Surgical Pathology of the Conducting System ofthe

25 Pages·2007·14.15 MB·English

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Brit. HeartJ., 1967,29, 646. r H
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Surgical Pathology of the Conducting System of the d a
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R. E. B. HUDSONt 6/h
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I am most grateful for the honour oflecturing in thence to define the danger zones to be avoided by .5
this historic hall and for the opportunity it affords the cardiac surgeon. .6
4
ofpublicizing an embarrassing but most important I have been interested in the conducting system 6
aspect ofintracardiac surgery. ofthe heart for many years, and my modest efforts on
Almost exactly 3 centuries ago, the Apothecaries have,Ithink,helpedtobringthissomewhatobscure 1
of London secured immortality when they stayed matterwithinthescopeofroutinehistology. When S
e
at their posts administering to the stricken during I joined the National Heart Hospital in 1948, the p
thegreatplagueofLondon,whenfashionablephysi- system was under a cloudandpeopleusedtoaskme tem
cians had fled the capital to seek immunity in the if I believed it existed. This wave ofuncertainty, b
e
countryside. And now today, you have a 20th initiated especially by the Glomsets and their r 1
century apothecary and pathologist come to plague colleaguesinthe1940s(GlomsetandGlomset,1940) 9
6
the cardiac surgeon. stimulated me and manyother workers to restudy 7
It is no coincidence that the amazing develop- the area. It isnowgenerallyagreed that there is a . D
o
ment of intracardiac surgery in the past few years well-defined neuromuscular system of impulse w
has beenaccompanied byano less astonishing suc- propagationandconductionintheheart,just as was nlo
cession of ingenious electrical machines for arti- definedinthebrilliantpioneerstudiesofHis(1893), a
d
ficially pacemaking or restoring the heart beat, and Kent(1893),Tawara(1906),KeithandFlack(1907), e
d
ftohroucgohrrtehcitsinhgas,diwsittuhrobuatncqeusestoifoni,tscornhfyetrhrmed. grAela-t oLtehweirs,imOmpopretnahleicmoenrt,emapnodraOrpipeesnohfeithmaetrg(r1e9a1t0)e,raanodf from
benefit to patients and brought relief to worried discoveryfrom1893-1910. Itisindeedastonishing h
physicians and surgeons, itmayhaveledto a some- that such fundamental revelations should everhave ttp
whatconceited senseoffalsesecuritythattraumatic come under suspicion, or even downright disbelief. ://h
injury to the natural conducting system is ofminor e
liimtpeorarttuarneceteasntidfyeiansgilythreemceodniterda,ryd.espTitheeacgurmobweirn-g ThCeONcDoUnCdTucItNiGngSYsSysTtEeMmOoFfTtHheEnNoorRmMalALheHarEtARcTom- art.bm
some, and often troublesome man-made devices prises 2 parts: first, the main generating station j.c
employed for these means, however, bear no com- known as the sinu-atrial node (or pacemaker), and o
m
pbuairlits-oinnwmietchhatnheislmastwihnigcpherNfaetcutrioenhoafstphreoveixdqeuidsiftoer psreicsoensdltyh,ethleessaetrrigo-evneenrtartiicnuglarstsaytisotnemk,nwohwinchascotmh-e on/
the appropriate reaction of the heart beat in all atrio-ventricular or A-V node of Tawara, together M
circumstances. When this natural system is work- withits forward extension as the bundle ofHis and arc
ing normally, therefore, it seems elementary that its terminal subdivisions (Fig. 1). h
ietvseirnyteegfrfiotryt.should be directed towards preserving atrPiralecniosedleyhtroavweltshetoimtphuelsAe-oVringiondaetiinsgniontthkenosiwnnu;- 2, 20
The object ofmylecture, therefore, is to present it is certainly via the atrial muscle, but whether by 23
the histological anatomy of the conducting system thespecificmyocardialpathwaysoriginallydescribed b
y
in the various conditions amenable to modem car- by Wenckebach (1907), Thorel (1909), and Bach- g
diacsurgery, to demonstrate thelesionsthatmaybe mann (1916), and more recentlyin studies byRobb ue
