Background: The vein of Marshall (VoM) is a promising target for atrial fibrillation (AF) treatment, matching with the ‘Coumel triangle ‘ by housing triggers, autonomic connections, and serving as a substrate for perimitral flutters. Lateral mitral line (ML) represents a fundamental part for AF treatment, but achieving bidirectional block through endocardial ablations is challenging. VoM ethanol infusion (VOM-EI) facilitates ML block, with the newly-formed bipolar lesion serving as an effectiveness index. Voltage analysis assessment after VOM-EI in predicting ML block is poorly investigated.
Purpose: To compare unipolar and bipolar low-voltage areas (LVAs) along VOM trajectory after VOM-EI, and their role in predicting ML block.
Methods: We enrolled 59 patients undergoing catheter ablation of persistent AF or ML-dependent atrial flutter. High-density voltage mapping of left atrium was followed by VOM-EI and LA remapping. The area width difference was obtained and defined as ∆LVA. Normal bipolar voltage cutoffs were 0.50 mV in sinus rhythm or 0.29 mV in AF. Unipolar cutoffs were 2.7 mV and 1.1 mV, respectively.
After VOM-EI, anatomical lesions included PVI, linear lesion for dome and ML isthmus. Systematic lines block validation was performed, defining ML block after coronary sinus (CS) electrograms sequence inversion (septal-to-lateral) during left atrial appendage pacing. Radiofrequency (RF) applications into the CS-great cardiac vein targeted epicardial gaps if present. Ablation time for ML block (AblTime) was obtained.
Results: In our cohort, 94.5% achieved ML block. Bipolar and unipolar low voltage areas after VOM-EI were 9,9 ± 6,9 cm2 and 12,2 ± 5,9 cm2 respectively. Bipolar ∆LVAs were significantly lower than unipolar ∆LVA (8.2 ± 6.5 cm2 vs. 9.4 ± 6.0 cm2; p=0.03) (Fig 1). A strong linear correlation between AblTime and bipolar ∆LVA (R: 0.76), and a significant correlation between AblTime and unipolar ∆LVA (R: 0.6) were found (Fig 2). Patients requiring RF applications into the CS for ML block (13/59, 22%) showed lower ∆LVAs in logistic regression for both bipolar (0.01) and unipolar (p=0.03) analyses.
Conclusions: VOM-EI induces unipolar LVAs wider than bipolar along the mitral isthmus trajectory. Unipolar and bipolar voltage analysis predicts a short time ML block achievement. Moreover, wider unipolar and bipolar LVAs following VOM-EI correlates with higher likelihood to avoid the targeting of epicardial gaps via the CS musculature.
