Electrophysiological Mechanisms of Typical Atrial Flutter After Atrial Switch Operation: Critical Role of the Septal Corridor

BACKGROUND: Peritricuspid, or cavotricuspid isthmus-dependent, atrial flutter is the most common arrhythmia in patients with dextro-transposition of the great arteries treated with atrial switch surgery, but its underlying mechanisms remain poorly understood. METHODS: Twenty consecutive patients with prior atrial switch surgery referred for atrial flutter ablation were included. All underwent transbaffle puncture and high-density mapping. Anatomic barriers, activation patterns, conduction velocities, and low-voltage areas were assessed. RESULTS: In all cases of peritricuspid atrial flutter, surgical incisions defined the posterior boundary of the circuit. The narrowest segment of the reentry was consistently located within a septal corridor bounded posteriorly by the baffle incision and anteriorly by the tricuspid annulus. Slow conduction (<30 cm/s) was identified in this septal corridor in 92% of peritricuspid flutters and in 85% of patients during sinus or paced rhythm. Low-voltage areas were limited and frequently colocalized with regions of slow conduction. No patient exhibited slow conduction or low voltage at the cavotricuspid isthmus. The septal corridor was also involved in 60% of nonperitricuspid reentrant atrial tachycardias. Programmed atrial stimulation with S2 mapping accentuated conduction delay in this region, with demonstration of functional block and induction of atrial flutter. CONCLUSIONS: In patients with dextro-transposition of the great arteries corrected by atrial switch, surgical incisions define posterior boundaries and create a narrow septal corridor, or baffle-tricuspid isthmus, characterized by slow conduction and a propensity for functional block. These anatomic and electrophysiological features likely underlie the high prevalence of peritricuspid reentry in this population, representing a ubiquitous critical substrate for arrhythmia initiation and maintenance. Systematic cavotricuspid isthmus ablation should, therefore, be considered in these patients.