External cardiac pacing: influence of electrode placement on pacing threshold.

External cardiac pacing is a recently reintroduced, effective method for emergency cardiac stimulation. The optimal electrode position and polarity for external pacing were determined in two groups of normal subjects. In six subjects there was no significant difference in pacing threshold when electrodes were positioned as follows: negative electrode in left parasternal region, positive electrode in right subscapular region; negative electrode in left parasternal region, positive electrode in left subscapular region; or negative electrode at cardiac apex, positive electrode in right parasternal region. In the remaining ten patients, pacing attempts were ineffective when electrode polarity was reversed. We conclude that exact electrode positioning is not crucial for external cardiac pacing, as long as the anterior or apical electrode is negative.