A Novel Mapping Annotation Technique to Facilitate Isthmus Detection in Scar-related Atrial Tachycardia Following Atrial Fibrillation Ablation

Introduction: The common ablation strategy of atrial tachycardia (AT) encountered after Atrial Fibrillation (AF) ablation relies on electroanatomic activation mapping (EAM), using a “conventional” window of interest (WOI) centered on the atrial signal of the CS catheter, in addition to entrainment maneuvers to detect the AT isthmus location. Entrainment can be challenging due to low signal-to-noise ratio, inability to capture scar tissue, and risk of AT termination. We describe a novel EAM annotation, using a WOI starting 40 ms prior to the earliest P wave on the surface 12-lead ECG, to detect the reentrant AT exit site. It is based on the mechanistic similarity between scar-related reentrant AT and scar-related ventricular tachycardia, where pacing from the tachycardia isthmus is characterized by a stimulus to QRS interval > 40 ms, reflecting a "slow conducting channel".

Methods: Patients with non CTI-dependent AT after prior AF ablation were included. The AT EAM was performed with CARTO using our novel annotation. Ablation was considered successful if the AT terminated during the ablation.

Results: 27 patients with 33 non-CTI-dependent AT classified as: mitral annulus (17/33), roof (9/33), anterior/posterior LA wall (5/33), and RA (2/33) AT, were included. A complete EAM was achieved in 31/33 AT, encompassing 94±4.6% of the AT cycle length. A clear “early meets late” line was identified in all 31 AT maps, confirming their reentrant mechanism. Low amplitude pre-P fractionated electrograms were found in 30/31 (97%) AT, occurring at a mean distance of 2 mm from the “early meets late” line. Ablation at these presumed isthmuses resulted in AT termination in 30/31 AT (97%). Notably, 17/31 AT terminated within 1-3 lesions indicating ablation at a critical isthmus.

Conclusion: We propose a novel EAM annotation to allow detection of the critical isthmus of post AF ablation AT easily and without reliance on entrainment. Ablation of these isthmuses results in termination of the AT in the majority of patients.