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

Abstract

Idiopathic left ventricular outflow tract ventricular arrhythmias (LVOT-VAs) arising from the LVOT are rare compared with the VAs arising from the RVOT. Idiopathic LVOT-VAs have been divided into four subgroups based on successful catheter ablation sites: the aorto-mitral continuity (AMC), the anterior site around the mitral annulus (MA), the aortic sinus cusps (ASC), and the epicardium. Recognition of the ECG characteristics of LVOT-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 of LVOT-VAs, except those with epicardial origins, are successfully treated with endocardial radiofrequency catheter ablation combined with pace mapping and the identification of the earliest ventricular electrogram with a prepotential, if it is recordable. In addition, LVOT-VAs originating from an inaccessible area in the LV summit of the epicardium, which cannot be treated by epicardial catheter ablation, should be differentiated from those in an accessible area using novel electrophysiological characteristics. Despite many morphological similarities among the subtypes of LVOT-VAs, the ECG characteristics and anatomical information obtained from visualization using computed tomographic image integration with electroanatomical mapping may advance the safety and success of catheter ablation of idiopathic LVOT-VAs.

1 Introduction

Radiofrequency catheter ablation (RFCA) has been established as an effective and safe non-pharmacological therapy for arrhythmias [1]. Idiopathic left ventricular outflow tract ventricular arrhythmias (LVOT-VAs) arising from the LVOT are rare compared with VAs arising from the right ventricular outflow tract (RVOT) [2]. Idiopathic repetitive monomorphic ventricular tachycardia (RMVT) and symptomatic monomorphic ventricular premature contractions (VPCs) are known to originate from the RVOT, and RFCA has been widely accepted as a curative therapy for RVOT-VAs due to the high success rate [3,4]. However, the success rate for LVOT-VAs has not been as high [3,5–8]. The ability to safely perform RFCA for LVOT-VAs is important because of their critically important anatomical origin. Four types of LVOT-VAs origins are known to exist within very close anatomical proximity. These are the aorto-mitral continuity (AMC) [9,10], the anterior sites around the 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 since they all exhibit a similar QRS morphology, including a right bundle branch block (RBBB) morphology in lead V1 or atypical left bundle branch block (LBBB) morphology associated with an early precordial transition in lead V2 [17]. Predicting the origin of the LVOT-VA by analyzing ECG characteristics is essential for evaluating the possibility 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 mapping and activation mapping of the RMVTs or frequent monomorphic VPCs were performed with a standard recording system and the roving catheter technique, as previously described [10,11]. Non-sustained RMVTs or repetitive monomorphic VPCs occurred spontaneously or were induced by an intravenous isoproterenol infusion. The VT was sensitive to isoproterenol and adenosine triphosphate, but insensitive to programmed pacing or burst pacing. These findings support a non-reentrant mechanism of triggered activity or automaticity rather than a reentrant mechanism [18–21]. In the ablation procedure, the RVOT area and pulmonary artery are usually mapped, followed by careful mapping of the LVOT area, MA, and ASC via the retrograde aortic approach and of the great cardiac vein (GCV) though the coronary sinus, if necessary [11,13,16]. RF energy is delivered using a non-irrigated catheter with a deflectable 4-mm tip and a temperature control system with a temperature setting of 55 °C during 60-s energy deliveries [10–14] or a 3.5-mm irrigated tip RF catheter (ThermoCool, Biosense Webster Inc.) with the temperature limited to 42 °C and the power to 30 W (a flow rate of 17 mL/min) during 40-s energy deliveries. RF energy is never delivered more than 3 times in any patient with VAs of an ASC origin [13]. In patients with VAs of ASC origin, coronary angiography should be performed prior to RFCA to ensure that the distance between the ablation catheter and the ostium of the left main coronary artery is >10 mm [13]. The target ablation site is determined primarily according to a perfect (12/12) or near-perfect (10–11/12) pace map with an early local activation time. Successful RFCA sites were considered the sites of origin of the VT or VPCs. In a previous report, a low-amplitude presystolic potential (prepotential) was frequently observed during the VT/VPCs at the successful ablation sites, suggesting that a slow conduction area is present between the ventricle and the ASC [14]. This prepotential could be a marker for a successful RFCA of LVOT-VAs [10]. In LVOT-VAs with an ASC origin, the site of a discrete prepotential with a ≥50-ms activation time may indicate a successful ablation site [22]. However, the mechanism of the prepotential recorded at successful sites in LVOT-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, pulmonary artery, aortic sinus of Valsalva, left ventricular epicardium, LVOT, left ventricular inferoseptum, and MA [3]. Recently, it was reported that idiopathic repetitive VAs can arise not only from the RVOT but also from the LVOT. However, idiopathic VAs arising from the LVOT are 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 artery origins is 52% and that of idiopathic VAs with LVOT, ASC, and epicardial origins is nearly 27%, for a total of 79% [3]. Meanwhile, the success rate of RFCA for idiopathic VAs with RVOT and pulmonary artery origins is high at 90–92%, but is only 55–60% in idiopathic VAs with LVOT, ASC, and epicardial origins. LVOT-VA ablation is more difficult than RVOT-VA ablation. Attaining optimal ablation sites in LVOT-VAs is difficult because of anatomical structures, as is the avoidance of complications.

