A FRACTALLY COATED, 1.3 MM(2) HIGH IMPEDANCE PACING ELECTRODE

Minimizing the geometric surface area of pacing electrodes increases i mpedance and reduces the current drain during stimulation, provided th at voltage (pulse-width) thresholds remain unchanged. This may be feas ible by coating the electrode surface to increase the capacity of the electrode tissue interface and to diminish polarization. Ten unipolar, tined leads with a surface area of 1.3 mm(2) and a ''fractal'' coatin g of lridium (Biotronik SD-V137) were implanted in the ventricle, and electrogram amplitude (unfiltered), slew-rate pacing threshold (0.5 ms ), and impedance (2.5 V; 0.5 ms) were measured by the 5311 PSA (Medtro nic). On days 0, 2, 5, 10, 28, 90, 180, 360 postimplant, sensing thres hold (up to 7.0 mV, measuring range 1-14 mV on day 360 only) and the s trength duration curve (0.5-4.0 V; 0.03-1.5ms; steps: 0.5 V; 0.01 ms, respectively) were determined, the minimum charge delivered per pulse (charge threshold), and the impedance were taken from pacemaker teleme try (Intermedics 294-03). Data were compared with those of an earlier series of 20 unipolar, tined TIR-leads (Biotronik) with a surface area of 10 mm(2) and a ''fractal'' coating of titanium nitride. With the m odel SD-V137 versus TIR, intraoperative electrogram amplitudes were 15 .1 +/- 6.1 versus 14.4 +/- 3.9 mV CNS), slew rates 3.45 +/- 1.57 versu s 1.94 +/- 1.06 V/s (P < 0.05), pacing thresholds 0.16 +/- 0.05 versus 0.52 +/- 0.15 V (P < 0.01) and impedance measurements 1,136 +/- 175 v ersus 441 +/- 73 Omega (P < 0.0001), respectively. During follow-up, s ensing thresholds were the same with both leads. Differences in pulse width thresholds lost its significance on day 28 but resumed on defy 3 60 (SD-V137: 0.08 +/- 0.04 ms; TIR: 0.16 +/- 0.06 ms at 2.5 V; P < 0.0 2). With an electrode surface of 1.3 mm(2), charge per pulse and imped ance consistently differed from control, being 0.15 +/- 0.15 versus 0. 66 +/- 0.20 mu C(P < 0.001) and 1,344 +/- 376 versus 538 +/- 79 Omega, respectively, one year after implantation (P < 0.0001). In summary, ' 'fractally'' coated small surface electrodes do not compromise sensing ; by more than doubling impedance against controls they offer pacing t hresholds (mainly in terms of charge) that are significantly lower tha n with the reference electrode.