Long RP interval tachycardia. What is the mechanism?

摘要

A 41-year-old man with a history of tachycardia refractory to multiple antiarrhythmic drugs was sent to our institution. His 12-lead electrocardiogram demonstrated incessant narrow QRS complex tachycardia with negative P waves in the inferior leads and long RP interval. Occasionally, the tachycardia terminated after a P wave and then was restarted after a sinusal beat. An EP study was performed during tachycardia. Intracardiac electrograms during tachycardia and response to pacing maneuvers are shown. What is the tachycardia mechanism?