Review

Idiopathic ventricular arrhythmias arising from the left ventricularoutflow tract: Tips and tricks

Koji Kumagai, MD, PhDn

Division of Cardiology, Gunma Prefectural Cardiovascular Center, 3-12 Kameizumimachi kou, Maebashi, Japan

a r t i c l e i n f o

Article history:Received 24 January 2014Received in revised form8 February 2014Accepted 14 February 2014

Keywords:Left ventricular outflow tractVentricular arrhythmiasAorto-mitral continuityMitral annulusAortic sinus cusps

a b s t r a c t

Idiopathic left ventricular outflow tract ventricular arrhythmias (LVOT-VAs) arising from the LVOT are rarecompared with the VAs arising from the RVOT. Idiopathic LVOT-VAs have been divided into four subgroupsbased on successful catheter ablation sites: the aorto-mitral continuity (AMC), the anterior site around themitral annulus (MA), the aortic sinus cusps (ASC), and the epicardium. Recognition of the ECG characteristics ofLVOT-VAs combined with anatomical information should facilitate their appropriate diagnosis and treatment.In particular, the AMC is located adjacent to the anterior site of the MA, ASC, and epicardium. All subtypes ofLVOT-VAs, except those with epicardial origins, are successfully treated with endocardial radiofrequencycatheter ablation combined with pace mapping and the identification of the earliest ventricular electrogramwith a prepotential, if it is recordable. In addition, LVOT-VAs originating from an inaccessible area in the LVsummit of the epicardium, which cannot be treated by epicardial catheter ablation, should be differentiatedfrom those in an accessible area using novel electrophysiological characteristics. Despite many morphologicalsimilarities among the subtypes of LVOT-VAs, the ECG characteristics and anatomical information obtainedfrom visualization using computed tomographic image integration with electroanatomical mapping mayadvance the safety and success of catheter ablation of idiopathic LVOT-VAs.

& 2014 Japanese Heart Rhythm Society. Published by Elsevier B.V. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.1. Ablation procedure for LVOT-VAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.2. Classification and frequency of idiopathic VAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.3. Identification of the origin of LVOT-VAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.4. Differentiation of LVOT and RVOT origins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41.5. Classification and frequency of LVOT-VAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.6. Anatomical structures in the LVOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.7. The aorto-mitral continuity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.8. Anterior MA, AMC, and ASC origins of LVOT-VAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.9. Stepwise ECG algorithm for LVOT-VAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.10. Representative cases of anterior MA, AMC, and ASC origins in LVOT-VAs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.11. Stepwise ECG algorithm for the origin of MA-VAs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.12. VAs originating from superior basal septal sites of the MA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.13. ECG characteristics of VAs originating from the aortic root . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.14. VAs originating from the summit of the LV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.15. Complications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Conflict of interest. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/joa

Journal of Arrhythmia

http://dx.doi.org/10.1016/j.joa.2014.03.0021880-4276/& 2014 Japanese Heart Rhythm Society. Published by Elsevier B.V. All rights reserved.

n Tel.: þ81 27 269 7455.E-mail address: kkumagai4917@yahoo.co.jp

Please cite this article as: Kumagai K. Idiopathic ventricular arrhythmias arising from the left ventricular outflow tract: Tips and tricks. JArrhythmia (2014), http://dx.doi.org/10.1016/j.joa.2014.03.002i

