Conduction disturbances of the left bundle branch system and their relationship to complete heart block: I. A review of experimental, electrophysiologic and electrocardiographic aspects

Interruption of the normal ventricular excitation process occurring in one or more of the three main divisions of the conduction system may determine specific electrocardiographic patterns. Patterns as well as initial, mean and terminal QRS vectors are presented for diagnosis of an isolated block in each of the three divisions. The experimental and clinical basis for each diagnosis is reviewed. The electrocardiographic diagnosis of block in each of the two divisions of the left bundle in the presence of right bundle branch block is reviewed, and the association of these conduction defects with myocardial infarction is illustrated. Also, the electrocardiographic basis for identification of divisional left bundle branch as opposed to conventional (predivisional) left bundle branch block is discussed. Because of the confusing terminology previously utilized and the lack of pathologic specificity of conduction disturbances affecting the divisions of the left bundle, it is recommended that the terms superior and inferior peri-infarction block be abandoned and the terms left anterior and posterior fascicular block be considered. These terms are anatomically and electrophysiologically correct and do not imply etiologic diagnoses.