Venice Chart International Consensus Document on Atrial Fibrillation Ablation: 2011 Update

This Venice Chart International Consensus Document on atrial fibrillation (AF) ablation represents an update of the initial document published in the Journal of Cardiovascular Electrophysiology in 2007.1 Since then, many technological developments and progress have been made and AF ablation has become a well-established, widespread treatment for patients with AF. Over the last decade, ablation of AF has focused on the left atrium (LA) and this has stimulated further investigation on gross and microscopic anatomy of the LA and of the neighboring structures. Knowledge of their architecture and mutual relationships is necessary to access, map, and ablate the LA in a safe and successful way. The anatomy and position of the fossa ovalis are major determinants for the electrophysiologists' ability to safely access the LA through transseptal catheterization. The dimensions of the fossa ovalis (average vertical diameter of 19 mm, average horizontal diameter of 10 mm, thickness of 1–3 mm)2 allow a safe double transseptal puncture. Table 1 reports the congenital or acquired disorders of the chest and cardiovascular structures possibly affecting the location of the fossa ovalis and, therefore, resulting in a more difficult transseptal access. Similarly, multiple previous transseptal catheterizations causing fibrosis of the fossa ovalis are the major variables associated with difficult puncture and penetration of the transseptal needle.3 Transseptal catheterization in the presence of a device occluding the fossa ovalis is possible, because its position is more cranial as compared to the fossa ovalis position.4 However, a careful approach and additional imaging are mandatory. Three-dimensional (3D) imaging of the LA and pulmonary veins (PVs) shows a wide range of variants of their anatomy.5 Specifically, the typical PV branching pattern with 4 distinct PV ostia (Fig. 1C) is present in approximately 20–60%, while a very frequent anatomical variant is the presence of a short or long common left trunk, observed in up to 75–80% of cases. The presence of supernumerary PVs, mainly right middle PV or right upper PV, is reported in 14–25% of cases. The criss-cross of myocardial fibers and the increased thickness of the muscular sleeves at the interpulmunary isthmus between the orifices of the ipsilateral PVs with the possibility of epicardially located intervenous muscular connections (Fig. 1B) may represent the anatomical basis for the complexity to achieve a permanent PV isolation by ablation techniques.6 Another critical structure for ablation procedure is the ridge or carine between LA appendage and left PVs (Fig. 1A). The ridge may be flat, round, or pointed in profile and is <5 mm wide in 75% of hearts suggesting that achieving catheter stability for adequate contact can be challenging most cases. (A) The left atrium viewed from the left side and dissected to show the myocardial strands extending over the left superior and inferior pulmonary veins (LSPV, LIPV). The left atrial appendage (LAA) is finger-like in shape. (B) This histologic section taken through the left pulmonary veins shows myocardial strands crossing between the veins (blue arrows). Masson's trichrome stain. (C) This histologic section shows the 4 pulmonary veins with myocardial extensions (stained brown) over the outer surface of the veins. The ovals indicate the veno-atrial junctions. Note the non-uniform thickness of the left atrial walls. The superior caval vein (SVC) is seen in cross section with its myocardial sleeve (green arrows). Elastic van Geison stain. RIPV, RSPV = right inferior, right superior pulmonary veins. Understanding the anatomic relationship between the LA/PV orifices and the left atrial ganglionated plexi (GP) explains how ablation in the LA not only results in PV electrical disconnection but it may cause also modification of the autonomic tone influence with an impact on the electrical activity.7 Transmural lesions8 in the medial region of the LA, septum and/or proximal coronary sinus (CS) may disrupt interatrial conduction pathways alternative to conduction over the Bachmann's bundle and, consequently, alter the postablation atrial propagation pattern. The very strict anatomical relationship between the LA and both the esophagus and the phrenic nerves9,10 is the major cause of concern of collateral damage to these 2 structures during AF ablation, resulting rarely in severe patient injury. Assessment of the individual anatomy, reduced power and continuous monitoring of the effect of ablation on these structures are all possible means to avoid their permanent or severe damage. The key points regarding the anatomy of structures relevant to AF ablation are reported in Table 2. The pathogenesis of AF is often multifaceted and the arrhythmia may develop in different disease conditions as well as