Journal of Arrhythmia ∎ (∎∎∎∎) ∎∎∎–∎∎∎

1. Introduction

Radiofrequency catheter ablation (RFCA) has been establishedas an effective and safe non-pharmacological therapy for arrhyth-mias [1]. Idiopathic left ventricular outflow tract ventriculararrhythmias (LVOT-VAs) arising from the LVOT are rare comparedwith VAs arising from the right ventricular outflow tract (RVOT)[2]. Idiopathic repetitive monomorphic ventricular tachycardia(RMVT) and symptomatic monomorphic ventricular prematurecontractions (VPCs) are known to originate from the RVOT, andRFCA has been widely accepted as a curative therapy for RVOT-VAsdue to the high success rate [3,4]. However, the success rate forLVOT-VAs has not been as high [3,5–8]. The ability to safelyperform RFCA for LVOT-VAs is important because of their criticallyimportant anatomical origin. Four types of LVOT-VAs origins areknown to exist within very close anatomical proximity. These arethe aorto-mitral continuity (AMC) [9,10], the anterior sites aroundthe mitral annulus (MA) [11,12], the aortic sinus cusps (ASC)[13,14], and the epicardium [15,16]. Differentiating among LVOT-VAs originating from these various sites has been difficult sincethey all exhibit a similar QRS morphology, including a right bundle

Fig. 1. Stepwise ECG algorithm for the determination of the location of the origins ofOT-VTs. LSV¼ left sinus of Valsalva; LV end¼ left ventricular endocardium; LV epi¼ leftventricular epicardium remote from the LSV; near His¼near the His bundle region;and RV¼right ventricular. (Reproduced with permission: Reference [26]).

Fig. 2. The anatomical location of the inflow and outflow tracts of the LV. The left fibrous trigone (asterisk) is represented between the ridges of the aortic and mitral annuli. LCC¼ leftcoronary cusp; RCC¼right coronary cusp; NCC¼non-coronary cusp; MA¼mitral annulus. (B) Two-dimensional computerized tomography images showing the relationships betweenthe ventricular myocardium and aortic sinus cusps. The arrowheads indicate the distal edge of the ventricular myocardium connecting to the left coronary cusp (L) and right coronarycusp (R), and the dotted line (right panel) indicates the ventriculoarterial junction (the ostium of the left ventricle [LV]). Ao¼aorta; LCA¼ left coronary artery; MV¼mitral valve.(Reproduced with permission: Reference [29]).

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branch block (RBBB) morphology in lead V1 or atypical left bundlebranch block (LBBB) morphology associated with an early pre-cordial transition in lead V2 [17]. Predicting the origin of the LVOT-VA by analyzing ECG characteristics is essential for evaluating thepossibility of safely performing RFCA.

1.1. Ablation procedure for LVOT-VAs

All anti-arrhythmic drugs were discontinued at least 5 half-lives before the electrophysiological study (EPS). Pace mappingand activation mapping of the RMVTs or frequent monomorphicVPCs were performed with a standard recording system and theroving catheter technique, as previously described [10,11].Non-sustained RMVTs or repetitive monomorphic VPCs occurredspontaneously or were induced by an intravenous isoproterenol

infusion. The VT was sensitive to isoproterenol and adenosinetriphosphate, but insensitive to programmed pacing or burstpacing. These findings support a non-reentrant mechanism oftriggered activity or automaticity rather than a reentrant mechan-ism [18–21]. In the ablation procedure, the RVOT area andpulmonary artery are usually mapped, followed by careful map-ping of the LVOT area, MA, and ASC via the retrograde aorticapproach and of the great cardiac vein (GCV) though the coronarysinus, if necessary [11,13,16]. RF energy is delivered using a non-irrigated catheter with a deflectable 4-mm tip and a temperaturecontrol system with a temperature setting of 55 1C during 60-senergy deliveries [10–14] or a 3.5-mm irrigated tip RF catheter(ThermoCool, Biosense Webster Inc.) with the temperature limitedto 42 1C and the power to 30 W (a flow rate of 17 mL/min) during40-s energy deliveries. RF energy is never delivered more than

Fig. 3. (A) The morphology of the LCC, AMC, and anterior MA origins of LVOT-Vas. Despite many morphological similarities, it was possible to characterize the subtypes ofLVOT-VAs in terms of the monophasic R waves in the precordial leads, transitional zone, and intrinsicoid deflection time. AMC¼aorto-mitral continuity; LCC¼ left coronarycusp; MA¼mitral annulus. (B) Successful ablation sites of LVOT-VAs. The location of the ablation catheter is in the left coronary sinus cusp, just below the left fibrous trigoneand anterior site of the MA. LCC¼ left coronary cusp; PA¼pulmonary artery; CS¼coronary sinus; AIV¼anterior interventricular vein; ABL¼ablation catheter; LCC¼ leftcoronary cusp; AMC¼aorto-mitral continuity; and MA¼mitral annulus.(Reproduced with permission: Reference [10]).