1.3 Identification of the origin of LVOT-VAs

The ECG characteristics of the VAs, anatomical information, and an EPS for successful ablation are useful for the identification of VA origins. In terms of ECG characteristics, the type in lead V1 (CRBBB type, CLBBB type, or QS pattern), morphology in lead I, location of the precordial transition zone, R/S-wave amplitude in V1/V2, and amplitude of the R wave in the inferior leads should be investigated. Furthermore, a comparison of the depth of the QS in aVR and in aVL should be made for the prediction of an RVOT or LVOT origin. Maximum deflection index (MDI) should be measured. An MDI ≥0.55 indicates the possibility of a VA with an epicardial origin [23]. The intrinsicoid deflection time (IDT) as the interval measured from the earliest ventricular activation to the peak of the R wave in lead V2 is also used because an epicardial origin of the ventricular activation (pseudo delta wave) may increase the duration of the initial part of the QRS complex on the surface ECG [24]. A peak deflection index >0.6 in a left coronary cusp (LCC) origin site is also a useful ECG predictor [25]. (1) In terms of anatomical information, visualization using computed tomography (CT) image integration into an electroanatomical mapping system assists in the ablation. (2) In terms of the EPS, activation mapping and pace mapping represent an important approach to a successful ablation.

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

Fig. 1. Stepwise ECG algorithm for the determination of the location of the origins of OT-VTs. LSV=left sinus of Valsalva; LV end=left ventricular endocardium; LV epi=left ventricular epicardium remote from the LSV; near His=near the His bundle region; and RV=right ventricular. (Reproduced with permission: Reference [26]).

1.4 Differentiation of LVOT and RVOT origins

We first need to distinguish an LVOT origin from an RVOT origin. The ECG characteristics of an RVOT origin are usually a CLBBB type in lead V1, an R wave in the inferior leads, and a precordial transition at lead V3 or V4. Distinguishing an LVOT origin from an RVOT origin is not terribly difficult. However, in some cases, VT or VPCs with a QRS morphology characteristic of an RVOT origin can actually have an LVOT origin. In such cases, the V2 transition ratio is a novel electrocardiographic measure that reliably distinguishes an LVOT from an RVOT origin in patients with a lead V3 precordial transition [27]. If the SR transition lead is V1 or V2, then the PVC origin is in the RVOT (100% specificity). If the SR transition lead is V3 or later, then the V2 transition ratio is measured. A transition ratio <0.6 predicts the possibility of an RVOT origin. A transition ratio ≥0.6 predicts the possibility of an LVOT origin (sensitivity 95% and specificity 100%). In some cases, VAs originating from the ASC have a preferential conduction to the RVOT area, which may be due to insulated myocardial fibers traveling 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 in lead V1 with an early precordial transition. They are mainly divided into 3 sites: an endocardial origin, coronary cusp origin, and epicardial origin [17]. The endocardial origin is further divided as follows: medio-superior aspect of the MA (AMC), anterior MA, and superior basal septum (which is adjacent to the His bundle area). 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 venous system with direct epicardial instrumentation [16].

1.6 Anatomical structures in the LVOT

Fig. 2A shows the anatomical location of the inflow and outflow tracts of the LV. A multi-dimensional CT (MDCT) was performed to define the anatomical position of the LVOT. This figure of the LVOT is viewed from the LV apex. The left fibrous trigone indicated by the asterisk is located between the ridges of the aortic and mitral annuli. The aortic leaflet of the mitral valve can hang between the inflow and outflow tracts of the left ventricle. There is no septal myocardium in the region beneath the left fibrous trigone and the valvular continuity. The superior basal septum is very close to the RCC site. Therefore, because the RCC site is located in the ventricular myocardium, the morphology of an RCC origin is indicated by a QS pattern in lead V1. In Fig. 2B, the distal edge of the ventricular myocardium connects with the LCC and RCC [29]. An RF application from the coronary cusp does not ablate the valve itself but rather the myocardium of the subepicardial region just beneath the valve because the AV junction exists just within the ventricular septum. The LV ostium is the common site of origin of idiopathic VAs [30].

