688

Bundle Branch Reentry Ventricular Tachycardia with TwoDistinct Left Bundle Branch Block Morphologies

CHAO-WEN WANG, M.D., RICHARD STERBA, M.D.,and PATRICK TCHOU. M.D.

From the Department of Cardiology, The Cleveland Clinic Foundation, Cleveland, Ohio

Bundle Branch Reentry VT with Two Morphologies. Introduction: Bundle branchreentry ventricular tachycardia (VT) is usually amenable to treatment with radiufrequency ab-lation. Different QRS morphologies during VT are possible when antero}^rade ventricular acti-vation is over tbe left bundte branch. Manifestations of tbis reentrant tachycardia witb morethan one QRS morphology witb anterograde activation via tbe right bundle have not been re-ported and would be unusual due to the more discrete anatomy of the right bundle brancb.

Methods and Results: An electropbysiologic study was conducted in a patient with dilatedventricle and diminished ventricular function with VT. Typical characteristics of bundlebrancb reentry were noted when VT was induced. The study was notable for tbe presence of aright bundle recording only dnring macroreentrant beats or VT and the distal location of tberecording. Radiofrequency ablation was performed. Postablation stinmlation again inducedVT, proven to be of tbe same bundle brancb reentry mechanism but of a different QRS mor-pbology. A second ablation was required for complete ablation of this patient's bundle branchreentry VT.

Conclusion: [n bundle brancb reentry utilizing tbe left bundle as the retrograde limb andthe rigbt bundle brancb as tbe anterograde limb of the circuit, VT of more than one distinctmorphology can be seen. Careful evaluation to a.ssess for the persistence of VT of tbe samemechanism is nece.ssury to ensure complete ablation of tbe reentrant circuit. Preexisting rightbundle disease and a dilated heart with more dispersed distal rigbt bundle brancbes may pre-dispose to such a phenomenon. (J Cardiovasc Electrophysiot. Vol. 8. pp. 6HH-()93. June 1997}

bundle branch reentrv, ventricular tachycardia

Introduction

Bundle branch ieenti-y ventricular tachycardiainvolving macmreentry within the His-Purkinje sys-tem accounts for approximately 6% of ventriculartachycardias studied in the eleclrophysiology lab-oratory.'- It is the niechimism of inducible sustainedmonomorphic ventricular tachycardia in 30% to50% of patients with idiopathic dilated cardiomy-opathy and in 5% to b% of patients with isch-emic heart disease.' The 12-lead ECG recordedduring sinus itiythm in such patients generally shows

Address ("or correspotidence: Patrick Tchou, M.D.., Chief, Sectionof Eleclrophysiology. Deparlmenl of Cardiology, The ClevelandClinic Foundation, 95{H) Euclid Ave.. Cleveland, OH 44195, Fax;216-445-3595: E-tnail: Tchoup@cesmtp.CCF.org

Manuscript received 7 January 1997; Accepled for publication 5March 1997.

a]i intiaventricular conduction delay. The QRS mor-phology during the tachycardia usually has a typ-ical left bundle hranch bkx:k pattem. This tachy-cardia can be readily treated with radiofrequencyahlation of the right bundle branch.^'' Follow-upfor a mean of up to 16 months has not demon-strated recuiTence of ventricular tachycardia ofthe same hundle hranch reentry mechanism.'-'̂ '* TTietypical circuit for this tachycardia involves retro-grade conduction up the left bundle hranch and an-terograde conduction down the right hundle hiiinch.All reported cases of tachycaidias using this reen-trant circuit show a single QRS motphology in agiven patient, generally a left hundle hranchbkx:k pattem with lett-axis deviation. However, thedistal right hundle does contain branches thatmay iillow manifestations of this reentrant tachy-cardia with more than one morphology. In this re-

Wang, et at. Bundle Branch Reentry VT with Two Morphologies 689

port, we describe electrophysiologic observationsconfirming the existence of such a phenomenon.