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3 times in any patient with VAs of an ASC origin [13]. In patientswith VAs of ASC origin, coronary angiography should beperformed prior to RFCA to ensure that the distance betweenthe ablation catheter and the ostium of the left main coronaryartery is 410 mm [13]. The target ablation site is determinedprimarily according to a perfect (12/12) or near-perfect (10–11/12)pace map with an early local activation time. Successful RFCA siteswere considered the sites of origin of the VT or VPCs. In a previousreport, a low-amplitude presystolic potential (prepotential) wasfrequently observed during the VT/VPCs at the successful ablationsites, suggesting that a slow conduction area is present betweenthe ventricle and the ASC [14]. This prepotential could be a markerfor a successful RFCA of LVOT-VAs [10]. In LVOT-VAs with an ASCorigin, the site of a discrete prepotential with a Z50-ms activationtime may indicate a successful ablation site [22]. However, themechanism of the prepotential recorded at successful sites inLVOT-VAs remains unknown.

1.2. Classification and frequency of idiopathic VAs

Tada et al. reported the following idiopathic VA sites of origin:the tricuspid annulus (septum and free wall), RVOT, pulmonaryartery, aortic sinus of Valsalva, left ventricular epicardium, LVOT,left ventricular inferoseptum, and MA [3]. Recently, it was reportedthat idiopathic repetitive VAs can arise not only from the RVOT butalso from the LVOT. However, idiopathic VAs arising from the LVOTare reportedly rare compared with those arising from the RVOT[2–8]. The incidence of LVOT-VAs has been reported to be 12% [8].The frequency of idiopathic VAs with RVOT and pulmonary arteryorigins is 52% and that of idiopathic VAs with LVOT, ASC, andepicardial origins is nearly 27%, for a total of 79% [3]. Meanwhile,the success rate of RFCA for idiopathic VAs with RVOT andpulmonary artery origins is high at 90–92%, but is only 55–60%in idiopathic VAs with LVOT, ASC, and epicardial origins. LVOT-VAablation is more difficult than RVOT-VA ablation. Attaining optimalablation sites in LVOT-VAs is difficult because of anatomicalstructures, as is the avoidance of complications.

1.3. Identification of the origin of LVOT-VAs

The ECG characteristics of the VAs, anatomical information, andan EPS for successful ablation are useful for the identification of VAorigins. In terms of ECG characteristics, the type in lead V1 (CRBBBtype, CLBBB type, or QS pattern), morphology in lead I, location ofthe precordial transition zone, R/S-wave amplitude in V1/V2, andamplitude of the R wave in the inferior leads should be investi-gated. Furthermore, a comparison of the depth of the QS in aVRand in aVL should be made for the prediction of an RVOT or LVOTorigin. Maximum deflection index (MDI) should be measured. AnMDI Z0.55 indicates the possibility of a VA with an epicardialorigin [23]. The intrinsicoid deflection time (IDT) as the intervalmeasured from the earliest ventricular activation to the peak ofthe R wave in lead V2 is also used because an epicardial origin ofthe ventricular activation (pseudo delta wave) may increase theduration of the initial part of the QRS complex on the surface ECG[24]. A peak deflection index 40.6 in a left coronary cusp (LCC)origin site is also a useful ECG predictor [25]. (1) In terms ofanatomical information, visualization using computed tomogra-phy (CT) image integration into an electroanatomical mappingsystem assists in the ablation. (2) In terms of the EPS, activationmapping and pace mapping represent an important approach to asuccessful ablation.

