Bundle branches

Abstract: The histopathological findings are reported in 11 cases of congenitally corrected transposition. For the purposes of this investigation, only hearts with a well-formed septum separating two ventricular sinuses were classed as corrected transposition. We did not, therefore, study any examples of single ventricle with inverted outlet chamber. Five of the cases formed the basis of a preliminary report, in which the distribution of conducting tissues in the anomaly was shown to differ from that reported in previous investigations. The six new cases confirmed this distribution. Thus, in all cases, the connecting atrioventricular node was anteriorly situated in the right atrium at the lateral junction of pulmonary and mitral valves. An anteriorly situated bundle descended into the morphologically left ventricle (right-sided) and encircled the anterolateral quadrant of the pulmonary outflow tract before descending on the anterior septum and bifurcating. The bundle branches were inverted. This distribution was ob...

Abstract: In the formed heart, it is convention to distinguish working myocardium (the primary function of which is contraction) from the conduction system (the primary function of which is the generation and conduction of the electrical impulse). The conduction system comprises separate components with distinct functions. The SAN, which contains the leading pacemaker, generates the impulse. The impulse is subsequently conducted, via the atrial myocardium, which in this sense is part of the conduction pathway as well, toward the AVN. With a delay, the impulse is then rapidly transmitted from the AVN via the bundle branches and PPN to ensure a coordinated activation of the ventricular myocardium from apex to base. Classic reports cover the anatomy,1 pathology,1 and histology2 of the adult and developing conduction system. The myocytes of the conduction system share with those of the ordinary working myocardium four basic elements: (1) contraction, (2) autorhythmicity, (3) intercellular conduction, and (4) electromechanical coupling. In the early embryonic heart tube, an ECG, similar to an adult ECG, can be recorded, indicating the presence of sequentially activated chambers.3 Given this observation, it is as confusing to accept the presence of a conduction system because it is functionally present as it is to deny its existence because it is not morphologically recognizable. Rather, it is of paramount importance to appreciate that the arrangement of myocyte populations, with distinct contractile, conductive, and pacemaking properties, establishes the coordinated activation of the heart. Departures from these tenets have led to a confusing and fruitless search for so-called “cardiac specialized tissues” during development. The obvious key question is how this arrangement is being achieved. Early cardiac development starts with the formation of a primary heart tube from the cardiogenic mesoderm (Fig 1⇓); this topic has been reviewed recently.4 The primary heart …

Abstract: The relationships among the His bundle, the origin of both bundle branches, and the interventricular (IV) septum were examined histologically in 32 human hearts, and the entire bundle branch systems were delineated in 13 of these. The His bundle in five hearts traversed the right IV septal crest, and the LBB origin was a very narrow stem (maximum 1.5 mm in cross-section) crossing from right to left through the inferior margin of the membranous septum. Proximal LBB anatomy was extremely variable, demonstrating multiple fiber groups which fanned out over the entire left septal surface. The LBB did not divide into two discrete divisions without multiple interconnections. The RBB formed an obtuse angle with the His bundle in 27 of 32 hearts. In those five hearts with "right-sided His bundles," the right bundle branch was a direct continuation. The clinical, electrophysiologic, and electrocardiographic implications of these anatomical observations are discussed.