We present the case of a 25 year-old man referred for an electrophysiological study due to
suspected pre-excitation as the cause of two recent syncopal episodes. The admission electrocardiogram
(ECG) showed a borderline PR interval of 120 ms and apparently small delta waves
visible in leads V2-V4. Intracardiac recordings showed a short HV interval of 18 ms that was
stable despite decremental atrioventricular conduction. A fasciculoventricular accessory pathway
was diagnosed. Administration of ajmaline normalized ECG and HV interval. We discuss
electrocardiographical features of this rare bypass tract. (Cardiol J 2010; 17, 1: 83-87

Jastrzębski, Marek

Kukla, Piotr

English

Via Medica Journals

www.cardiologyjournal.org 83CASE REPORTCardiology Journal2010, Vol. 17, No. 1, pp. 83–87Copyright © 2010 Via MedicaISSN 1897–5593Address for correspondence: Marek Jastrzębski, MD, 1st Department of Cardiology and Hypertension, Kopernika 17,31–501 Kraków, Poland, tel: +48 12 424 73 00, fax: +48 12 424 73 20, e-mail: mcjastrz@cyf-kr.edu.plReceived: 02.01.2009 Accepted: 16.04.2009Fasciculoventricular accessory pathway:A misleading and unusual bypass tractMarek Jastrzębski1, Piotr Kukla211st Department of Cardiology and Hypertension, University Hospital, Kraków, Poland2Department of Internal Medicine, Specialistic Hospital, Gorlice, PolandAbstractWe present the case of a 25 year-old man referred for an electrophysiological study due tosuspected pre-excitation as the cause of two recent syncopal episodes. The admission electrocardio-gram (ECG) showed a borderline PR interval of 120 ms and apparently small delta wavesvisible in leads V2–V4. Intracardiac recordings showed a short HV interval of 18 ms that wasstable despite decremental atrioventricular conduction. A fasciculoventricular accessory path-way was diagnosed. Administration of ajmaline normalized ECG and HV interval. We dis-cuss electrocardiographical features of this rare bypass tract. (Cardiol J 2010; 17, 1: 83–87)Key words: pre-excitation, fasciculoventricular accessory pathway, syncope,delta waveCase reportA 25 year-old man was referred for an electro-physiological study due to suspected pre-excitationas the cause of two recent syncopal episodes. Healso had a history of occasional, well-tolerated,short-lasting episodes of heart palpitations, and ofempirical antiepileptic pharmacotherapy adminis-tered during childhood after apparently similar syn-copal episodes.The admission electrocardiogram (ECG)showed a borderline PR interval of 120 ms and ap-parently small delta waves visible in leads V2–V4(Fig. 1A). The Wolff-Parkinson-White diagnosis wasfurther supported by an intracardiac electrogramshowing a short HV interval of 18 ms (Fig. 1B). De-spite very proximal positioning of the His bundlecatheter (to avoid recording the right bundle branchpotential) it was not possible to obtain a His bundledeflection that would not merge with ventricular de-polarization (Fig. 1C). Other electrophysiologicalstudy findings were a PA interval of 22 ms, an AHinterval of 80 ms, a Wenckebach block cycle lengthof 380 ms, dual atrioventricular nodal physiologywith occasional single ‘echo’ beats, and a retrogradeWenckebach cycle length of 420 ms with a concen-tric retrograde atrial activation pattern on coronarysinus catheter.However, surprisingly, despite features sug-gestive of pre-excitation, QRS morphology re-mained constant without any change in the degreeof pre-excitation during incremental atrial pacingand during premature atrial extrastimuli. Moreover,a non-sustained narrow QRS tachycardia that wasinduced (Fig. 2) presented QRS morphology iden-tical to that seen during sinus rhythm. This wasincompatible with an atrioventricular AP. Becauseof the differences in conduction properties betweenatrioventricular (AV) node and AP, the degree ofpre-excitation (especially in a case of minimalpre-excitation) is variable during incremental atrialpacing and during premature atrial extrastimuli.In contrast, a pre-excitation pattern similar to thatobserved with a superoparaseptal AP (as in the84Cardiology Journal 2010, Vol. 17, No. 1www.cardiologyjournal.orgFigure 1. A. A 12-lead electrocardiogram showing subtle pre-excitation; B. Intracardiac electrograms with a standardHis catheter location; C. Intracardiac electrograms with a proximal His catheter location; A — atrial, V — ventricular.Figure 2. Tachycardia induction using double atrial extrastimuli: S1S1 = 500 ms, S1S2 = 350 ms, S2S3 = 270 ms. Thekey aspect of this tracing is that the HV interval and the degree of pre-excitation remained constant, despite fourdifferent AH intervals, strongly suggestive of bystander