Characterization of the mitral isthmus for atrial fibrillation ablation using intracardiac ultrasound from within the coronary sinus.

BACKGROUND: Atrial fibrillation (AF) ablation involving the mitral isthmus and/or the coronary sinus (CS) may result in circumflex artery (Cx) or other collateral structure damage.
OBJECTIVE: The purpose of this study was to investigate the feasibility of intracardiac echocardiographic (ICE) imaging from within the CS to characterize mitral isthmus anatomy and guide ablation.
METHODS: A 9-Fr sheath was introduced into the CS of 30 patients before AF ablation. A 9-Fr rotational ICE catheter was then advanced within the sheath to the distal CS adjacent to the lateral left atrial (LA) wall. Serial cross-sectional images to document the relations of the LA, Cx, CS, esophagus, and pericardium were obtained at multiple points within the CS during a pullback to the CS ostium.
RESULTS: The Cx was identified in 62/150 positions in 25/30 patients. The median (range) of the LA-Cx distance was 3.3 mm (0.7-19.6 mm), and the median CS-Cx distance was 2.0 mm (0.4-9.7 mm). The esophagus was seen in 36/150 positions in 17/30 patients. The median CS-esophagus distance was 4.0 mm (1.4-16.2 mm). The proximity of the Cx and esophagus to the LA and CS varied considerably. The median CS-mitral annulus distance was 11.9 mm (4.1-21.6 mm). After CS cannulation, the ICE imaging took 5 +/- 2 minutes and required 120 +/- 60 seconds of fluoroscopy.
CONCLUSIONS: Mitral isthmus anatomy can be accurately characterized by rotational ICE imaging from within the CS. There is great variability in the location and proximity of the Cx, CS, esophagus, and pericardium to the LA. Real-time identification of these structures could help to plan ablation strategies and potentially reduce complications.