Left Anterior Arborization Block Combined with Right Bundle Branch Block in Canine and Primate Hearts

Abstract

Interruption of anterior fibers of the left bundle branch system together with right bundle branch block was accomplished experimentally in canine and primate hearts. In both species the electrocardiographic effects included a major alteration of the mean electrical axis to a superior and anterior direction. Epicardial excitation was markedly delayed anteriorly, causing widening of the QRS complex in standard electrocardiographic leads. Normal outward intramural spread of excitation in anterior regions of the left ventricle was reversed after left anterior arborization block alone. After addition of right bundle branch block, intramural spread of excitation was again directed outwardly but was markedly delayed in endocardia] onset. Electrical effects of these blocks could be "corrected" individually or in combination by introducing synchronized electrical stimuli distal to each lesion. A scheme is proposed by which various forms of intraventricular conduction disturbance can be defined in terms of block of one or more divisions of a three-pronged system of rapid ventricular excitation.ADDITIONAL KEY WORDS intraventricular conduction disturbances left axis deviation masquerading block QRS widening bilateral bundle branch block epicardial excitation posterior precedence transmural excitation synchronous endocardial stimulation dog baboon• The electrocardiographic consequences of complete block of either the left or the right branches of the bundle of His are well established, but speculation existed regarding the significance of, subtotal interruption of these conduction pathways (1). Recent experimental studies established the effect of disturbances in anterior and posterior rami of the left branch system in the canine heart (2) and specifically confirmed the relationship This investigation was supported in part by Veterans Administration Clinical Investigator Program, Houston Veterans Administration Hospital, and by U. S. Public Health Service Research Grants HE-05435 and HE-10400 from the National Heart Institute.Accepted for publication November 27, 1967. of left anterior arborization block to left axis deviation in the primate (3). Several authors (4-7) speculated on the electrical phenomena which might derive from block of all the right bundle branch together with only a portion of the left bundle branch. However, morphologic data essential to corroboration were meager (8).The results described here demonstrate the characteristic features attending an anatomically verified combination of left anterior arborization block and right bundle branch block. Such features include not only a unique form of complexes recorded from standard electrocardiographic leads, but also marked alterations of observed epicardial and transmural patterns of excitation.Methods Studies on 24 mongrel dogs weighing about 15 kg and 10 baboons constitute the basis

Association of right bundle-branch block with left superior or inferior intraventricular block. Its relation to complete heart block and Adams-Stokes syndrome.

“…They assume that the underlying conduction abnormality frequently is interruption of the right bundle-branch and of the superior subdivision of the left bundle. Recent experiments on canine 436 Right Bufldle-branch Block with Left Superior or Inferior Intraventricular Block and primate hearts substantiate this assumption tion disturbances which may lead to complete (Watt et al, 1968). heart block, still remains undescribed.…”

“…heart block, still remains undescribed. This is To our knowledge, the association of left inferior probably due to the fact that the clinical concept of intraventricular block with right bundle-branch left inferior intraventricular block has been only block, as a sign of bilateral bundle-branch conduc-recently proposed by Pryor and Blount (1966 The concepts of these authors are mainly founded on experimental work which indicates that the terminal forces of the QRS complex are shifted inferiorly after laceration of the inferior division of the left bundle (Uhley and Rivkin, 1964;Watt and Pruitt, 1965 Fig. 2) whose successive tracings show left inferior intraventricular block alone, and associated with right bundle-branch block and advanced degree of atrioventricular block (lead III).…”

Left Posterior Fascicular Block in Canine and Primate Hearts

“…'-When appropriate, the right bundle branch was severed with a knife introduced into the right ventricular cavity through the anterior free wall. 2 Before and after left posterior fascicular block and again after right bundle-branch block, electrocardiograms were recorded from standard unipolar and bipolar extremity leads, from unipolar chest leads, from an esophageal (posterior) lead, and from atraumatic exploring epicardial leads.…”

Focal Lesions in the Canine Bundle of His: THEIR EFFECT ON VENTRICULAR EXCITATION

“…• In both canine and primate hearts, interruption of some, but not all, of the fibers in the left bundle branch and its terminal fascicular network at midseptal level delays excitation of that portion of the left ventricular wall supplied by the interrupted fibers (1)(2)(3)(4). This delay is reflected in specific, characteristic electrocardiographic changes in direct epicardial leads.…”

“…Left anterior fascicular block is reflected in electrocardiograms of humans by left axis deviation and is probably the commonest cause of that phenomenon (6,11). Combined with right bundle branch block, left anterior fascicular block produces a more extreme deviation of the mean QRS axis in a superior, anterior direction (3). Such combined block frequently is associated with fibrosis in the anterolateral portion of the ventricular septum (9,12) and often coincides with or precedes some degree of atrioventricular block (7,9,10).…”