True and false left anterior hemiblock: vectorcardiographic study.

For confirming the configuration of the QRS loop in left anterior hemiblock, 82 cases with the frontal QRS vector above minus 30 degrees were collected and classified by the configuration of the horizontal QRS loop. Thereafter, a comparison has been made between the configuration of the QRS loop in clinical cases and that in the authors' construction method, and the following findings for criteria of left anterior hemiblock are obtained. 1) The afferent limb of the frontal QRS loop is dislocated to the left and more superiorly. 2) The efferent and afferent limbs of the horizontal QRS loop are located left posteriorly. The configuration of the horizontal QRS loop is long and narrow and the direction of inscription is clockwise, a figure of 8 or counterclockwise. 3) Cases with the right posterosuperior dislocation of the afferent limb of the QRS loop is excluded from left anterior hemiblock.