Catheter Ablation of Tachyarrhythmias From the Aortic Sinuses of Valsalva

Transcription

1 Circulation Journal Official Journal of the Japanese Circulation Society REVIEW Catheter Ablation of Tachyarrhythmias From the Aortic Sinuses of Valsalva When and How? Hiroshi Tada, MD, PhD The aortic root is at the center of the heart. Each of the aortic sinuses of Valsalva, positioned at the base of the aortic root, is in contact with the atrial myocardium and/or ventricular myocardium at their bases, which enables mapping and ablating of some ventricular arrhythmias with an outflow tract origin and supraventricular tachycardias (ie, atrial tachycardia, accessory pathways) from the aortic sinuses of Valsalva. These arrhythmias have characteristic electrocardiographic findings associated with their origins, and almost all are difficult to ablate from an atrial or ventricular endocardial site. Site-specific and potential complications, such as a coronary artery occlusion or atrioventricular block, can occur with catheter ablation at the aortic sinuses of Valsalva. Therefore, accurate diagnosis and proper ablation at the aortic sinuses of Valsalva are required for a cure. This review describes the anatomic features of the aortic sinuses of Valsalva and focuses on the diagnosis and radiofrequency catheter ablation of arrhythmias that can be ablated from this site. (Circ J 2012; 76: ) Key Words: Aortic sinus of Valsalva; Catheter ablation; Supraventricular tachycardia; Ventricular arrhythmia Radiofrequency (RF) catheter ablation has been established as an effective and curative therapy for ventricular tachycardias (VTs) or symptomatic premature ventricular contractions (PVCs) originating from the outflow tract (VT/PVCs). 1 3 Although most of these arrhythmias have their origin in the right ventricular outflow tract (RVOT), 1 3 it has become clear that some could be ablated from the aortic sinuses of Valsalva. 1 6 Furthermore, recent studies have demonstrated that some supraventricular tachycardias are also abolished by RF catheter ablation within the aortic sinuses of Valsalva Anatomy of the Aortic Root The aortic root, which is the portion of the aortic valve from its position at the left ventricular (LV) outlet to its junction with the ascending portion of the aorta (sinotubular junction), forms the center of the heart It is adjacent but to the right and posterior of the subpulmonary infundibulum, with its posterior margin wedged between the orifice of the mitral valve and the muscular ventricular septum (Figure 1A). The basal portion of the aortic root consists of the sinus of Valsalva, fibrous interleaflet triangles, and the valvular leaflets themselves (Figure 1B). The aortic root is connected to the muscular ventricular septum, with the remaining one-third in fibrous continuity with the aortic leaflet of the mitral valve. The right coronary sinus of Valsalva (RSV) and the anterior part of the left coronary sinus of Valsalva (LSV) are connected with the ventricular musculature at their bases (Figures 1,2A). Although ventricular arrhythmias can be ablated either within or below the RSV or LSV, it is the myocardium of the LV ostium that is the target for ablation. 16,17 The remaining posterior part of the LSV and the entire non-coronary sinus of Valsalva (NSV) do not come in direct contact with the LV myocardium, and the NSV is exclusively composed of fibrous walls (Figures 1,2). 12,15 The RVOT is usually situated slightly anterior and superior to the RSV and is adjacent to the superior area of the RVOT (Figure 2). The right atrial appendage and superior vena cava/right atrial junction may overlie portions of the RSV. The NSV is the most posterior of the 3 sinuses, and is located between the right and left atria, immediately anterior to the interatrial septum (Figure 2). In some patients, the posterior portion of the RSV can be related to the interatrial septum or to the anteroseptal portion of the annular, anteroseptal portion of the right atrium. The LSV is typically not anatomically related to either the right or left atrium. Importantly, the commissure between the NSV and RSV is located immediately adjacent to the commissure of the anterior and septal leaflets of the tricuspid valve. The joining of these commissures forms the membranous portion of the interventricular septum and is the location of the penetrating bundle of His and, more distally, the origin of the left bundle branch. The compact atrioventricular (AV) node itself is located more posteriorly and inferiorly to this commissure. The fast pathway Received January 17, 2012; accepted February 20, 2012; released online March 6, 2012 Cardiovascular Division, Institute of Clinical Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Japan Mailing address: Hiroshi Tada, MD, PhD, Cardiovascular Division, Institute of Clinical Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tennodai, Tsukuba , Japan. htada@md.tsukuba.ac.jp ISSN doi: /circj.CJ All rights are reserved to the Japanese Circulation Society. For permissions, please cj@j-circ.or.jp