For idiopathic VOT-VAs, including those originating from the LVendocardium and epicardium, a novel ECG algorithm (Fig. 1) wasreported with a high sensitivity of 88% and specificity of 95% foridentifying the optimal ablation site [26].

1.4. Differentiation of LVOT and RVOT origins

We first need to distinguish an LVOT origin from an RVOTorigin. The ECG characteristics of an RVOT origin are usually aCLBBB type in lead V1, an R wave in the inferior leads, and aprecordial transition at lead V3 or V4. Distinguishing an LVOTorigin from an RVOT origin is not terribly difficult. However, insome cases, VT or VPCs with a QRS morphology characteristic of anRVOT origin can actually have an LVOT origin. In such cases, the V2transition ratio is a novel electrocardiographic measure thatreliably distinguishes an LVOT from an RVOT origin in patientswith a lead V3 precordial transition [27]. If the SR transition lead isV1 or V2, then the PVC origin is in the RVOT (100% specificity). Ifthe SR transition lead is V3 or later, then the V2 transition ratio ismeasured. A transition ratio o0.6 predicts the possibility of anRVOT origin. A transition ratio Z0.6 predicts the possibility of an

Fig. 4. The morphology of ASC-Vas. Patients with ASC-VAs have a variabletransitional zone in leads V1–4 and various QRS morphologies in leads I and V1,and, in some cases, monophasic R waves in all precordial leads. ASC¼aorticsinus cusps.

Fig. 5. Stepwise ECG algorithm for conjecturing the sites of origin of LVOT-Vas.AMC¼aorto-mitral continuity; ASC¼aortic sinus cusps; and MA¼mitral annulus.

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LVOT origin (sensitivity 95% and specificity 100%). In some cases,VAs originating from the ASC have a preferential conduction to theRVOT area, which may be due to insulated myocardial fiberstraveling across the ventricular outflow septum [28].

1.5. Classification and frequency of LVOT-VAs

The origins of LVOT-VAs have an RBBB or LBBB morphology inlead V1 with an early precordial transition. They are mainlydivided into 3 sites: an endocardial origin, coronary cusp origin,and epicardial origin [17]. The endocardial origin is further dividedas follows: medio-superior aspect of the MA (AMC), anterior MA,and superior basal septum (which is adjacent to the His bundlearea). The coronary cusp origin is also further divided into 3 sites:the LCC, right coronary cusp (RCC), and non-coronary cusp (NCC).Epicardial origins are approached using the coronary venoussystem with direct epicardial instrumentation [16].

1.6. Anatomical structures in the LVOT

Fig. 2A shows the anatomical location of the inflow and outflowtracts of the LV. A multi-dimensional CT (MDCT) was performed todefine the anatomical position of the LVOT. This figure of the LVOTis viewed from the LV apex. The left fibrous trigone indicated bythe asterisk is located between the ridges of the aortic and mitralannuli. The aortic leaflet of the mitral valve can hang between theinflow and outflow tracts of the left ventricle. There is no septalmyocardium in the region beneath the left fibrous trigone andthe valvular continuity. The superior basal septum is very close tothe RCC site. Therefore, because the RCC site is located in theventricular myocardium, the morphology of an RCC origin isindicated by a QS pattern in lead V1. In Fig. 2B, the distal edge ofthe ventricular myocardium connects with the LCC and RCC [29].An RF application from the coronary cusp does not ablate the valveitself but rather the myocardium of the subepicardial region justbeneath the valve because the AV junction exists just within the

ventricular septum. The LV ostium is the common site of origin ofidiopathic VAs [30].

