[Stimulation thresholds of implanted cardiac pacemakers (author's transl)]

The Vario-pacemaker EM 169 makes it possible, without additional equipment, to determine stimulation thresholds after implantation. A study on 149 patients with implanted pacemakers demonstrated characteristic temporal changes in stimulation threshold: starting with a mean value of 0.57 +/- 0.18 V on implantation, a maximal value of 1.93 +/- 0.66 V to 2.00 +/- 0.58 V was reached between the eighth and fourteenth days. The threshold remained constant at this level for a time and then oscillated downwards from the third month onward to values of about 1.55 to 1.70 V. However, when the electrode was dislodged or dislocated, there was in most instances an increased threshold and, during the same test, variations in threshold values. In general, electrode dislocation could be diagnosed in time with the vario-principle, before failure of stimulation at maximal voltage of 5.2 V. In 17 of 140 cases of implantation (12%) the electrode position had to be revised: in 13 electrode dislodgement was diagnosed even before failure of stimulation at full voltage of 5.2 V. The reported results suggest that occurrence of an exit block is always due to electrode dislodgement. In addition, it is clear retrospectively that in most cases of dislocation primary fixation of the electrode in the trabeculations of the right ventricle had been unsatisfactory.