Peripheral Ramification of the Cardiac Conducting System

Peripheral Ramification of the Cardiac Conducting SystemBy WILLIAM G. ESMOND, M.D., G. ALLEN MOULTON, M.D., R. ADAMS COWLEY,

M.D., SAFUH ATTAR, M.D., AND EMIL BLAIR, M.D.

THE IMPORTANCE of a thorough appre-ciation of the anatomy of the cardiac

conducting system by the cardiac surgeon re-pairing congenital cardiac defects has beenpreviously stressed by Kirklin et al.1 andTruex and Bishof.2 In 160 patients under-going open-heart operation at this center,permanent complete heart-block occurred intwo patients and right bundle-branch block(RBBB) in 15 patients.3 The developmentof complete heart-block' 4or RBBB followingcardiac surgery has been reported previouslyby other investigators.4-8 Electrocardiographicevidence of RBBB has been attributed todirect injury to the right bundle in the ven-tricular septum5 7 during repair of septaldefects. The observation by Coggin6 that, indogs, RBBB appeared at the time the rightventricular wall was incised, even though theseptum was untouched, has been noted in anumber of human patients at the Universityof Maryland. This paper presents the resultsof examination of the peripheral ramificationsof the cardiac conducting system, seeking apossible cause of this phenomenon.

Material and MethodsObservations and dissections were imiade of the

conducting systeins of 10 bovine, 2 laimbs', 5 goats',5 canine, and 60 human hearts, all in the freshstate, as shortly after death as possible. Humanhearts were studied 3 to 24 hours post mortem.Specific areas of the conduction system were fixedin 10 per cent formaldehyde, paraffin embedded,and sectioned 3- to 5-,t thick. Sections stainedfor glycogen by Best's carmine technique and forelastic and collagenous fibers by the Verhoeff-VanGieson technique were subjected to histologicalexamination. Injection of the conduction systemof bovine and lanlb-hearts with India ink facilitated

From the Division of Thoracic Surgery, Depart-manet of Surgery, anid the Department of Pathology,University of Maryland School of Medicine, Balti-more, Maryland.

Supported by U. S. Public Health Service Grants1-2618 (C5) and H-5636 (C2).

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the tracing of sinall branches of the conductionsvstem. In dog-hearts, the conducting systemwas accentuated by treating the fresh specimenswith Lugol's solution.

ObservationsRight Ventricle

The bovine conducting system was promi-nent under the endocardium in both ventricles.When observed through a paraseptal cut fromthe pulnonic valve to the apex, the right bun-dle branch entered a prominent moderatorband, a cylindrical muscle from 0.25 to 1 cm.in diameter passing from the base of the pap-illary muscle of the conus to the base of theanterolateral papillary muscle (fig. 1). Injec-tion of its sheath with India ink demonstratedthis and numerous small branches to all parts.with a prominent branch toward the pulmonicvalve. The lamb-hearts had a similar largeimoderator band; in the goat-hearts, the mod-erator band was very fine. The dog-heart dif-fers in that the bundle descends directly alongthe septum to the septally attached aniteriorpapillary muscle; theniee, as branching trans-ventricular conducting bundles, to the ante-rior ventricular wall, where a prominentbranch aseends toward the pulmonic valve(fig. 2).Moderator bands are described with varying

frequency in the human heart. Human heartsfrom 60 consecutive autopsies revealed a mod-erator band which was freely traversing theright ventriele for varying, although fre-quently short, distances (fig. 3).

Histological examinatioll showed varyingamounts of Purkinje-like fibers traversing thebands between the bundle of His and the pap-illary muscle and anterior ventricular wall.Operative incision into the anterior wall, thenmoderator band, or the septal course of thebundle carries a high probability of producingvarving amounts of RBBB.

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Figure 3Human heart, right ventricle. Large moderatorband carrying the right bundle branch is shownconnecting the septum to the aKnterior wall of theright ventricle.

Figure 1Beef heart, right ventricle. Large moderator bandhas been tracnsected.

Figure 2Dog's heart, right ventricle, showing origin ofpapillary muscles on septal wall and transven-tricular conducting bundle (arrow) to anterior wall.

