Upper Loop Reentry Revisited: Clinical Features, Mechanisms, and Therapeutic Approaches-Insights From a Case Series

Upper loop reentry (ULR) is a macroreentrant atrial flutter rotating around the upper right atrium. Initially described over 20 years ago as originating from conduction gaps in the crista terminalis, ULR has more recently been reported in association with cardiac surgeries and atrial fibrillation ablation. However, its clinical features and optimal ablation strategies remain poorly defined.

We retrospectively analyzed six consecutive cases diagnosed with ULR and treated with catheter ablation (5 males, age 61.2 ± 12.8 years) at our institution.

ULR occurred in various clinical settings: following superior transseptal approaches (n = 2), after surgical repairs of congenital heart disease (n = 2), and related to atrial fibrillation ablation (n = 2). Slow conduction zones (SCZs) associated with ULR were variably located at the crista terminalis/sinus venosus, near surgical incision lines, or within low-voltage areas in the right atrium. In one case, no distinct SCZ was identified. Ablation strategies were individualized, including focal ablation at identifiable SCZs, linear ablation between anatomical structures, or intercaval linear ablation. In all cases, the tachycardia was successfully terminated, and no further arrhythmia was inducible.

This case series highlights the heterogeneous nature of ULR circuits and their occurrence across diverse clinical backgrounds. Tailored ablation strategies based on individual arrhythmia substrates are effective for successful elimination of ULR.