Peripheral Ramification of the Cardiac Conducting System

ciation of the anatomy of the cardiac conducting system by the cardiac surgeon re-pairing congenital cardiac defects has been previously stressed by Kirklin et al.1 and Truex and Bishof.2 In 160 patients under-going open-heart operation at this center, permanent complete heart-block occurred in two patients and right bundle-branch block (RBBB) in 15 patients.3 The development of complete heart-block ' 4or RBBB following cardiac surgery has been reported previously by other investigators.4-8 Electrocardiographic evidence of RBBB has been attributed to direct injury to the right bundle in the ven-tricular septum5 7 during repair of septal defects. The observation by Coggin6 that, in dogs, RBBB appeared at the time the right ventricular wall was incised, even though the septum was untouched, has been noted in a number of human patients at the University of Maryland. This paper presents the results of examination of the peripheral ramifications of the cardiac conducting system, seeking a possible cause of this phenomenon. Material and Methods Observations and dissections were imiade of the conducting systeins of 10 bovine, 2 laimbs', 5 goats', 5 canine, and 60 human hearts, all in the fresh state, as shortly after death as possible. Human hearts were studied 3 to 24 hours post mortem. Specific areas of the conduction system were fixed in 10 per cent formaldehyde, paraffin embedded, and sectioned 3- to 5-,t thick. Sections stained for glycogen by Best's carmine technique and for elastic and collagenous fibers by the Verhoeff-Van Gieson technique were subjected to histological examination. Injection of the conduction system of bovine and lanlb-hearts with India ink facilitate