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How to Ablate Ventricular Tachycardia in Patients with Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia

Victor Bazan, MD, PhD; Fermin C. Garcia, MD

Introduction

Arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is a genetically determined disorder of the ventricular myocardium predominantly concerning the right ventricular (RV) free wall, in which the normal cardiomyocytes are replaced by fibrous and/or fatty tissue. Other structural changes include RV dilatation and segmental wall motion abnormalities, along with baseline ECG abnormalities and a family history of the disease, all of which are incorporated into several major and minor conventional and revised criteria for the definitive diagnosis of ARVC/D.^1,2 In view of a relatively low incidence of familial cases of ARVC/D in the series of ARVC/D patients undergoing ventricular tachycardia (VT) ablation, the term “cardiomyopathy” more adequately expresses a genetically determined muscular disorder interacting with environmental or acquired factors triggering the phenotypic development of the disease.^2–10 The definition of ARVC/D as a presumably degenerative disease (“dysplasia”) is counterbalanced by the lack of progression of the RV scarred area in a significant number of ARVC/D patients undergoing repeated electroanatomic mapping for recurrent VT.³ Additionally, the fact that VT recurrences after successful ablation usually occur within the first months after the index ablation procedure endorses the principle that incomplete ablation, rather than substrate progression, accounts for a suboptimal mid- and long-term arrhythmia control outcome after ablation in the setting of ARVC/D.^{3,8,9,10–13}

The myocardial substrate favoring the occurrence of VT is concentrated to the RV free wall, usually sparing the RV septum. The affected regions are usually the anterior infundibular portion of the RV, the basal inferior RV (in proximity to the acute angle of the heart), and the RV apex, completing the so-called “triangle” of the dysplasia.^11,12 Interestingly, although histologically affected, the RV apex is not a frequent site of origin of VTs in the setting of ARVC/D, unlike the two former regions.

It is nowadays accepted that ARVC/D is an “epicardium-to-endocardium” disease process, in which the pathological process of fibro-fatty replacement of the RV free wall myocardium progresses from the epicardium (epi) to the endocardium (endo).¹³ As a consequence of this, a more extensive VT substrate is usually encountered at the epi aspect of the RV free wall as compared to the endo counterpart (Figure 52.1). This observation has been corroborated by several series of ARVC/D patients undergoing VT ablation, especially when VT recurs after a prior endo ablation procedure.^9,10,14 In this sense, the critical parts of the VT circuit becoming ablation targets are predominantly found at the epi RV free wall side (around two-thirds of cases).^9,10 Subendocardial boundaries of fibrous tissue and occasional RV free wall thickening may also impede radiofrequency energy applications delivered from the endo surface to reach VT circuits located deep in the RV free wall myocardium, thus warranting epi access to achieve successful VT elimination (Figure 52.2).¹⁴

Right ventricular tachycardia in the setting of ARVC/D typically shows a left bundle branch (LBBB) QRS pattern in lead V₁ and a late R-wave progression throughout the precordial ECG leads, thus suggesting a VT site of origin at the RV free wall. Basal inferior RV-VTs in this setting also show a superior axis (frequently at ≤ –45°). Alternatively, VTs originating from the infundibular anterior portion of the RV (low RV outflow tract) demonstrate an inferior QRS axis (frequently at +90°; Figure 52.3).

A prominent epi scar not targeted for initial ablation accounts for the high incidence of VT recurrences after endo ablation.^8,14,15 It is suggested by this that those ARVC/D patients presenting with a limited endo area of abnormal electrograms (EGMs), late VT termination during radiofrequency delivery, and/or clinical VT recurrence after endo ablation should be considered for epi ablation with the anticipation of a prominent epi VT substrate.

In this chapter, we shall discuss how to ablate ventricular tachycardia in the setting of ARVC/D, including patient and preprocedural preparation, baseline and VT ECG clues to set for the suspicion of a prominent epi VT substrate and/or an epi VT site of origin, endo and epi ablation techniques, and management of complications related to this procedure.

