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How to Ablate Non-Outflow Right Ventricular Tachycardia

Jason S. Bradfield, MD; Fermin C. Garcia, MD; Luis Saenz, MD; Kalyanam Shivkumar, MD, PhD

Introduction

The majority of ventricular tachycardias (VTs) or premature ventricular contractions (PVCs) originating from the right ventricle (RV) in patients with structurally normal hearts arise from the RV outflow tract (RVOT). However, approximately 10% of VT/PVCs may arise from other sites within the RV, based on data from one high-volume quaternary care center.¹ Strategies for work-up, mapping, ablation, and follow-up of patients with these non-outflow sites of origin will be discussed.

Preprocedure Planning

When non-outflow left bundle branch block (LBBB) morphology VT/PVCs are seen on 12-lead electrocardiogram,² it raises the possibility of underlying RV pathology, and consideration should be given to further preablation imaging in addition to a transthoracic echocardiogram. In this situation, arrhythmogenic right ventricular cardiomyopathy (ARVC) and cardiac sarcoidosis should be considered. When these pathologies remain in the differential diagnosis, consideration should be given to cardiac magnetic resonance imaging and cardiac positron emission tomography imaging prior to considering ablation.

Once underlying structural or inflammatory pathology has been ruled out, attention is directed to localization of idiopathic foci, which tend to cluster in a few anatomic regions.

Mapping and Ablation

Tricuspid Valve Annulus

Idiopathic VT/PVCs arising from the mitral valve are well known, but tricuspid valve annulus (TVA) VT/PVCs have also been described.^1,3,4 The complex anatomy of the tricuspid valve and its relationship to surrounding structures such as the RVOT, the aortic root, and the right coronary artery are shown in Figure 35.1. VT/PVCs from the TVA always have a left bundle branch block (LBBB) morphology, with a late transition and variable axis depending on location (Figure 35.2). In the manuscript by Tada and colleagues,³ free wall origin was more likely to be associated with a small R wave in V₁. In addition, the QRS duration was also longer, the precordial transition was later, and notching of the QRS was more frequent with free wall origin.

The septal TVA is continuous with what is considered “parahisian,” given that the origin of these arrhythmias is approximately 1 to 3 “o’clock” on the TVA. Given the complexity of this region and the difference in ablation strategy, parahisian VT/PVCs are discussed in more detail in a separate chapter. Parahisian VT/PVCs have a LBBB pattern but with an early transition. QRS duration can be relatively narrow given the septal location. Unlike outflow VT/PVCs, ECG lead aVR can be positive and the R wave tends to be greater in lead II than in lead III.

When mapping TVA VT/PVCs, stability on the superior and lateral TVA can be a challenge. Therefore, a deflectable sheath (Agilis, St. Jude, Austin, TX) is recommended in this situation. Once positioned on the annulus in an antegrade approach (Figure 35.2), counterclockwise torque on the sheath/catheter unit can move the ablation catheter tip toward the lateral aspect of the superior TVA. Risk of perforation increased when mapping the lateral TVA. Therefore, newer contact force-sensing catheters (St. Jude Medical; Biosense Webster, Irvine, CA) may be of benefit when mapping the lateral TVA, to ensure reasonable contact, without excess.

The antegrade approach is associated with poor contact and instability because of the displacement of the TVA during systole and diastole. When approaching the TVA antegrade, the leaflets of the tricuspid valve come between the ablation catheter and the arrhythmia site of origin. This anatomic relationship not only can interfere with lesion formation and successful ablation, it can also risk valve damage/perforation. In fact, the described poor contact/instability and leaflet interference explain most of the failed attempts to ablate TVA PVCs/VT, based on the experience of the authors.

Therefore, it is often preferred to approach TVA PVCs/VT with a “retroflexed” approach. (Figures 35.3 and 35.4) During the retroflexed approach, RAO imaging and intracardiac echocardiogram (ICE) guidance are needed to slip the catheter between the tricuspid valve leaflets and the myocardial site of origin. When utilized in this fashion, the torque placed on the catheter typically results in the opposite effect as when utilizing an antegrade approach. Contact force and stability is typically improved with a retroflexed technique, as once in place, simple undeflection improves contact. The ventricular to atrial (V:A) signal ratio should be > 1 at the ablation site.

