[Stable stimulation impedance of steroid electrodes in various impulse amplitudes: indications for low polarization of the electrode-myocardium interface]

The reduction of electrode surface area leads to an increase of pacing impedance which may be caused either by higher tissue resistance or by greater polarization occurring at the electrode-myocardium interface. The impedance of steroid-eluting leads with both 8 mm2 surface area (CapSure 4003, Medtronic n = 12) and with 4 mm2 (030-368, Telectronics, n = 8) were compared to the impedance of a high polarizing Elgiloy lead (PE 60/4 DN, Biotronik; n = 7). All leads were connected to the same unipolar VVI pacemaker (Pasys 8329, Medtronic). Pacing impedance was measured at 0.8, 1.6, 2.5, 5.0, and 8.0 volts pulse amplitude and at 0.05, 0.25, 0.5, 1.0, 2.0 msec pulse duration. Impedance of the Elgiloy lead was constant at 0.05 and 0.25 msec, but increased at longer pulse durations for pulse amplitudes below 5.0 volts. Both steroid-eluting leads had constant impedance at each pulse duration. The impedance of the 4 mm2 lead was significantly higher than of the 8 mm2 lead. In contrast to the Elgiloy lead, impedance of the steroid-eluting leads is not influenced by pulse-dependent factors such as polarization, indicating that the higher impedance of the 4 mm2 steroid-eluting lead is caused by a higher tissue resistance and not by greater polarization.