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Clinical Electrophysiology

Editor-in-Chief

Dr. David J. Wilber.

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Verapamil-Sensitive Upper SeptalIdiopathic Left Ventricular Tachycardia
Prevalence, Mechanism, andElectrophysiological Characteristics
Ahmed Karim Talib, MD, PHD,* Akihiko Nogami, MD, PHD,* Suguru Nishiuchi, MD,y Shinya Kowase, MD,zKenji Kurosaki, MD,z Yumie Matsui, MD,x Satoshi Kawada, MD,k Atsuyuki Watanabe, MD,kMasatsugu Nozoe, MD, PHD,{ Kikuya Uno, MD, PHD,# Atsuhiko Yagishita, MD,** Yasuteru Yamauchi, MD,**Yoshihide Takahashi, MD,yy Taishi Kuwahara, MD,yy Atsushi Takahashi, MD,yy Koji Kumagai, MD, PHD,yShigeto Naito, MD,y Tetsuya Asakawa, MD,zz Yukio Sekiguchi, MD,* Kazutaka Aonuma, MD, PHD*

ABSTRACT

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OBJECTIVES This study sought to demonstrate the prevalence, mechanism, and electrocardiographic and electro-

physiological characteristics of upper septal idiopathic left fascicular ventricular tachycardia (US-ILVT).

BACKGROUND ILVT is classified into left anterior and posterior types with no clear data about US-ILVT.

METHODS Among 193 ILVT patients, we identified 12 patients (6.2%; age 41 � 22 years, 7 men) with US-ILVT.

RESULTS Of 12 patients with US-ILVT, 6 patients (50%) had previous history of radiofrequency catheter ablation

for common ILVT. Sustained VT (cycle length: 349 � 53 ms) was seen in all patients with a QRS interval slightly wider

(104 � 18 ms) than that during sinus rhythm (90 � 19 ms). The VT exhibited an identical QRS configuration as sinus

rhythm in 6 (50%) and incomplete right bundle branch block configuration in another 6. His-ventricular interval during

VT was always shorter than that during sinus rhythm (27 � 5 ms vs. 47 � 10 ms). Purkinje potentials were activated in a

reverse direction to that of common ILVT; namely, the diastolic potential (P1) was activated retrogradely but the pre-

systolic potential (P2) was activated antegradely. At the left upper-middle ventricular septum, P1 potential was recorded

during VT, preceding the QRS by 54 � 20 ms. Radiofrequency catheter ablation at that site eliminated the VT with no

recurrence during a 58 � 35 months of follow-up.

CONCLUSIONS US-ILVT is an identifiable VT that shares common criteria with ILVT and has a narrow QRS

interval. Some US-ILVT cases appeared after common ILVT ablation. It is a reverse type of common ILVT

(orthodromic form) with baseline morphological abnormalities that might provide a potential substrate for such VT.

(J Am Coll Cardiol EP 2015;1:369–80) © 2015 by the American College of Cardiology Foundation.

V erapamil-sensitive fascicular tachycardia isthe most common form of idiopathic leftventricular tachycardia (ILVT). It was first

recognized as an electrocardiographic entity by Zipes

m the *Cardiovascular Division, Faculty of Medicine, University of Tsuku

fectural Cardiovascular Center, Maebashi, Japan; zDepartment of Hear

kohama, Japan; xDepartment of Cardiology, Saiseikai Izuo Hospital, Osa

spital, Fukuyama, Japan; {Division of Cardiology, Cardiovascular and

kuoka, Japan; #Sapporo Heart Center, Sapporo Cardiovascular Clinic, Sapp

d Cross Hospital, Tokyo, Japan; yyCardiovascular Center, Yokosuka Kyos

ision, Yamanashi Kosei Hospital, Yamanashi, Japan. Dr. Nogami has rec

ston Scientific; and an endowment from Medtronic and Johnson & Johnso

ationships relevant to the contents of this paper to disclose.

nuscript received April 15, 2015; revised manuscript received May 11, 201

et al. (1), who defined its morphology as right bundlebranch block (RBBB) and left axis deviation. That VTwas successfully suppressed by radiofrequency cath-eter ablation (RFCA) at the vicinity of the left

ba, Tsukuba, Japan; yDivision of Cardiology, Gunma

t Rhythm Management, Yokohama Rosai Hospital,

ka, Japan; kDivision of Cardiology, Fukuyama City

Aortic Center, Saiseikai Fukuoka General Hospital,

oro, Japan; **Department of Cardiology, Musashino

ai Hospital, Yokosuka, Japan; and the zzCardiologyeived lecture honoraria from St. Jude Medical and

n. All other authors have reported that they have no

5, accepted May 21, 2015.