2 792 TADA H Figure 1. (A) Diagram of the aortoventricular membrane that covers the left ventricular (LV) ostium. The red arrows indicate the zone where the left and right aortic sinuses of Valsalva come in contact with the ventricular myocardium of the LV ostium. (B) Relationship between the aortic valve and mitral valve. The basal portion of the aortic root consists of the sinuses of Valsalva, fibrous interleaflet triangles, and the valvular leaflets themselves. The aortic root is connected to the muscular ventricular septum, with the remaining one-third in fibrous continuity with the aortic leaflet of the mitral valve (light pink areas below the left and noncoronary aortic sinuses of Valsalva). A-M, aortic-mitral; AML, anterior mitral leaflet; L, left aortic sinus of Valsalva; LA, left atrial; LFT, left fibrous trigone; N, non-coronary sinus of Valsalva; PML, posterior mitral leaflet; R, right sinus of Valsalva. input to the AV node, however, is located directly posterior to this commissure and is thus related to the anterior portion of the NSV. The triangle between the right- and non-coronary leaflets adjoins the interventricular part of the membranous septum, which together with the right fibrous trigone, forms the central fibrous body (Figure 1B). This anatomical relationship is important because energy application in the NSV and RSV is potentially associated with a substantial risk for AV nodal block. 18 Ventricular Arrhythmias The connection of the myocardium of the LV ostium to the RSV and anterior part of the LSV enables abolition of VT/ PVCs arising from this portion by application of RF energy within these 2 aortic sinuses. Recently, 2 cases of successful elimination of VT/PVCs by catheter ablation from the NSV have been reported. 19,20 However, it is very rare because the ventricular myocardium is not adjacent to the NSV. Outflow tract VT/PVCs, including those with origins in these 2 aortic sinus, usually demonstrate a single bundle branch block QRS morphology with an inferior axis, and triggered activity is considered as their mechanism. 21 The VT/PVCs arising from the LSV and RSV should be differentiated from those arising from the RVOT (RVOT-VT/PVCs) in order to obtain a cure and avoid futile RF energy applications and ensuing complications (Figures 3A,4A). Ventricular Arrhythmias Arising From the LSV (LSV-VT/PVCs) To differentiate VT/PVCs arising from the left side (LVOT, LSV or LV epicardium remote from the LSV) and those from the right side (RVOT-VT/PVCs), the precordial R-wave transition, 1,2 QRS morphology in lead I, 1,2 R-wave duration in lead V1 or V2, and R/S-wave amplitude ratio in lead V1 or V2 2,4 are useful. Early precordial R-wave transition and the presence of an S-wave in lead I favor LSV-VT/PVCs rather than ROVT- VT/PVCs (Figure 3B-a,b). 2 Some patients with LSV-VT/ PVCs have a late R-wave transition (after V3), which may be explained by preferential conduction to the RVOT. 22 An R/Swave amplitude index (calculated from the greater percentage of the R/S-wave amplitude ratio in lead V1 or V2) 0.3 and an R-wave duration index (calculated percentage by dividing the QRS complex duration by the longer R-wave duration in lead V1 or V2) 50% are both useful for differentiating LSV-VT/ PVCs from RVOT-VT/PVCs (Figure 3B-c,d). 2,4 A high R/Swave amplitude ratio in lead V1 or V2 may reflect a more posterior location of the LSV compared with an endocardial area of the RVOT. Although an S-wave ( 0.1 mv) in lead V6 is present in VT/PVCs of an LV endocardial origin, it is absent in VT/PVCs arising from the LSV or LVOT just beneath the LSV. 2,5 Recently, the V2 transition ratio for differentiating between VT/PVCs arising from the left side and those from the right side 23 and the transition zone (TZ) index for distinguishing aortic sinus VT/PVCs from RVOT-VT/PVCs 24 were reported. The use of these novel ECG criteria may increase the accuracy of diagnosis. Even if the earliest ventricular activation of a VT/PVC is at the LSV, some VT/PVCs cannot be ablated from the LSV because of the distance from the LSV. These OT-VTs (Epi-VT/ PVCs) are thought to originate from the LV epicardial portion around the transitional area from the great cardiac vein to the anterior interventricular vein or LV summit. 6,25 Neither the R/Swave amplitude index nor the R-wave duration index is helpful for differentiating LVEpi-VT/PVC from LSV-VT/PVC because most LVEpi-VT/PVCs fulfill the criteria of LSV-VT. 2 The LVEPi-VT/PVCs are often associated with S-waves in lead I, an early R-wave transition ( lead V3), and a degree of slurring

