Recovery of Mitral Isthmus Conduction Leads to the Development of Macro-Reentrant Tachycardia After Left Atrial Linear Ablation for Atrial Fibrillation

Abstract

Background-Left atrial linear ablation for atrial fibrillation (AF) may be proarrhythmic, leading to left atrial macro-reentrant tachycardia (LAT). Whether due to failure to achieve block initially or to recovery of conduction after ablation is unknown. This study was designed to evaluate the frequency of recovery of mitral isthmus (MI) conduction compared with cavo-tricuspid isthmus (CTI) conduction, and the relationship between recovery of MI conduction and postablation LAT. Methods and Results-Of 163 patients with AF who underwent circumferential pulmonary vein ablation plus left atrial linear ablation, in whom MI and CTI ablation produced bidirectional conduction block, 52 underwent repeat ablation for recurrent atrial arrhythmias (AF or LAT). Of these 52 patients, coronary sinus ablation was required in 48 to achieve bidirectional MI block at the index ablation. During repeat ablation, MI and CTI conduction was assessed in sinus rhythm. At repeat ablation, MI conduction had recovered in 38 of 52 patients, as compared with CTI conduction which recovered in only 12 of 52 patients (Pϭ0.001). At repeat ablation, the recurrent clinical arrhythmia in 12 patients was MI-dependent LAT. Recovery of MI conduction was associated with development of MI-dependent LAT (Pϭ0.01). Conclusions-Despite using bidirectional conduction block as a procedural end point, recovery of MI conduction is common and may lead to LAT after left atrial linear ablation for AF. The reason for greater recovery of MI versus CTI conduction is unknown but could be due to differences in isthmus anatomy or lower power used for ablation in the left versus right atrium. (Circ Arrhythm Electrophysiol. 2011;4:832-837.)

A Review of Mitral Isthmus Ablation

“…This would fit with the peri-venous tissue having the greatest myocardial depth from a post-mortem study [39]. However, this is not reflected in other studies which reported a need for epicardial CS ablation in the majority of patients [36]. Our experience is that most reconnections occur at the annular end of the line which could be ablated either endocardially or epicardially.…”

“…However, there is limited data on the recurrence of mitral isthmus conduction after an initially successful ablation. Based on a small number of patients having redo-procedures due to recurrence of AF and/or organised atrial tachycardia, the rate of resumption of conduction of the mitral isthmus in this selected population ranged from 62% to 90%, although there is clearly a selection bias [33-36]. In a prospective randomised study, Sawhney et al reported that in patients with paroxysmal AF, mitral isthmus ablation increased the risk of subsequently developing atypical left atrial flutters [37].…”

“…In a prospective randomised study, Sawhney et al reported that in patients with paroxysmal AF, mitral isthmus ablation increased the risk of subsequently developing atypical left atrial flutters [37]. More recently, the same group reported from a retrospective series a high incidence of mitral isthmus reconduction which was significantly associated with the development of mitral isthmus dependent flutter [36]. In another retrospective series looking at 50 patients who had perimitral flutters either during the index procedure or follow up, prior mitral isthmus ablation was associated with a higher risk of developing perimitral flutter, suggesting that mitral isthmus ablation may be pro-arrhythmic despite achieving bi-directional block acutely [38].…”

“…Nevertheless, it is clear from several studies that these "gaps" do not always lead to clinical tachycardia. In fact, the majority of these "gaps" do not manifest as perimitral flutter [35,36]. It may be because "gaps" alone are not sufficient to support macroreentrant tachycardia and other factors may be necessary for initiation and/or perpetuation of macroreentry.…”

Atrial Tachycardias Following Atrial Fibrillation Ablation

“…Another question is whether these tachycardias are due to originally incomplete lines only or recovery of conduction. Sawney and co-authors [33] found that recovery of mitral isthmus conduction after initial achievement of block is common, 73 % and is associated with the emergence of peri-mitral flutter in 32%. They concluded that using electrophysiological endpoints alone might not be enough for maintaining long term results and at least in some patients it would be best to avoid mitral isthmus ablation if possible.…”