Demonstration of Persistent Conduction Across the Mitral Isthmus via the Vein of Marshall With High-Density Activation Mapping
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A 63-year-old man with hypertension, chronic kidney disease, and persistent atrial fibrillation was evaluated at our institution for a recurrent atrial tachycardia. Two previous ablations for atrial fibrillation had consisted of pulmonary vein isolation and a stepwise approach with defragmentation in the left atrium.
The patient underwent an electrophysiology study, and an atrial tachycardia (cycle length, 320 ms) was induced spontaneously with catheter manipulation. Conventional mapping and entrainment was consistent with a perimitral flutter. An endocardial activation map in the left atrium was attempted with the Rhythmia mapping system (Boston Scientific, Marlborough, MA), although the tachycardia was unstable obviating complete map creation of the circuit. After radiofrequency ablation targeting the mitral isthmus and converting the arrhythmia to sinus rhythm, an endocardial activation map while pacing adjacent to the mitral line (Figure [A]) revealed early activation distal to the pacing site (on the opposite side of the line) consistent with an epicardial bypass tract.