[An inordinate elevation in pacing threshold after myocardial electrode implantation]

An inordinate elevation in pacing threshold beyond a maximal output of the pulse generator was observed in 4 patients during the acute interval following permanent pacemaker implantation using a myocardial electrode. Pacemaker implantation was performed in these patients (9 months, 11 months, 5 years and 32 years of age) for the treatment of brady-arrhythmias (complete A-V block or atrial fibrillation) developed following open heart surgery. In two infants, hypopotassemia caused transient pacing failure due to an increase in threshold over 5 volt. In other two patients, threshold increased to levels more than 10 volt within 36 and 12 days probably due to unsuitable pacing site, and then the pulse generators were removed. It is important to measure threshold periodically after permanent pacemaker implantation and to consider the possibility of an inordinate elevation in threshold.