Left Ventricle

When the left ventricle was opened fromnthe mitral valve toward the apex between the


Figure 4Beef heart, left ventricle. Partial dissection of leftbundle branch and transventricular conductingbundles.

papillary muscles, the left bundle branch wasseen deseending the septum and was dissectedfrom beneath the junction of the right and

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Figure 5Human heart., left ventricle, demonstrating partialdissection of the left bundle branch, and demon-strating its continuation into the arborization ofthe transventricular cavity conducting bundle.

noneoronary aortic cusps (figs. 4 and 5). Itangled sharply over the muscular septum toreach the septal surface and descended be-neath the endocardium, branching into severalbundles which lie free in the ventricular cav-

ity in their course to the papillary mnuseles(figs. 6 and 7). Injection of the sheath of theleft bundle in bovine and lamb's hearts withIndia ink outlined the entire system, includ-ing many fine arborizations across the trabecu-lae carneae to the ventricular wall (fig. 8).

This descent and arborization into thetransventricular conducting bundles and thetrabeculae carneae was demonstrated in bo-vine, lamb's, goat's, dog's, and human hearts.Histological examination confirmed that Pur-kinje-type conducting elements in the bundleof His were in continuity with transventricu-lar conducting bundles of even less than 1-mm.

diameter (figs. 9 and 10). The elastic andconnective tissues of the endocardium and thebundle continued, and surrounded the trans-ventricular cavity conducting bundles. Con-tinuity of the Purkinje-like conduction fiberscould also be traced along trabeculae carneaeat the apex.The routine postmortem method of opening

human hearts by knife or enterotome fromwithin the cavity frequently severs thosebranches traversing the ventricular cavity.Careful incision between the papillary mus-cles and extension through the mitral valveis the best way to follow the ramifications ofthe conducting system descending the septumand its branches traversing the cavity to thepapillary muscles as free-lying bands.

DiscussionThe cardiac conduction system in man and

four species of mammals has a generally com-mon pattern, but with some specific differ-ences. In all species the right bundle branchtraverses a moderator band to reach the ante-rior ventricular wall.

Operative incision into the right ventricularwall in this vicinity carries the possibility ofinjury to these conducting fibers and of pro-ducing varying degrees of RBBB. This canbe minimized if one first makes a small inci-sion in the outflow tract, palpates the anteriorpapillary muscle, and extends the incisionlaterally to miss this structure.

Left bundle-branch transventricular cavityconduction bundles to the papillary muscleswere found in all species of mammalian heartsstudied, confirming the traditional concepts ofTawara9 and Holmes.10 The significance of the"pseudotendons" as part of the left bundlebranch to the papillary muscles was not ap-preciated by Glomset and Glomset."1

Apical left ventricular incisions for thepurpose of cannulation or insertion of dilatorscannot avoid the apical fine conducting net-work. Transventricular cavity bundles to thepapillary muscles, however, should be avoidedby careful insertion of cannulas or instru-ments.

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Figure 6Human heart, left ventricle, with unusually thick muscular transventricular cavitybundle (arrow) containing branch of conducting system to anterolateral papillary muscle.

Figure 7Huma,n heart, left ventricle, showing high take-off of transventricular conductingbundle to apex of posteromedial papillary muscle.


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Figure 8Beef heart, left ventricle. India-ink injection of left bundle branch and transventricularconducting bundles.

may be essential to ensure simultaneous con-traction of papillary muscles and ventricularwall in order to avoid overstretching of thepapillary muscles. This distribution appearsto afford a more direct oblique-radial and cir-cular route for impulses than is afforded bytraversing the septum to the apex and ascend-ing into the papillary muscles and ventricularwall. The presence of large amiiounts of elasticand collagenous fibers indicates some durabil-ity of these transventricular bundles, but dam-age by manipulation or instrumentation ispossible.