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TABLE

Patient #

1

2

3

4

5

6

7

8

9

10

11

12

Mean

ECG ¼ ele

ABBR EV I A T I ON S

AND ACRONYMS

ECG = electrocardiographic

H-V = His-ventricular

ILVT = idiopathic left

ventricular tachycardia

LAF = left anterior fascicle

LPF = left posterior fascicle

LV = left ventricle

LVS = left ventricular septum

RBBB = right bundle branch

block

RF = radiofrequency

RFCA = radiofrequency

catheter ablation

US = upper septal

US-ILVT = upper septal

idiopathic left ventricular

tachycardia

VT = ventricular tachycardia

VTCL = ventricular tachycardia

cycle length

Talib et al. J A C C : C L I N I C A L E L E C T R O P H Y S I O L O G Y V O L . 1 , N O . 5 , 2 0 1 5

Left Upper Septal VT O C T O B E R 2 0 1 5 : 3 6 9 – 8 0

370

posterior fascicle (LPF) (2). Another less com-mon type of fascicular VT, characterized byRBBB morphology and right axis deviation,which has been described by Ohe et al. (3),can be suppressed by RFCA at the left ante-rior fascicle (LAF) area (3,4).

These types of VT have been studiedalmost extensively; however, little is knownabout the prevalence, mechanism, and sur-face electrocardiographic (ECG) and electro-physiological characteristics of upper septal(US) fascicular idiopathic left ventriculartachycardia (US-ILVT) (5–7). After analyzingdata from 9 different experienced centers,the purpose of this study was to clarify theabove-mentioned points along with the re-sults of long-term follow-up after RFCA.

METHODS

STUDY POPULATION. From February 2006through September 2014, in a multicenterstudy analyzing data of 193 patients who

underwent electrophysiological study of verapamil-sensitive fascicular VT, we identified 12 patients(7 men, mean age: 41 � 22 years) who had distinctECG and electrophysiological characteristics of US-ILVT. In each patient, after detailed medical historyand examination, structural heart diseases were ruledout by a standard investigation protocol including12-lead ECG, chest radiographs, echocardiography,cardiac computed tomography when appropriate, andcoronary angiography when indicated. The study

1 Patient Characteristics

Age(yrs) Sex Presentation

Previous CommonILVT Ablation

18 M Palpitation 1 session

15 M Syncope 2 sessions

38 M Palpitation 1 session

24 F Palpitation 2 sessions

83 F Palpitation None


64 F Syncope None

66 M Palpitation None

35 M Palpitation 2 sessions

41 M Palpitation 2 sessions


42 M Palpitation None

41 � 22

ctrocardiography; ILVT ¼ idiopathic left ventricular tachycardia.

was approved by the local research ethics committeesof the participating institutes, and all patients gavetheir written informed consent.

ELECTROPHYSIOLOGY STUDY. An electrophysiologystudy was performed after withdrawing all antiar-rhythmic drugs for $5 half-lives. Standard multi-electrode catheters were placed in the high rightatrium, His-bundle region, and right ventricularseptum. Programmed atrial and ventricular stimu-lation was performed using a maximum of 3extrastimuli at 2 different driven cycle lengthsfrom the right atrium and right ventricular septum.If sustained VT was not induced, the stimulationwas repeated during isoproterenol infusion (0.5 to2.0 mg/min).

MAPPING AND ABLATION. RFCA was performed in10 patients. In the remaining 2 patients (#4 and #6)who had the same clinical and electrophysiologicalcharacteristics of US-ILVT, RFCA was not performed,but an electrophysiological study was done. Througha femoral arterial approach, a 7-F quadripolar steer-able electrode catheter with a 4-mm tip and 2-mminterelectrode spacing between the distal 2 elec-trodes was positioned at the interventricular septumof the left ventricle to record the intracardiac elec-trograms, as well as to pace and ablate. In a few pa-tients, an octapolar or decapolar steerable electrodecatheter with 1.25-mm electrode length and 2-mminterelectrode spacing (Boston Scientific, Natick,Massachusetts; or St. Jude Medical, Minnetonka,Minnesota) was positioned at the left ventricularseptum (LVS). A 3-dimensional electroanatomical

