Achieving durable mitral isthmus block: Challenges, pitfalls, and methods of assessment

Abstract

Background and objectives Macroreentrant atrial tachycardias often occur following atrial fibrillation ablation, most commonly due to nontransmural lesions in prior ablation lines. Perimitral atrial flutter is one such arrhythmia which requires ablation of the mitral isthmus. Our objectives were to review the literature regarding ablation of the mitral isthmus and to provide our approach for assessment of mitral isthmus block. Methods We review anatomical considerations, ablation strategies, and assessment of conduction block across the mitral isthmus, which is subject to several pitfalls. Activation sequence and spatial differential pacing techniques are discussed for assessment of both endocardial and epicardial bidirectional mitral isthmus block. Results Traditional methods for verifying mitral isthmus block include spatial differential pacing, activation mapping, and identification of double potentials. Up to 70% of cases require additional ablation in the coronary sinus (CS) to achieve transmural block. Interpretation of transmural block is subject to six pitfalls involving pacing output, differentiation of endocardial left atrial recordings from epicardial CS recordings, identification of a slowly conducting gap in the line, and catheter positioning during spatial differential pacing. Interpretation of unipolar electrograms can identify nontransmural lesions. We employ a combined epicardial and endocardial assessment of mitral isthmus block, which involves using a CS catheter for epicardial recording and a duodecapolar Halo catheter positioned around the mitral annulus for endocardial recording. Conclusions The assessment of transmural mitral isthmus block can be challenging. Placement of an endocardial mapping catheter around the mitral annulus can provide a precise assessment of conduction across the mitral isthmus.

Endocardial and epicardial activation maps for three-dimensional perimitral flutter using a three-dimensional mapping system: a case report

“…It has been reported that the heat sinks due to the presence of the CS, coronary artery blood flow, and thickness of the muscular layer influence the factors that make it challenging to create the MI block line. 5 In this case, the potential remained in the intramural tissue alone in the MI line due to the heat sink. In addition, a study reported that the base of the LAA and ridge are also sites through which multiple bundles pass, such as the VOM and septopulmonary and septoatrial bundles.…”

Comparison of the Anterior Septal Line and Mitral Isthmus Line for Perimitral Atrial Flutter Ablation Using Robotic Magnetic Navigation

“…Despite the fact that the MI ablation line is relatively short (averaging 35 mm with a range of 15 and 52 mm), bidirectional block is difficult to achieve by endocardial ablation only. Due to the existence of epicardial connections and myocardial sleeves around the CS and the vein of Marshall [4,6,14,15], epicardial ablation or ablation within the coronary sinus is often needed to achieve a bidirectional block. Ablation within the CS increases the risk of CS and circumflex artery injury, cardiac tamponade by steam pop, and thrombosis [6].…”

“…First, as the soft magnetic catheter guided by RMN is quite stable and easy to control with micromovements in the anterior septal area, a bidirectional conduction block is routinely feasible to achieve. In contrast, it is often difficult to obtain adequate contact without a steerable sheath by the manual catheter ablation technique for the AS line [15]. Second, RMNguided ablation in the AS line area is safe and effective.…”

Acute conduction recurrence of mitral isthmus: Incidence, clinical characteristics, and implications

“…3,5 Many studies focused on the achievement, validation and evaluation of successful MI ablation. [9][10][11] Nevertheless, during follow-up, recurrent MI conduction was frequently encountered and has led to complex atrial arrhythmias in clinical practice. 5,12,13 Therefore, a critical endpoint of MI ablation should be the durability of bidirectional conduction block, and not only the block per se.…”