A wide complex tachycardia with changing atrial activation sequence.

Change of the retrograde atrial activation sequence during radiofrequency (RF) ablation of left-side accessory pathway can be due to another accessory pathway, another mechanism for the tachycardia, or due to intraatrial conduction block, partial or complete, caused by RF delivery to a site proximal to the site of insertion of the accessory pathway. In this case report, a temporary complete intraatrial conduction block was created by RF delivery proximal to the site of accessory pathway insertion, causing a change in the retrograde atrial activation sequence during ongoing tachycardia that was terminated by ablation at the insertion site of accessory pathway. ©2011, The Authors. Journal compilation ©2011 Wiley Periodicals, Inc.