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. LCC=left coronary cusp; RCC=right coronary cusp; NCC=non-coronary cusp; MA=mitral annulus. (B) Two-dimensional computerized tomography images showing the relationships between the 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 coronary cusp (R), and the dotted line (right panel) indicates the ventriculoarterial junction (the ostium of the left ventricle [LV]). Ao=aorta; LCA=left coronary artery; MV=mitral valve.(Reproduced with permission: Reference [29]).

1.7 The aorto-mitral continuity

Since the aortic and mitral valves are coupled through the fibrous AMC, the aortic leaflet of the mitral valve can hang between the inflow and outflow tracts of the left ventricle [31,32]. The right and left fibrous trigones are expansions of the fibrous tissue at either end of the area of the aortic–mitral valvular continuity. From the histological perspective, each of the fibrous trigones around the valvular annulus exhibited a variation in the completeness of the fibrous tissue [33]. This suggests that the aberration of the musculature in the fibrous trigone becomes an ectopic focus with a non-reentrant mechanism such as triggered activity [10].

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

VAs with LVOT origins can originate from various adjacent origin 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 the monophasic R waves in the precordial leads, transitional zone, and IDT. Basically, the LVOT-VA origins have an RBBB or LBBB type morphology in lead V1 with an early precordial transition. However, patients with ASC-VAs have a variable transitional zone in leads V1–4 and various QRS morphologies in leads 1 and V1, and in some cases, there are monophasic R waves in all precordial leads (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-VAs and anterior MA-VAs [10]. All patients with AMC-VAs exhibited monophasic R waves with no S waves in almost all precordial leads, whereas those with anterior MA-VAs had S waves (such as an Rs or RS pattern) in many of the precordial leads other than lead V6 [10]. This suggests that ventricular activation in AMC-VAs is directed only in the anterior direction, which is located in the most posterior LVOT region corresponding to the AMC (left fibrous trigone).

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 of LVOT-VAs in terms of the monophasic R waves in the precordial leads, transitional zone, and intrinsicoid deflection time. AMC=aorto-mitral continuity; LCC=left coronary cusp; MA=mitral 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 trigone and anterior site of the MA. LCC=left coronary cusp; PA=pulmonary artery; CS=coronary sinus; AIV=anterior interventricular vein; ABL=ablation catheter; LCC=left coronary cusp; AMC=aorto-mitral continuity; and MA=mitral annulus.(Reproduced with permission: Reference [10]).

Fig. 4. The morphology of ASC-Vas. Patients with ASC-VAs have a variable transitional 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. ASC=aortic sinus cusps.

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

1.9 Stepwise ECG algorithm for LVOT-VAs

A stepwise ECG algorithm with a 73% accuracy for LVOT-VAs is shown in Fig. 5. The ECG characteristics of LVOT-VAs consist of an RBBB morphology in lead V1 or atypical LBBB morphology associated with an early precordial transition in lead V2 [17]. All LVOT-VAs have similar ECG characteristics; however, AMC-VAs have an RBBB configuration with an inferior axis and monophasic R waves in almost all precordial leads. ASC-VAs have a broad precordial transition in leads V1–V4 and various morphologies in leads I and V1. The distribution of the origin in the septal myocardium beneath the aortic valve might contribute to the broad precordial transition and the various morphologies in leads I and V1 [10]. When comparing anterior MA-VAs and ASC-VAs, an IDT ≥85 ms identified anterior MA-VAs with a 75% sensitivity and 83% specificity. The QRS duration and IDT in patients with AMC-VAs and anterior MA-VAs were significantly greater than those in patients with ASC-VAs. In addition, there was no significant difference in QRS duration and IDT between AMC-VAs and anterior MA-VAs, suggesting that both origins were located deeper in the subepicardium than the origins of ASC-VAs. Furthermore, there was no significant difference among groups in the R wave amplitude in the inferior leads, which also implies the close proximity of these anatomical locations. In particular, it was difficult to define the differences between AMC-VAs and anterior MA-VAs because their sites of origin may have been distributed along the boundary region of the aortic and mitral annuli (near the left fibrous trigone) to the anterior aspect of the MA. It is possible that anterior MA-VAs overlap with AMC-VAs [10].

