A straightforward assessment of anterior mitral isthmus lines block
Authors: Guido Lopez L E , Martinez Cossiani M , Merino D , Martinez Maldonado M E , Castrejon Castrejon S , Carton Sanchez A J , Sanchez Somonte P , Jauregui Abularach M , Ciechanski E , Kassa K , Handayani A , Sanz Verdejo B , Merino J 
Published: May 2024

Abstract

Background
Complex atrial fibrillation (AF) and left atrial flutter (LAFL) ablation procedures often involve creating lines on the anterior wall of the left atrium, such as the anterior septal and lateral mitral isthmus lines.

Purpose
This study aims to evaluate the role of a simplified criteria to demonstrate the achievement of conduction block across the anterior wall of the left atrium ("anterior mitral isthmus") after linear ablation (LA).

Methods
Patients scheduled for persistent AF or LAFT ablation were prospectively recruited. The procedure employed a homogeneous LA strategy that included the anteromedial, anterolateral and roof lines. The following intervals were measured before and after LA, placing a multipolar catheter in the left atrial appendage (LAA) in order to register the earliest egm in a reproducible position: 1) P-LAA: conduction time from the sinus P wave onset to the LAA, 2) IASp-LAA: conduction time pacing at CL 500 ms from the interatrial septum to the LAA, 3) CSp-LAA: conduction time pacing at CL 500 ms from the distal CS to the LAA, 4) LAA-QRS onset. Patients with linear ablation were further divided according to the presence or block (BG) or non-block group (NBG) in the anterior at the end of the procedure, demonstrated with a high-density activation map. A parallel control group (CG) of patients with paroxysmal AF without LA was also included for comparison.
Statistical analysis involved the Kruskal-Wallis and Mann-Whitney test with Bonferroni correction.

Results
21 patients were enrolled in the study: mean age 66.67 years (± 8.48), 80% male sex. Among them, 16 had AF and AFL and underwent LA, while the remaining 5 constitute the CG.
Baseline measures before LA did not exhibit significant differences compared to the CG with mean values for P-LAA at 93±20 ms (P=2.35), IASs-LAA at 82±27 ms (P=1.94), CSs-LAA at 52±17 ms (P=0.91), and LAA-QRS at 80±27 ms (P=1.82).
However, upon comparing the BG and NBG, significant differences emerged in P-LAA (82±10 ms vs. 11±5 ms (P=0.002) and IAS-LAA (83±17 ms vs. 27±24 ms (P=0.004), while no significant differences were observed in the remaining intervals. In comparisons between the BG and the CG, significant differences were noted in P-LAA (82±10 ms vs. 16±10 ms (P=0.01) and IAS-LAA (83±17 ms vs. 1.2±17 ms (P=0.01), without differences in the other intervals. Conversely, when comparing NB to the CG, no significant differences were observed in any of the intervals. Finally, P-LAA &gt;70 ms and the IASp-LAA &gt;55 ms showed a sensitivity of 100 % and specifitity of 100 vs. 87% respectively to discriminate anterior wall block.

Conclusion
The simple measurement of the P-LAA and IAS-LAA interval proves highly valuable in evaluating anterior mitral isthmus lines block, serving as a complementary approach to conventional maneuvers. P-LAA &gt;70 ms and IASp-LAA &gt; 55 ms could be usefull to discriminate anterior wall block.Anterior linear ablation with block