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.