CHRONIC VENTRICULAR PACING USING AN OUTPUT AMPLITUDE OF 1.0 VOLT

Thirty-seven patients (21 merle, 16 female, mean age 71 years) receive d identical DDD pacemakers. They also received the same bipolar ventri cular passive fixation electrode, which has a microporous tip of plati num-iridium, a surface area of 5.8 mm(2), and steroid elution. Eightee n months after implantation the ventricular charge threshold [mu C] wa s measured telemetrically at 0.5, 1.0, and 2.0 V, respectively. For th e 1.0 and 2.0 V amplitudes the pulse duration was increased until the charge per pulse [mu C] was twice the threshold value, thus giving a 1 00% safety margin in terms of charge (''safety charge''). Patients who had ventricular capture at 0.5 V were permanently programmed to 1.0 V (30/37 patients), while those who did not capture at 0.5 V were set t o 2.0 S' (7/37 patients). In both cases, the pulse duration was progra mmed according to the rationale of ''safety charge.'' During a routine follow-up period of 6 months, no complications were observed and none of the patients suffered from symptoms indicating loss of ventricular capture. Twenty-four-hour Holter recordings, obtained from all patien ts at the end of the follow-up with the output parameters unchanged, r evealed constant ventricular capture. In patients with chronic stable pacing thresholds and steroid-eluting low threshold leads who have cap ture at 0.5 V, chronic ventricular pacing at an output amplitude of 1. 0 V is feasible, and if seems to be safe if the pacing threshold is me asured as charge delivered per pulse and a 100% safety margin in terms of charge is programmed. Reducing the output amplitude to well below the battery voltage may increase pacemaker longevity.