Preprocedural Planning

A strict analysis of the baseline and VT 12-lead ECG has been proven useful to identify underlying RV cardiomyopathy, therefore ruling out idiopathic VT.16–22 Ventricular tachycardia “pleomorphism” and observation of several clinical VT QRS morphologies are suggestive of underlying RV scar. Furthermore, idiopathic VTs commonly have their VT site of origin at the septal aspect of the RVOT, thus presenting with an earlier R-wave transition at the precordial leads and narrower, taller, and unnotched R waves in the inferior ECG leads.¹⁷ Combining the baseline and the VT QRS complex, T-wave inversions in leads V₁–V₃ in sinus rhythm, along with a VT QRS duration ≥ 120 ms in lead I, VT QRS notching and VT R-wave transition at V₅ or later have been incorporated into a diagnostic algorithm differentiating idiopathic RVOT-VT from RVOT-VTs occurring in the setting of ARVC/D.¹⁸ There are several baseline and VT ECG clues indicative of underlying RV cardiomyopathy. These include postexcitation ECG “Epsilon” waves (the surface surrogate of the late-activated RV free wall areas potentially responsible for myocardial reentry), incomplete or complete right bundle branch block (RBBB), T-wave inversion in the anterior precordial (V₁–V₄) and the inferior leads, and selective > 25 ms QRS complex prolongation in leads V₁–V₃, also indicating the late and/or slow activation of some RV free wall areas.^11,19,20

Additional ECG clues are not only predictive of underlying RV scar, but also indicate a prominent epi > endo substrate, thus augmenting the likelihood of incomplete VT elimination upon sole endo ablation and setting for the necessity of epi or endo–epi combined ablation.^21–22 The Precordial QRS amplitude ratio (ΣQRSmv V₁–V₃ / ΣQRSmv V₁–V₆) measures the ratio between the sum of the QRS amplitudes in the anterior precordial leads and the total sum of all precordial QRS amplitudes.²¹ Unsuccessful VT ablation from the endo (and therefore suspicion of a prominent ARVC/D epi substrate) is accompanied by a ΣQRSmv V₁–V₃ / ΣQRSmv V₁–V₆ of ≤ 0.48. QRS complex fragmentation (i.e., deflections of the QRS at its beginning, on top of the R wave or in the nadir of the S wave when QRS duration is < 120 ms) is another manifestation of extended slow conducting areas within the RV myocardium, frequently involving the epi and yielding a poor arrhythmia control outcome with endo ablation, especially when QRS fragmentation is registered in ≥ 3 ECG leads.²² Extensive T-wave inversion and QRS prolongation are also indicative of extensive disease, poor arrhythmia control outcome after ablation, and LV involvement.^19,20 Finally, analysis of the 12-lead VT QRS complex may help identifying an epi VT origin within the RV free wall. During VT, the initial portion of the QRS complex corresponds to the local transmural depolarization of the ventricular wall. During epi VT, the QRS initial forces are thus a manifestation of an epi-to-endo transmural initial vector of ventricular depolarization. An initial Q/q wave is indicative of this initial vector of ventricular depolarization travelling away from a locally representative ECG lead, whereas an initial r/R wave is demonstrative of the opposite direction. In the RV, identification of a Q wave in leads I and, especially, V₂ (directly confronted to the anterior RV) are associated with an epi origin for VTs arising from the anterior RV free wall, a frequent VT site of origin in the setting of ARVC/D.²³ Endocardial VTs arising from this RV region will show a rS pattern in both leads I and V₂. Likewise, a Q wave in leads II, III, or aVF (as opposed to a rS pattern) distinguishes epi from endo VTs arising from the basal-inferior RV, the most frequent site of origin of VTs in the setting of ARVC/D (Figure 52.4). Interval criteria do not apply to RV-VTs, due to a less prominent distribution of the specialized conducting system in the RV free wall and a less pronounced RV wall thickness.^23–25

Patient Preparation

Twelve-lead ECG documentation of all VT morphologies, whenever feasible, is of high interest, as has been emphasized. Extensive electroanatomical mapping, especially in the setting of large RV myocardial scars, will hence be accompanied by the identification of critical parts of tachycardia circuits (circuit isthmuses and exit sites) in which a particular VT QRS morphology is reproduced during pace mapping, mimicking that obtained during the spontaneous clinical VT. These specific areas become a potential target for RF energy delivery. Additionally, surface electrocardiographic recording (12-lead ECG or limited telemetry tracings) as well as implantable cardioverter-defibrillator (ICD) EGMs, if available, are used to compare spontaneous and induced VT during the procedure. The 12-lead ECG characteristics are predictors of the location of the arrhythmia and aid in preparing upfront for an early epi approach, for which specific patient’s preparation, including the need for general anesthesia, is of special concern.23,26

