The ventricular gradient and altered ventricular activation patterns

The ventricular gradient vector was determined in normal persons and in cases with left and right bundle branch block (BBB) by means of the best fit method from body surface potential mapping data. Similar measurements were also made in cases with artificial ventricular pacing and the G vector during sinus rhythm was compared with that of the paced beats. Results indicated that the magnitude of the G vector in cases with BBB was smaller than in normal persons. The directional change in the G vector was found to be along the direction of the QRS change in the majority of cases with left BBB. In right BBB, the direction of the G change was variable but the angle between the QRS change was less than 90 degrees on average. Following right ventricular pacing a small increase of the G magnitude was observed acutely, which was opposite in direction to the QRS change. Possible mechanisms are discussed. The G changes in left and right BBB are considered to be based on certain chronic processes, different from those involved in the acute immediate effect of altered activation.