Methods and Patient Description

A 37-year-old man with a history of aortic in-sufficiency underwent multiple aortic valve re-placements. He had a dilated left \entricle with aleft ventricular end-systoHc diameter of 50 mmand an end-diastolic diameter of 67 mm. Therewas mild-to-moderale systolic dysfunction with anestimated ejection fraction of 40% to 45%. He pre-sented with three episodes of palpitations of sud-den onset unrelated to activities. On Holter mon-itoring, these episodes were noted to correlate witha wide complex tachycardia having a left bundlebranch block morphology at rates of 135 to 150beats/min (Fig. 1). His resting 12-lead ECG dur-ing sinus rhythm suggested an incomplete rightbundle branch block morphology, with left ante-rior fascicular block (Fig. 4A).

After informed consent was obtained, standardelectropbysiologic .study using three multipolarcatheters'* was performed. Radiofrequency cathe-ter ablation was performed using a large-tippedelectrode catheter.**

Results

Baseline electrograms showed a prolonged HVinterval of 78 msec (Fig. 2A). After multiple at-tempts at localizing a His- or right bundle poten-tial, the electrogram shown in Figure 2A demon-sUated the best recording that could be obtainedduring sinus rhythm. As the electrogram charac-teristics indicate, this is a very proximal recordingof the His bundle.

A more distal His- or proximal rigbt bundlerecording could not be found, perhaps due to un-derlying conduction system di.sease. During ven-

Figure 1. Holter recording of clinical tachycardia. Episodesof wide comptex tachycardia of a left bundte branch bloctcQRS morphology at rates of 135 to 150 beats/min correlatedwith the patient's .symptoms of patpitations.

tricLiIar pacing at a cycle length of 400 msec, asingle premature extrastimulation at 3(X) msec in-duced a sustained monomorphic ventricular tachy-cardia that had a left bundle branch block QRSmorphology with left-axis deviation (Fig. 2B). Asingle ventricular extrastimulation reproducibly in-duced this tachycardia. The small proximal Hisrecording was difficult to discern once the tachy-cardia was initiated. However, a more distal rightbundle potential could be recorded during macro-reentrant beats and tachycardia (Fig. 3A). Ven-tricular activation was preceded by right bundleactivation with spontaneous vaiiations of V-V in-tervals preceded by similar changes in right bun-dle-right bundle (RB-RB) intervals (Fig. 3A. leftpanel). The distal right bundle potential wasrecorded only during ventricular pacing-inducedmacroreentrant beats or during tachycardia and wasnot seen during sinus beats (Fig. 3A. right panel).Radiofrequency ablation at the site of this rightbundle potential was performed. Programmed ven-tricular stimulation could no longer induce thisventricular tachycardia. The sinus rhythm QRSmoiphology after tlie first ablation is .shown in Fig-ure 4B. Note that the QRS in V, shows a largerR' than at baseline.

Postablation ventricular pacing with double pre-mature extrastimulation induced a second sustainedmonomorphic ventricular tachycardia {Fig. 38, leftpanel). This tachycardia also had left bundle branchblock QRS morphology but now had a right infe-rior axis. Such a QRS morphology is not typicallyassociated with a bundle branch reentry mecha-nism. However, right bundle potentials could berecorded preceding a macroreentrant beat and dur-ing tachycardia (Fig. 3B). Again, the right bundleelectrogram was not seen during sinus rhythm (Fig.3B, right panel). Spontaneous variations in V-Vintervals during tachycardia were again precededby similar changes in the RB-RB intervals (Fig.3B, left panel). Therefore, a second ventriculartachycardia with a distinctly different QRS mor-phology, although still of the typical hundle branchreentry mechanism, was induced alter the initialablation. The site of the right bundle recording dur-ing the second ventricular tachycardia was some-what more proximal than the site of right bundleablation for the first tachycardia. Radiofrequencyabiation was again peribmied. After successful ab-lation of this second morphology of ventriculartachycardia, no further ventricular tachyciirdia wasinducible. even during isoproterenol infiision. TheQRS morphology after the second ablation is il-lustrated in Figure 4C.