iOncft*loiSbtcertriecd1k9lb,ayn1d9o66pG.eoordaatlilonLsecitnurteh,eSaorceieatyitoofccAuppotiheesc,araiensd, ApalunltdedwP,oertfkroeirrs(e,1x9a6hm1op)wleeav,nedrb,yJaiTmnrceulseuxd(i1na9gn63d)t,hSemhyawstrihtbeeere,(n19h6da5iv)se.- st. Prote
tAddress: 35Wimpole Street,LondonW.I. noted theextensions fromthe 2nodesintotheatrial c
646 ted
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SurgicalPathology ofthe Conducting System ofthe Heart 647 r He
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FIG. 1.-Diagramofconductingsystem. NotehowthebundleofHispenetratestherightsideofthecentral d
fibrous bodytoreachthetopoftheinterventricular septum. fro
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myocardium. In general, the sinu-atrial node from the U-loop made by the right (90%) or left h
maintains sinus rhythm; if it should break down, (10%)circumflexarteryasitdipsbeneaththeinter- ttp
the lesser station can take over, resulting in A-V ventricular vein at the posterior crus of the heart, ://h
nodal rhythm; ifthis node or its terminal branches made by the junction ofthe four chambers. The ea
abrleocdkarmesauglet.d, Ivtarwioouulsd,tyhpoewsevaenrd, bdeegprreeessumofpthueoaurst r5i5ghptecrirccenutm,flaenxdarttheeryAth-uVssnuopdpelieisnt9h0eSpe-rAnceondteionf rt.bm
to claim that histological study can always explain hearts, and could more reasonably be called the j.c
an electrocardiographic arrhythmia, and, in this, "arteryofsuddendeath"thantheanteriordescend- om
the writerfullyagrees withRossi (1964). It seems ingartery(James, 1965). Aninjectionx-raymicro- o/
ievnicdoemnptlettheatkannoywldeidsgcreepoafnctihees sayrsettehme,rdeusueltinoftouurrn sdecnospiitciesstuwdeyrebygrCelaatrekstei(n19t6h5e)tswhoownoeddest.hat capillary n Ma
tothevirtualimpossibilityofhistologicaldistinction Sympathetic innervation derives from the upper rc
between conducting cells andordinarymyocardium 5 thoracic dorsal nerve roots via the paravertebral h 2
in areas remote from the well-defined pathways and stellate ganglia; stimulation causes acceleration , 2
known to all workers. of the pacemaking impulse. Parasympathetic in- 02
bloTohdeanwdhoblyeasuytsotneommiicsnaedreveqsu.atelFyig.su2ppslhioewdswhiotwh ntehrevsaitniuo-natrisiavlinaotdheeavnadgit,htehleefrtivgahgtuvsatghuesAs-uVppnloydien;g 3 by
thebloodsupplyisarranged. Thesinu-atrialnode stimulation causes decreased activity of the nodes g
u
isnourished bythearterialcircleattheentryofthe (Truex, 1961). es
s(u5p5e%r)iororvelenfat (c4a5va%,)wchiircchumdfelreixvecsorfornoamrythareterriigehs.t Sinu-atrial Node. The sinu-atrial (S-A) node t. Pro
TheA-Vsystemisfedbypenetratingseptalarteries, of Keith and Flack (1907), also known as Lewis's te
arising anteriorly from the anterior descending pacemaker (Lewis et al., 1910), lies at some point cte
branch of the left coronary artery, and posteriorly around the arterial circle at the junction of the d b
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FIG. 2.-Diagram ofcoronary circulationto showthe sinu-atrialnodefedbybranchesfromeitherrightor ed
ldeefstcceinrdciunmgflceoxroanrtaerryieasr,tearnydatnhdebHyisp-osTtaewrairorapseynsetteramtibnygabnrtaenricohrespefnreotmratthiengU-blraonocphweshifcrhomthethreiglhetft(aunstuearlliyo)r fro
c[iRrecpurmofdluexcedartferryommatkheesauatrhoour'nsd btoheokasCcaerndd(iPiounvbgalsicicunalttaeirrovnesPn)attrLhitocdul.lo]agryv(e1i9n65)at, tbhye cpoousrtetreisoyrocfruEsdwoafrtdheArhenaorltd. httpm
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superior vena cava with the right atrium (Fig. 3). that there are three types ofcell in the human and ea
Areliablelandmarktoit,whichIdescribedin 1959, canine pacemaker. First, principal or P cells, rt.b
isthesummitoftherightatrium,thatis,thehighest which have a relatively primitive structure with m
point of its junction with the superior vena cava. scanty myofilaments, and which may be the actual j.c
