364

Arrhythmia RoundsSection Editor: George J. Klein, M.D.

Narrow Irregular QRS Tachycardia with AV Dissociation: WhatIs the Mechanism?

JESUS CASTILLO CASTILLO, M.D., PABLO PENAFIEL VERDU, M.D.,JUAN MARTINEZ SANCHEZ, Ph.D., and ARCADI GARCIA ALBEROLA, Ph.D.

From the Electrophysiology Unit, Department of Cardiology, Virgen de la Arrixaca University Hospital, Murcia, Spain

Arrhythmia Rounds. A 39-year-old woman with no structural heart disease and frequent episodesof sudden onset palpitations was referred for the electrophysiological study. During the study, a slightlyirregular narrow QRS tachycardia with AV dissociation was repeatedly induced and spontaneously termi-nated. Apparently, irregular cycles and termination of the tachycardia were related to the dissociated sinusrhythm: atrial depolarizations timed when the AV junction was refractory were able to reset the tachycar-dia, while early atrial depolarizations caused its termination. This observation was enough to diagnose thetachycardia mechanism in our case. (J Cardiovasc Electrophysiol, Vol. 24, pp. 364-366, March 2013)

atrioventricular dissociation, atrioventricular node reentry, catheter ablation, junctional tachycardia, supraven-tricular tachycardia

Case Summary

A 39-year-old woman with no structural heart disease andfrequent episodes of sudden onset palpitations was referredto our department. Baseline 12-lead ECG and conduction AVintervals were normal. During catheter placement, a slightlyirregular narrow QRS tachycardia with AV dissociation wasinduced and spontaneously terminated (Fig. 1). Dual-AVnode physiology was observed during programmed atrialstimulation. Subsequently, both fixed and programmed ven-tricular or atrial stimulation were able to induce repeatedlynonsustained and sustained episodes of tachycardia, alwayswith AV dissociation even during isoproterenol infusion. Ap-parently, irregular cycles and termination of the tachycardiawere related to the dissociated sinus rhythm: atrial depolar-izations timed when the AV junction was refractory wereable to reset the tachycardia (Fig. 2) while early atrial depo-larizations caused its termination (Fig. 3). During sustainedepisodes, postpacing interval from the right ventricle mea-sured consistently 174 milliseconds. What is the involvedmechanism?

Commentary

Figure 2 shows an irregular narrow QRS complex tachy-cardia with longer cycle lengths between 402 and 420 mil-liseconds and shorter cycle lengths between 350 and 358

No disclosures.

Address for correspondence: Jesus Castillo Castillo, C/Dr. Perez Ma-teo 1, Bl. 7, Esc. 3, 2◦ D, 03550 San Juan, Alicante, Spain. E-mail:jesus_kastillo@hotmail.com

Manuscript received 10 September 2012; Revised manuscript received 20September 2012; Accepted for publication 25 September 2012.

doi: 10.1111/jce.12026

milliseconds, while the atrium is dissociated from the ventri-cle with a cycle length of 510 milliseconds. The differentialdiagnosis includes focal ventricular tachycardia originated inthe septum closely to His bundle, focal AV junctional ectopictachycardia (JET), atrioventricular node reentry tachycardia(AVNRT), nonreentrant supraventricular tachycardia due todouble ventricular response to sinus rhythm, and concealednodofascicular tachycardia with unilateral upper commonpathway block. Ventricular tachycardias originated close toHis bundle have left bundle branch block morphology anda short HV interval. Under these considerations ventriculartachycardia may be ruled out in our case because of fixedand normal HV interval, and identical QRS morphology tothat of sinus rhythm. Additionally, the lack of any associ-ation between atrium and ventricle rules out the possibilityof AV conduction of sinus rhythm. An alternative explana-tion could be a concealed nodoventricular or nodofasciculartachycardia with unilateral upper common pathway. How-ever, the postpacing interval would be expected to be shortif the circuit included retrograde conduction over a retro-gradely conducting nodoventricular inserting into the rightventricle.

Thus, the diagnostic dilemma remains between JET andAVNRT. Frequent and short episodes of palpitations, spon-taneous initiation and termination, and permanent retrogradeconduction block both during tachycardia and sinus rhythmare suggestive findings of JET. On the other hand, in a JETa regular impulse formation in the His bundle area wouldbe expected, although it also has been described as intrinsicirregular beats formation resulting in an irregularity of the ec-topic rhythm.1 Figures 2 and 3 show the response to late andearly premature atrial depolarization, respectively. Detailedanalysis of Figure 2 shows that the first and third sinus beatreach AV junction when it is refractory. In the case of a JET,one would expect no perturbation of the next His deflection inthis phase of the tachycardia cycle because of the concealedretrograde invasion of the AV node by the ectopic activity.

