Transient changes in QRS morphology during a narrow complex tachycardia: What is the mechanism?

The observation of electrograms and electrocardiograms recorded in sinus rhythm can offer important initial information about the mechanism of arrhythmia. Some patients may have both bundle branch aberrancy or a bystander pathway or multiple pathways, giving rise to varying degrees of QRS fusion. There is need to focus on any change in cycle length of the tachycardia and morphology of QRS during tachycardia. This article is protected by copyright. All rights reserved.

Fast and slow narrow complex tachycardia in one patient: two of a kind?

A 35-year-old female was referred to our hospital. For more than ten years, she had had complaints of two types of paroxysmal palpitations, both with a sudden onset. The first type was rapid and often accompanied by light-headedness; the second she described as much less rapid, better tolerated, and often terminated by the Valsalva manoeuvre. The incidence and duration of both types of paroxysms were increasing. In the emergency room of the referring hospital, the tachycardia was terminated with intravenous verapamil. The electrophysiological study revealed normal conduction parameters. Premature atrial beats (due to catheter manipulation) or delivered atrial extra stimuli over a wide range easily induced two types of tachycardia. AV node modification by radiofrequency ablation using the posterior approach was performed. With this approach, RF ablation of the caudal extension of the AV node is performed, which modifies the slow pathway, so that the reentrant circuit is interrupted. After this intervention, no tachycardia whatsoever could be induced and during followup (8 months), no recurrent arrhythmia of any kind occurred.