fasciculoventricular AP.A B C D85Marek Jastrzębski, Piotr Kukla, Fasciculoventricular accessory pathwaywww.cardiologyjournal.orgpresent case) and a fixed HV interval with a con-stant degree of pre-excitation during incrementalatrial pacing, premature atrial stimuli or supraven-tricular tachycardia, are hallmarks of a fasciculov-entricular AP [1–3].The induced tachycardia showed pre-excitationidentical to that during sinus rhythm, since in bothsituations the fasciculoventricular AP acted asa bystander. The P waves during the tachycardia,which were visible after the QRS complexes, wereevidently positive in leads II and III (Fig. 2), exclud-ing from the diagnosis atrioventricular nodal reen-trant tachycardia. Concentric and decremental ret-rograde activation pattern during ventricular pac-ing narrowed the differential diagnosis to atrialtachycardia or atrioventricular reentry tachycardiausing a concealed superior or superoparaseptal AP.Moreover, Figure 2 shows fortuitous right ventricu-lar premature depolarization originating close to thetip of the right ventricular catheter (positioned atthe midseptum) and appearing 20 ms before the Hisbundle that did not influence the timing of subse-quent atrial depolarization, a finding strongly argu-ing against the presence of a concealed atrioven-tricular AP. Therefore, a probable diagnosis of fo-cal atrial tachycardia was made. Due to the difficultinducibility and short-lasting nature of the arrhyth-mia, this diagnosis could not be confirmed by en-trainment or other differentiating maneuvers. How-ever, the induced arrhythmia that was well tolerat-ed, short lasting and inducible only on high-doseisoprenaline, was considered of little or no clinicalsignificance and the procedure was aborted at thisstage. Finally syncope was attributed to epilepsisand empirical anti-epileptic therapy was re-intro-duced. During ambulatory follow-up of 10 months— syncope did not recur.DiscussionFasciculoventricular bypass tracts are consid-ered a very rare form of pre-excitation [4]. The trueprevalence of these APs is probably underestimat-ed because of usually minimal pre-excitation in theECG and asymptomatic course [3]. Electrocardio-graphic characterization of fasciculoventricular APsis based on only a few published cases and caseseries [1, 2].Signs of manifest pre-excitation in ECG can besubtle, depending on the location of the AP and thedifference between conduction times through thatAP and the atrioventricular node. In the presentcase, an apparent small septal q wave in V6 couldargue against pre-excitation [4]. However, asindicated by Bogun et al. [4], a tiny delta wave pro-ducing an rsR’ pattern with a very small r wave canlead to the erroneous conclusion that a q wave inV6 is present. Careful QRS examination in the V6suggested that our case was such an example.Therefore, the present ECG, despite only small in-itial QRS slurring and borderline PR interval, indeedindicates the presence of subtle pre-excitation. Inthe era of interventional treatment of arrhythmias,it is important to differentiate pre-excitation patterndue to fasciculoventricular AP and superoparasep-tal AP. In both situations, the ECG picture mightbe similar and an erroneous assumption that a su-peroparaseptal AP is present might lead to an un-necessary and risky ablation attempt close to theAV node and His bundle. The ECG picture in thepresent patient was more compatible with the di-agnosis of fasciculoventricular AP, since, unlikesuperoparaseptal atrioventricular APs, fasciculo-ventricular APs often characterize a QRS of no morethan 120 ms and an R wave duration in V1 of lessthan 35 ms [1, 2].Another important observation suggestive offasciculoventricular AP is the presence of minimaland constant degree of pre-excitation despite dif-ferent PR intervals and despite different heart rates.However, a final diagnosis can be made only dur-ing electrophysiological study with observation ofa short and constant HV interval despite decremen-tal AV conduction with prolongation of the AH in-terval or atrioventricular block or observation of anunchanged pre-excitation pattern during His bun-dle extrasystole [5].If the refractory period of a fasciculoventricu-lar AP is longer than the AV node refractory period(and also the His bundle refractory period), thenproperly timed premature atrial depolarization canblock in the fasciculoventricular AP with immedi-ate QRS normalization and HV interval prolonga-tion, thus showing the impact of the fasciculoven-tricular fiber on the ECG picture. However, thiscould not be achieved in our case despite severalattempts, probably due to the short refractory pe-riod of