Parahisian VT/PVCs,5–7 unlike other TVA VT/PVCs, can potentially be mapped and ablated from multiple sites including the RV, left ventricle (LV), or above the aortic valve in the non-/right coronary cusp. When ablating from the RV, the best site for ablation can either be inferior or superior to the best His bundle signal.⁵ Strategies include finding sites with either no His signal or a far-field His signal of low amplitude that still has a local ventricular activation pre-surface QRS. When mapping in the RV, taking a more apical position or one superior to the His (in the RAO fluoroscopic or 3D electroanatomic view) is lower risk then moving more basal or inferior.

Pace mapping is a strategy often utilized early in a procedure to understand the general area of origin or exit of a given VT/PVC. This strategy can also be utilized when mapping PVCs when the PVC burden during the procedure is low and activation mapping cannot be utilized to the degree desired. Pace mapping can be useful on the TVA; however, when utilized from the septal TVA/parahisian region can be fraught with error given the potential for direct His capture as well as variable exits sites given the septal location.

Ablation

Choice of ablation catheter can vary. At sites distant from the conduction system, irrigated ablation catheters can be used safely though may be unnecessary to form adequate lesion sets. A 3.5-mm externally irrigated system such as THERMOCOOL (Biosense Webster, Diamond Bar, CA) can be set at 30 W and power titrated down if temperatures reach over 42°C. Irrigated ablation may be of benefit as the significant contact utilizing a retroflexed approach in addition to the position between the tricuspid valve annulus and the valve leaflet may cause a nonirrigated catheter to heat quickly with low-power delivery.

Similar settings can be utilized for contact force catheters, where contact of 20 to 30 grams can be targeted. Contact force catheters may be ideally suited for TVA PVCs/VTs as catheter instability/poor contact is thought to be the most common reason for procedural failures. When the site of origin is distant from the conduction system, the authors recommend ablation at 30 W and 20 to 30 grams of pressure, with the lesion continued for 1 minute after the arrhythmia is eliminated. As the location gets more septal, lower power should be utilized with the initial lesion to ensure no conduction system issues arise and the power can be titrated up as needed with close monitoring.

When ablation is undertaken at the anteroseptal region, a nonirrigated catheter should be used if possible to minimize risk of atrioventricular (AV) block. A 4-mm nonirrigated catheter can be used with ablation parameters of 50 W and max temperature of 55°C. If at a high risk of AV block, the power can be started at 20 to 30 W and titrated up as needed. In true parahisian cases, near the local conduction system, utilization of a nonirrigated ablation catheter is often best to form small lesions unless attempting to ablate in the coronary cusp, in which case an irrigated catheter may be utilized to minimize the risk of char formation that could embolize to the coronary arteries or the brain.

Much like with AV node reentry tachycardia ablation, junctional rhythms can be seen with ablation of basal septal RV VT/PVCs including those from the anteroseptal and septal (parahisian) TVA.8 If the junctional rate is slow, the risk of significant AV node damage is limited, but rapid junctional beats may suggest increased risk and ablation should be terminated and ablation position reassessed. If junctional beats are seen with anterior PVCs/VT, then the catheter likely has poor contact and has moved septally, and ablation should be terminated.

Moderator Band, Papillary Muscles, and VF-Right Fascicular Ablation

The three-dimensional (3D) intracavitary anatomy of the RV is complex and includes the moderator band and the papillary muscles. The moderator band is a muscular structure that connects the RV septum to the base of the anterior papillary muscle and/or right ventricular free wall. It traverses the RV cavity and can have highly variable length and width. Its site of origin relative to the tricuspid valve and apex can also be variable. Fascicular fibers are present within the moderator band and likely play a role in PVC-induced VF. (Figure 35.5)

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