3 Ablation From the Aortic Sinuses of Valsalva 793 Figure 2. (A) Computed tomography images. (a) Short-axis view. (b) Long-axis view. The ventricular myocardium at the left ventricular ostium is in contact with the bases of the right sinus of Valsalva (RSV) and left sinus of Valsalva (LSV) (red arrows). However, no myocardium is found at the base of the NSV (yellow arrows). (B) Cross-sectional magnetic resonance image at the level of the cardiac base showing the topographic relationship of the aortic sinus of Valsalva to the surrounding cardiac structures in a control subject. (a) Short-axis view. (b) Apical 5-chamber view. Note that there is no ventricular myocardium just beneath the non-coronary sinus of Valsalva (N). L, left aortic sinus of Valsalva; L(R)A, left (right) atrium; L(R)V, left (right) ventricle; R, right sinus of Valsalva; RAA, right atrial appendage; VS, ventricular septum. (Modified from Hiramatsu et al 37 with permission.) of the R-waves. 2,26,27 Also, a Q-wave ratio of avl to avr >1.4 or an S-wave amplitude >1.2 mv in lead V1 is often found. 2,26 Recent studies demonstrated that a maximum duration index, calculated by dividing the QRS duration by the earliest time to the maximum deflection in any of the precordial leads, , and a peak deflection index, determined in the inferior lead presenting the tallest R wave by dividing the time from the QRS onset to the peak QRS deflection by a total QRS duration >0.6, 29 both predict LVEpi-VTs with a high accuracy. A stepwise ECG algorithm for determining the origin of an outflow tract tachycardia has been reported (sensitivity 88%; specificity 96%; Figure S1). 2 During the ablation procedure, mapping and pacing at the transitional zone from the great cardiac vein to the anterior interventricular vein (distal portion of the great cardiac vein) are useful for differentiating between LSV-VT/PVCs and LVEPi- VT/PVCs. 30 If the earliness of ventricular activation during the VT/PVCs at the distal portion of the great cardiac vein to that at the LSV is 10 ms or if the QRS morphologies during pace mapping at the distal portion of the great cardiac vein is quite similar to the clinical VT/PVCs, there is a fair possibility that the VT/PVCs are LVEPi-VT/PVCs. 30 Ventricular Arrhythmias Arising From the RSV (RSV-VT/PVCs) The RSV is directly in contact with the ventricular myocardium (Figures 1,2), and RF energy application at the RSV generates a lesion at the crest (very high portion) of the interventricular septum. 17 The RSV is positioned just posterior to the inferior portion of the RVOT near the His-bundle region (Figure 2). Therefore, the ECG morphology of RSV-VT/PVCs is similar to that of VT/PVCs arising from near the His-bundle region (Figure 5A): 2,31,32 Compared with conventional RVOT-VT/ PVCs arising from the superior portion of the RVOT and LSV- VT/PVCs, a taller R-wave in lead I, smaller R-wave amplitude in all the inferior leads, smaller ratio of the R-wave amplitude in leads II and III, and a QS pattern in lead V1 are found with these arrhythmias. In lead avl, a QS pattern or any R-wave is also found in both VT/PVCs. However, RSV-VT/PVCs usually have a QS pattern, probably because their origin is higher

4 794 TADA H Figure 3. (A) Representative 12-lead ECGs of premature ventricular contractions originating from the left sinus of Valsalva (LSV) and right ventricular outflow tract (RVOT). (B) Differences in the precordial R-wave transition (a), incidence of an S-wave in lead I (b), R-wave duration index (c), and R/S-wave amplitude index (d) between ventricular tachycardias with a right ventricular origin (RV) and those with a left ventricular origin (LV). (Modified from Ito et al 2 with permission.) than that of VT/PVCs arising from near the His-bundle region. The precordial R-wave transition is later than LSV-VT/PVCs. A recent study of pace mapping at the RSV demonstrated that a broad small R-wave in lead V2 is another characteristic finding of RSV-VT/PVCs. 33 In any event, when VT/PVCs have these ECG findings and the earliest activation is from near the His-bundle region of the RV, mapping in the RSV should be performed to identify the precise origin of the arrhythmia to achieve a cure (Figures 5B,C). Ventricular Arrhythmias Arising From Near the Junction of the LSV and RSV (LR-J-VT/PVCs) Although rare, the LV myocardium below the junction of the LSV and RSV (LR-J) can be a source of VT/PVCs. The interleaflet triangle between the LSV and RSV consists of fibrous tissue, and does not include ventricular myocardium (Figure 1B). Therefore, it is