Circulation Journal REVIEW Official Journal of the Japanese Circulation Society http://www.j-circ.or.jp 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 . 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 character- istic 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 atrio- ventricular 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 ar- rhythmias that can be ablated from this site. (Circ J 2012; 76: 791 – 800)

Key Words: Aortic sinus of Valsalva; Catheter ablation; Supraventricular tachycardia; Ventricular arrhythmia

adiofrequency (RF) catheter ablation has been estab- left coronary sinus of Valsalva (LSV) are connected with the lished as an effective and curative therapy for ven- ventricular musculature at their bases (Figures 1,2A). Al- R tricular tachycardias (VTs) or symptomatic premature though ventricular arrhythmias can be ablated either within ventricular contractions (PVCs) originating from the outflow or below the RSV or LSV, it is the myocardium of the LV tract (VT/PVCs).1–3 Although most of these arrhythmias have ostium that is the target for ablation.16,17 The remaining pos- their origin in the right ventricular outflow tract (RVOT),1–3 it terior part of the LSV and the entire non-coronary sinus of has become clear that some could be ablated from the aortic Valsalva (NSV) do not come in direct contact with the LV sinuses of Valsalva.1–6 Furthermore, recent studies have dem- myocardium, and the NSV is exclusively composed of fibrous onstrated that some supraventricular tachycardias are also abol- walls (Figures 1,2).12,15 The RVOT is usually situated slightly ished by RF catheter ablation within the aortic sinuses of Val- anterior and superior to the RSV and is adjacent to the supe- salva.7–11 rior area of the RVOT (Figure 2). The right atrial appendage and superior vena cava/right atrial junction may overlie por- tions of the RSV. The NSV is the most posterior of the 3 si- Anatomy of the Aortic Root nuses, and is located between the right and left atria, immedi- The aortic root, which is the portion of the from ately anterior to the (Figure 2). In some its position at the left ventricular (LV) outlet to its junction patients, the posterior portion of the RSV can be related to the with the ascending portion of the (sinotubular junction), interatrial septum or to the anteroseptal portion of the annular, forms the center of the heart.12–16 It is adjacent but to the anteroseptal portion of the right . The LSV is typically right and posterior of the subpulmonary infundibulum, with not anatomically related to either the right or left atrium. Im- its posterior margin wedged between the orifice of the mitral portantly, the commissure between the NSV and RSV is lo- valve and the muscular ventricular septum (Figure 1A). The cated immediately adjacent to the commissure of the anterior basal portion of the aortic root consists of the sinus of Valsal- and septal leaflets of the . The joining of these va, fibrous interleaflet triangles, and the valvular leaflets them- commissures forms the membranous portion of the interven- selves (Figure 1B). The aortic root is connected to the muscu- tricular septum and is the location of the penetrating bundle lar ventricular septum, with the remaining one-third in fibrous of His and, more distally, the origin of the left bundle branch. continuity with the aortic leaflet of the . The right The compact atrioventricular (AV) node itself is located more coronary sinus of Valsalva (RSV) and the anterior part of the 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, 1-1-1 Tennodai, Tsukuba 305-8575, Japan. E-mail: [email protected] ISSN-1346-9843 doi: 10.1253/circj.CJ-11-1554 All rights are reserved to the Japanese Circulation Society. For permissions, please e-mail: [email protected]