690 Journal of Cardiovascular Electrophysioloyy Vol. 8, No. 6. June 1997

aVf

HBE 1-3

RVA

i—\l\—^i 1̂—l̂ h~~i—

BFigure 2. His-bundle eleetrogram. Baseline electrograms show prolonged HV interval of 78 msec, consistent with His-Pur-kinje disease (A). The .small proxinml His recording was difficidt ta discern once ventricular fachyiardia was initiated fB).Sustained monomorphic ventricular tachycardia of a left bundle branch block QRS morphology was induced with a .tinglepremature extrastimulation at 300 msec during ventricular pacing at a cycle length of 400 m.\ec.

Discussion

This case illustrates several unique features ofbundle branch reentry ventricular tachycardia. Pre-vious reports have identified bundle branch reen-try ventricular tachycardia of two distinct QRSmorphologies in a single patient,^* one having aright bundle branch block and the other having aleft bundle branch block QRS pattem. These twomorphologies have been attrihuted to counter-clockwise (type A) or clockwise (type C) rotationof the reentrant circuit.^ Theoretically, the clock-wise rotating reentrant circuit of bundle branchreentry (type C) can have markedly different QRSmorphologies, depending on whether the leftventricle is activated via the anterior or the poste-rior fascicle. However, because the right bundle isanatomically more discrete,'" it would be unusualto expect two very distinct QRS morphologieswhen the tachycardia is of the typical counter-clockwise (type A) variety. This report is uniquein describing the appearance of a second QRS mor-phology for this type of bundle branch reentry ven-tricular tachycardia. Both ventricular tachycardiashad retrograde activation of the left bundle withanterograde activation of the right bundle, yet theQRS morphologies were distinctly different.

In this case, preexisting right bundle disease wasnoted. The QRS morphology during normal si-

nus rhythm showed an incomplete right bundlebranch bkxrk paitem. A proximal right bundle eiec-trogram could not be recorded during sinus rhythm,probably due to disease within that pK>rtion of iheright bundle. Consequently, mapping these |X)len-tials in the usual kx:ation of the mid to high sep-tum was not p<issible. The conduction delay in theright bundle branch resulted in recording of a Uvcai ventricular eleetrogram before distal right bun-dle activation during sinus rhythm, thus maskingthe distal right bundle potential as well. The rightbundle potential was recorded more distally onlyduring macroreentrant beats and ventricular tachy-cardia, when ventricular activation most likely oc-curred exclusively via the right bundle. The firstablation was performed at a site where the RB-Vinterval was very short. Thus, this RB site wasvery likely near the site of the earliest ventricularactivation. This first ablation was likely pertbrmedat a site distal to the first branch point of theright bundle. As a result, the bundle branch reen-try ventricular tachycardia was able to persist, asdemonstrated by the emergence of a second ven-tricular tachycardia of the same mechanism butwith a different QRS morphology with inferioraxis. This second morphology of ventricuUir tachy-cardia clearly used a circuit involving another dis-tal branch of the right bundle. It is remarkable thata distinctly different QRS morphology can emerge

Wang, el al. Bundle Branch Reentry VT with Two Morphologies 691

RB 1-3

RB .1-4

B

RB 3-4 * -

RBl-2

Figure 3. Right hundle recording during macroreentrant beats and tachycardia. A more distal right hundle potential wasrecorded during ventricular tachycardia (A. left panel). However, thi.s right bundle potential was not .seen during sinusrhythm {A. right panel). This ab.sence may he related fo underlying conduction delay within the right bundle hranch. whichprevented ir.s recording during sinus rhythm. Sitiiilarty, after ihe second ahlation. the right bundle recording could only he ob-tained during macroreentrant beats (B, right panel) or during the tachycardia (B. left panel).

from a second breakthrough .site, especiiUly a QRSmorphology that is typically associated withearly activation of the right ventricular outflow re-gion. Although the appearance of the ventriculartachycardia may suggest a right ventricular out-flow tract origin, the right bundle recording clearlyidentified the QRS of this tachycardia as being ac-tivated via the right bundle. The appeiirance of thisdistinctly different QRS morphology may be re-lated to the anatomic dispersion of the distal rightbundle branches in some hearts where the ven-tricular septum may be distorted by left ventricu-lar enlargement or perhaps with right ventricularenlargement.

