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Circulation, Vol 54, 1010-1013, Copyright © 1976 by American Heart Association

ARTICLES

Left anterior and left posterior hemiblock in tricuspid atresia and transposition of the great vessels: observations and electrocardiographic nomenclature and electrophysiologic mechanisms

J Schatz, E Krongrad and JR Malm

A patient with tricuspid atresia and characteristic electrocardiographic features of counterclockwise and superiorly oriented frontal plane QRS loop (left anterior hemiblock) is presented. Operative intervention resulted in a clockwise and inferior rotation of the frontal QRS loop (left posterior hemiblock) without the development of complete left bundle branch block. This observation suggests that the electrocardiographic pattern of left anterior hemiblock may result from other mechanisms in addition to block of the left bundle branch fibers oriented toward the anterior part of the left ventricle. The case further suggests that electrocardiographic patterns of apparent A- V conduction defects may not be at all associated with true block in the A-V conduction system. Further, it emphasizes the fact that various electrophysiologic mechanisms may account for identical electrocardiographic patterns.