A randomized controlled clinical study to quantify the effect of small changes in the design of pacing electrodes on threshold voltages.

A double-blind randomized study of three pacing leads, identical in all ways except for the surface of their electrodes, is presented. The leads were implanted in 30 patients. Ten patients (Group A) received a standard Laserdish lead (dish electrode with laser pores), 10 patients (Group B) received a platinum-iridium coated modified Laserdish electrode, and 10 patients (Group C) received a platinum-iridium coated dish electrode identical to that in Group B except for the absence of laser pores. All leads were implanted by the same operator via the subclavian vein and all patients received an Optima MPT pulse generator. Direct measurement at implantation of pacing threshold and endocardial electrograms showed no significant difference between the three groups (mean +/- standard deviation voltage thresholds 0.30 +/- 0.06 V at 0.5 ms and 0.21 +/- 0.05 V at 1.0-ms pulse durations, R wave amplitude 7.6 +/- 3.2 mV). Significant differences (P = 0.001) were found in threshold impedances at implant (Group A 940 omega, Group B 782 omega, Group C 673 omega). Ten further measurements of voltage threshold were made over the next 2 years. Overall, at a pulse duration of 1.0 ms, a significantly reduced (P < 0.025) threshold voltage was found for both the electrode with pores and platinum-iridium coating compared with pores alone (20%), and with pores and platinum-iridium coating compared with the coating alone (18%). There was no significant difference between using platinum-iridium alone or pores alone. We have shown that a controlled randomized study, using electrodes that are identical except for the characteristics being assessed, can enable effects of small differences in electrode design to be quantified.