Left atrial posterior wall isolation the icing on

Authors: Rong Bai

Publish Date: 2016/05/16

Volume: 46, Issue: 3, Pages: 199-201

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Abstract

Catheter ablation for symptomatic drugresistant atrial fibrillation AF has emerged as a promising new therapeutic option over the past decade Most paroxysmal AF PAF is initiated by premature beats from the pulmonary veins PVs Therefore catheter ablation that electrically isolates PVs could abolish the arrhythmia However especially in more server cases like persistent or longstanding persistent AF Per AF PVs are not the only source and nonPV triggers may arise from any part of the heart but most commonly from the coronary sinus left atrial posterior wall LAPW left atrial appendage LAA and superior vena cava SVC 1 These structures also serve as substrates to maintain AF episodes after they start In view of this it is recommended by the consensus statements that substrate modification should be considered on top of PVs isolation PVI in Per AF cases 2 There is no unique technique of atrial substrate modification while LAPW isolation has been adapted at many centers worldwide and shown to improve the success rate of AF ablation by many isolated studies 3 4 5 In this issue of JICE He et al reported their results of a metaanalysis on the efficacy and safety profile of adding LAPW isolation to PVI during AF ablation procedures 6 Five studies with 594 AF patients were included and the pooled data clearly showed that LAPW isolation reduces atrial tachyarrhythmia recurrence with comparable procedurerelated complications and procedural time associated with PVIalone strategy Although sample size is small compared to other AFrelated trials this study included the largest series of AF patients treated with LAPW isolation + PVI strategy and provided solid evidence favoring this approach Before data from a largescale randomized controlled clinical trial become available He et al’s paper can potentially represent a reference for this topicWhile we are emphasizing that PVs play a crucial role in the development of AF we should remember that the LAPW and the PVs are embryological “siblings” Actually each PV we see in adult forms by two parts that join together during the human heart development A primitive vein sprouts out of the LA which bifurcates twice to give four PVs which grow towards the developing lungs A plexus of veins is formed in the mesoderm enveloping the bronchial buds these veins will meet with the developing PVs out of the left atrium to establish a connection at the fifth week of gestation As the left atrium LA develops it progressively incorporates the common PV into the LA wall until all four PVs enter the LAPW separately The incorporated PVs form the smooth posterior wall of the LA while the trabeculated portion of the LA comes to occupy a more ventral aspect 7 8 Anatomically there is an abrupt change in LA subendocardial fiber orientation as this bundle traverses the posterior LA between the PVs which create a basis of reentry 9 10 Indeed previous work using noncontact mapping has demonstrated significant conduction abnormalities in the posterior LA during sinus rhythm in patients with PAF 9 Additionally the LAPW myocytes have a higher incidence of delayed afterdepolarizations larger late sodium currents but smaller inward rectifier potassium currents The LAPW myocytes also have larger intracellular Ca2+ transient and sarcoplasmic reticulum Ca2+ contents but a less protein expression of NaCa exchanger 11 It is not uncommon to see firings from the LAPW initiating AF episodes Hence underlying tissue architecture and electrophysiological characters in the LAPW may form the substrate for onset and maintenance of AF When AF becomes sustained atrial remodeling including fibrosis fatty and lymphomononuclear infiltration are more pronounced in the LA septum and LAPW 12 13 Acknowledging the aforementioned we are confident that the LAPW should be considered as a target following PVI when ablating AF It is expected that this approach will result in a more favorable outcome as compared to PVIalone The question being left unanswered even by He et al’s study is whether we should include LAPW isolation in all AF ablation procedures as data has shown PVIalone is sufficient to eliminate PAF It seems reasonable to add LAPW isolation on top of PVI if AF has progressed to an advanced stage and the LA has undergone significant remodeling as in the cases we recently described 5To modify AF substrate in the LAPW electrically isolating this structure is the goal Issues remaining controversial include how to perform LAPW ablation and what is the definition of LAPW isolation The socalled box ablation is derived from the Cox maze IV surgical procedure 14 It connects bilateral PVencircling lesions by placing two linear lesion sets both superiorly on the roof and inferiorly at the bottom of the LA In this way the entire LAPW is believed to be isolated from the rest of the atria which can be confirmed by an entrance block of the LAPW with or without exit block The technique developed by Natale’s group however requires more extensive ablation targeting all nearfield potentials in the LAPW Both entrance block and electrical silence of the LAPW are used as the endpoint of Natale’s approach 15 The study by Dr He et al failed to distinguish these techniques from each other due to small sample size and might introduce bias Because of the complex architecture of the atrial musculature electrical isolation of the LAPW by a set of linear lesions is always technically difficult Gaps are unavoidable on ablation lines and dormant conduction may become manifested in the following months Posterior interatrial connections also allow firings in the LAPW to penetrate epicardially and trigger AF episodes 9 Therefore elimination of all LAPW electrical activations is more likely associated with longterm benefitsHe et al’s study indicated that procedural time and rate of procedurerelated complications did not differ between PVIalone and PVI + LAPW isolation strategies regardless of the technique utilized for LAPW isolation One may question on the LA mechanical function after LAPW isolation However it is important to understand that the contractility of the LA mainly rely on the anterior portion of LA wall while the LAPW has limited contribution Another unique rare but lethal complication associated with extensive LAPW ablation is atrialesophageal fistula Caution should be taken when pursuing LAPW isolation and new technologies including contact force and esophageal temperature monitoring will help minimize this complicationGiven the embryological homology of the PVs and the LAPW and the primary electrophysiological role of these two structures in the development of AF it is reasonable to include LAPW isolation in AF ablation procedures in addition to PVI at least in cases with nonparoxysmal AF Further studies especially randomized controlled clinical trials are warranted to identify the optimal strategy to achieve LAPW isolationThis work was supported the “National Natural Science Foundation of China” NSFC81370290 the “Beijing Natural Science Foundation” 7161003 and the “Capital Health Research and Development of Special 201622062” Dr Bai is supported by the Program of Beijing HighCaliber Talent from Overseas BHTO201410007 and is an awardee of the Overseas HighLevel Talent of the Phoenix Plan of the Chaoyang District Beijing

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