INFLUENCE OF PROGRAMMED SAFETY MARGINS FO R PACING ON THE LONGEVITY OF MODERN DUAL-CHAMBER PACEMAKERS

In 55 consecutive patients with the same dual chamber pacemaker (Relay , Intermedics) and different pacing leads, the influence of different safety margins for pacing on battery current was investigated. 2.8 +/- 0.9 years after implantation, atrial and ventricular pulse-width thre sholds (t(RS)) (ms) were determined at 0.5, 1.0, and 2.0 V, and the ch arge delivered at threshold was telemetered. If t(RS) was < 1.50 ms at 0.5 V, an amplitude of 1.0 V was programmed in the atrium and the ven tricule; if t(RS) was < 1.50 ms at 1.0 V, then an amplitude of 2.0 V w as chosen. Two times the charge threshold (2 X Q(RS)), two times the v oltage threshold (2 X U-RS), and three times the pulsewidth threshold (3 X t(RS)) were programmed as the safety margins for pacing. With eve ry safety margin, battery current (I-Bat) (mu A) was averaged from tel emetric readings in D00 mode with 70 bpm. I-Bat was significantly lowe r with 2 X Q(RS) as compared with 2 X U-RS (13.43 +/- 1.0 vs. 14.20 +/ - 1.2 mu A, p < 0.01) and as compared with 3 X t(RS) (13.99 +/- 1.2 mu A, p < 0.05). Pacemaker longevity derived from these current data was significantly longer with 2 X Q(RS) (112 +/- 8 months) as compared wi th 2 X U-RS (106 +/- 9, p < 0.01) and as compared with 3 X t(RS) (108 +/- 8, p < 0.05). If current consumption is compared intraindividually in dependance on the programmed amplitude, battery current is signifi cantly lower at 1.0 V as compared with 2.0 V resulting in a mean reduc tion of 0.63 mu A (-4.9%, p < 0.05) and an average gain in longevity o f 5 months. This applies to every safety margin tested. Differences in battery current caused by the safety margins will translate into a gr eater gain in longevity in future pacemaker models with reduced intern al current consumption.