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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, fi- brous 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 non- coronary 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 V1 or V2, and R/S-wave amplitude ratio in lead V1 or V22,4 are this commissure and is thus related to the anterior portion of useful. Early precordial R-wave transition and the presence of the NSV. The triangle between the right- and non-coronary an S-wave in lead I favor LSV-VT/PVCs rather than ROVT- leaflets adjoins the interventricular part of the membranous VT/PVCs (Figure 3B-a,b).2 Some patients with LSV-VT/ septum, which together with the right fibrous trigone, forms PVCs have a late R-wave transition (after V3), which may be the central fibrous body Figure 1B( ). This anatomical relation- explained by preferential conduction to the RVOT.22 An R/S- ship is important because energy application in the NSV and wave amplitude index (calculated from the greater percentage RSV is potentially associated with a substantial risk for AV of the R/S-wave amplitude ratio in lead V1 or V2) ≥0.3 and an nodal block.18 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/ Ventricular Arrhythmias PVCs from RVOT-VT/PVCs (Figure 3B-c,d).2,4 A high R/S- The connection of the myocardium of the LV ostium to the wave amplitude ratio in lead V1 or V2 may reflect a more pos- RSV and anterior part of the LSV enables abolition of VT/ terior location of the LSV compared with an endocardial area PVCs arising from this portion by application of RF energy of the RVOT. Although an S-wave (≥0.1 mV) in lead V6 is within these 2 aortic sinuses. Recently, 2 cases of successful present in VT/PVCs of an LV endocardial origin, it is absent elimination of VT/PVCs by catheter ablation from the NSV in VT/PVCs arising from the LSV or LVOT just beneath the have been reported.19,20 However, it is very rare because the LSV.2,5 Recently, the V2 transition ratio for differentiating be- ventricular myocardium is not adjacent to the NSV. Outflow tween VT/PVCs arising from the left side and those from the tract VT/PVCs, including those with origins in these 2 aortic right side23 and the transition zone (TZ) index for distinguish- sinus, usually demonstrate a single bundle branch block QRS ing aortic sinus VT/PVCs from RVOT-VT/PVCs24 were re- morphology with an inferior axis, and triggered activity is ported. The use of these novel ECG criteria may increase the considered as their mechanism.21 The VT/PVCs arising from accuracy of diagnosis. the LSV and RSV should be differentiated from those arising Even if the earliest ventricular activation of a VT/PVC is at from the RVOT (RVOT-VT/PVCs) in order to obtain a cure the LSV, some VT/PVCs cannot be ablated from the LSV be- and avoid futile RF energy applications and ensuing complica- cause of the distance from the LSV. These OT-VTs (Epi-VT/ tions (Figures 3A,4A). PVCs) are thought to originate from the LV epicardial portion around the transitional area from the great cardiac vein to the Ventricular Arrhythmias Arising From the LSV anterior interventricular vein or LV summit.6,25 Neither the R/S- (LSV-VT/PVCs) wave amplitude index nor the R-wave duration index is helpful To differentiate VT/PVCs arising from the left side (LVOT, for differentiating LVEpi-VT/PVC from LSV-VT/PVC because LSV or LV epicardium remote from the LSV) and those from most LVEpi-VT/PVCs fulfill the criteria of LSV-VT.2 The the right side (RVOT-VT/PVCs), the precordial R-wave transi- LVEPi-VT/PVCs are often associated with S-waves in lead I, tion,1,2 QRS morphology in lead I,1,2 R-wave duration in lead an early R-wave transition (≤lead V3), and a degree of slurring

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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) ; R, right sinus of Valsalva; RAA, right atrial appendage; VS, ventricular septum. (Modified from Hiramatsu et al37 with permission.)

