[Threshold in surveillance of pacemaker wearers]

Measurement of the threshold is important in the follow-up of pacemaker patients; it permits the assessment of the safety margin, between, on the one hand, the electrical impulse, and, on the other, the possible output of the pacemaker. In fact, one can only rarely obtain relative threshold measurements in the clinical situation using non-invasive techniques; this ability is limited to some units made only by a few pacemaker manufacturers. A decrease in the margin of safety may result from two main causes: an increase in the absolute threshold or a decrease in the pacemaker pulse amplitude due to depletion of the cells, or to electronic failure. If safety margin is reduced, and operative procedure is required to achieve the correct diagnosis by precise measurements of the absolute threshold.