the myocardium of the LV ostium adjacent to the bases of the LSV and RSV that is the target for ablation (Figure 1). Because of the anatomic location of the origin of the arrhythmia, LR-J-VT/PVCs seem to be associated with ECG findings that are between those of LSV-VT/ PVCs and RSV-VT/PVCs (Figure 6A). Recently, a qrs pattern in leads V and a QS morphology in lead V1 with notching on the downward deflection with a precordial transition at lead V3 35 have been reported as relatively specific ECG findings of LR-J-VT/PVCs. When the earliest activation is found around the LR-J, and especially when RF energy application within the LSV or RSV has failed, mapping below these aortic sinuses should be performed carefully (Figures 6B,C). As mentioned before, a detailed ECG analysis should help determine the origin of VT/PVCs arising from the aortic sinuses of Valsalva. Moreover, some combinations of the ECG findings are useful for differentiating LSV-VT/PVCs, RSV- VT/PVCs, and LR-J-VT/PVCs. However, the LSV, RSV, and LR-J are located adjacent to each other within a relatively narrow region, and the relative location of these structures to the ECG electrodes, especially the precordial leads, might affect the ECG findings. Therefore, when VT/PVCs arise from the LSV near the LR-J, or from the RSV near the LR-J, complete differentiation of those 3 VT/PVCs by the ECG findings will be difficult, and real-time intracardiac echocardiography 36 might be required to precisely determine the anatomical origin of the VT/PVCs. The point to be emphasized is the importance of a deliberate 12-lead ECG analysis before the ablation procedure. Prior knowledge of the origin of the VT/PVC enables detailed and careful mapping of the narrow region within and adjacent to the aortic root, thus avoiding futile mapping and ablation at inappropriate sites, and also shortening the procedure time, which may enhance the success rate.

5 Ablation From the Aortic Sinuses of Valsalva 795 Figure 4. Premature ventricular contraction (PVC) arising from the left sinus of Valsalva (LSV). (A) 12-lead ECG during a PVC and during pace mapping from the LSV. An excellent pace map was obtained at the successful ablation site. (B) Intracardiac recordings from the successful ablation site. A sharp potential preceding the QRS complex (arrow) is shown. (C) Left coronary artery (Left) and fluoroscopic images during the radiofrequency catheter ablation (Right) obtained in the right anterior oblique (RAO 35 ) and left anterior oblique (LAO 45 ) projections showing the ablation sites. Abl, ablation catheter; d, distal; GCV-AIV, 2Fr octapolar electrode catheter placed from the great cardiac vein and anterior interventricular vein; HRA, high right atrium; HBE, His bundle electrogram; p, proximal; uni., unipolar recording; RV, right ventricle. (Modified from Tada et al 25 with permission.) Supraventricular Arrhythmias RF energy applications within the aortic sinuses of Valsalva could eliminate focal atrial tachycardias (ATs) 7,8,10,37 43 and accessory pathways. 9,44 47 The NSV is adjacent to the atrial myocardium on the epicardial aspect (Figure 2). On the other hand, part of the LSV comes in contact with the left atrium, but there is a distance between the greatest portion of the RSV and the atrial myocardium. Based on this anatomic feature, it is within the NSV that most ATs are successfully ablated. 7,8,10,11,37 41 Only a few ATs successfully ablated within the RSV or LSV have been reported. 10,41,42 It has been shown that irrigated RF applications at the NSV consistently result in left atrial lesions located between the floor of the fossa ovalis and the mitral annulus, an area that can be difficult to map using either a retrograde or transseptal puncture approach. 17 With excellent catheter stability within the NSV, catheter ablation at this site may be highly effective in the deeper tissues that are otherwise not accessible because of limited catheter stability and tissue contact. In the case of accessory pathways, successful elimination can be achieved with RF energy application at the NSV for anteroseptal pathways and at the LSV for left anterior pathways. Myocardial sleeves cross the aortic valve plane and extend into the NSV. 48 Thus, in the region of the NSV, there is close anatomic proximity between the ventricular myocardium (just below and extending above the NSV) and atrial myocardium (adjacent to the interatrial septum), allowing for possible electrically active myocardial connections, constituting an accessory pathway. 45 Left anterior accessory pathways occur rarely because the junction between the aortic and mitral valves is a continuous fibrous ring. However, it has been shown that very rarely the muscular connections can pass from the left atrial myocardium through the area of fibrous continuity between the leaflets of the aortic and mitral valves, and insert into the LV myocardium. 