Linear Lesions
Linear ablation is defined as the creation of lines that serve as electrical barriers with the purpose of achieving a bidirectional conduction block to prevent macro-reentrant circuits. This approach typically targets the mitral and cavo-tricuspid isthmus (CTI), and the roof of the LA (Figure 3). However, achieving durable bidirectional block across the lines is often complicated by the formation of gaps, which in turn have pro-arrhythmic effects (28). The STAR AF II trial showed that empirical roof and mitral isthmus lines had no additive benefit to PVI, and the CLEAR-AF (Catheter Ablation Therapy for Persistent Atrial Fibrillation) trial demonstrated similar results (25,29): although more patients achieved sinus rhythm during ablation with ancillary lines, no long-term benefit was related to this finding. Interestingly, in patients with extensive linear ablations atrial tachycardia (AT) was the most common recurrent arrhythmia, as opposed to patients with circumscribed ablations, who most frequently relapsed with AF. In EARNEST-PVI trial, 85% of patients underwent additional linear ablation and did not have a significantly better outcome than the PVI only group at 12 months(30). When performing mitral isthmus ablation, the use of adjunctive VOM ethanol infusion has been shown to be associated with a higher rate of mitral isthmus block and arrhythmia free survival mainly driven by a lower AT recurrence (31-33).
CTI ablation is currently the standard treatment for CTI-dependent atrial flutter (AFL) and has also been proposed as an adjunctive strategy for non-PAF. Pontoppidan et al. (34) conducted a randomized controlled trial (RCT) on patients with AF undergoing PVI without a history of AFL and failed to show any additional benefit of CTI ablation in terms of freedom from either AF or AFL. Similarly, Mesquita et al. (35) showed in a propensity score analysis that empiric CTI ablation in addition to PVI did not improve AF free survival. Results from a Korean RCT with a longer follow up of 3.4 years were also not in favor of empiric CTI lines (36).Comparable findings were replicated in a sub-group study included in a meta-analysis of 1400 patients, in which CTI ablation did not have any additional benefit in AF with or without AFL (37). These results can be explained by the low frequency of typical AFL after PVI (2.8%), most of which are related to significant right atrial dilation (38). (Figure 4)