Main text (words count: 2935)
Ventricular tachycardia and premature ventricular complexes (PVCs) arising from right ventricular outflow tract (RVOT) are the most common type of ventricular arrhythmias (VAs) in patients without structural heart disease [1]. Radiofrequency ablation is now the gold standard of treatment in this setting due to high efficacy rates and optimal safety profile [2]. Using fluoroscopy and then electro-anatomical mapping, in order to standardize mapping and ablation procedures, RVOT was conventionally divided into a “septal” wall, postero-medially oriented and facing the aortic root and the proximal part of aorta, and the antero-laterally directed free wall. Each one was therefore divided in three equal areas, named 1 posterior, 2 median and 3 anterior [3]. RVOT arrhythmias more commonly originate and could be ablated from the septal areas than from free wall [4]. During the last few years, the pulmonary valve (PV) and the pulmonary artery (PA) have attracted much attention as reliable sites of origin of RVOT-type arrhythmias. Since seminal reports by Timmermans et al, several series of left bundle branch block (LBBB) type VAs were described originating from or above the pulmonary valve [5,6]. Distinct EKG features may rise suspicion of PVCs originating from PV or PA, larger R/S ratio in V2, late (≥ V4) precordial transition, tall R waves in the inferior leads, predominantly negative forces in I, aVL/aVR ratio of Q wave amplitude >1 [7-9]. In order to acquire better contact with the cusps above the PV and on the PA wall the ablator catheter can be advanced and deflected in a “candy cane” shape (reversed U-curve technique) [10-12]. Interestingly, mapping in these regions reveals a late sharp potential in the sinus beats which inverses becoming pre-potential during PVCs. In a recent experience, Zhang and colleagues performed radiofrequency ablation of RVOT-type VAs based on the mapping and ablation of pulmonary sinus cusps (PSCs) as the first-line strategy, eliminating 90% (81/90) of arrhythmias [13]. According to this observation it could be speculated that PV represents the “real” source of the ectopy, historically considered to originate from regions below the valve, and ablation in ROVT is efficacy “simply” when disconnects the focus from the rest of myocardium. Interesting histopathological observations support this theory by showing that ventricular myocardium may extend into the PA beyond the semilunar valve. These myocardial sleeves, which are as long as those located in the pulmonary veins and enhancing atrial fibrillation, are characterized by abnormal automaticity and/or triggered activity, thus capable of firing the ventricular ectopy [14,15]. Myocardial voltage extension into the pulmonary artery in humans has been also demonstrated in vivo using a three-dimensional (3D) mapping system (CARTO, Johnson & Johnson, Biosense Webster) integrated with intracardiac echocardiography (ICE) scans (CARTOSOUND module) to accurately localize the PV plane. Near field, high voltage electrograms were recorded in 11 out of 24 patients (46%) with an ablation catheter above the, ICE localized, PV. In all patients, arrhythmic foci were localized in the PA (median 8.2 mm above the PV) and reclassified as pulmonary arterial arrhythmias [16]. This example shows how ICE has undoubtedly improved our understanding and approach to manage these arrhythmias and how accurate and detailed characterization of the PV and its contiguous structures is crucial for mapping, ablating, and better reclassifying the origin of these types of VAs. Aim of this paper is to provide an illustrated step-by-step guide on how to use ICE with the CARTOSOUND module to visualize and reconstruct 3D shell of the RV, the PV, as well of other anatomical structures (i.e., the aortic valve and coronary arteries) to perform aware and safe ablation in this region.