[Threshold changes in chronic transvenous cardiac pacing]

Alterations in stimulation threshold in long term transvenous cardiac pacing were recorded by serial measurements in 33 patients with EM 169 "Vario" pacemakers and additionally in 286 patients at operative revisions up to 6 years post implantation. A rapid threshold increase within the first 4 weeks was followed by stabilization at 160% of initial value. After about 1 1/2 years a further continuous increase of threshold with an annual rate of 15% occured. Prognostic calculations in individual cases, however, seem to be difficult because of frequent and considerable variations.