Utility of Small Dose Pilsicainide in Suppressing Atrial Fibrillation and Inducing a Target Slow-Fast AVNRT.

BACKGROUND: Although pilsicainide has concentration-dependent effects on cardiac conduction, its specific impact-particularly at low doses-on atrioventricular (AV) nodal slow pathway conduction and atrioventricular nodal re-entrant tachycardia (AVNRT) sustainability remains unclear. CASE SUMMARY: A 74-year-old woman presented with narrow-QRS tachycardia. During electrophysiological study, atrial extrastimulation induced an atrio-His interval jump and a single echo beat, but repeatedly triggered atrial fibrillation requiring cardioversion. Low-dose pilsicainide (20 mg) suppressed atrial arrhythmias but markedly prolonged antegrade slow pathway conduction, rendering sustained tachycardia inducible. Entrainment and His-refractory ventricular extrastimulation confirmed slow-fast AVNRT, which was successfully treated with slow pathway ablation. DISCUSSION: Low-dose pilsicainide may facilitate sustained slow-fast AVNRT by disproportionately prolonging antegrade slow pathway conduction, thereby promoting reentry. Marked atrio-His interval prolongation relative to atrial conduction delay, alongside an unchanged ventriculo-atrial interval, supports a selective antegrade slow pathway mechanism.