Precordial Pacing Windows

The threshold peak current for cardiac pacing with 10 ms rectangular pulses applied to precordial electrodes was determined in 18 anesthetized dogs (average weight 20.8 kg). The entire left and right precordium was mapped with a 1 cm diameter (cathode) electrode, paired with a 10 cm diameter reference electrode on the opposite chest. It was found that the lowest current required for pacing corresponded to the region of the apex beat on the left chest. At this site the average pacing threshold with the 1 cm electrode was 34.3 mA (peak). No sharply defined low pacing current area was found on the right chest, indicating that the location for the right chest electrode is not critical. The term "pacing window" is introduced to identify the region on the precordium where the pacing threshold is lowest. Studies were also performed to determine the manner in which the pacing current increased as electrode diameter was increased beyond the diameter of the pacing window. It was determined that little is to be gained with a left chest electrode larger than 5 cm in diameter in this animal study.