Sinus Rhythm ECG Verapamil-Sensitivity

Small Q-wave in leads I, II, III, aVL, and aVF Yes

Deep S-wave in lead IDeep Q-wave in lead III

Yes

Small Q-wave in leads II, III, and aVF Yes

Deep S-wave in leads I and aVLSmall Q-wave in lead III

Yes

Deep S-wave in lead aVL Not administrated

Small S-wave in lead aVL Not administrated

Deep S-wave in lead III Yes

Deep S-wave in leads III and aVF Yes

Deep S-wave in lead IDeep Q-wave in leads III and aVF

Yes

Deep Q-wave in lead III Yes

Small S-wave in lead ISmall Q-wave in lead III

Not administrated

Deep S-wave in lead aVL Yes

FIGURE 1 Morphological Changes During Sinus Rhythm Caused by the Previous RFCA

for Common ILVT

An S-wave in leads I and aVL and Q waves in lead III and aVF were observed after the

previous radiofrequency catheter ablation (RFCA) at the left posterior fascicular vicinity for

treatment of common idiopathic left ventricular tachycardia (ILVT) (Patient #9).

TABLE 2 ECG Characteristics of US-ILVT

Patient #QRS Duration DuringSinus Rhythm (ms)

QRS DurationDuring VT (ms)

Precordial QRSConfiguration During VT VT Axis

1 90 105 Identical to sinus QRS RAD




5 128 128 Identical to sinus QRS Similar to sinus axis

6 90 90 Identical to sinus QRS Similar to sinus axis

7 80 130 IRBBB type Similar to sinus axis




11 80 118 IRBBB type Normal but slightlydifferent fromsinus axis

12 60 75 IRBBB type Normal but slightlydifferent fromsinus axis

Mean 90 � 19 104 � 18

IRBBB ¼ incomplete right bundle branch block; RAD ¼ right-axis deviation; US ¼ upper septal; other abbrevi-ations as in Table 1.

J A C C : C L I N I C A L E L E C T R O P H Y S I O L O G Y V O L . 1 , N O . 5 , 2 0 1 5 Talib et al.O C T O B E R 2 0 1 5 : 3 6 9 – 8 0 Left Upper Septal VT

371

system (CARTO, Biosense-Webster, Diamond Bar,California; or NavX system, EnSite, St. Jude Medical)was used in 9 patients.

In 8 of 10 patients who underwent RFCA, an irri-gation catheter was used. In the majority of the cases,RF energy was delivered for 30 to 120 s during sinusrhythm to avoid any left bundle or atrioventricularblock. Maximum power was 50 W. When using anonirrigated catheter, RFCA was done in temperature-controlled mode at a maximal target temperature of55�C and maximum power of 50 W. We performedRFCA in this region using a low power output(i.e., 10 W), which was increased gradually whilecarefully monitoring for the development of junc-tional rhythm or atrioventricular block. After ablation,programmed stimulation was repeated with andwithout isoproterenol infusion.

FOLLOW-UP. The patients were monitored for 1 to 3days after the ablation. After discharge, the patientswere followed up in an outpatient clinic at an intervalof 3 months in the first year after ablation; after that,they were followed up at approximately yearly in-tervals. The follow-up period was for 58 � 35 months(12 to 112 months) without using any antiarrhythmicmedications.

STATISTICAL ANALYSIS. The values are given as themean � SD. The significance of the differences be-tween groups was assessed by the Student t test.Changes in electrophysiological parameters wereanalyzed by paired Student t test. A p value of <0.05was considered statistically significant.

RESULTS

PREVALENCE AND CLINICAL CHARACTERISTICS. Among193 patients who were referred for the therapy ofILVT, 12 patients (6.2%) had US type. The patientcharacteristics are shown in Table 1. There were 7 menand 5 women between 15 and 83 years of age. All hadnormal LV systolic function. Ten patients (83%) pre-sented with palpitations and 2 presented with syn-cope associated with VT. Intravenous administrationof verapamil was used in 9 patients, and was effectivein VT termination in all. Six patients (50%) had aprevious history of common ILVT, which was treatedby RFCA. Among them, 4 patients had 2 ablationsessions for common ILVT.

