Variation in the precordial QRS transition zone in normal subjects.

From body surface potential map data for 51 normal young men (with QRS axis between 0 and 90 degrees) both the spatial QRS area vector and the isoarea map of the QRS were obtained. Acting on Grant's assumption that the transition zone defined a plane perpendicular to the spatial QRS vector, we determined the angular shift in altitude and azimuth required to move the spatial vector of each individual to the position of the group mean. We then shifted the precordial map of the transition zone of each individual with the same angular correction. These resulting transition zone boundaries clustered much closer to each other, but did not move into absolute coincidence. We interpreted the nearness-to-fit to be an estimate of the degree to which the precordial QRS configurations conformed to a common simple vector or dipolar pattern.