This point also corresponds with the upper end of pacing cells; secondly, typical ordinary (working) om
the crest ofthe right atrial appendage. The node myocardium,withabundantmyofilamentsandmito- o/
most commonly lies in the epicardial fat just below chondria, lying mainly at the node periphery; and n
and to the right ofthis summit. Occasionally the thirdly, transitional cells, with a structure some- M
a
mainpartofthenodeliesmoremediallyorlaterally, whereintermediate betweenthesetwo (James etal., rc
but with the sole exception ofsingle atrium, I have 1966). h 2
found the summit to be a reliable guide to its loca- Itisunfortunatethatthepathologists'oldcustom , 2
tion in all hearts (Hudson, 1960). In mirror- of opening the right atrium at necropsy by a con- 0
2
image dextrocardia, as might be expected, the node joined cut through both vene cavae usually makes 3
lies in the precisely corresponding situation at the adequatestudyofthe pacemaker more difficult,and by
root ofthe left-sided superior vena cava (Fig. 4). I would urge interested workers to preserve the g
u
Fig. 5 illustrates the histological appearances of shapeofthesuperiorvenacavaintact bylight wool- e
s
talhseonsohdoewsantdheitnsoedsesenetxitaelnlsyiomnysocdaorwdniawlarsdtrsucitnutroe;thiet pacItkiinsguinfftohretuynwaitsehttoooitnhvaetsttihgeatreigthhteantordiael.appen- t. Pro
right atrium. Recent electron-microscopic studies dage should be a favourite sitefor surgicalmanipu- te
by James and his colleagues in Detroit have shown lations, cannulation, and sutures, which commonly cte
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Surgical Pathology ofthe Conducting System ofthe Heart 649 e
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FIG. 3.-Anatomyofsinu-atrialnodeinrelationtothesummitoftherightatrialjunctionwiththesuperior 67
vena cava. R.A., right atrium; R.A.A., right atrial appendage; R.Pulm.Art., right pulmonary artery; . D
S.V.C.,superiorvenacava. o
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inflicthemorrhagictraumainandaroundthenode, the bundle ofHis, its temiinal branches, and their lo
asillustrated inthethree examples inFig. 6;in6A, subendocardial ramifications ending in Purkinje ad
thenode is virtually obliterated. cells. ed
Trauma may also be causedbyocclusivedamage The node and bundle lie between the ostium of fro
tothecircumflexartery(leftorright)whichsupplies the coronary sinus in the right atrium and the root m
the arterial circle about which the pacemaker is ofthe membranous septum (pars membranacea) at h
disposed. theseptalconmissureofthetricuspidvalve(Fig.7). ttp
Soon after its formation, the bundle usually starts ://h
Atrio-ventricular (A-V) System of His-Tawara. yieldingathinsheetofleftfascicleswhichfandown ea
TheA-VsystemcomprisestheA-VnodeofTawara, in the left ventricular subendocardium from below rt.b
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Sinu-atriel o
Node m
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FIG. 4.-(A) Anatomyofsinu-atrialnodeinmirror-imagedextrocardia;allowingfortheinversion,itsrelation ted
totherightatrialsummitisnormal. (B) Longitudinalsection. (H. andE.x6.) b
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tFhIeG.e5x.te-nGseinoensraulphwiasrtdolsogtyoowfartdhsestihneu-asturpiearlionrodvee.na(cAa)vNaoadnedldyionwgnawraorudnsdainntdobtehleowritghhetnaotdreiuamr.tery(.HolNmoet'es art.b
silvermethod. x12.) (B)Detailofanareanearthenodeartery(topright). Themuscleispalerthanthe m
wavy fibrous tissue. The elastic fibrils stain black (elastic-Van Gieson. x66.) (C) Individual muscle j.c
cellsofnodewhichareinterwoven. (D)Myocardiumofadjacentrightatrium. (CandDstainedbyHolme's o
m
silvermethod. x474.) [ReproducoefdEfdrwoamrdthAeranuotlhdor('Psubbloioskh,erCsa)rdLitodv.a]scularPathology (1965),bycourtesy o/
n
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the pars membranacea, which fills in the area be- Inpassingfromatriumtoventricle,thebundleof a