SURFACE ECG FINDINGS. The baseline ECG exhibi-ted sinus rhythm in all patients with QRS durationof <120 ms. A notable finding was the presence of aQ-wave in the inferior leads and/or an S-wave inlead I and/or aVL. No structural abnormalities couldexplain these findings in 6 patients, whereas in the

FIGURE 2 Different ECG Patterns During Sinus Rhythm and the US-ILVT

Ventricular tachycardia (VT) can be classified into 2 distinct QRS morphological types: type

1: an identical precordial QRS configuration to that during sinus rhythm (A, B); and type 2:

incomplete right bundle branch block (RBBB) pattern (C, D). Both types can be divided into

subgroups according to the axis: (A) an identical precordial QRS configuration to that of

sinus rhythm with right axis deviation (Patient #2); (B) an identical QRS configuration and

axis to those of sinus rhythm (Patient #6), (C) an incomplete RBBB configuration with an

identical QRS axis to that of sinus rhythm (Patient #9), and (D) an incomplete RBBB

configuration with normal axis but different from that of sinus rhythm (Patient #12). ECG ¼electrocardiography; US-ILVT ¼ upper septal idiopathic left ventricular tachycardia.

Continued on the next page



372

remaining 6 patients, those morphological changesdeveloped after previous RFCA session(s) at the LPFvicinity, which resulted in new or deepening Q wavesin the inferior leads and/or appearance of or deep-ening S waves in lead I and/or aVL (Table 1, Figure 1).

As shown in Table 2, all patients presented withsustainedmonomorphic VT (cycle length: 349� 53ms)with QRS duration slightly wider than that duringsinus rhythm (104 � 18 ms during VT vs. 90 �19 ms during the VT, p ¼ 0.882). Figure 2 shows

representative ECG during sinus rhythm and VT. TheVT can be classified into 2 distinct QRS morphologicaltypes: 1) type 1: 6 patients (50%) had an identical pre-cordial QRS configuration to that during sinus rhythmwith right axis deviation in 4 patients (Figure 2A)and an identical QRS configuration and axis to that ofsinus rhythm in the remaining 2 patients (Figure 2B);and 2) type 2: 6 patients (50%) had incomplete RBBBpattern with an identical QRS axis to that duringsinus rhythm in 4 patients (Figure 2C) and normal QRSaxis but slightly different from that during sinusrhythm in the remaining 2 patients (Figure 2D).

ELECTROPHYSIOLOGICAL CHARACTERISTICS, MAPPING,

AND ABLATION. The electrophysiological findings aresummarized in Table 3. All the treated patients hadnormal His-ventricular (H-V) interval during sinusrhythm. The US-VT was induced spontaneously dur-ing catheter manipulation in 3 patients, by burst atrialpacing in 4 patients, burst ventricular pacing in2 patients, and by programmed ventricular extra-stimulus in 2 patients. During VT, retrograde activa-tion of the His bundle was recorded before the onsetof the QRS complex with an H-V interval that wasalways shorter during VT than that during sinusrhythm (27 � 10 ms vs. 47 � 5 ms, p < 0.001). Theelectrophysiological characteristics are summarizedin Table 4. Overdrive pacing from the right atrium wasattempted in 9 patients; however, ventricular capturewas seen in only 4 patients because of atrioventric-ular block during atrial entrainment pacing in the restof the patients. In these 4 patients, there was evi-dence of constant and progressive fusions consistentwith transient entrainment and suggesting a reen-trant mechanism of the VT.

Typical surface ECG and intracardiac electrogramsof a patient with US-ILVT are shown in Figure 3(Patient #9). During sinus rhythm, baseline ECGexhibited normal conduction intervals. The patientdeveloped common ILVT in which his ECG showedRBBB configuration and left axis deviation. A fewyears later, after 2 ablation sessions for commonILVT, the patient developed US-ILVT. ECG duringsinus rhythm showed an S-wave in lead I and aQ-wave in leads III and aVF. ECG during VT exhibitedincomplete RBBB pattern and an identical QRS axis tothat of sinus rhythm (Figure 3A). Figure 3B showsintracardiac recordings during sinus rhythm, com-mon ILVT, and US-ILVT. During sinus rhythm, adecapolar electrode catheter on the LVS revealedthat the conduction propagated antegradely gener-ating a pre-systolic potential (P2), which was recordedafter the His-bundle potential and before the onset ofthe QRS complex, suggesting LPF and the adjacent

