A NEW STEROID-ELUTING SCREW-IN ELECTRODE

A new lead design was tested that combined a small microporous steroid -eluting electrode with an insulated, exposed helix for active fixatio n. This lead (model 5078, Medtronic, Inc., group I, n = 10) was compar ed to a conventional model (model Y 60 BP, Biotronik) with a larger su rface of polished platinum-iridium, equipped with a fixed, noninsulate d screw but without steroid elution (group II, n = 10). The two lead m odels were studied in the atrial position of dual chamber pacing syste ms, which all had a tined ventricular lead (model 5024, Medtronic, Inc .), with essentially the same steroid-eluting tip as the new active fi xation lead design. Sensing and pacing data were recorded acutely and during 1 year of follow-up, via the telemetry of a Relay pulse generat or (Intermedics, Inc.). Intraoperatively, unfiltered atrial electrogra m amplitudes did not differ between groups (group I: 7.12 +/- 2.56 m V vs group II; 6.42 +/- 1.87 m V; P > 0.05), nor did sensing thresholds 1 year after implantation (group I: 5.33 +/- 1.70 mV vs group II: 4.2 6 +/- 1.40 mV, P > 0.05). Atrial pacing thresholds as measured during surgery at a pulse width of 0.5 msec were lower in group I (0.49 +/- 0 .15 V) than in group II (0.68 +/- 0.19 V, P < 0.05). From day 5 throug h day 360 of follow-up, the difference in atrial pacing thresholds was highly significant (P < 0.01), with a smaller peaking of early thresh olds and a much lower scattering of data for the steroid screw-in lead s than for controls. Chronic thresholds as measured 1 year postimplant in terms of minimum charge delivered for capture were 0.20 +/- 0.03 m uC in group I versus 0.54 +/- 0.11 muC in group II (P < 0.01). There w as no difference between groups on the ventricular level, both acutely and during follow-up. If the active fixation atrial lead was compared to its tined ventricular counterpart in group I, pacing thresholds on ly differed within the early days postimplant, but they were virtually identical from week 3 through 1 year. It is concluded that the novel pacing lead design effectively combines low energy pacing with more ve rsatility in electrode positioning by use of the active fixation mecha nism.