in the normal heart. It is well recognized that increased atrial mass, decreased conduction velocity, and decreased atrial refractoriness with increased dispersion are all pro-fibrillatory factors. Irrespective of the underlying mechanism, the onset and maintenance of AF requires an event (trigger) that initiates the arrhythmia and the presence of a predisposing substrate that perpetuates it. Additional factors (e.g., inflammation or autonomic tone) may also cooperate as "modulators" in facilitating initiation or continuation of AF. Although approximately 10% of AF patients have no evident cardiac disorder (so-called "lone" AF), the arrhythmia usually occurs in patients with structural heart disease. Hypertension, coronary heart disease, valvular heart disease, dilated cardiomyopathy, and heart failure are the most frequent pathological conditions associated with AF. Atrial enlargement is often present, although it is difficult to establish if it represents the cause or the consequence of AF. Atrial fibrosis and loss of myocardial tissue may be either a substrate for AF (due to coexisting heart disease) or a result of fibrillating atria and part of the so-called structural remodeling.11 A number of studies provide irrefutable evidence for a genetic component in the case of lone AF.12 Genetic linkage analyses have revealed AF chromosome loci for genetic defects in various potassium channels and the gap junctional protein Connexin40.13 Relatively rare forms of familial AF have also been associated with inherited channelopathies such as Brugada, long QT and short QT syndromes, as well as with cardiomyopathies.13,14 Increased automaticity and single and multiple circuit reentry can cause AF. These mechanisms are not mutually exclusive; it is likely that areas of focal firing and areas of reentry are present simultaneously in varying degrees in the majority of patients. The PVs are an important source of ectopic beats; they are capable of initiating frequent paroxysms of AF, which can be eliminated by treatment with radiofrequency ablation.15 Other anatomical structures that may also provide ectopic beats triggering AF are the superior vena cava, the vein of Marshall, the musculature of CS, the posterior wall of the LA, and LA appendage.16 The 3D anatomical structure of the atrial muscle is likely to be a crucial factor in determining the ultimate fibrillatory behavior. Indeed, high frequency stimulation of the PVs originates wavebreaks in areas of abrupt fiber orientation and wall thickness changes in the posterior wall of the LA.17 The autonomic tone is thought to play an important role in the pathogenesis of AF. Vagal stimulation shortens refractory period, and sympathetic stimulation increases calcium loading and automaticity. Combined, these actions result in early afterdepolarizations and triggered firing that may initiate AF.18–21 Interruption of nerves from the GP to the PVs may explain the frequent elimination of focal firing produced by PV isolation procedures during ablation therapy. These findings support the role of GP activity in the onset and perpetuation of AF, and may explain the success of early ablation studies targeting only the GP.22 Once established, AF begets AF through a self-perpetuation process called structural and electrical remodeling.23,24 At the structural level, AF causes atrial fibrosis, dilatation, increased compliance, and reduced contractility. Ultrastructural changes of myocytes lead to the so-called dedifferentiation, because myocytes return to the fetal phenotype.11 At the electrical level, progressive shortening and dispersion of refractory periods are the main changes occurring during AF. The key points regarding the pathophysiology AF ablation are reported in Table 3. At present, multiple approaches for catheter ablation of AF have been developed. The current techniques focus on the elimination of mechanisms involved in the initiation and maintenance of AF, which are essentially represented by triggers (PVs and non-PV foci) and substrate (autonomic and electrophysiologic). The different techniques proposed for catheter ablation of AF include PV isolation, electrogram-based ablation or complex fractionated atrial electrograms (CFAEs) ablation, linear lesions, autonomic GP ablation, AF nests ablation, and sequential ablation strategy. "PV isolation" is considered the cornerstone of current AF catheter ablation techniques and is aimed at the electrical disconnection of the PV from the adjacent LA. The PV isolation comprises segmental/ostial PV ablation, circumferential PV ablation, and circumferential/antral PV isolation (Fig. 2). (A) Segmental/ostial isolation: the isolation of PVs is performed at level of the ostium (black ring) and verified by means of a CMC (blue ring) sequentially positioned at each PV. The red dots correspond to the application of RF energy. The arrow indicates the CMC. (B) Circumferential/antral