FIGURE 2 Continued


373

Purkinje potentials (Figure 3B, left panel). Duringcommon ILVT, a diastolic potential (P1) and pre-systolic potential (P2) were seen (Figure 3B, middlepanel). Whereas P1 was recorded earlier from theproximal than from the distal electrodes, P2 wasrecorded earlier from the distal than from the prox-imal electrodes. His-bundle potential was recordedafter the onset of the QRS complex (negative H-Vinterval). During US-ILVT (Figure 3B, right panel), P1

was recorded earlier from the distal than from theproximal electrodes, whereas P2 was recorded earlierfrom the proximal than from the distal electrodes,similar to that during sinus rhythm. His-bundle po-tential preceded the onset of the QRS complex by 32ms, which was shorter than that during sinus rhythm(45 ms). Figure 3C shows the position of a decapolarcatheter on the LVS. An ablation catheter was posi-tioned at the upper-middle ventricular septum(Figure 4A) where the diastolic P1 preceded the onsetof the QRS interval by 52 ms. Entrainment from thissite resulted in concealed fusion and post-pacinginterval–ventricular tachycardia cycle length (VTCL)difference of 5 ms and an interval between the pacingstimulus and QRS onset of 52 ms, equal to the P-QRSinterval during VT (Figure 4B). VT was slowed andterminated by RF energy application at this sitewithin a few seconds (Figure 4C) and VT becamenoninducible.

Anatomically, the ablation site was selected at theleft upper-middle ventricular septum, mid-way be-tween the His-bundle recording site and the LV apex.Ablation at the most basal portion of the LVS was notperformed to avoid left bundle/atrioventricularblock. Electrophysiologically, the ablation site wascharacterized by the presence of the diastolic Pur-kinje potential (P1) during VT and the absence of bothHis-bundle and atrial potentials during sinus rhythm.A diastolic Purkinje potential (P1) at the successfulablation site preceded the QRS onset (P1-QRS) by55 � 21 ms (Table 4). Entrainment pacing at theablation site was performed in 9 patients and resul-ted in concealed fusion in 4 patients and a post-pacing interval–VTCL difference of 16 � 5 ms. In theremaining 5 patients, selective capture of the dia-stolic Purkinje potential (P1) was not obtained.

UPPER SEPTAL ILVT SUBTYPES. Although almostsimilar electrophysiological findings of the successfulablation site were observed in all patients who un-derwent RFCA, the H-V interval during VT and theVTCL were relatively longer in morphological type 1group (an identical precordial QRS configurationto that during sinus rhythm) than in type 2 group(incomplete RBBB pattern); H-V interval: 31 � 11 ms

versus 22 � 5 ms; VTCL: 368 � 61 ms versus 329 �40 ms, for type 1 and type 2 groups, respectively.

COMPLICATIONS AND FOLLOW-UP. No atrioven-tricular block was seen during or after the RFCA.In 1 patient (#12), transient left bundle branch blockwas seen, which recovered 8 s after the discontinua-tion of the RF energy delivery. One patient (#9)developed a mild worsening of an already existingright axis deviation. During 58 � 35 months (12 to 229months) of follow-up of ablated patients, no VTrecurrence was seen without using any antiarrhythmicmedications in any patient. In 2 patients (#4 and #6)who did not undergo RFCA, treatment with beta-blockers and verapamil was started. There have been

FIGURE 3 Surface and Intracardiac ECG During Sinus Rhythm, Common ILVT, and US-ILVT (Patient #9)

(A) The baseline sinus ECG exhibited normal axis with normal conduction intervals, and the common ILVT ECG exhibited RBBB configuration and

left axis deviation. After RFCA for the common ILVT, QRS configuration during sinus rhythm exhibited an S-wave in lead I and Q waves in leads

III and aVF. A few years after common ILVT ablation, the patient developed US type, which exhibited incomplete RBBB configuration and

normal axis. (B) Intracardiac recordings during sinus rhythm, common ILVT, and US-ILVT, demonstrating the activation sequence of the dia-

stolic potential (P1) (red arrows) and pre-systolic Purkinje potential (P2) (blue arrows) during each rhythm. For the detail, see the text. (C)

Fluoroscopic images in the right anterior oblique (RAO) and left anterior oblique (LAO) views demonstrating the position of the diagnostic

decapolar catheter at the left ventricular septum (LVS). A ¼ atrial electrogram; H ¼ His-bundle potential; HBE ¼ His-bundle electrogram;

HRA ¼ high right atrium; RVS ¼ right ventricular septum; other abbreviations as in Figures 1 and 2.




374

FIGURE 3 Continued


375

no recurrences during a period of 11 and 13 months,respectively.

