Shortening of ventriculoatrial interval after ablation of an accessory pathway

A 21-year old man with history of 8 year palpitation was referred for electrophysiologic study and possible radiofrequency ablation. Physical examination and transthoracic echocardiographic study did not disclose any abnormality. Baseline ECG showed normal sinus rhythm with normal PR and QRS intervals and no evidence of preexcitation. Antiarrhythmic drugs (propranolol and verapamil) were discontinued two days before the procedure. Baseline intervals in sinus rhythm were as follows: sinus cycle length=690 msec, AH=74 msec, HV=37 msec, QRS=90 msec, PR=133 msec. The minimal pacing cycle length maintaining 1:1 antegrade conduction (AVWP) was 320 msec and the minimal pacing cycle length maintaining 1:1 retrograde conduction (VAWP) was 400 msec. Single extrastimulus testing in the right atrium and the right ventricular apex leaded to a sustained narrow complex tachycardia. The arrhythmia was a short PRlong RP tachycardia with following characteristics: cycle length=376 msec, AH=141 msec, HV=42 msec, VA=200 msec, HA (HRA) =236 msec, HA (His) =243 msec and eccentric atrial activation during the arrhythmia (Figure 1). The arrhythmia was easily reproducible with stable hemodynamic.