[Comparative studies of thresholds after implantation of pacemaker leads of different size (author's transl)].

Within the first 14 days after implantation, thresholds were measured at three transvenous pacemaker electrodes with different surface areas. It should be verified, 1. to what extent a correlation existed between maximal threshold increase and electrode surface, 2. how electrode impedance and 3. how the amplitudes of the R-wave voltages developed. The results were: At initial implantation, thresholds were all the lower the smaller the electrode-surface area was. On overage, 9-10 days after implantation the highest thresholds were reached. Thereby, in small surface area electrodes the threshold-increase factor was greater than in larger ones. In all cases the current threshold increase exceeded that one for voltage thresholds. 14 days later, thresholds had dropped again compared to the maximum. And this decrease was depending on the electrode-surface area also. The electrode impedance decreased after implantation to rise later on once more to 80-88% of the original value. The magnitude of the detected R-wave was independent on electrode-surface area. Indeed, using small surface electrodes, signal reductions up to 50% could be found. But 14 days later they reached again 80-95% of the initial amplitude. The key finding there is that when applying small surface-area electrodes and presuming suitable initial thresholds it seems to be possible to connect low-output pacemakers (output 5,4 V and impluse duration 0.25 ms or 4 V at 0.5 ms) to those electrodes. By this reduction of the safety margin, a considerable increase in pacemaker lifetime could be achieved.