DISCUSSION

MAIN FINDINGS. This is the first study to demon-strate that 6.2% of ILVT cases are due to US-ILVT,which is characterized as follows: 1) one-half of thepatients had a previous history of RFCA for commonILVT, mostly multiple ablation sessions; 2) normalsinus ECG and intracardiac conduction intervals withthe presence of minor morphological abnormalities

TABLE 3 Electrophysiological Characteristics of US-ILVT

Patient #VT Induction

ModeVTCL(ms)

H-V IntervalDuring

Sinus Rhythm(ms)

H-V IntervalDuring VT

(ms)

1 Spontaneous 340 55 20

2 Atrial pacing 320 45 25


4 Spontaneous 440 Notavailable

Notavailable


6 Ventricular pacing 350 55 50

7 Ventricular pacing 300 43 Notavailable




11 Ventricularextrastimulation

400 42 22

12 Ventricularextrastimulation

350 42 20

Mean 349 � 53 47 � 5 27 � 10

H-V ¼ His-ventricular; VTCL ¼ ventricular tachycardia cycle length; other abbre-viations as in Tables 1 and 2.

including Q waves in the inferior limb leads and/orS waves in limb leads I and/or aVL; 3) VT exhibiting anidentical precordial R-wave progression to that ofsinus rhythm or incomplete RBBB morphology;4) during VT, retrograde activation of the His-bundlebefore the QRS onset occurring with an H-V intervalsignificantly shorter during VT than that during sinusrhythm; 5) the presence of common characteristics ofre-entrant common ILVT such as inducibility withventricular and/or atrial stimulation, entrainment,and verapamil-sensitivity; and 6) successful VTablation at the left upper-middle ventricular septum,where the diastolic Purkinje potential (P1) was recor-ded during VT.

Although sporadic cases of left US-VT have beenreported (5–7), to the best of our knowledge, this is

TABLE 4 Entrainment and Ablation Characteristics of US-ILVT

Patient #EntrainmentFrom HRA

Concealed FusionDuring Entrainmentat the Successful Site

PPI-VTCL(ms)

P1-QRS atSuccessful Site

(ms)

1 Yes Yes 14 35

2 Not attempted Not attempted Not attempted 50

3 AVB Yes 18 50

4 Not attempted RFCA not done Not available Not available

5 Yes No Not available 82

6 Not attempted RFCA not done Not available Not available

7 AVB Yes 22 52

8 Yes No Not available 90

9 Yes Yes 5 52

10 AVB No Not available 35



Mean 16 � 5 55 � 21

AVB ¼ atrioventricular block; HRA ¼ high right atrium; PPI ¼ post-pacing interval; RFCA ¼ radiofrequencycatheter ablation; other abbreviations as in Tables 1 to 3.

FIGURE 4 Entrainment and Successful Ablation of US-ILVT (Patient #9)

(A) Ablation catheter was positioned at upper-middle septum of the left ventricle. (B) The diastolic P1 preceded the onset of the QRS by 52 ms.

Entrainment from this site resulted in concealed fusion and post-pacing interval–ventricular tachycardia cycle length (PPI-VTCL) difference

of 5 ms and an interval between the pacing stimulus and QRS onset of 52 ms, equal to the P1-QRS interval during VT. (C) A radiofrequency energy

application at this site slowed and terminated the VT within a few seconds. ABL ¼ ablation catheter; other abbreviations as in Figures 1 to 3.




376

the first study to fully demonstrate the prevalence,mechanism, and clinical and electrophysiologicalcharacteristics of this type of VT.

BASELINE ECG. In all patients, although the baselineECG exhibited normal conduction intervals, minormorphological changes in the limb leads were seenincluding Q waves in the inferior leads and/or S wavesin leads I and/or aVL. Interestingly, these ECGchanges developed after common ILVT ablation in

50% of the patients, indicating that the local RF en-ergy that was applied to the Purkinje fiber network ofthe LPF area resulted in conduction damage to theLPF and created those ECG changes. It is noteworthythat in 6 patients who had undergone RFCA forcommon ILVT, the original VT was completely cured.In the rest of the patients, these morphological ab-normalities were of an unknown etiology. Whetheriatrogenic or idiopathic, these morphological changesindicate local conduction damage that might have

FIGURE 4 Continued


377

created a slow conduction area and provided a sub-strate for re-entry resulting in the US-ILVT.ECG CHARACTERISTICS OF UPPER SEPTAL ILVT.