of the R-waves.2,26,27 Also, a Q-wave ratio of aVL to aVR >1.4 similar to the clinical VT/PVCs, there is a fair possibility that or an S-wave amplitude >1.2 mV in lead V1 is often found.2,26 the VT/PVCs are LVEPi-VT/PVCs.30 Recent studies demonstrated that a maximum duration index, calculated by dividing the QRS duration by the earliest time to Ventricular Arrhythmias Arising From the RSV the maximum deflection in any of the precordial leads,28 ≥0.55, (RSV-VT/PVCs) and a peak deflection index, determined in the inferior lead The RSV is directly in contact with the ventricular myocardium presenting the tallest R wave by dividing the time from the QRS (Figures 1,2), and RF energy application at the RSV generates onset to the peak QRS deflection by a total QRS duration >0.6,29 a lesion at the crest (very high portion) of the interventricular both predict LVEpi-VTs with a high accuracy. A stepwise septum.17 The RSV is positioned just posterior to the inferior ECG algorithm for determining the origin of an outflow tract portion of the RVOT near the His-bundle region (Figure 2). tachycardia has been reported (sensitivity 88%; specificity 96%; Therefore, the ECG morphology of RSV-VT/PVCs is similar Figure S1).2 to that of VT/PVCs arising from near the His-bundle region During the ablation procedure, mapping and pacing at the (Figure 5A):2,31,32 Compared with conventional RVOT-VT/ transitional zone from the great cardiac vein to the anterior in- PVCs arising from the superior portion of the RVOT and LSV- terventricular vein (distal portion of the great cardiac vein) are VT/PVCs, a taller R-wave in lead I, smaller R-wave amplitude useful for differentiating between LSV-VT/PVCs and LVEPi- in all the inferior leads, smaller ratio of the R-wave amplitude VT/PVCs.30 If the earliness of ventricular activation during the in leads II and III, and a QS pattern in lead V1 are found with VT/PVCs at the distal portion of the great cardiac vein to that these arrhythmias. In lead aVL, a QS pattern or any R-wave is at the LSV is ≥10 ms or if the QRS morphologies during pace also found in both VT/PVCs. However, RSV-VT/PVCs usu- mapping at the distal portion of the great cardiac vein is quite ally have a QS pattern, probably because their origin is higher

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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 al2 with permission.)

than that of VT/PVCs arising from near the His-bundle region. tion is found around the LR-J, and especially when RF en- The precordial R-wave transition is later than LSV-VT/PVCs. ergy application within the LSV or RSV has failed, mapping A recent study of pace mapping at the RSV demonstrated that below these aortic sinuses should be performed carefully a broad small R-wave in lead V2 is another characteristic find- (Figures 6B,C). ing of RSV-VT/PVCs.33 In any event, when VT/PVCs have these ECG findings and the earliest activation is from near the As mentioned before, a detailed ECG analysis should help His-bundle region of the RV, mapping in the RSV should be determine the origin of VT/PVCs arising from the aortic si- performed to identify the precise origin of the arrhythmia to nuses of Valsalva. Moreover, some combinations of the ECG achieve a cure (Figures 5B,C). findings are useful for differentiating LSV-VT/PVCs, RSV- VT/PVCs, and LR-J-VT/PVCs. However, the LSV, RSV, and Ventricular Arrhythmias Arising From Near the Junction of LR-J are located adjacent to each other within a relatively nar- the LSV and RSV (LR-J-VT/PVCs) row region, and the relative location of these structures to the Although rare, the LV myocardium below the junction of ECG electrodes, especially the precordial leads, might affect the LSV and RSV (LR-J) can be a source of VT/PVCs. The the ECG findings. Therefore, when VT/PVCs arise from the interleaflet triangle between the LSV and RSV consists of LSV near the LR-J, or from the RSV near the LR-J, complete fibrous tissue, and does not include ventricular myocardium differentiation of those 3 VT/PVCs by the ECG findings will be (Figure 1B). Therefore, it is the myocardium of the LV ostium difficult, and real-time intracardiac echocardiography36 might adjacent to the bases of the LSV and RSV that is the target for be required to precisely determine the anatomical origin of the ablation (Figure 1). Because of the anatomic location of the VT/PVCs. The point to be emphasized is the importance of a origin of the arrhythmia, LR-J-VT/PVCs seem to be associ- deliberate 12-lead ECG analysis before the ablation procedure. ated with ECG findings that are between those of LSV-VT/ Prior knowledge of the origin of the VT/PVC enables detailed PVCs and RSV-VT/PVCs (Figure 6A). Recently, a qrS pat- and careful mapping of the narrow region within and adjacent tern in leads V1–334 and a QS morphology in lead V1 with to the aortic root, thus avoiding futile mapping and ablation at notching on the downward deflection with a precordial tran- inappropriate sites, and also shortening the procedure time, sition at lead V335 have been reported as relatively specific which may enhance the success rate. ECG findings of LR-J-VT/PVCs. When the earliest activa-

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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 record- ings 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 oc- tapolar 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 al25 with permission.)