Castillo et al. Arrhythmia Rounds 365

Figure 1. Twelve-lead ECG acquired after spontaneous initiation of a narrow QRS complex tachycardia with apparent AV dissociation. ∗P waves.

Figure 2. Response to atrial spontaneous depolarization timed when the AV junction is refractory (A) with corresponding ladder diagram (B). Notice thatthe first and third sinus beats (∗) influence the next His deflection by early engagement of the slow pathway. A = atrium; AVN = atrioventricular node; His =His bundle; HRA = high right atrium; Hisd = distal His; RVa = right ventricular apex; UCP = upper common pathway; V = ventricle.

Nevertheless, atrial depolarization timed to atrioventricularjunction refractoriness causes an advance of the next Hisand ventricular deflections (Fig. 2), indicating that antero-grade AV nodal slow pathway conduction is possible during

the tachycardia. In Figure 3, the third sinus complex is ableto penetrate anterogradely through the fast pathway whilethe anterograde front is spreading over the slow pathway.The fact that the following His deflection is not advanced

366 Journal of Cardiovascular Electrophysiology Vol. 24, No. 3, March 2013

Figure 3. Response to early atrial spontaneous depolarization (A) with corresponding ladder diagram (B). Notice that the second sinus (∗) beat influencesthe next His deflection by early engagement of the slow pathway, while the third (arrow) penetrates anterogradely through the fast pathway causing a collisionwith the retrograde activation front.

suggests a collision in the fast pathway causing the tachycar-dia termination. Conversely, an early premature atrial de-polarization during a JET would be able to advance thesubsequent His by resetting the tachycardia focus withouttermination. Thus, these responses confirm the reentrant na-ture of the tachycardia around the atrioventricular node andexclude the diagnosis of JET.2

Owing to the lack of retrograde conduction over the atri-oventricular node, radiofrequency delivery was considered anunsafe option, since it would not have been possible to detecta fail in retrograde conduction to the atrium during the re-sultant junctional rhythm. Therefore, we decided to performcryoablation; a single application at the posterior anatomicalarea of Koch triangle resulted in noninducibility of AVNRT.Unfortunately, few days later a recurrence of the tachycardiawas documented. In a second procedure, we finally deliveredradiofrequency at the same anatomical area of Koch trian-gle, resulting in nodal ectopic beats with no atrial conductionand subsequent noninducibility of the tachycardia. After afollow-up of 6 months, the patient remains asymptomatic.

This report is a rare case of AVNRT with permanent com-plete retrograde block. Different VA block patterns have beenpreviously described; nevertheless, 1:1 or other VA conduc-tion patterns were resumed after isoproterenol infusion.3 Theunderlying mechanism involves an unidirectional retrogradeblockade from the tachycardia circuit to the rest of the atrium.

However, it is not possible to know if the block is located inthe proximal compact node (including nodal extensions) orin a perinodal transitional cell envelope.4

Under this condition, the differential diagnosis betweenJET and AVNRT is difficult, taking into account the lowspecificity of the clinical and diagnostic tests. However, bothrhythms have specific response to atrial stimuli deliveredat different phases of the tachycardia cycle.2 Interestingly,since the tachycardia is not perturbing the sinus rhythm, inour case, the diagnosis could be made trustworthly just withcatheter placement without the need for pacing or performingother maneuvers.

References

1. Roten L, Tanner H: Irregular tachycardia: What is the mechanism? PartI. Europace 2009;11:115-116.

2. Padanilam BJ, Manfredi JA, Steinberg LA, Olson JA, Fogel RI, Prys-towsky EN: Differentiating junctional tachycardia and atrioventricularnode re-entry tachycardia based on response to atrial extrastimuluspacing. J Am Coll Cardiol 2008;52:1711-1717.

3. Morihisa K, Yamabe H, Uemura T, Tanaka Y, Enomoto K, Kawano H,Nagayoshi Y, Kaikita K, Sumida H, Sugiyama S, Ogawa H: Analysisof atrioventricular nodal reentrant tachycardia with variable ventricu-loatrial block: Characteristics of the upper common pathway. PacingClin Electrophysiol 2009;32:484-493.

4. Mazgalev TN, Ho SY, Anderson RH: Anatomic-electrophysiologicalcorrelations concerning the pathways for atrioventricular conduction.Circulation 2001;103:2660-2667.