1.7. The aorto-mitral continuity

Since the aortic and mitral valves are coupled through thefibrous AMC, the aortic leaflet of the mitral valve can hangbetween the inflow and outflow tracts of the left ventricle[31,32]. The right and left fibrous trigones are expansions of thefibrous tissue at either end of the area of the aortic–mitral valvularcontinuity. From the histological perspective, each of the fibroustrigones around the valvular annulus exhibited a variation in thecompleteness of the fibrous tissue [33]. This suggests that theaberration of the musculature in the fibrous trigone becomes anectopic focus with a non-reentrant mechanism such as triggeredactivity [10].

1.8. Anterior MA, AMC, and ASC origins of LVOT-VAs

VAs with LVOT origins can originate from various adjacentorigin sites including the AMC, anterior sites around the MA, ASC,and epicardium (Fig. 3A). Despite many morphological similarities,the subtypes of LVOT-VAs can be characterized in terms of themonophasic R waves in the precordial leads, transitional zone, andIDT. Basically, the LVOT-VA origins have an RBBB or LBBB typemorphology in lead V1 with an early precordial transition. How-ever, patients with ASC-VAs have a variable transitional zone inleads V1–4 and various QRS morphologies in leads 1 and V1, andin some cases, there are monophasic R waves in all precordialleads (Fig. 4). In nearly all patients, there are no S waves in lead V6.The early transitional zone is located in leads V1–2 in AMC-VAsand anterior MA-VAs [10]. All patients with AMC-VAs exhibitedmonophasic R waves with no S waves in almost all precordialleads, whereas those with anterior MA-VAs had S waves (such asan Rs or RS pattern) in many of the precordial leads other thanlead V6 [10]. This suggests that ventricular activation in AMC-VAs

Fig. 6. Morphologies of ventricular arrhythmias on 12-lead electrocardiograms and their locations at the aortomitral continuity. Magnetic resonance imaging displays theanatomical structures around the fibrous trigone. (A) Three-chamber view of the heart. The arrowhead shows the aortomitral continuity, the site at which the ablation wasperformed. (B) Short-axis view: the dotted lines specify the anterior, middle, and posterior parts of the aortomitral continuity. Part of the left coronary sinus can be seen.(C) (early transition pattern, Case 1) and (D) (early transition with a “qr” pattern in V1, Case 3) Electrocardiograms of ventricular arrhythmias originating from the anteriorpart and (E) (rebound transition pattern, Case 6) mid-part of the aortomitral continuity. AV, aortic valve; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, rightatrium; and RVOT, right ventricular outflow tract. ‘a’ and ‘p’ with arrows indicate the anterior and posterior directions respectively.(Reproduced with permission: Reference [35]).

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is directed only in the anterior direction, which is located in themost posterior LVOT region corresponding to the AMC (left fibroustrigone).

Successful ablation sites for ASC, AMC, and anterior MA originsare shown in Fig. 3B. The location of the ablation catheter is in theleft coronary sinus cusp, just below the left fibrous trigone and theanterior site of the MA. Coronary angiography shows the leftcoronary artery and ASC. Aortography also shows the ASC. It isimportant to compare the endocardial electrogram recorded fromthe LVOT, such as from the coronary cusp, with those recordedsimultaneously from the transitional area from the GCV to theanterior interventricular vein (AIV; the subepicardial region).When the earliest endocardial ventricular activation precedingthat recorded from the AIV cannot be found, the origin of the VAmay be in the epicardium.

1.9. Stepwise ECG algorithm for LVOT-VAs

A stepwise ECG algorithm with a 73% accuracy for LVOT-VAs isshown in Fig. 5. The ECG characteristics of LVOT-VAs consist of anRBBB morphology in lead V1 or atypical LBBB morphologyassociated with an early precordial transition in lead V2 [17].All LVOT-VAs have similar ECG characteristics; however, AMC-VAshave an RBBB configuration with an inferior axis and monophasicR waves in almost all precordial leads. ASC-VAs have a broadprecordial transition in leads V1–V4 and various morphologies inleads I and V1. The distribution of the origin in the septalmyocardium beneath the aortic valve might contribute to thebroad precordial transition and the various morphologies in leads Iand V1 [10]. When comparing anterior MA-VAs and ASC-VAs, anIDT Z85 ms identified anterior MA-VAs with a 75% sensitivity and