(just below and extending above the NSV) and atrial myocar- Supraventricular Arrhythmias dium (adjacent to the interatrial septum), allowing for possible RF energy applications within the aortic sinuses of Valsalva electrically active myocardial connections, constituting an ac- could eliminate focal atrial tachycardias (ATs)7,8,10,37–43 and ac- cessory pathway.45 Left anterior accessory pathways occur cessory pathways.9,44–47 The NSV is adjacent to the atrial myo- rarely because the junction between the aortic and mitral valves on the epicardial aspect (Figure 2). On the other hand, is a continuous fibrous ring. However, it has been shown that part of the LSV comes in contact with the left atrium, but there very rarely the muscular connections can pass from the left is a distance between the greatest portion of the RSV and the atrial myocardium through the area of fibrous continuity be- atrial myocardium. Based on this anatomic feature, it is within tween the leaflets of the aortic and mitral valves, and insert into the NSV that most ATs are successfully ablated.7,8,10,11,37–41 the LV myocardium.49,50 This approach, as well as the trans- Only a few ATs successfully ablated within the RSV or LSV septal approach, may be considered if the retrograde transaortic have been reported.10,41,42 It has been shown that irrigated RF approach fails.46 applications at the NSV consistently result in left atrial lesions located between the floor of the and the mitral an- ECG Characteristics of ATs Arising From the Aortic Sinuses nulus, an area that can be difficult to map using either a retro- of Valsalva grade or transseptal puncture approach.17 With excellent cath- Interpretation of the P-wave morphology in ATs remains chal- eter stability within the NSV, catheter ablation at this site may lenging because the onset of the P-wave is not always distin- be highly effective in the deeper tissues that are otherwise not guishable during the tachycardia. At present, there is not a accessible because of limited catheter stability and tissue con- sufficient ECG algorithm for accurately identifying the origin tact. In the case of accessory pathways, successful elimination among the aortic sinuses or for differentiating ATs arising can be achieved with RF energy application at the NSV for from the aortic sinuses from tachycardias located elsewhere. anteroseptal pathways and at the LSV for left anterior path- However, from the results of studies using a large number of ways. Myocardial sleeves cross the aortic valve plane and ex- patients,8,10,11 ATs arising from the NSV (NSV-ATs) have a tend into the NSV.48 Thus, in the region of the NSV, there is negative/positive P-wave in lead V1. A recent study10 reported close anatomic proximity between the ventricular myocardium that the P-wave morphological features in leads I and aVL are

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Figure 5. Premature ventricular contraction (PVC) arising from the right sinus of Valsalva (RSV). (A) 12-lead ECG. (B) Intracar- diac 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 tion within the aortic sinuses of Valsalva, but in a few cases of NSV-ATs from LSV-ATs: a positive P-wave in leads I and left-sided RF ablation with the retrograde approach across the aVL was more likely to be a NSV-AT, with a negative/positive aortic valve, aortic regurgitation or a leaflet perforation follow- or isoelectric P-wave supportive of an LSV-AT, which can be ing ablation has been reported,52 suggesting the importance of reasonably explained by the more leftward position of the LSV a gentle, slow-moving and precise manipulation of the catheter compared with the NSV. at the aortic root. Generally, deeper lesions are created using an irrigated-tip RF ablation catheter compared with a conven- Specific Considerations for Catheter Ablation tional RF or cryoablation catheter when the energy application is delivered in the NSV,17 suggesting a lower power setting Within the Aortic Sinuses of Valsalva may be better for irrigated RF ablation in the aortic sinuses of Before performing catheter ablation within the aortic sinuses Valsalva. of Valsalva, coronary angiography or selective angiography of In LSV-VT/PVCs, a distinct potential that precedes the QRS the aortic sinuses should be performed to ensure the distance complex (pre-potential) is often recorded at the ablation site between the ablation catheter and coronary ostium is more than within the LSV during VT/PVCs, and it is considered to be 10 mm and to visualize the anatomy of the aortic root useful for identifying the successful ablation site (Figure 4B).5,25 (Figure 4C).5 Angiography of both should be This potential recorded within the LSV may represent activa- performed to rule out any anomalies.51 Coronary angiography tion of the pathway connecting the arrhythmia origin to the should be performed once again after the ablation procedure to ventricular myocardium.53 rule out any coronary spasms, stenoses, or occlusions. A previ- The aforementioned anatomic features of the 3 aortic si- ous experimental study with porcine demonstrated that nuses are responsible for the differences in the electrogram a temperature setting of 55–60°C with a non-irrigated RF abla- recordings within these aortic sinuses:37,43 the NSV electro- tion caused no damage to the aortic valve, whereas a tempera- grams during sinus rhythm have a larger atrial amplitude than ture setting >70°C was associated with valve-tissue damage.5 ventricular amplitude, and the ratio of the atrial amplitude to Therefore, a maximum power of 35 W, maximum electrode- the ventricular amplitude is usually >1, which is apparently tissue interface temperature of 55°C, and duration of each RF different from the LSV and RSV electrograms (Figure 7).37 energy application of 30–60 s are the recommended settings for Analysis of the electrogram is helpful for identifying the cor- non-irrigated RF ablation at the aortic sinus of Valsalva to rect positioning of the mapping/ablation catheter at the aortic avoid any potential complications.5 Not in the case of RF abla- sinuses of Valsalva during the ablation procedure.