SummaryThe study of the peripheral distribution of

the right bundle branch in bovine, dog's,goat 's, lamb 's, and human hearts demonstratesan anatomical basis for the production ofvarying degrees of right bundle-branch blockon operative incision of the anterior wall ofthe right ventricle.The left branch of the cardiac conducting

system, with its transventricular cavity con-ducting bundles to the papillary muscles andthe ventricular wall in bovine, dog's, goat's,lamb's, and human hearts, offers an anatomi-

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cal basis for varying degrees of disturbancein left ventricular conduction due to operativeincision or instrumentation in the left ven-tricle. Comparative anatomical studies in manand animals show conducting fibers whichtraverse the ventricular cavities in structurespreviously termed pseudotendons or falsechords.

In man, the existence of these transventric-ular cavity conducting bundles has not beenemphasized, probably because of the tradi-tional methods of opening the heart atautopsy.The combined electrocardiographie and ana-

tomical concepts provide a useful backgroundfor caution in open-heart operation, leststretching during manipulative procedures orcutting these peripheral conducting bundlesproduces irrevocable conduction-damage.

AcknowledgmentWe wish to thank Mr. Lewis A. Jager and Miss

Ann V. Johnson for preparing the tissue sectionsand David G. Esmond for assistance in the dissections.

Figure 9Photomicrograph. Oblique section of a 1-mm. hu-man transventricular conducting bundle from theleft ventricle containing muscle fibers (light color)of the conducting system. (Verhoeff-Van Giesonstain, X 260.)

References1. KIRKLIN, J. W., HARSHBARGER, H. C., DONALD,

D. E., AND EDWARDS, J. E.: Surgical correc-tion of ventricular septal defect: Anatomicand technical considerations. J. Thoracic Surg.33: 45, 1957.

Figure 10Photomicrograph. Longitudinal section of a 1-mm. human transventricular conductingbundle from the left ventricle containing muscle fibers continuous with the leftbundle branch. (Verhoeff-Van Gieson stain, X 610)


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2. TRUEX, R. C., AND BISHOF, J. K.: Conductionsystem in human hearts with intraventricularseptal defects. J. Thoracic Surg. 35: 421, 1958.

3. SCHERLIS, L., AND LEE, Y. C.: Right bundle-branch block following open heart surgery. Amn.J. Cardiol. 8: 780, 1961.

4. DUSHANE, J. W., KIRKLIN, J. W., PATRICK, R. T.,DONALD, D. E., TERRY, H. R., JR., BURCHELL,H. B., AND WOOD, E. H.: Ventricular septaldefects with pulmonary hypertension: Surgi-cal treatment by means of a nmechanical pumilp-oxygenator. J.A.M.A. 160: 950, 1956.

5. DICKENS, J., MARANHAO, V., AND GOLDBERG, H.:Right bundle-branch block: Vectorcardiographicand electrocardiographic study of veentricularseptal defects following open heart surgery.

Circulation 20: 201, 1959.6. COGGIN, C. J., WAREHAM, E. E., AND SELVESTER,

R. H.: Postventriculotomy right bundle-branch

block: Its etiology (abstract). Circulation 22:

734, 1960.7. FISHER, J. M., THEILEN, E. O., JANUARY, L. E.,

AND EHRENHAFT, J. L.: Electrocardiographicsequelae of right ventriculotoMy in patients with

ventricular septal defects. Circulation 22: 280,1960.

8. KITTLE, C. F., SANTOS, E. M., AND DIMOND, E. G.:Persistent right bundle-branch block due topulmonic valvotomy and infundibulectomy. Am.Surgeon 22: 80, 1956.

9. TAWARA, S.: Das Reizleitungssystemii des Sang-stierherzeus. Jena, Fisher, 1906.

10. HOLMAES, A. H.: Auriculo-ventricular bundle inmammals. J. Anat. 55: 269, 1920-21.

11. GLOMSET, D. J., AND GLOMSET, A. T. A.: Mor-phologic study of cardiac coaiduction systemin ungulates, dog and man. Am. Heart J. 20:677, 1940.


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ATTAR and EMIL BLAIRWILLIAM G. ESMOND, G. ALLEN MOULTON, R. ADAMS COWLEY, SAFUH

Peripheral Ramification of the Cardiac Conducting System

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1963 American Heart Association, Inc. All rights reserved.

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