High-resolution activation mapping revealed residual connections in 21.6% of patients meeting standard pacing criteria for mitral line block, often due to epicardial bridging connections.
Observational (n=56)
Does high-resolution activation mapping identify pseudoblock better than standard pacing criteria in patients undergoing posterior mitral line ablation?
Standard pacing criteria for posterior mitral line block frequently fail to detect epicardial bridging connections, which can be identified by high-resolution activation mapping and targeted for ablation.
BACKGROUND: The mitral isthmus is the critical element of perimitral reentrant tachycardias. Prolongation in transisthmus conduction time and differential pacing techniques are commonly used to determine block. However, these may not distinguish block from slow conduction or conduction via epicardial bridging connections. The aim of this study was to examine these standard criteria for mitral line block with endocardial and epicardial activation mapping. METHODS: In 56 patients, posterior mitral line was performed using radiofrequency ablation. Conduction block was defined as transisthmus time (≥100 ms) and reversal of coronary sinus activation during pacing from the left atrial appendage. These results were compared with high-resolution activation mapping (Rhythmia) of the endocardium and epicardium via the coronary sinus. RESULTS: Mitral block determined by pacing was achieved in 51 out of 56 (91%) patients. In 11 out of 51 (21.6%), activation mapping demonstrated residual endocardial (3/11; 27.2%) or epicardial (8/11; 72.7%) connections. Epicardial bridging connections were distant from the line (2.4±1.6 cm), inserting laterally at the proximal-middle coronary sinus and septally at the left atrial ridge. Patients with residual conduction were prone to complex circuits involving the epicardium (7/11; 63.6%). Mitral line block was achieved in 75% by targeting these insertion site(s). The transisthmus conduction time had limited predictive value for distinguishing block from pseudoblock. CONCLUSIONS: Standard criteria for posterior mitral line block may not distinguish block from pseudoblock. In particular, epicardial bridging connections can result in prolonged transisthmus conduction time and reversal in coronary sinus activation to falsely suggest block. These connections are a frequent cause for complex circuits, and their insertion site(s) can be targeted for ablation.
Barkagan et al. (Tue,) conducted a observational in Perimitral tachycardias (n=56). High-resolution endocardial and epicardial activation mapping vs. Standard pacing criteria for mitral line block was evaluated on Residual endocardial or epicardial connections despite meeting standard pacing criteria for mitral block. High-resolution activation mapping revealed residual connections in 21.6% of patients meeting standard pacing criteria for mitral line block, often due to epicardial bridging connections.
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