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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, .

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 Hira- matsu et al37 with permission.)

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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 . 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 al37 with permission.)

Fortunately, most reported cases of catheter ablation of for catheter placement and determination of the ablation site, NSV tachycardias originating from near the AV node or His- and angiography is usually performed to obtain detailed infor- bundle region have not resulted in impairment of AV conduc- mation about the coronary arteries and aortic sinuses of Val- tion. However, in 1 case complete AV block from RF energy salva. Nonetheless, the use of a 3-dimensional electroanatomi- delivery at the NSV was reported.18 Therefore, much attention cal mapping system (ie, CARTO® [Biosense-Webster, Inc., should be paid to the delivery of RF energy at that site. Wheth- Diamond Bar, CA, USA], Ensite NavX® [St. Jude Medical, er or not a His-bundle potential can be recorded at the NSV Inc, St. Paul, MN, USA]),54,55 and integration between elec- should be assessed before the RF energy application in order troanatomical mapping and computed tomography, magnetic to avoid this particular complication. However, during tachy- resonance imaging or intracardiac echocardiography56 are use- cardia, it is difficult to confirm whether or not there is a His- ful for understanding the detailed anatomy of the aortic root bundle potential, probably because of greater baseline drift and its surrounding structure (ie, coronary artery, His bundle and artifact during the tachycardia than during sinus rhythm or region) and for identifying the precise position of the catheter a wider distance between the His-bundle region and the abla- in the heart. The stability of the ablation catheter and its contact tion catheter during the tachycardia than during sinus rhythm status with the target site during RF ablation are important to (Figure 8).37 Therefore, the presence of a His-bundle potential achieve effective ablation, and should be checked using fluo- during sinus rhythm should be assessed before ablation at the roscopic observation during RF energy application. Intracar- NSV. To avoid impairment of AV conduction during RF en- diac echocardiography can provide more precise and detailed ergy delivery, it is useful to be aware of any prolongation of information than fluoroscopy on the stability and contact status the PQ, A-H, or H-V interval. Therefore, the delivery of RF of the catheter with the target site, as well as the catheter’s lo- energy at the NSV during sinus rhythm is safer than during the cation and its relationship to the surrounding structures in real tachycardia. Also, the power of the RF energy should be in- time.36,57 The use of these modalities may reduce procedure- creased gradually from a low wattage (ie, 10–15 W). The RSV related complications and fluoroscopy time and, thus, enhance is also adjacent to His bundle region, and the His bundle po- the success rate. tential is recorded more often at the RSV than the NSV during sinus rhythm.37 Therefore, RF ablation in the RSV should be Acknowledgments performed in the same manner as in the NSV. The author gratefully thanks all the cardiac physicians and the nursing, During the ablation procedure, fluoroscopy is widely used echo laboratory, clinical engineering and radiology staff members in the

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