Substrate characterization of the cavotricuspid isthmus using isochronal late activation mapping in patients with right atrial flutter: diagnostic insights and future perspectives

Cavotricuspid isthmus-dependent atrial flutter (CTI-AFl) is the most well-known form of macro-reentrant atrial tachycardia involving the right atrium. Linear ablation at the area of the cavotricuspid isthmus (CTI) is the empirical technique of choice for the interruption of the circuit, owing to favorable anatomical characteristics (narrow area clearly defined by the anatomical obstacles of the tricuspid annulus and the orifice of the inferior vena cava). Beyond these anatomical features, CTI has also been suggested as a zone of slow conduction that contributes to the propagation of the tachycardia. Isochronal Late Activation Mapping (ILAM) is a functional substrate mapping technique originally introduced for ventricular tachycardias. ILAM reveals areas of conduction slowing that may serve as critical isthmuses of arrhythmia circuits.

In the current study we aim to assess the functional substrate of the CTI by using ILAM in order to reveal areas of conduction slowing in patients with history of CTI-AFl.

Patients scheduled for first time catheter ablation for CTI-AFl are included in the study. Activation mapping of the CTI area is performed by pacing from the proximal electrodes of the coronary sinus catheter (500ms pacing cycle length) using a three-dimensional mapping system (CARTO-3, Biosense Webster Inc., Irvine, CA) and a multipolar diagnostic catheter (OctaRayTM, Biosense Webster, Inc). Maps are retrospectively manually annotated at the offset of the local bipolar electrogram deflection. ILAM is created by distributing the activation to eight equally divided isochrones. Isochronal crowding is defined as an area with more than 3 isochrones within a 1cm radius.

In this preliminary report of our ongoing study, 10 patients with history of CTI-AFl were included. The mean age of the patients in the cohort was 55.4±2.3 years, 6 were males and 4 had a history of atrial fibrillation. Mean mapping points per map were 3278±1900. ILAM during pacing from the coronary sinus revealed at least one area of isochronal crowding in all patients.

In a cohort of patients with history of CTI-AFl, at least one area of isochronal crowding was present during functional substrate mapping in all cases. The confirmation of the aforementioned finding in a larger cohort may provide a novel diagnostic tool for the identification of patients prone to manifest CTI-AFl.