tweentherightandnon-coronaryaorticvalvecusps. His must penetrate the valve rings of the heart rc
h
Whatisleftofthebundle,afterthesefasciclescease, somewhere. It does so in the most protected and 2
continues as the right branch, descending near the convenient situation, that is, through the right , 2
endocardial surface just behind and below the fibroustrigone, whichistherightpartofthe central 02
crista supraventricularis. It is believed by some fibrous bodymade bythe contiguous fibrous annuli 3 b
that the impulse may also be conveyed across the of the mitral, tricuspid, and aortic valves (Fig. 8). y
cavityoftheleftventricleby"falsetendons"which During this course, the bundle may become dis- gu
are sometimes found as delicate threads linking the rupted and this is the lesion underlying congenital es
septum to the bases ofthe papillary muscles ofthe heart block; it is obvious, too, that this situation t. P
mitral valve; the writer has certainly identified makes the bundle and branches highly vulnerable ro
muscle in these cords, but cannot state whether or in valve surgery, as will be shown later. te
not this is conducting tissue. Fig. 9 illustrates the histological appearances of cte
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SurgicalPathology ofthe Conducting System ofthe Heart 651 ea
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Fallot F. 6 Follot M.12 V.S.D. MI23 . D
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FIG. 6.-Three examples ofsurgical trauma in or near the sinu-atrial node (arrows). In A, the node is n
virtuallyobliterated byhaemorrhage. InBandC,therearedarkareasofhremorrhagenearthenode. (All lo
a
stainedbyhzematoxylin-eosin. x5-7.) d
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AV-SYSTEM - ANATOMICAL RELATIONS fro
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MembranacSeuparovCernitstraicularis LCeofrtonary OsRtiigaht Membranaca eft http://h
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Coronary 2
Sinus Coronary , 2
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Left M tral 2
Ventricle Valve 3
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FIG. 7.-Diagramofatrio-ventricular systemofHis-Tawara. Theleft-hand drawing shows theA-Vnode es
(adwjhaiccehntistdoitvhiedecdoriontnoarryigshitn-uast,rieaxlt-elnedfti-nvgenftorriwcaurladraasntdheinbtuenrdvlenetroifcHuilasripnotrhteiobnassbeyofthtehetrmiecmusbpriadnvoaulvsesaettpatcuhm- t. P
ment). Thebundlegivesoffleftfasciclesand,whenthesecease,proceedsastherightbranch. Theright- ro
handdrawingshowsthebundleofHisinthebaseofthemembranous septumbetweentheright-andnon- te
rceolraotniaornyofaotrhteicAv-aVlvenocduesptso;tfhreommititr,allefvtalfavsecircilnegsifsaninddiocwatnedt,hethleofutgshidietolifesthoenitntheerfvaerntsriidceuloafrtsheisptpuamr.tofTthhee cted
septum. b
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FIG.8.-Dissectionofvalveringsofheartseenfromabove,andtherelationshiptotheA-Vsystem; the bundle r 19
ofHispenetrates therightportionofthecentralfibrous body(right fibrous trigone)made bythecontiguous 6
7
annuliofthemitral,aortic, andtricuspidvalves. . D
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the normalA-V system transectedat intervals from fascicles will still be seen as they are cut running w
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node to branches. The A-V node (A) lies just forwards and downwards from above but they lo
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under the right atrial endocardium, hugging the appearlower ineachsucceedingsectionandeventu- d
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centralfibrous body, which is blackinthepictures. ally only the right branch will be seen, often as a d
At its widest, it is about 5 mm. or more high, and quitedistinctcordofmyocardium,whichcansome- fro