the AP. Selective blocking of the fasciculo-ventricular fiber with normalization of QRS mor-phology can also be achieved by administration ofa class IA antiarrhythmic drug [6]. Therefore, for dia-gnostic purposes, 50 mg ajmalin was administeredintravenously. Within minutes, this resulted in PRprolongation, HV normalization, disappearance ofthe delta wave, increased R wave amplitude in V1and the appearance of a septal Q wave in V6 (Fig. 3).These effects were similar to those described byIto et al. [6], and were considered final confirma-86Cardiology Journal 2010, Vol. 17, No. 1www.cardiologyjournal.orgFigure 3. Findings five minutes after intravenous ajmaline administration. A 12-lead electrocardiogram and intracardiacelectrograms showing PR prolongation, HV normalization, disappearance of the delta wave, increase in amplitude ofthe R wave in V1 and appearance of a septal Q wave in V6, as compared to the data shown in Figure 1.tion that a fasciculoventricular AP was indeed re-sponsible for the minimal, constant pre-excitationpattern in the ECG of our patient.However, these rare APs are considered a mis-leading electrocardiographical curiosity rather thana substrate for arrhythmias. Specifically, it is im-possible for these APs to cause fast ventricular re-sponse during atrial fibrillation and syncope becausethe fasciculoventricular AP takes off below the AVnode, from the His-Purkinje system. Moreover, fas-ciculoventricular bypass tracts were never proved tobe a substrate for re-entrant arrhythmias, probably be-cause of the close proximity to the native conductionsystem that precludes conduction delay necessary forestablishment of re-entry. Consequently, the pre-excitation in our case, although present, was unre-lated to the patient’s symptoms. However, coexist-ence of a bystander fasciculoventricular pathway withother accessory pathways or different arrhythmias,like atrioventricular nodal reentrant tachycardia oratrial tachycardia or even symptoms suggestive ofarrhythmias, might be very misleading.In conclusion, a fasciculoventricular AP maymimic an atrioventricular AP pre-excitation pattern,and this can lead to diagnostic and therapeutic di-lemmas in the context of heart palpitations and/orsyncope. The current case shows the classic elec-trocardiographical and electrophysiological featuresof this rare AP variant.Limitations of the studyIn the current case despite exclusion of mani-fest atrioventricular accessory pathway and firmdiagnosis of fasciculoventricular pathway, exclusionof a concomittant, concealed septal accessory path-way was based only on single observation that ear-ly premature ventricular depolarization during tachy-cardia did not advance next atrial depolarization;parahisian pacing was not performed and otherdiagnostic maneuvers were not feasible due toprompt spontaneous termination of the tachycardia.Moreover, it was not possible to completely excluderelationship between the induced tachycardia andsyncopal episodes. Nevertheless, the non-sustainedtachycardia that was induced during high-dose iso-prenaline infusion was well tolerated and was like-ly a non-clinical arrhythmia, further clinical courseof the patient seems to support that.87Marek Jastrzębski, Piotr Kukla, Fasciculoventricular accessory pathwaywww.cardiologyjournal.orgAcknowledgementsThe authors do not report any conflict of inter-est regarding this work.References1. Oh S, Choi YS, Choi EK et al. Electrocardiographic characteris-tics of fasciculoventricular pathways. Pacing Clin Electrophysiol,2005; 28: 25–28.2. Sternick EB, Rodriguez LM, Gerken LM, Wellens HJ. Electro-cardiogram in patients with fasciculoventricular pathways:A comparative study with anteroseptal and midseptal accessorypathways. Heart Rhythm, 2005; 2: 1–6.3. Josephson ME. Preexcitation syndromes. In: Josephson ME ed.Clinical cardiac electrophysiology. Lippincott Williams &Wilkins, Philadelphia 2008.4. Bogun F, Kalusche D, Li YG, Auth-Eisernitz S, Gronefeld G,Hohnloser SH. Septal Q waves in surface electrocardiographiclead V6 exclude minimal ventricular preexcitation. Am J Cardiol,1999; 84: 101–104.5. Tung R, Sklyar E, Josephson M. An unusual form of preexcitation:Fasciculoventricular bypass tract. Heart Rhythm, 2008; 5: 1767–1768.6. Ito M, Onodera S, Noshiro H et al. Effect of class Ia antiarrhyth-mic agents on fasciculoventricular fibers. J Electrocardiol, 1990;23: 323–329.

Fasciculoventricular accessory pathway: A misleading and unusual bypass tract

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Fasciculoventricular accessory pathway: A misleading and unusual bypass tract

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