Clinical and Electrophysiological Characteristics of Marshall Bundle-Related Atrial Tachycardia: Considerations Based on a Definitive Diagnosis

Abstract

Background: Conventional endocardial mapping cannot fully elucidate Marshall bundle (MB)-related atrial tachycardia (AT).

Objectives: This study aimed to clarify the clinical and electrophysiological characteristics of MB-related AT definitively diagnosed using catheter insertion.

Methods: Forty-eight patients with AT who had previously undergone mitral isthmus ablation were enrolled in this study. A 1.6-F hexapolar electrode catheter was inserted into the vein of Marshall (VOM) if endocardial left atrial mapping showed centrifugal propagation and post-pacing intervals after entrainment pacing suggested a macro-re-entrant mechanism. MB-related AT was diagnosed only when activation along the VOM was consistent with the propagation of the AT circuit, and post pacing interval within the VOM approximated the tachycardia cycle length.

Results: Among 48 patients, 20 were diagnosed with MB-related AT. The activation direction along the VOM was predominantly descending (n = 13), rather than ascending (n = 7). There were diverse breakthrough sites to the endocardium along the course of the VOM. Two patients experienced persistent AT despite a conduction block in the VOM. Thirteen patients underwent chemical ablation with ethanol injection, and the remaining 7 underwent radiofrequency ablation at the earliest endocardial activation sites or mitral isthmus areas. Acute termination of AT was observed in 20 patients. No recurrence was observed in the group that underwent chemical ablation; however, 4 patients in the radiofrequency group experienced recurrence (n = 0 of 13 vs n = 4 of 7).

Conclusions: Understanding the distinct clinical and electrophysiological characteristics of MB-related AT can facilitate the diagnosis and treatment of this AT type.

Keywords: Marshall bundle; ablation; atrial tachycardia; ethanol; mitral isthmus.