PV isolation: the isolation of PVs is performed at level of the antrum and the CMC is moved all around the PVs and the posterior wall of LA. (C) Circumferential PV ablation: the ablation is performed by using a 3D electroanatomical mapping and creating a circumferential lesion around each PV (1-2 cm outside the ostium); verification of PVs isolation by means of a CMC is not strictly required for this technique. (D) Double Lasso technique: the isolation of PVs is performed by means of continuous circular lesions around both ipsilateral PVs and verified by means of 2 CMCs placed within the superior and inferior Pvs. CMC = circular mapping catheter; LIPV = left inferior PV; LSPV = left superior PV; RIPV = right inferior PV; RSPV = right superior PV; PV = pulmonary vein. A truly segmental PV isolation requires ablation inside the vein or very close to the output into the atrium15,25 (Fig. 2A). It is now appreciated that ablation in the PVs themselves needs to be avoided as much as possible, primarily due to concern for development of PV stenosis. Therefore, the segmental/ostial PV isolation technique in the strictest sense has generally fallen out of favor. For segmental/ostial PV isolation, a circular mapping catheter (CMC) of variable diameter (15–25 mm) is inserted into the LA through a long introducer via the transseptal route, and is positioned sequentially at the ostia of the 4 PVs25 (Fig. 2A). Alternatively, a multielectrode array system can be used. The ablation catheter is positioned at the ostium of the vein on the atrial side; a series of segmental lesions are then created until isolation of the vein can be demonstrated by disappearance of the venous potentials on the CMC (i.e., entrance block). Electrical disconnection of the PVs can be also demonstrated by pacing from inside the PVs (i.e., exit block). Ablation can be performed in sinus rhythm or during AF. The literature data display complete agreement as to the need to achieve isolation of all 4 PVs. Circumferential PV ablation using 3D electroanatomical mapping was initially described by Pappone et al.26,27 Initially, the lesion set was limited to wide (>0.5 cm outside PV ostia) circumferential lesions around and outside the PV ostia but over time it was modified with wider (1–2 cm outside PV ostia) circumferential lesions (Fig. 2C). Radiofrequency (RF) energy is applied continuously on the planned circumferential lines, as the catheter is gradually dragged along the line, often in a to-and-fro fashion over a point. Successful lesion creation at each point is considered to have taken place when the local bipolar voltage has decreased by 90% or to <0.05 mV. This technique, as initially designed, did not involve verification of PV isolation (Fig. 2C). Many other centers have adopted this technique, some of which have added circular mapping to verify PV electrical isolation. The key to this technique for PV isolation is delivery of the ablation lesions to the vestibule or "antrum" of the PV, which is the funnel-shaped portion of the LA (or perhaps more accurately the PV) that is proximal to the PV-LA junction or so called "ostium." The antrum includes the entire posterior wall and extends anteriorly to the right PVs on the septum (Fig. 2B). Various tools, according to operator preference, can monitor the identification of this region during the ablation procedure. Selective pulmonary venography is used by many centers to establish the relevant anatomy. Intracardiac echocardiography (ICE) offers a better definition of the LA and proximal PV anatomy and allows localizing catheter position.28Computerized 3D mapping and navigation techniques (Carto, NavX, etc.) are useful means to clarify the anatomy of the region and provide a method of nonfluoroscopic catheter guidance. These techniques might be made more anatomically accurate by registration with other imaging techniques such as magnetic resonance (MR) or computed tomography (CT). Technologies to perform "near real time" imaging in the EP laboratory, such as with rotational angiography, are available and might help to address some of the shortcomings of preprocedural imaging, but to date are still not sufficiently effective to result in widespread adoption. The use of a CMC for PV isolation procedures has become incredibly widespread. For the CMC guided ablation technique, 1 or 2 (double Lasso technique; Fig. 2D)29 CMCs are placed within the ipsilateral superior and inferior PVs or within the superior and inferior branches of a common PV during RF delivery. RF ablation is applied until absence or dissociation of all PV potentials are documented by CMCs within the ipsilateral superior and inferior PVs. RF ablation catheter technologies might include standard tip (e.g., 4 mm), large tip (e.g., 8 mm), and closed or open irrigation. With the use of nonirrigated or closed-irrigation ablation catheter technologies, many centers employed ICE during lesion