Fig. 7. ECG recordings obtained during an electrophysiological study and catheter positioning at the successful ablation site in a patient with an ASC-VT. (A) A pace map with anear-perfect match. (B) The earliest activation (prepotential, arrow) preceded the QRS onset (Vo) by 32ms during a ventricular premature contraction (VPC). The unipolar signal alsohas a QS morphology with a fast downstroke slope. A¼atrial potential; V¼ventricular potential. (C) The location of the ablation catheter is in the left coronary sinus cusp. Coronaryangiography shows the left coronary artery and aortic sinus cusps. His¼His bundle region; CSp and CSd¼proximal to distal sites of the coronary sinus; uni¼unipolar electrogram.(Reproduced with permission: Reference [10]).

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83% specificity. The QRS duration and IDT in patients with AMC-VAs and anterior MA-VAs were significantly greater than those inpatients with ASC-VAs. In addition, there was no significantdifference in QRS duration and IDT between AMC-VAs and anteriorMA-VAs, suggesting that both origins were located deeper in thesubepicardium than the origins of ASC-VAs. Furthermore, therewas no significant difference among groups in the R waveamplitude in the inferior leads, which also implies the closeproximity of these anatomical locations. In particular, it wasdifficult to define the differences between AMC-VAs and anteriorMA-VAs because their sites of origin may have been distributedalong the boundary region of the aortic and mitral annuli (near theleft fibrous trigone) to the anterior aspect of the MA. It is possiblethat anterior MA-VAs overlap with AMC-VAs [10].

On the other hand, Dixit et al. reported that AMC-VAs had a qRmorphology in lead V1 [34]. Furthermore, the AMC has been

divided into two sites: the anterior and middle parts [35]. In VAsoriginating in the anterior AMC part, an early R/S wave transitionwas found in the precordial leads, with equal R and S amplitudesin V2, rS in V1, and R in V3. In those originating in the middle partof the AMC, there was a special transition pattern defined asrebound, with equal R and S amplitudes in V2 and high R waves inV1 and V3. In the anterior part of the AMC, the S/R ratios in leadsV1 and V2 are 41 (Fig. 6).

1.10. Representative cases of anterior MA, AMC, and ASC origins inLVOT-VAs

Figs. 7 and 8 show representative LVOT-VAs originating fromthe ASC (LCC) and AMC, respectively. The CARTO (CARTO, BiosenseWebster, Inc., Diamond Bar, CA, USA) system helps in defining the

Fig. 8. ECG recordings obtained during an electrophysiological study and catheter positioning at the successful ablation site (RAO351 and LAO451) in a patient with an AMC-VT. (A) A pace map with a near-perfect match. (B) The earliest activation (prepotential, arrow) preceded the QRS onset (Vo) by 32 ms during a VPC. (C) The location of theablation catheter is just below the AMC of the mitral annulus. Note that the left Judkin's catheter is located at the ostium of the left main coronary artery (LMCA).(Reproduced with permission: Reference [10]).

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ablation sites. In the CT image integration of the electroanatomicalmapping, the successful ablation site was found to be just belowthe LMT ostium. The distance between the LMT ostium and theablation site was 12.1 mm (Fig. 9A). The CARTO images alsoindicated that the AMC (the left fibrous trigone) was anatomicallylocated in close proximity to the anterior site of the MA and ASC.An activation map of VAs originating from the AMC duringbigeminy shows a focal pattern (Fig. 9B).

