Concealed Retrograde Conduction in CompleteAtrioventricular Block

By STAFFORD I. COHEN, M.D., L. KENT SMITH, M.D., JULIAN M. AROESTY, M.D.,PANAGIATOS VOUKYDIS, M.D., PH.D., AND EUGENE MORKIN, M.D.

SUMMARYAtrio-ventricular (A-V) conduction and retrograde concealed conduction were assessed in 13 patients with

complete heart block distal to the His bundle. Antegrade conduction was defined by His bundle study. Thepresence or absence of retrograde concealed conduction of the atrio-ventricular node was determined dur-ing ventricular pacing. Four instances of retrograde concealed conduction of the A-V node were observed.

Additional Indexing Words:Atrioventricular node His bundle

INCOMPLETE TRANSMISSION of impulsesacross the atrioventricular (A-V) junction has held

a special fascination for many investigators.'14 Variedinvestigational techniques including venous pulsewaves, standard electrocardiograms, and directcatheter electrode recordings from the cardiacchambers have been used to further the understand-ing of retrograde transmission of impulses into theA-V junction. In this report, His bundle study haspermitted identification of retrograde concealed con-duction of the A-V node in four of 13 patients withcomplete heart block distal to the His bundle.

MethodsAtrioventricular node conduction was studied in 13

patients with complete heart block who were referred forcardiac pacing. Catheter recordings of His bundle elec-trograms were performed by the method described byScherlag et al.5 The intracavitary bipolar electrogramdefined atrial excitation (A), His bundle excitation (H), andventricular excitation (V).5'- The A-H interval generallydelineated A-V node conduction time, the normal range ofwhich is 50 to 120 msec. Measurements were made from theonset of the A wave to the first clear deflection of the Hwave.

His bundle electrograms were validated by an increase inthe A-H interval during either spontaneous or induced atrialpremature beats.5

Observations of retrograde concealed conduction weremade during complete heart block when the right ventricle

From the Cardiac Unit, Department of Medicine, Beth IsraelHospital and Harvard Medical School, Boston, Massachusetts.

Supported in part by a training grant from the National Heartand Lung Institute (HL 05909).

Address for reprints: Dr. Stafford I. Cohen, Department ofMedicine, Beth Israel Hospital, 330 Brookline Avenue, Boston,Massachusetts 02215.

Received April 23, 1974; revision accepted May 7, 1974.

was being excited by another pacing catheter. The groupstudied consisted of eight men (average age, 74 years) andfive women (average age, 79 years).

Results

Atrioventricular node conduction time was normalin eight patients with block distal to the His bundleand was prolonged (10 block of the A-V node) in theremaining five patients with distal block. His bundlestudy documented four instances of retrograde con-cealed conduction of the A-V node (figs. 1, 2) amongthe 13 patients.

Discussion

Langendorf 7 noted in his initial description ofconcealed conduction that "the prolongation of theP-R interval after interpolated ventricular systoles isthe most obvious example of this phenomenon." If theA-V node or junction is penetrated by the retrogradeimpulse of the premature systole, which does not thenadvance to the atria, the next atrial impulse of sinusorigin may find the A-V node partially refractorybecause of the concealed retrograde conduction of theprevious premature ventricular systole. The partiallyrefractory state is evident from the transformation ofthe conduction velocity of the post extrasystolic beatto an abnormally prolonged duration as compared toatrioventricular conduction of control beats. His bun-dle studies by some investigators have attributed thepost extrasystolic delay in P-R interval to prolongedA-V node conduction.10'11

Retrograde concealed conduction of the A-V nodein the presence of third degree block is impossible torecognize by standard electrocardiographic methods.Identification of altered A-V transmission (P-R inter-val) is not possible because of the absence of related R

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RETROGRADE CONDUCTION IN A-V BLOCK

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Figure 1

Retrograde concealed conduction of the A-V node. A-V block is present, Ventricular excitation (V) is under the influenceof a ven tricular pacemaker (E) The si te of A v block is below the bundle of His. A V node conduction is defined b y theA H in terval. As the E-A in terval gradually shortens frorn 640 msec to 1 95 msec in four cycles, A V node conduction time

gradually lengthens from 66 msec to 200 msec before A-V node conduction is blocked. The progressive delay in

orthograde conduction is the result of partial retrograde penetration of the A-V node by the preceding excitation whicliorigina ted in the ven tricle. The las t E-A interva 1 is too brief to permi t adequa te recovery ofA V node refr(ic toriness in thcarea that had earlier been affected by partial penetration. Abbreviations: In this and other figures. II = standard ECGlead IL BE = Bipolar electrogram. AAtria. H = His bundle.