Fig. 5. Stepwise ECG algorithm for conjecturing the sites of origin of LVOT-Vas. AMC=aorto-mitral continuity; ASC=aortic sinus cusps; and MA=mitral annulus.

On the other hand, Dixit et al. reported that AMC-VAs had a qR morphology in lead V1 [34]. Furthermore, the AMC has been divided into two sites: the anterior and middle parts [35]. In VAs originating in the anterior AMC part, an early R/S wave transition was found in the precordial leads, with equal R and S amplitudes in V2, rS in V1, and R in V3. In those originating in the middle part of the AMC, there was a special transition pattern defined as rebound, with equal R and S amplitudes in V2 and high R waves in V1 and V3. In the anterior part of the AMC, the S/R ratios in leads V1 and V2 are >1 (Fig. 6).

Fig. 6. Morphologies of ventricular arrhythmias on 12-lead electrocardiograms and their locations at the aortomitral continuity. Magnetic resonance imaging displays the anatomical structures around the fibrous trigone. (A) Three-chamber view of the heart. The arrowhead shows the aortomitral continuity, the site at which the ablation was performed. (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 anterior part 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, right atrium; and RVOT, right ventricular outflow tract. ‘a’ and ‘p’ with arrows indicate the anterior and posterior directions respectively.(Reproduced with permission: Reference [35]).

1.10 Representative cases of anterior MA, AMC, and ASC origins in LVOT-VAs

Figs. 7 and 8 show representative LVOT-VAs originating from the ASC (LCC) and AMC, respectively. The CARTO (CARTO, Biosense Webster, Inc., Diamond Bar, CA, USA) system helps in defining the ablation sites. In the CT image integration of the electroanatomical mapping, the successful ablation site was found to be just below the LMT ostium. The distance between the LMT ostium and the ablation site was 12.1 mm (Fig. 9A). The CARTO images also indicated that the AMC (the left fibrous trigone) was anatomically located in close proximity to the anterior site of the MA and ASC. An activation map of VAs originating from the AMC during bigeminy shows a focal pattern (Fig. 9B).

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 a near-perfect match. (B) The earliest activation (prepotential, arrow) preceded the QRS onset (Vo) by 32ms during a ventricular premature contraction (VPC). The unipolar signal also has a QS morphology with a fast downstroke slope. A=atrial potential; V=ventricular potential. (C) The location of the ablation catheter is in the left coronary sinus cusp. Coronary angiography shows the left coronary artery and aortic sinus cusps. His=His bundle region; CSp and CSd=proximal to distal sites of the coronary sinus; uni=unipolar electrogram.(Reproduced with permission: Reference [10]).

Fig. 8. ECG recordings obtained during an electrophysiological study and catheter positioning at the successful ablation site (RAO35° and LAO45°) 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 32ms during a VPC. (C) The location of the ablation 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]).

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 CARTO image. Ao=aorta; AMC=aorto-mitral continuity; ASC=aortic sinus cusps; LA=left atrium; LMCA=ostium of the left main coronary artery; LV=left ventricular, PA=pulmonary artery; and RV=right ventricular.

1.11 Stepwise ECG algorithm for the origin of MA-VAs

Kumagai et al. have reported a stepwise ECG algorithm for conjecturing the sites of origin of MA-Vas [11]. The anterior MA-VA origin is one of the 4 subgroups of MA-VT origins: anterior, anterolateral, lateral, and posterior. Briefly, the precordial transition is observed in leads V1 or V2. When there is no S wave in lead V6, an IDT ≥85 ms is identified as an anterior MA-VT. When an S wave is present in lead V6, the polarity of the R wave in the inferior leads is positive for anterolateral and lateral origins and negative for a posterior origin. An R wave in lead aVF ≥1.6 mV identified a Group II ECG with a 100% sensitivity and 83% specificity.

A second ECG algorithm for conjecturing the sites of origin of MA-VAs has also been reported. According to the ECG characteristics of this algorithm, VAs originating from the LV free wall of the posterior MA and anterolateral MA are characterized by a notching of the late phase of the QRS complex in the inferior leads as well as a 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 septal site. This VT is characterized by the presence of monophasic R waves in lead I and an S wave in the inferior leads. The transitional zone of the precordial R wave is in lead V1. Monophasic R waves are present in all precordial leads. The earliest activation precedes the QRS onset by 22 ms at the successful ablation site on the left anteroseptum. A His potential and prepotential are found at a site proximal to the ablation catheter. A successful ablation depends on the earliest potential with a prepotential. To avoid an atrio-ventricular conduction block, an ablation site without a His potential should be selected.