1.11. Stepwise ECG algorithm for the origin of MA-VAs

Kumagai et al. have reported a stepwise ECG algorithm forconjecturing the sites of origin of MA-Vas [11]. The anterior MA-VAorigin is one of the 4 subgroups of MA-VT origins: anterior,anterolateral, lateral, and posterior. Briefly, the precordial transi-tion is observed in leads V1 or V2. When there is no S wave in leadV6, an IDT Z85 ms is identified as an anterior MA-VT. When an Swave is present in lead V6, the polarity of the R wave in theinferior leads is positive for anterolateral and lateral origins andnegative for a posterior origin. An R wave in lead aVF Z1.6 mVidentified a Group II ECG with a 100% sensitivity and 83%specificity.

A second ECG algorithm for conjecturing the sites of origin ofMA-VAs has also been reported. According to the ECG character-istics of this algorithm, VAs originating from the LV free wall of theposterior MA and anterolateral MA are characterized by a notchingof the late phase of the QRS complex in the inferior leads as well asa longer QRS duration [12].

1.12. VAs originating from superior basal septal sites of the MA

Fig. 10 shows an MA-VT originating from a superior basal septalsite. This VT is characterized by the presence of monophasic Rwaves in lead I and an S wave in the inferior leads. The transitionalzone of the precordial R wave is in lead V1. Monophasic R wavesare present in all precordial leads. The earliest activation precedes

the QRS onset by 22 ms at the successful ablation site on the leftanteroseptum. A His potential and prepotential are found at a siteproximal to the ablation catheter. A successful ablation depends onthe earliest potential with a prepotential. To avoid an atrio-ventricular conduction block, an ablation site without a Hispotential should be selected.

1.13. ECG characteristics of VAs originating from the aortic root

Fig. 11 shows a summary of idiopathic VAs originating from theaortic root [29]. Such idiopathic VAs more frequently originate inthe LCC than the RCC, and rarely originate in the NCC because it issurrounded by the right and left atrial walls. On ECG, RBBB andQRS morphology with a right inferior axis is observed only in VAswith an LCC origin. Furthermore, a greater R wave amplitude inthe inferior leads is observed in the LCC and a QS wave in lead V1is observed in the RCC. A qrS wave in lead V1 is observed in theRCC/LCC commissure. An R wave in lead aVL is observed only inVAs originating in the NCC. As the origin moves from the RCC tothe LCC, an S wave appears in lead I, the lead III/II ratio becomesgreater, the precordial transitional zone moves clockwise, and thedepth of the QS in lead aVL becomes deeper than that in aVR [29].In a previous report, the ECG characteristics of PVCs from the RCC/LCC commissure had a QS morphology in lead V1 with notching onthe downward [36] Late potentials in sinus rhythm are observed atthe site of a successful ablation, indicating ventricular myocardialextensions.

1.14. VAs originating from the summit of the LV

Fig. 12 shows images of the LV summit. The LV summit isdefined on the basis of fluoroscopy and coronary angiography asthe region on the epicardial surface of the LV near the bifurcationof the left main coronary artery bounded by an arc (black dottedline) from the superior LAD to the first septal perforating branch(black arrowheads) anteriorly and laterally to the LCx [16].

Fig. 9. (A) The successful ablation site of a VA originating from the LCC in a CARTO image. (B) Activation map during bigeminal VPCs originating from the AMC in the CARTOimage. Ao¼aorta; AMC¼aorto-mitral continuity; ASC¼aortic sinus cusps; LA¼ left atrium; LMCA¼ostium of the left main coronary artery; LV¼ left ventricular,PA¼pulmonary artery; and RV¼right ventricular.

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The GCV divides the LV summit into a superior portion (theinaccessible area) and inferior portion (the accessible area).

