Rare narrow QRS tachycardia with atrioventricular dissociation: A case report

BACKGROUND: Most Mahaim fibers are right free-wall atriofascicular accessory pathways with only antegrade conduction. Concealed Mahaim fiber is not very rare; however, concealed nodoventricular fiber is a very rare kind of retrograde accessory pathway in supraventricular tachycardia with atrioventricular (AV) dissociation. Only a few cases about successful ablation of the nodoventricular accessory pathway have been reported. We describe the case of a 32-year-old woman who underwent an electrophysiology study and radiofrequency (RF) ablation of a rare narrow QRS tachycardia with AV dissociation. CASE SUMMARY: A 32-year-old woman with a history of paroxysmal palpitation was admitted to our hospital for RF ablation. Electrocardiography revealed a narrow QRS complex tachycardia with the same morphology in sinus rhythm. Echocardiography showed no structural heart disease. A right-sided concealed AV accessory pathway and a right-sided concealed nodoventricular accessory pathway were involved in the orthodromic atrioventricular reciprocating tachycardia. His bundle-ventricular interval during tachycardia was the same as that in sinus rhythm. The tachycardia could be initiated and entrained by ventricular pacing. Premature right ventricular stimulus introduced during the His-bundle refractory period when tachycardia occurred was able to advance the next atrial potential. The earliest atrial activation was mapped near the proximal slow AV nodal pathway. RF ablation of both accessary pathways was successfully performed under the guidance of a three-dimensional mapping system by recording the earliest retrograde atrial potential, and tachycardia could no longer be induced. CONCLUSION: Narrow QRS tachycardia with AV dissociation is inducible by concealed nodoventricular fiber and ablated by recording the earliest retrograde atrial potential.