The Exact Criteria for Evaluation of Complete Mitral Isthmus Block

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Background: Complete mitral isthmus (MI) conduction block is associated with a high cure rate for atrial fibrillation (AF). Methods and Results: Thirty consecutive patients with persistent AF underwent circumferential pulmonary vein antrum ablation and linear ablation at left atrial roof and cavotricuspid isthmus (CTI) and MI. After sinus rhythm was restored, PV isolation and linear block of the 3 lines were confirmed by previously described criteria, with additional ablation if necessary. Then isoproterenol infusion/atrial burst pacing was used to induce atrial tachycardias (ATs). And an additional maneuver for validate bidirectional MI block was used by demonstrating multi-sites activation detours along the whole linear leison while pacing from proximal coronary sinus, followed by attempts to close the residue gaps. The induce method was repeated at the end of the procedure. All PV were isolated and linear block was achieved in all ablated lines before the rigorous criterion was used to assess MI block. And ATs were induced in 16/30 (69.5%) patients (16 AT). However, MI was found not completely blocked in 8 (26%) patients through additional pacing and mapping. After ablation of persistent gaps, ATs were induced in only 2/30 (9.5%, p=0.007) patients (2 AT). Conclusions: A rigorous criteria for evaluation of complete conduction block at the MI is necessary for the catheter ablation of AF.