A VA originating from the LV summit is accurately predicted byan RBBB pattern, the transition zone, an R wave amplitude ratio inleads III to II, a Q wave amplitude ratio in leads aVL to aVR, and Swaves in lead V6 [16]. VAs that have an RBBB pattern, a transitionzone earlier than lead V1, an aVL/aVR amplitude ratio of 1.1, and Swaves in V5 or V6 may be successfully ablated from within theGCV, AIVV, or accessible area. VAs with a lead III/II amplitude ratioof 1.25 and an aVL/aVR amplitude ratio of 1.75 may be ablatedusing a pericardial approach. When the amplitude of the R wavesin the inferior leads is higher during VAs than during pacing fromthe GCV and AIVV, the VA origin may be in the inaccessible area.PVCs arising from the inaccessible area never produce a perfect

pace map when paced from any endocardial or epicardial site, andnotably have a higher R wave amplitude in the inferior leads. Theinaccessible area is located at the most superior site in the LV,followed by the GCV and AIVV. In this region, catheter ablation isunlikely to be successful due to the presence of a thick layer ofepicardial fat. Surgical approaches may allow for the dissection ofthe epicardial fat and a direct application of ablative energy to thisregion.

1.15. Complications

First, care should be taken to avoid any injury to the coronaryartery. In ASC-VAs, coronary angiography should be performed beforeRFCA to ensure that the distance between the ablation catheter and

Fig. 10. A representative case of a VA originating from a superior basal septal site. A¼atrial potential; ABL¼ablation catheter; CSp and CSd¼proximal to distal sites of thecoronary sinus; His¼His bundle region; uni¼unipolar electrogram; and V¼ventricular potential.

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the ostium of the left main coronary artery is greater than 10mm [13].Radiofrequency ablation at sites adjacent to the successful ablation siteprovokes sinus bradycardia followed by atrio-ventricular conductionblock. This may trigger a vagal reflex through stimulation of the vagal

pathways or receptors in the anterior epicardial fat pads neighboringthe RCC. Transient sinus bradycardia, transient complete atrio-ventricular conduction block during ablation within the RCC, and athermal effect on the anterior epicardial fat pad's parasympathetic

Fig. 12. Computed tomographic (left panels) and fluoroscopic (right panels) images exhibiting the summit of the LV. The white dotted line indicates the inaccessible area andred dotted line indicates the accessible area. The white arrowheads indicate the first diagonal branch of the LAD. ABL indicates the ablation catheter; Ao, aorta; CS, coronarysinus; HB, His bundle; LAO, left anterior oblique; LMCA, left main coronary artery; PA, pulmonary artery; and RAO, right anterior oblique.(Reproduced with permission: Reference [16]).

Fig. 11. Two-dimensional computerized tomography image and representative 12-lead electrocardiograms of premature ventricular contractions or ventricular tachycardiaoriginating from the aortic root. L¼ left coronary cusp; LA¼ left atrium; N¼non-coronary cusp; R¼right coronary cusp; RA¼right atrium; and RV¼right ventricle.(Reproduced with permission: Reference [29]).

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Please cite this article as: Kumagai K. Idiopathic ventricular arrhythmias arising from the left ventricular outflow tract: Tips and tricks. JArrhythmia (2014), http://dx.doi.org/10.1016/j.joa.2014.03.002i

ganglia resulting in vagal stimulation may occur [37]. Finally, manip-ulations should be performed carefully because aortic or mitralregurgitation as a mechanical trauma might occur.

2. Conclusions

With the exception of some LVOT-VAs with an epicardial origin,all subtypes of LVOT-VAs (AMC, anterior sites of the MA, and ASC) aresuccessfully treated with endocardial RFCA combined with pacemapping and detection of the earliest ventricular electrogram witha prepotential. Despite many morphological similarities among theLVOT-VA subtypes, they can be differentiated using electrocardio-graphic characteristics to safely perform RFCA. LVOT-VAs originatingfrom the inaccessible area of the epicardium at the LV summit shouldbe differentiated from those originating from the accessible area,which is accessible by epicardial catheter ablation, using novelelectrophysiological characteristics. The ECG characteristics and ana-tomical information obtained from visualization using image inte-gration with electroanatomical mapping may advance the safe andsuccessful RFCA of idiopathic LVOT-VAs.

Conflict of interest

The author declares that there is no conflict of interest.

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