Assessment of long-term stability of chronic ventricular pacing thresholds in steroid-eluting electrodes

Sixteen patients with Medtronic 4003 steroid-eluting electrodes implanted in the ventricular position were followed over 5 years. In each patient a special type of Medtronic 2443 pacemaker was implanted to allow programming of output at 1.35 V. Chronic threshold values in these patients measured at an output of 1.35 V were stable over the first 18 months of follow-up. Mean values were: 0.06 +/- 0.03 msec at 6 months and 0.08 +/- 0.02 msec at 18 months; these did not differ from each other significantly. However, during the period from 18 to 36 months postimplantation, a significant increase in mean pacing threshold was observed: 0.08 +/- 0.02 msec at 18 months postimplantation versus 0.14 +/- 0.05 msec at 36 months (P < 0.01). After 36 months, the chronic pacing threshold remained stable until the end of the 5-year follow-up period. Further long-term study of chronic threshold behavior of steroid-eluting electrodes measured at low amplitudes is warranted.