49,50 This approach, as well as the transseptal approach, may be considered if the retrograde transaortic approach fails. 46 ECG Characteristics of ATs Arising From the Aortic Sinuses of Valsalva Interpretation of the P-wave morphology in ATs remains challenging because the onset of the P-wave is not always distinguishable during the tachycardia. At present, there is not a sufficient ECG algorithm for accurately identifying the origin among the aortic sinuses or for differentiating ATs arising from the aortic sinuses from tachycardias located elsewhere. However, from the results of studies using a large number of patients, 8,10,11 ATs arising from the NSV (NSV-ATs) have a negative/positive P-wave in lead V1. A recent study 10 reported that the P-wave morphological features in leads I and avl are

6 796 TADA H Figure 5. Premature ventricular contraction (PVC) arising from the right sinus of Valsalva (RSV). (A) 12-lead ECG. (B) Intracardiac recordings from the successful ablation site. (C) Fluoroscopic images obtained in the right anterior oblique (RAO 35 ) and left anterior oblique (LAO 45 ) projections showing the ablation sites. Note that, although the ablation catheter in the RSV was positioned very close to that at the lower portion of the right ventricular (RV) outflow tract, the local ventricular activation at the RSV (arrow) obviously preceded that at the RV. Bi, bipolar recording; Abl, ablation catheter; HBE, His-bundle electrogram. likely to be the more useful ECG findings for distinguishing NSV-ATs from LSV-ATs: a positive P-wave in leads I and avl was more likely to be a NSV-AT, with a negative/positive or isoelectric P-wave supportive of an LSV-AT, which can be reasonably explained by the more leftward position of the LSV compared with the NSV. Specific Considerations for Catheter Ablation Within the Aortic Sinuses of Valsalva Before performing catheter ablation within the aortic sinuses of Valsalva, coronary angiography or selective angiography of the aortic sinuses should be performed to ensure the distance between the ablation catheter and coronary ostium is more than 10 mm and to visualize the anatomy of the aortic root (Figure 4C). 5 Angiography of both coronary arteries should be performed to rule out any anomalies. 51 Coronary angiography should be performed once again after the ablation procedure to rule out any coronary spasms, stenoses, or occlusions. A previous experimental study with porcine hearts demonstrated that a temperature setting of C with a non-irrigated RF ablation caused no damage to the aortic valve, whereas a temperature setting >70 C was associated with valve-tissue damage. 5 Therefore, a maximum power of 35 W, maximum electrodetissue interface temperature of 55 C, and duration of each RF energy application of s are the recommended settings for non-irrigated RF ablation at the aortic sinus of Valsalva to avoid any potential complications. 5 Not in the case of RF ablation within the aortic sinuses of Valsalva, but in a few cases of left-sided RF ablation with the retrograde approach across the aortic valve, aortic regurgitation or a leaflet perforation following ablation has been reported, 52 suggesting the importance of a gentle, slow-moving and precise manipulation of the catheter at the aortic root. Generally, deeper lesions are created using an irrigated-tip RF ablation catheter compared with a conventional RF or cryoablation catheter when the energy application is delivered in the NSV, 17 suggesting a lower power setting may be better for irrigated RF ablation in the aortic sinuses of Valsalva. In LSV-VT/PVCs, a distinct potential that precedes the QRS complex (pre-potential) is often recorded at the ablation site within the LSV during VT/PVCs, and it is considered to be useful for identifying the successful ablation site (Figure 4B). 5,25 This potential recorded within the LSV may represent activation of the pathway connecting the arrhythmia origin to the ventricular myocardium. 53 The aforementioned anatomic features of the 3 aortic sinuses are responsible for the differences in the electrogram recordings within these aortic sinuses: 37,43 the NSV electrograms during sinus rhythm have a larger atrial amplitude than ventricular amplitude, and the ratio of the atrial amplitude to the ventricular amplitude is usually >1, which is apparently different from the LSV and RSV electrograms (Figure 7). 37 Analysis of the electrogram is helpful for identifying the correct positioning of the mapping/ablation catheter at the aortic sinuses of Valsalva during the ablation procedure.

