On the absolute magnitude of the human lead vector.

Twelve cases with temporary artificial pacing were used to investigate on the efficacy of a bipolar current source within the heart to generate potential variations in Frank lead ECGs. A constant current, subthreshold square pulse was applied to the catheter electrodes and the artefact was recorded with the Frank system. Assuming that the Frank system was normalized and orthogonal, the lead vector magnitude was calculated as 0.58 ohm/cm on the average. The value of the lead vector was inversely related to the thorax size. The direction of the vector determined from the recorded potentials approximated the direction of the catheter tip on the X-ray film. In addition, similar measurements were made with a homogeneous torso model and the results were compared with those of clinical cases.