Behavior of stimulating threshold according to surface area of various electrodes at initial implantation and replacement

Abstract

In 150 patients with a pacemaker, voltage and current at threshold, electrical impedance and amplitude of the QRS complex were measured at initial implantation and replacement.
Comparison was made between myocardial and endocardial types according to the surface area.
At initial implantation, each patient showed a voltage threshold less than 0.9 volt. The threshold elevated to 2.0 to 2.3 volt at replacement (P<0.001). No significant differences in the increse, however, were seen clinically in types or surface area.
In cases in which a high stimulating threshold was recorded at replacement, the threshold was measured at various pacing pulse width. As the pulse width increased, i.e., amount of electrical energy increased, the threshold voltage decreased. though significant changes in the threshold were uncommon in the chronic stage, a few patients indicated a sudden increase. The fact should be kept in mind seriously in the management of patients with a pacemaker.