from it, fine muscle fibres can be traced upwards times beidentified inacasualsectionoftheseptum. m
into therightatrium; superficial fibres usually con- h
nectwiththetricuspidvalvering. In(B),thenode ttp
isbecomingmore compactandstartingtopenetrate SURGICAL LESIONS OF A-V SYSTEM ://h
the central fibrous body to form the bundle ofHis The present studymay be divided into two main ea
(C) which lies on the crest ofthe muscular septum parts, the first dealing with lesions associated with rt.b
in the base of the membranous septum. The valve surgery in otherwise normal hearts, and the m
bundle usually starts giving off the sheet of left second with lesions resulting from the repair of j.c
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fascicles which run down in the endocardium just congenitalmalformations; inthelattergroup, a few m
beneath the endocardial plain muscle (D), and at non-surgical examples are included to make the o/
some point, these fibres take on the appearance of range ofabnormalities studied more complete. n
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Purkinje cells, large, vacuolated-looking fibres with
a
scanty peripheral fibrils (D-right picture). Left rc
fascicles continue to spring from the bundle and Valve Surgery h 2
fan down over the left side from the region ofthe As has been noted already, the central fibrous , 2
membranous septum. Eventually, these left fas- body and membranous septum (which are really a 0
2
cicles cease, and just before this the system will continuous structure) are formed bythe contiguous 3
b
appear to bifurcate (E). During its course, the tricuspid, mitral, and aortic valve rings. The y
bundlesends Mahaim fibres (Mahaim, 1947) direct bundleofHispenetratestherightpartofthecentral g
u
into the top of the muscular septum. From this fibrous body in passing from atrium to ventricle, e
s
point forwards, the main bundle, less its left andisthereforeatriskinoperationsonthesevalves, t. P
fascicles,continuesastherightbranch,whichmoves especially the aortic valve. Indeed, a growing ro
overtowardstheright side oftheseptumeventually literature has been accumulating ever since open- te
emerging in the subendocardial zone (F). Left heartsurgerybecamepossible,recordingthevarious cte
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FIG. 9.-HistologyofA-V systematintervalsfromtheA-Vnodetothebranches-seetext. [Reproduced te
fromHudson,R.E.B.(1963). Thehumanconductingsystemanditsexamination. J.clin.Path.,16,497, cte
bycourtesyoftheEditorandPublishers.] d
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became partly detached. Top right is a view of left heart chambers after removal of the prosthesis. 6
l(Ay)mpahnodcy(tBi)cA-inVfinltordaetiosnh.owi(nxg4lyamnpdhocxyt18i.c)inf(iEl)traatniodn.(F)(xBi3faurncdatxio1n8.-)vir(tCu)alanddes(tDr)ucBtuinodnlbeyofhHliesmosrhrohwaignigc 7. D
necrosis and inflammation. (x45 and x18.) (G) and (H) Right branch-slightlymphocytic infiltration o
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(x1-9and x18.) (All sections stainedbyhlematoxylin-eosin.) n
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arrhythmias which have followed surgical trauma graft (5 cases). In one patient with homograft de
to thesystem. Earlierreportssometimesregistered replacement ofa calcified bicuspid valve, complete d
aggrieved surprise at this natural complication; it heart block was also present before operation (Fig. fro
certainly stimulated the current resurgence of 11); in another, the mitral valve was replaced by a m
ainntPderrmoesabtlabfinloyrtmhteehdeanchaeotamromtmosyn(eoHfsuttdhsleoesnAi,-onV19rs6ey5ps)o.tretmedihnansorbmeaeln wSetraIrenrma-leElnd,6watcrhadessiersp,argosesestrihraelasinhsgiis(ntFgoilgfo.rgoy12m)d.i3s7cltAoolsl6e1d6yhpeaeatrmisoe.nrt-s http://h
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heart block following aortic valve replacement. rhagic trauma, sometimes with necrosis, concen- a