7 Ablation From the Aortic Sinuses of Valsalva 797 Figure 6. Premature ventricular contraction (PVC) arising from near the junction of the left and right sinuses of Valsalva (LSV, RSV). (A) 12-lead ECG. (B) Intracardiac recordings from the successful ablation site. (C) Fluoroscopic images obtained in the right anterior oblique (RAO 35 ) and left anterior oblique (LAO 45 ) projections showing the ablation sites. Abl, ablation catheter; GCV- AIV, 2Fr octapolar electrode catheter placed from the great cardiac vein and anterior interventricular vein; PA, pulmonary artery. Figure 7. Comparison of the local electrograms recorded at the aortic sinus of Valsalva in 7 control subjects. (A) Amplitude of the atrial electrogram. (B) Amplitude of the ventricular electrogram. (C) Amplitude ratio of the atrial electrogram to the ventricular electrogram. LSV, left sinus of Valsalva; NSV, non-coronary sinus of Valsalva; RSV, right sinus of Valsalva. (Modified from Hiramatsu et al 37 with permission.)

8 798 TADA H Figure 8. Representative electrograms recorded at the non-coronary sinus of Valsalva (NSV) during sinus rhythm (A) and an atrial tachycardia (B) in a patient with an atrial tachycardia originating from near the atrioventricular node. The radiograms obtained in the right anterior oblique (RAO 35 ) and left anterior oblique (LAO 45 ) projections show the successful ablation site (C). A tiny but distinct His bundle deflection (His) was recorded from the distal electrode of the ablation catheter positioned within the NSV. A, atrial electrogram; Dist, distal; HBE, His-bundle electrogram; HRA, high right atrium; Prox, proximal; RVA, right ventricular apex; Uni, unipolar; V, ventricular electrogram. (Modified from Hiramatsu et al 37 with permission.) Fortunately, most reported cases of catheter ablation of NSV tachycardias originating from near the AV node or Hisbundle region have not resulted in impairment of AV conduction. However, in 1 case complete AV block from RF energy delivery at the NSV was reported. 18 Therefore, much attention should be paid to the delivery of RF energy at that site. Whether or not a His-bundle potential can be recorded at the NSV should be assessed before the RF energy application in order to avoid this particular complication. However, during tachycardia, it is difficult to confirm whether or not there is a Hisbundle potential, probably because of greater baseline drift and artifact during the tachycardia than during sinus rhythm or a wider distance between the His-bundle region and the ablation catheter during the tachycardia than during sinus rhythm (Figure 8). 37 Therefore, the presence of a His-bundle potential during sinus rhythm should be assessed before ablation at the NSV. To avoid impairment of AV conduction during RF energy delivery, it is useful to be aware of any prolongation of the PQ, A-H, or H-V interval. Therefore, the delivery of RF energy at the NSV during sinus rhythm is safer than during the tachycardia. Also, the power of the RF energy should be increased gradually from a low wattage (ie, W). The RSV is also adjacent to His bundle region, and the His bundle potential is recorded more often at the RSV than the NSV during sinus rhythm. 37 Therefore, RF ablation in the RSV should be performed in the same manner as in the NSV. During the ablation procedure, fluoroscopy is widely used for catheter placement and determination of the ablation site, and angiography is usually performed to obtain detailed information about the coronary arteries and aortic sinuses of Valsalva. Nonetheless, the use of a 3-dimensional electroanatomical mapping system (ie, CARTO [Biosense-Webster, Inc., Diamond Bar, CA, USA], Ensite NavX [St. Jude Medical, Inc, St. Paul, MN, USA]), 54,55 and integration between electroanatomical mapping and computed tomography, magnetic resonance imaging or intracardiac echocardiography 56 are useful for understanding the detailed anatomy of the aortic root and its surrounding structure (ie, coronary artery, His bundle region) and for identifying the precise position of the catheter in the heart. The stability of the ablation catheter and its contact status with the target site during RF ablation are important to achieve effective ablation, and should be checked using fluoroscopic observation during RF energy application. Intracardiac echocardiography can provide more precise and detailed information than fluoroscopy on the stability and contact status of the catheter with the target site, as well as the catheter s location and its relationship to the surrounding structures in real time. 36,57 The use of these modalities may reduce procedurerelated complications and fluoroscopy time and, thus, enhance the success rate. Acknowledgments The author gratefully thanks all the cardiac physicians and the nursing, echo laboratory, clinical engineering and radiology staff members in the

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