The QRS morphology during this VT was quite

FIGURE 5 Schematic Representation of the Intraventricular Activat

(A) During sinus rhythm, the impulse propagates antegradely down the

from P2 to P1 at the point of fusion; therefore, P1 is buried in the local ve

in the reverse direction. VT activation propagates antegradely from the

fascicle (LAF) and LPF are the antegrade limbs of the re-entrant circuit, w

at the middle septum. All the hypothetical circuits are demonstrated in

decremental property and verapamil-sensitivity. The red undulating line

the unsolved parts in the circuit. LBB ¼ left bundle branch; other abbre

characteristic, with a narrow QRS complex and eitheran identical QRS configuration to that of sinus rhythmor an incomplete RBBB configuration, and the limbleads exhibited either normal axis or right axis

ion Sequence During Sinus Rhythm, Common ILVT, and US-ILVT

left posterior fascicle (LPF) giving rise to P2 then the activation goes

ntricular activation. (B) During common ILVT, P1 and P2 are activated

basal to the apical site. (C) During US-ILVT, both the left anterior

hereas the retrograde activation occurs via the abnormal Purkinje fiber

the RAO position. P1 refers to a specialized Purkinje tissue with

represents a zone of slow conduction. The dotted lines indicate

viations as in Figures 1 to 3.

FIGURE 6 Hypothetical Circuits of 2 Morphological Subtypes (Type 1 and Type 2)

The blue arrows represent the antegrade limbs of the VT circuit. There is difference in the hypothetical distance between the His-bundle and

the upper turn-around point of the US-ILVT. See the text for details. Abbreviations as in Figures 1 and 2.



378

deviation. It is known that ILVT arising from theintraventricular conduction system typically haveRBBB morphology and left (common form) or right(uncommon form) axis depending on the Purkinjenetworks involved (1–4). In the US type, the pres-ence of a narrow QRS interval, almost identicalQRS morphology to that of sinus rhythm, andnormal frontal plane axis indicate a near-normalactivation using the US His-Purkinje network thatis not significantly different from the normal ven-tricular depolarization. Some of the present caseshad been misdiagnosed as supraventricular tachy-cardia in previous hospitals because of their QRSconfiguration and their verapamil-sensitivity. Thepresent study calls attention to the observationthat narrow-QRS tachycardia can have a ventricularorigin and should be considered, especially inpatients with a history of RFCA of Purkinje-relatedarrhythmias.

ELECTROPHYSIOLOGICAL CHARACTERISTICS. In addi-tion to the presence of the general electrophysio-logical characteristics of ILVT, 2 importantcharacteristics were seen in US-ILVT. First, duringVT, retrograde activation of the His bundle wasrecorded before the onset of the QRS complex withan H-V interval that was significantly shorter thanthat during sinus rhythm, and this can be used to

differentiate this tachycardia from supraventriculartachycardia. This is in contrast to the common formof ILVT where His potential is usually recorded afterthe QRS onset (8). Second, during the VT, diastolicPurkinje potential preceding the His potential wasrecorded from the left upper-middle ventricularseptum, where the left bundle potential was recordedduring sinus rhythm. Targeting that diastolic poten-tial resulted in VT termination.

MECHANISM OF THE TACHYCARDIAS AND CIRCUIT

DIAGRAM. Overwhelming evidence suggests thatILVT is caused by a re-entrant circuit incorporatingthe Purkinje system with an excitable gap and a slowconduction area (8,9). To demonstrate the VT circuitin US-VT, the patient mentioned in Figures 3 and 4is taken as an example. During sinus rhythm, theconduction propagated antegradely (proximal todistal) generating a pre-systolic Purkinje potential(P2) followed by the ventricular activation (Figure 3B,left panel). During common ILVT, the activationpropagated antegradely from the basal to the apicalsite on the LVS (Figure 3B, middle panel). On the otherhand, in US-ILVT, the activation sequence of P1 wasfrom the distal to proximal septum, whereas theactivation sequence of P2 was from the proximal todistal septum, similar to that during sinus rhythm(Figure 3B, right panel).

PERSPECTIVES

COMPETENCY IN MEDICAL KNOWLEDGE: US-ILVT is a rare

but identifiable VT and is a reverse type of common ILVT

(orthodromic form) with baseline morphological abnormalities

that might provide a potential substrate for such type of VT.

TRANSLATIONAL OUTLOOK: Whole circuits of common

(posterior type), uncommon (anterior type), ILVT and US-ILVT

are still unclear, especially the slowest and longest part in the

circuit. Further studies are needed to explore its biomedical

mechanism.


