The "SPEM" (Studio Policentrico Elettrocateteri Membrane): a multicenter study on membrane leads

SPEM is a multicenter randomized double-blind study performed to test the acute and chronic electrophysiological behavior of three different ventricular leads: (1) an ion exchange membrane with 30-microgram dexamethasone elution in a contoured activated carbon tip lead (Membrane 1400T, 30 patients); (2) the same lead design without steroid (Membrane 1401T, 24 patients); and (3) the same lead design without steroid or membrane (control group, 27 patients). Twenty-three of the 81 patients were women; the mean age for all patients was 74 +/- 10 years. Parameters are calculated both in uni- and bipolar configuration at implant and at follow-up after 1, 5, 15, 30, 90, 180, and 360 days. Implant threshold (chronaxie = 0.413 +/- 0.280 ms, rheobase = 0.264 +/- 0.099 V), signal amplitude (13.45 +/- 5.87 mV), and slew rate (2.05 +/- 1.38 V/s) reveal no significant differences. Pacing impedance values both at implant (unipolar 571 +/- 165 omega; bipolar 605 +/- 123 omega) and at follow-ups (unipolar 480 +/- 72 omega; bipolar 518 +/- 75 omega) are slightly lower in the unipolar configuration. At 15 and 30-day follow-ups, control group and nonsteroid leads show a higher threshold value growth (in unipolar from 0.16 +/- 0.11 to 1.19 +/- 0.85 microJ; in bipolar from 0.18 +/- 0.13 to 1.24 +/- 0.88 microJ) than the membrane steroid leads (in unipolar from 0.13 +/- 0.11 to 0.70 +/- 0.39 microJ; in bipolar from 0.23 +/- 0.32 to 0.76 +/- 0.36 microJ); the threshold of nonsteroid leads decreases after 1-3 months and it settles at the same threshold level of the leads with membrane and steroid (in unipolar 0.60 +/- 0.33 microJ; in bipolar 0.55 +/- 0.26 microJ), which has been stable since the first month. The ion exchange membrane is effective in reducing the chronic pacing threshold like acute steroid elution at low doses, but membrane alone does not prevent an acute pacing threshold increase through the first month postimplant.