Theprocedure ofremovingthe original valve cusps trated in the bundle of His and left fascicles and rt.b
andthe suturingoftheringofaprosthesis orofthe oftenobscuringtheoriginoftherightbranch. The m
aortic rim of a homograft into the subcoronary A-V node usually escaped serious damage though j.c
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position, all occur dangerously near to the bundle itshowedinfiltrativehemorrhage. Afeatureofthe m
ofHisanditsbranches. Thefrequencywithwhich serieswasthewayinwhichthehemorrhagetracked o/
this complication occurs varies, ofcourse, with the along the connective tissue ofthe left fascicles and n M
skill and knowledge of the surgeon; fortunately, rightbranch;thisfacilitatedthetracingofthelatter, a
many of the lesions are temporary, due usually to which so often was difficult or impossible to define rc
h
hemorrhage, and will probably resolve, with dis- atits origin. Indeed, itwasoften easiertoidentify 2
appearance of the heart block. In other cases, the more distal portion of the right branch by its , 2
persistent heart block may play its part in a fatal hemorrhagic"halo"andthentotraceitproximally. 02
outcome. In a recent report, Gannon et al. (1966) 3 b
found post-operative complete heart block in 16 of y
124 patients who hadaortic valve replacement by a CongenitalMalformations gu
Starr-Edwards or Magovern prosthesis; 15 needed The A-V system was studied in the following es
artificial pacing and 9 died. congenital malformations. t. P
The present study included 6 examples of com- Atrialseptaldefect:atrio-ventricularis communis; ro
pleteheartblockfollowingaorticvalvereplacement, ostium primum; and ostium secundum. te
bya Starr-Edwards valve (1 case, Fig. 10)orhomo- Sinus of Valsalva aneurysm. cte
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FIG. 11.-Pre-andpost-operativeheartblockinamanof60whohadhomograftreplacementofacongenital rt.2
calcifiedbicuspidvalve. Hediedinventricularfibrillation2daysafteroperation. (A)A-Vnode-nolesion. 9
(B)Penetration segmentofbundle ofHis,obliteratedbyhemorrhage. (C)BundleofHisandleftfascicles .5
obliterated by hnmorrhage. (D) Virtual destruction ofbifurcation area by hemorrhage and calcification; .6
4
thearrowsindicatesurvivingleftfascicles. (E)Rightbranch(arrows);leftfasciclesobscuredbyhsemorrhage. 6
(Note thehomograftattop rightinD andE.) (Allsections stainedhematoxylin-eosin. x2 8.) o
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FIG. 12.-Post-operative heart block in aman of44 years, following replacement ofthe aortic valve by a M
homograft and ofthe mitral valve by a Starr-Edwards prosthesis 3 dayspreviously. The sinu-atrial node a
wasnormal. (A)A-Vnodehemorrhage(darkareas). (x4.) (B)BundleofHisobliteratedbyhemorrhage. rc
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(x4.) (C)BundleofHis;haemorrhagicnecrosiswithabscessformation;thehemorrhageisspreadingalong 2
tahrerolwesftifnadsiciccaltees.the(xri4g.h)t b(raDn)cTh.hic(kxen1-d6o.)car(dEi)umRiogvhetrlbyrianngcthhewiatthteintusahteedmolrefrthfaagsiciccl"ehsa(lloef"t.arr(oxws2)0;.)right , 20
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Aneurysm ofthe membranous septum. attheother, wasfirstphotographed frombothsides by
Ventricular septal defect: isolated; and Fallot's after inserting marker threads of cotton to locate g
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tetrad. subsequent sections, and after trimming off one e
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DCeoxrtrreocctaerddtiraa.nsposition. sciodmeeorfathleonbglotchketloenfgactihliotaftethiedernitgihctaloorrileefnttabtoitontoomf t. Pro
the serial sections on the glass slides. The block te
The selected blockoftissue, includingthecoron- was then taken through a slow paraffin-embedding c
ary sinus at one end and the supraventricular crest process, and in most cases, cut into serial sections ted
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