delivery to assess for the formation of microbubbles30 and to monitor in this way tissue overheating.31 With the use of open-irrigation ablation catheters this is no longer relevant. There has been development of new technologies to assist the operator with PV isolation for AF catheter ablation. Various balloon-based technologies have been under investigation, generally designed specifically to deliver arcs or circumferential lesions at the PVs.32 Such technologies have included the use of cryothermy,33–35 laser,36,37 ultrasound,38–40 and RF energy.41–43 Typically these technologies have employed a noncompliant balloon and have suffered from inability to isolate the PVs proximally, particularly at the antrum, but instead achieve isolation more distally at the ostium of the PV or even within the PV itself.44,45 This latter issue has been the "Achilles heel" of such balloon technologies, as the resulting lesion delivery at such a distal location has been associated with lower efficacy, by not addressing more proximal sites of triggers, and with an increase in complications such as PV stenosis and phrenic nerve damage. Other balloon-based technologies are under development that would employ a compliant balloon to address these shortcomings.37 Another new technology has been the development of catheters with various lengths and shapes of the effective ablation delivery region. With use of such catheters, delivery of arcs or lines of lesions might be facilitated.46,47 Robotic technologies have been developed for use for catheter navigation. Presently, 2 of such technologies are available.48,49 One technology utilizes magnetic fields to navigate special magnetic catheters. The magnetic field can be manipulated at a remote workstation to direct the tip of the catheter. A significant advantage of the magnetic catheter is the physical property of being quite floppy, with virtually no ability to generate excessive contact force against the myocardium to prevent a risk of perforation. This allows for manipulation of the catheter without or at least with much reduced fluoroscopic guidance. A major limitation of this robotic technology is the inability to control additional catheters, such as the CMC and/or the ICE catheter. The use of this magnetic robotic technology for AF catheter ablation has been reported with comparable efficacy and safety to manual techniques.50–52 Another robotic technology that has become available is a system that employs a deflectable sheath controlled at a remote workstation. The primary advantage of this system is the ability to use standard catheters rather than specialized catheters as with the magnetic robotic system. However, this system does not offer the safety of the magnetic catheters with regards to potential for excessive forces to the myocardium, so the risk of perforation remains an issue. Reports from centers with extensive experience has demonstrated comparable results to manual methods and reduced fluoroscopy times.53,54 Different patterns of electrograms have been targeted during radiofrequency catheter ablation of AF.21,55–64 Among these, CFAEs have been most widely studied. In the initial report by Nademanee et al., the definition of CFAE included: (1) atrial electrograms composed of 2 deflections or more, and/or perturbations of the baseline with continuous deflections of a prolonged activation complex over a 10-second recording period, and (2) atrial electrograms with very short cycle lengths (≤120 ms) averaged over a 10-second recording period. Intraoperative mapping of AF has shown that CFAEs are found mostly in areas of slow conduction or at points where the wavelets turn around at the end of arcs of functional Such CFAEs have and studies have to these CFAEs in to and prevent of In the by Nademanee et al., regarding patients with AF mapping of both atria was performed during or AF. CFAEs using bipolar at to and by the presence of voltage RF ablation of the with CFAEs was performed in an to the to this of the patients of arrhythmia at However, other studies have shown results with some or no when ablation of CFAEs or in with PV isolation is in patients AF to a the of CFAE ablation to PV isolation increases the of sinus rhythm maintenance in patients with and AF, but does not provide in patients with Therefore, further studies are to clarify the real of CFAE ablation in patients with AF. lesions used initially with the of the multiple wavelets that AF. It is not that ablation procedures a strategy. The of linear lesions is the of conduction the use of tip ablation catheters with 3D anatomical lesion creation remains lesions have been reported to be associated with of AF either to sinus rhythm or to atrial further that such lesions may at least in some patients the substrate for of these are and linear lesions to be Such may be observed during the procedure or Although complete linear lesions can such the development