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COHEN ET AL.

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Absence of retrograde concealed conduction during A-V block. A-V node conduction time remains unchanged (87 msec)dulring E-A internals of 700 msec and 350 msec. Panel B demonstrates no change in A-V node condutction at the E-A inter-vol of 248 msec.

waves. The His bundle electrogram, however, doesdefine A-V node conduction time in those instances ofthird degree block distal to the His bundle. We haveidentified four examples of retrograde concealed con-duction of the A-V node in the presence of thirddegree block distal to the His bundle. In each case,antegrade A-V node conduction time gradually in-creased as stimulated ventricular excitation precededand approached atrial excitation. Eventuallyorthograde conduction block in the A-V node wasidentified by an absence of the His potential. Werecognize in theory that the recording catheter mayhave moved from the area of the His bundle.However, in most studies, the characteristics of theatrial and His bundle waves did not significantlychange even in the presence of very short ventricularpacemaker stimulus-P intervals (fig. 3). Incrementalincreases of A-H time until absence of the H wavecould be interpreted as Wenckebach (Mobitz 1) blockof the A-V node combined with third degree block dis-tal to the His bundle.'2 The proof of retrograde con-cealed conduction at the A-V node is shown byshortening, rather than prolongation, of the A-H in-terval which follows an ineffective pacemakerstimulus (fig. 2).Gupta and Haft'3 in this country and Peuch and

Grolleau14 in France have reported one instance ofretrograde concealed conduction of the A-V node in asimilar setting. Our data confirms and firmly es-tablishes this unusual phenomenon of retrograde con-cealed conduction of the A-V node in the presence ofthird degree block in the distal conducting system ofman.

References1. M v-KE/ziF J: The extrasystole: A contribution to the

functional pathology of the primitive cardiac tissue. Q J Med1: 131, 1907

2. L\SLEIT EE: The regular occurence of interpolatedextrasystoles. Heart 1: 83, 1909

3. LEWZIS T, MA.siTvEs AM: Observations upon conduction in themammalian heart Heart 12: 209, 1925

4. LRnfR Concealed A-V conduction: The effect ofblocked impulses on the formation and conduction subse-quent impulses. Am Heart j 35: 542, 1948

5. SC EIMILAG; BJ, LAU SH, HSLFASNT RH, BnERKOWxIT? WD, STE5IN E,D,\I.in.-o AN: Catheter technique for recording His bundleactivity in man. Circulation 39: 13, 1969

6. Dx'axio AN, LxA SH, HELIAN-T RH, STEIN E, BEIKOWvITZWD,C(oIIF\ SI: Study of atrioventricular conduction in man usingelectrode catheter recordings of His bundle activity. Circula-tion 39: 287, 1969

7 Suisni v. BJ, NAHLLA OS, LisTrE JW, SAiMET P: Analysis ofatrioventricular conduction by direct intracardiac record-ings. J Mt Sinai Hosp 37: 266, 1970

8. D. \Iv'\lo AN, L ..u SH: Clinical value of the electrogram of theconducting system. Progr Cardiovasc Dis 13: 119, 1970

9. SnHEIxRL.c BJ, S\NIEI PS, HELFAMIA RH: His bundleelectrogram. Circulation 46: 601, 1972

10. DxALvi1o AN, LxU SH. Concealed and supernormalatrioventricular conduction. Circulation 43: 967, 1971

11. NExnULA OS, Co01EN SL, SAiMET P, LISTER J, SCHEIrLx; B,HILDEJi F: Localization of A-V conduction defects in man byrecording of the His bundle electrogram. Am J Cardiol 25:228, 1973

12. ROSE.\ KM, EIInSANi AA, SIN-so MA, RAnIviFOOLA SH:Simultaneous block proximal and distal to His bundle. ArchIntern Med 131: 588, 1973

13. Guv-n PK, H AFT JI: Retrograde ventriculo-atrial conduction incomiplete heart block. Studies with His bundle elec-trography Am J Cardiol 30: 408, 1972

14. PEU H P, GBOLIL,xu LL: Activite du fasceau de His normale etpathologique. Paris, Sandoz, 1972, p 164

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VOUKYDIS and EUGENE MORKINSTAFFORD I. COHEN, L. KENT SMITH, JULIAN M. AROESTY, PANAGIATOS

Concealed Retrograde Conduction in Complete Atrioventricular Block

Print ISSN: 0009-7322. Online ISSN: 1524-4539 Copyright © 1974 American Heart Association, Inc. All rights reserved.

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