Narrow QRS tachycardia with 1:1 VA conduction and irregular cycle length: what is the mechanism?

摘要

A 48-year-old man was referred for electrophysiologic study because of first manifestation of palpitations (pulse beat >200/min). During the tachycardia he felt dizziness. The effect of vagal maneuvers was not evaluated by the patient. Until this event, the patient was free of cardiac symptoms or disease. Electrophysiologic study was performed by positioning multipolar catheters in the high right atrium, at the His bundle, in the coronary sinus (CS), and in the right ventricular apex. A narrow QRS complex tachycardia (CL 340-500 ms) was induced mechanically during the insertion of the catheters. This tachycardia mimicked atrial fibrillation in the surface ECG owing to a beat-to-beat irregularity of cycle length. However, close inspection of the 12-lead ECG revealed P waves in a 1:1 ratio to the QRS complexes. What is the mechanism of this tachycardia?