The absence of a right bundle recording duringnormal sinus rhythm, related to the underlying rightbundle disease noted previously, is in contrast to aclear recording of the right bundle potential withmacroreentrant beats and during ventriculartachyciirdia. In the setting of preexisting right bun-dle branch disease, as reflected by the incompleteright bundle branch bkx:k QRS moiphology dur-ing sinus rhythm, it becomes important to mapthe right bundle not only during sinus rhythm butalso with V, or during the reentrant ventriculartachycardia. During sinus rhythm, the right bun-dle potential may not be recorded in ihe usual lo-cation of the mid to higb septum due to conduc-

692 Journal of Cardiovascular Electrophysiology Vol. 8, No. 6, June 1997

Figure 4. Sinus rhythm 12-lead ECG. (A) ECG during sinus rhythm at rest. After the first ablation, the QRS morphology isnotable for a more prominent R' in lead VI (B). The R' becomes minimally more prominent after the .second ahlation (C).

tion disease and delay. Even though the distal rightbundle may be able to generate an adequate po-tential for recording, sucb a potentijil can be maskedduring sinus rhythm by kKal ventricuUir activation,which had propagated from the left ventricle. Onlytbrough removal of this local ventricular activationduring V̂ or during ventricular tacbycardia couldthis distal right bundle potential be exposed andrecorded properly. TTierefore. tbe usual approach tomapping a right bundle during sinus rbythm maynot apply to patients witb conduction delay in tbeproximal right bundle.

The data presented in tbis report would indi-cate that one can ablate too distally in the right bun-dle. For this patient, the tlrst site of ablation wasbeyond the first branching point of the right bun-dle. Despite eliminating the ventricular tachycardiaassociated with the first QRS morphology, thisablation did not eliminate all possibilities of reen-try but only shifted the exit of tbe reentrant circuit.Ablation, then, may be incomplete if it is perfonnedat a site distal to the first branch point of the rightbundle. Additional ablation may be necessary if thebundle briinch reentry circuit persists using anotherremaining limb of tlie distal right bundle branches,

Tbe markedly different QRS morphology of thesecond ventricular tachycardia could mislead oneinto denying its macroreentrant nature. Past reportshave shown that there are no recurrences of ven-tricular tachycardia of bundle branch reentry mech-anism after radiofrequency ablation of the rightbundle, although such ablation may unmask ven-tricular tachycaidias of other mechanisms.'̂ '' Tbus,a ventricular mchycardia with a different QRS mor-

phology induced after right bundle ablation couldeasily and mistakenly be attributed to a mecha-nism otber than bundle branch reentry. Our datain this case indicate that a different QRS mor-phology does not rule out bundle branch reentryas a mechanism of a second ventricular tachycar-dia. Caieful search for a right bundle recordingduring ventricular tachycardia or at least during asingle reentrant beat should be perfonned to ruleout such a mechanism.

In summary, the electrophysiologic observationsin this unique case demonstrate that bundle branchreentry ventricular tachycardias that use the leftbundle as the retrograde limb and the right bundlebrancb as the anterograde limb of the circuit maygenerate more than one distinct QRS moqihology.Preexisting rigbt bundle branch disease and a di-lated heart with more dispersed distal rigbt bundlebranches may predispose to such a phenomenon.Careful mapping to localize tbe ablation site of thedistal right bundle may need to be performed dur-ing induced macroreentrant beats or ventriculartachycardia, as these potentials could be hiddenduring sinus rhythm. Although bundle hranch reen-try venuicular tiichycardia is aii entity tbat resptHidsreadily to ablation, this therapy may be more chal-lenging to apply in the setting of preexisting rightbundle disease with a dilated heart.

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Wang, et al. Bundle Branch Reentry VT with Two Morphologies 693

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