379

Taking these findings together, the hypotheticalcircuit of the US-ILVT is depicted in Figure 5. Duringsinus rhythm (Figure 5A), the sinus impulse propa-gates antegradely down the LPF giving rise to P2 thenthe activation goes from P2 to P1 at the point of fusion;therefore, P1 is buried in the local ventricular activa-tion (8). During common ILVT (Figure 5B), P1 and P2

are activated in the reverse direction, which explainswhy the activation sequenced of P2 is reversed duringsinus rhythm and VT. We suggest that the US-ILVT(Figure 5C) is a “reverse common” or “fast-slow”

variant of ILVT, where both LAF and LPF are theantegrade limbs of the re-entrant circuit, whereasthe retrograde activation occurs via the abnormalPurkinje fiber at middle fascicular area. Although Hisbundle and right bundle branch are bystanders, theywere activated just after the activation of LAF andLPF. This explains why this VT exhibits a narrow QRSconfiguration with a near-normal activation sequenceand inferior axis. P1 represents the common retro-grade limb of the circuit during the VT and can be asuitable ablation target.

Furthermore, the US-ILVT cases with identicalprecordial QRS configuration to that of sinus rhythm(type 1) had a longer H-V interval than did those withincomplete RBBB configuration (type 2); hence, theupper turn around site of the former is more basalthan that of the latter. Longer VTCL in type 1 groupfurther supports such a hypothesis and indicates alarger re-entry circuit in morphological type 1 thanthat in type 2 group (Figure 6).

ARRHYTHMOGENESIS OF UPPER SEPTAL ILVT. Althoughthe presence of a trifascicular (anterior, posterior, andmiddle) left Purkinje system was proved by manyhistological studies mainly on the basis of animal orpost-mortem examinations (10,11), the exact cause ofthe rarity of US-ILVT is unknown. Two possibilitiesmay explain this. 1) A modification of the conductionproperties of the Purkinje network without blockingthe conduction of the LPF. Because 50% of our pa-tients had previous RFCA session(s) in the vicinity ofthe LPF, it is possible that, after ablating the distalLPF for the treatment of common ILVT, the new VToccurred more proximally in the His-Purkinje system,rendering the QRS complex narrower. It is note-worthy that our ILVT cases were ablated in experi-enced centers and the VT was successfully ablatedwithout any further recurrence of the original VT. Forinstance, Figure 1 shows the baseline and post-ablation ECG of Patient #9 who had ablation result-ing in loss of the S waves with the appearance of newQ waves in the inferior limb leads and deeper S wavesin leads I and aVL, indicating local damage to the

distal LPF. Although such a finding has been pro-posed as one of effective endpoints for ablation ofILVT in some studies (12), it pre-disposed the patientto US-ILVT. And, 2) recently, in an in vivo study of theisolated conduction within the left His-Purkinje sys-tem in 25 patients, Long et al. (13) found that the LBBbifurcated into 2 divisions conforming to the LAF andLPF in 23 patients, and into 3 divisions conforming toLAF, left middle, and LPF in only 2 patients, sug-gesting a low incidence of septal fascicle in humanhearts that may partially explain such a very lowincidence of US-VT.

STUDY LIMITATIONS. The most significant limitationwas the sample size. However, to the best of ourknowledge, this was the first study to reflect thedisease rarity and open a new window for mappingand ablation of US-ILVT, for which, catheter ablationwas avoided for fear of creating an atrioventri-cular block. Furthermore, depending on the opera-tor’s preference, good entrainment mapping was notobtained in all cases.

CONCLUSIONS

US-ILVT is a rare but identifiable VT that sharesthe common criteria of ILVT such as inducibilitywith ventricular and atrial stimulation, entrainment,and verapamil-sensitivity with a narrow QRS interval.It is a reverse type of common ILVT (orthodromicform), using the LPF (or LAF) as the antegrade limb ofthe re-entry circuit, with baseline morphological ab-normalities that might provide a potential substratefor such type of VT.

REPRINT REQUESTS AND CORRESPONDENCE: Dr.Akihiko Nogami, Cardiovascular Division, Facultyof Medicine, University of Tsukuba, 1-1-1 Tennodai,Tsukuba 305-8575, Japan. E-mail: [email protected].

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KEY WORDS ablation, left fascicle, leftupper septum, ventricular tachycardia,verapamil

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