Wide QRS complex tachycardia with a 1:1 AV relationship

Abstract

or the management of sudden-onset tachycardia. He had experienced 3 episodes of palpitation attacks, lasting for a couple of hours each, during the last 6 months. A regular, wide QRS complex tachycardia (WCT) at 150 beats/min with a prominent retrograde P wave on the surface electrocardiogram (ECG) was documented during the last attack, which was terminated by drip infusion of pilsicainide administered at another hospital. He did not experience loss of consciousness or dizziness during his palpitation attacks. The findings of other investigations, including physical examination, two-dimensional echocardiography, chest radiography, and laboratory tests, were unremarkable. Cardiac electrophysiological study (EPS) was performed after written informed consent was obtained. Venous access was performed via the right femoral and subclavian veins. Three 5-French quadripolar catheters were advanced to the right ventricular apex, right atrial appendage, and His-bundle region. A 5-French decapolar catheter was placed within the coronary sinus (CS), with a proximal electrode located at its ostium. During the EPS study, a WCT with a cycle length of 330 ms was induced by a ventricular extrastimulus. The morphology of the 12-lead ECG was consistent with that of the clinical tachycardia and showed the right bundlebranch block pattern and left axis deviation. Intracardiac ECG showed a 1:1 atrioventricular (A-V) relationship (Fig. 1). What is the cause of this tachycardia?