Fig. 10. A representative case of a VA originating from a superior basal septal site. A=atrial potential; ABL=ablation catheter; CSp and CSd=proximal to distal sites of the coronary sinus; His=His bundle region; uni=unipolar electrogram; and V=ventricular potential.

1.13 ECG characteristics of VAs originating from the aortic root

Fig. 11 shows a summary of idiopathic VAs originating from the aortic root [29]. Such idiopathic VAs more frequently originate in the LCC than the RCC, and rarely originate in the NCC because it is surrounded by the right and left atrial walls. On ECG, RBBB and QRS morphology with a right inferior axis is observed only in VAs with an LCC origin. Furthermore, a greater R wave amplitude in the inferior leads is observed in the LCC and a QS wave in lead V1 is observed in the RCC. A qrS wave in lead V1 is observed in the RCC/LCC commissure. An R wave in lead aVL is observed only in VAs originating in the NCC. As the origin moves from the RCC to the LCC, an S wave appears in lead I, the lead III/II ratio becomes greater, the precordial transitional zone moves clockwise, and the depth 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 on the downward [36] Late potentials in sinus rhythm are observed at the site of a successful ablation, indicating ventricular myocardial extensions.

Fig. 11. Two-dimensional computerized tomography image and representative 12-lead electrocardiograms of premature ventricular contractions or ventricular tachycardia originating from the aortic root. L=left coronary cusp; LA=left atrium; N=non-coronary cusp; R=right coronary cusp; RA=right atrium; and RV=right ventricle.(Reproduced with permission: Reference [29]).

1.14 VAs originating from the summit of the LV

Fig. 12 shows images of the LV summit. The LV summit is defined on the basis of fluoroscopy and coronary angiography as the region on the epicardial surface of the LV near the bifurcation of the left main coronary artery bounded by an arc (black dotted line) from the superior LAD to the first septal perforating branch (black arrowheads) anteriorly and laterally to the LCx [16]. The GCV divides the LV summit into a superior portion (the inaccessible area) and inferior portion (the accessible area).

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 and red 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, coronary sinus; 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]).

A VA originating from the LV summit is accurately predicted by an RBBB pattern, the transition zone, an R wave amplitude ratio in leads III to II, a Q wave amplitude ratio in leads aVL to aVR, and S waves in lead V6 [16]. VAs that have an RBBB pattern, a transition zone earlier than lead V1, an aVL/aVR amplitude ratio of 1.1, and S waves in V5 or V6 may be successfully ablated from within the GCV, AIVV, or accessible area. VAs with a lead III/II amplitude ratio of 1.25 and an aVL/aVR amplitude ratio of 1.75 may be ablated using a pericardial approach. When the amplitude of the R waves in the inferior leads is higher during VAs than during pacing from the 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, and notably have a higher R wave amplitude in the inferior leads. The inaccessible area is located at the most superior site in the LV, followed by the GCV and AIVV. In this region, catheter ablation is unlikely to be successful due to the presence of a thick layer of epicardial fat. Surgical approaches may allow for the dissection of the epicardial fat and a direct application of ablative energy to this region.

1.15 Complications

First, care should be taken to avoid any injury to the coronary artery. In ASC-VAs, coronary angiography should be performed before RFCA to ensure that the distance between the ablation catheter and the ostium of the left main coronary artery is greater than 10 mm [13]. Radiofrequency ablation at sites adjacent to the successful ablation site provokes sinus bradycardia followed by atrio-ventricular conduction block. This may trigger a vagal reflex through stimulation of the vagal pathways or receptors in the anterior epicardial fat pads neighboring the RCC. Transient sinus bradycardia, transient complete atrio-ventricular conduction block during ablation within the RCC, and a thermal effect on the anterior epicardial fat pad's parasympathetic ganglia resulting in vagal stimulation may occur [37]. Finally, manipulations should be performed carefully because aortic or mitral regurgitation 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) are successfully treated with endocardial RFCA combined with pace mapping and detection of the earliest ventricular electrogram with a prepotential. Despite many morphological similarities among the LVOT-VA subtypes, they can be differentiated using electrocardiographic characteristics to safely perform RFCA. LVOT-VAs originating from the inaccessible area of the epicardium at the LV summit should be differentiated from those originating from the accessible area, which is accessible by epicardial catheter ablation, using novel electrophysiological characteristics. The ECG characteristics and anatomical information obtained from visualization using image integration with electroanatomical mapping may advance the safe and successful RFCA of idiopathic LVOT-VAs.

Conflict of interest

The author declares that there is no conflict of interest.