Preprocedural cardiac imaging techniques (especially MRI) are useful to identify and characterize the RV myocardial substrate and its transmural distribution and extension.²⁷ CT-scan or MRI images can be merged to the electroanatomical reconstruction of the RV, in order to more precisely provide anatomical landmarks to guide ablation. In this sense, however, we give priority to the use of intracardiac echocardiography (ICE) to both recognize the RV structures serving as an anatomic guidance and to localize and characterize the RV free wall scar distribution during ongoing RV catheter mapping, in order to identify potential targets for ablation.²⁸

Ablation Procedure

Endocardial Electroanatomical Voltage Mapping

Beyond the usefulness of endo electroanatomical voltage mapping to characterize the RV free wall myocardial substrate favoring the occurrence of ARVC/D-VT, it has been demonstrated that identification and quantification of endo bipolar voltage abnormalities (low voltage, late/fractionated/split potentials) provide significant added value for the long-term arrhythmic risk assessment in this setting.^29–31 These observations endorse the indication for initial ARVC/D substrate characterization by means of endo electroanatomical voltage techniques as a first step of the mapping/ablation procedure.³² In those cases in which incessant hemodynamically tolerated VT is not the baseline rhythm, the first step of the ablation procedure should consist of a detailed characterization of the endo electroanatomical voltage map (Figure 52.5).

We usually insert a long introducer (LAMP-90 or large-curve Agilis, St. Jude Medical, St. Paul, MN) from the right femoral vein and position it in the inflow aspect of the RV. We consider this essential, as a long catheter sheath will dramatically enhance catheter stability and support, which is usually a matter of special concern when dealing with patients with ARVC/D, who usually present with dilated RA and significant tricuspid regurgitation. We further deploy an ICE catheter in the right heart that permits for real-time monitoring, in order to anatomically guide the mapping and ablation procedures. Careful identification of valvular structures during RV-VT ablation is critical. The tricuspid valve is identified at the base of the RV by means of the typical fluoroscopic valvular motion, by the registering of bipolar recordings demonstrating both atrial and ventricular signals of approximately equal amplitude in the mapping catheter, and upon direct visualization using echocardiographic confirmation by ICE imaging. The pulmonic valve is identified by advancing the mapping catheter into the pulmonary artery and slowly withdrawing it back into the RV, until a bipolar ventricular EGM is identified, along with consistent pacing capture. We then confirm the mapping catheter’s position under direct visualization by ICE. These valvular sites are given a “location-only” tag in the electroanatomical map, in order to avoid their influence in the bipolar voltage color map for identifying areas of RV scar tissue. Intracavitary points should also be usually excluded from the final map, with the exception of those points representing true anatomic structures (i.e., papillary muscle or moderator band), as confirmed by direct visualization by ICE.

We usually perform detailed electroanatomic mapping of the endo RV surface in a point-by-point fashion. Alternatively, new electroanatomical mapping techniques allowing for rapid and multiple point acquisition may be considered. As for the latter approach, precise editing of the resulting map with elimination of internal points may be necessary in order to precisely depict the endocardial RV cavity. Peak-to-peak signals aligned with the QRS are measured automatically and manually confirmed for each point in the former technique. The reference values for normal endo voltage are represented in a color scale and set at 1.5 mV.33 Abnormal signals representing diseased myocardial tissue and border zone are considered between 0.5 to 1.5 mV. Myocardial RV dense scar is represented below 0.5 mV and is usually associated with noncapture at 10 mA and 2-second pulse width.^33,34 Fractionated and late potentials extending beyond the QRS are tagged in the map and are of particular utility when pace mapping is used to correlate the arrhythmia with the diseased myocardium that incorporates a critical portion of the reentrant VT circuit. Areas of abnormal voltage usually involve perivalvular structures within the free wall of the RV, and it is emphasized that high-density mapping around these areas should be performed (Figure 52.6).

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