A dynamic electrical record of the pathway of human His bundle activation from surface mapping

Body surface potential maps of human His bundle activity have been difficult to product for two reasons: (1) The peak surface potentials are often less than 5 muv, and (2) the simultaneous atrial repolarization potentials frequently exceed 100 muv. We have therefore amplified surface signals 25 times the standard gain of 1000, and then removed by cross-correlation the static pattern of atrial repolarization for serial 1-msec maps of the P-R segment in five normal men. A consistent finding emerged: a positive anterior chest peak appeared 40 msec before QRS onset, and then-within 10 msec-spread out into a long, low transverse mound before disappearing in 5 more msec. The map data were analytically converted to serial electrical sources: the center of electrical activity moved first slightly down, then directly forward, before retracing its path and disappearing. The retrace and accompanying surface spread-out strongly suggests diverging dipolar sources. Thus the data fit a simple heart source which moves anteriorly and then breaks into two (right and left)-as expected from activation of the bundle of His and its bifurcation into left and right bundle branches.