and 62 ventricular 1.5-mm2 unipolar steroid-eluting pacing electrodes were implanted in 64 patients. Pacing thresholds, lead impedance, and sensing measurements were measured via pacemaker telemetry within 24 hours postimplant, and at 1, 2, 3, 4, 6, 12, 24, and 52 weeks. Acute pacing impedances measured via a pacing systems analyzer were 1,039 +/- 292 (atrial) and 1,268 +/- 313 ohms (ventricular). A 10%-15% decline in the mean telemetered atrial and ventricular pacing impedances was observed at 1 week, but thereafter remained stable. Acute pacing thresholds at 0.5 ms were 0.5 +/- 0.3 V (atrial) and 0.4 +/- 0.1 V (ventricular). Filtered P and R wave amplitudes were 3.7 +/- 2.3 mV and 14.9 +/- 5.9 mV, respectively. In 21 patients, no complications related to the atrial electrode were observed. Of 62 patients with ventricular electrodes, 4 patients (6%) experienced complications and required surgical intervention. On these, causative factors included micro-dislodgment (1 patient), and perforation (1 patient). Sudden unexplained exit block occurred late (> 6 weeks) in two patients. In the remainder of patients, pacing thresholds and sensed electrogram amplitudes remained stable throughout the 52-week follow-up period.

The present study validates that smaller surface (i.e., 1.5 mm2) steroid-eluting electrode designs offer excellent pacing and sensing performance with significantly higher pacing impedances. Although questions remain as to the cause of late exit block in two patients in this series, this relatively small surface electrode design offers promise toward achieving greater pacing efficiency and a theoretical 13%-16% (minimum) enhancement in permanent pacemaker longevity.