Benefits of smaller electrode surface area (4 mm2) on steroid-eluting leads

The purpose was to test whether a reduction of pacemaker electrode surface area below 8 mm2 improves leads that elute steroid from the electrode tip to the surrounding myocardium. A standard-sized 8 mm2 lead with 1 mg dexamethasone was implanted in 12 patients and a lead with 4 mm2 electrode surface area and 0.5 mg dexamethasone in ten patients. Pacing threshold, impedance, and sensing threshold were measured at implantation and after 1, 4, and 12 weeks. Pacing thresholds were similar for both groups and were always less than or equal to 0.8 V at 0.5 msec pulse duration in all patients. Impedance was significantly higher (P less than 0.05) for the 4 mm2 lead (implantation: 726 +/- 119 ohms; 1 week: 596 +/- 71 ohms; 4 weeks: 624 +/- 68 ohms; 12 weeks: 643 +/- 56 ohms) than for the 8 mm2 lead (implantation: 422 +/- 43 ohms; 1 week: 402 +/- 48 ohms; 4 weeks: 439 +/- 57 ohms; 12 weeks: 449 +/- 61 ohms). R wave amplitudes did not differ between both groups; no sensing failure occurred at 5 mV sensitivity. Compared to the 8 mm2 lead the reduction of surface area to 4 mm2 did not influence pacing threshold, but resulted in a higher pacing impedance. The amount of pacing energy was lower in the smaller-sized electrode. For clinical impact, low pacing threshold and high impedance leads are the condition to implant pulse generators with smaller battery capacity.