of a gap in conduction along such lines has the potential for a effect and can For patients in atrial has been as well as in right atrial is PV isolation, ablation of the right atrial may be but on may be of limited added PV isolation Ablation of the isthmus the inferior of the left PV has been widely in patients with One limitation of the isthmus ablation is that it can radiofrequency in the distal with its safety conduction is A number of approaches have been proposed to this balloon of the to the effect of the during and modification of the to a more With wide circumferential PV isolation the between the is reduced an LA can be created sufficiently to ablation adjacent to the can be with a short lesion the 2 the creation of a linear lesion between the inferior of the has been in to complete a isolation of the posterior LA This latter technique has the advantage of a large of high frequency activity where triggers and are more likely to than other of the linear ablation on the wall of the LA to be of potential in the heart are produced by the and cardiac autonomic The cardiac autonomic system of autonomic GP located in on the left and right atria left inferior left right inferior right and in the of In patients with AF, stimulation cycle 10 a during AF and the identification and of left atrial These GP may represent a of AF ablation. For GP ablation, RF energy be applied to each a to is each RF a is still present, RF energy is until the is of the to at each GP generally requires RF for but when close to the In a of patients with AF ablation of the left atrial GP by PV antrum isolation, GP ablation to PV antrum decreased the of PV firing from of patients GP ablation to only of the patients GP PV antrum isolation was then which eliminated PV firing in the patients The in this and studies of the elimination of PV firing by PV isolation, without targeting the sites of may be by the of the extending from the GP to the PV A relationship is present between CFAE and GP ablation. GP ablation often the majority of a much than the CFAE CFAE ablation may much of the by the without ablation of the GP et have developed a system for mapping using in sinus This mapping sites in which the bipolar atrial electrograms high myocardium or the so-called AF The targeted AF without PV isolation, as a approach for AF ablation. et compared CFAE sites and AF in an of AF and that these sites did not anatomical Typically for AF ablation, RF delivery for the potentials the et the role of AF ablation to PV isolation and isolation in a The of AF ablation in a 10% of as compared to PV isolation and superior vena A approach has been developed in patients with AF with different that multiple atrial The of the sequential ablation is of AF. This can be by from AF either to sinus rhythm more to which is then and The in PV isolation using isolation. only of AF at that the is It requires ablation targeting continuous electrical focal areas with The last linear lesions and is used in case of the 2 The isthmus is the as a last the observed in achieving a complete Once sinus rhythm has been PV isolation and linear lesions are for and areas if It be that this approach represents an extensive procedure associated with significant and requires careful and However, it is associated with success in AF, particularly when AF is during the procedure. In to permanent lesion contact force technology and is under The contact force within the distal tip of a mapping and ablation catheter contact results using the catheter and safety in using this new technology for PV studies the of contact force during AF ablation result also in alternative means of contact force utilizes local changes between catheter tip and cardiac The with the electroanatomical mapping system and initial and studies have shown its during mapping and ablation within the The ability to during ablation better lesion very early data a between and lesion studies are to assess the during AF ablation. The remote magnetic mapping and ablation system by catheter within a magnetic field of The system 8 electrical that can be no magnetic of the is are under way to the mapping within The robotic by can be on and of mapping and ablation catheters. The system is available in and can be with electroanatomical mapping system. data are limited with 1 patients to assess the ability to navigate and within the heart. A new electroanatomical mapping system is being developed that a mapping catheter to of mapping points within data indicate that the system is to complex left atrial in The key points regarding the techniques and technologies for AF catheter ablation are reported in Table The used for catheter ablation of AF on the of AF being include of a lesion of AF during and of AF There is still the of such in AF In patients with AF, it is possible that the of AF during ablation is In these patients

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