Simultaneous antegrade dual AV node conduction initiates AV nodal re-entrant tachycardia (a rare initiation mechanism).

Typical atrioventricular nodal reentrant tachycardia (AVNRT) is the most common paroxysmal supraventricular tachycardia among adults. The concept of dual pathway physiology remains widely accepted, although this physiology likely results from the functional properties of anisotropic tissue within the triangle of Koch, rather than anatomically distinct tracts of conduction. AVNRT is typically induced with anterograde block over the fast pathway and conduction over the slow pathway, with subsequent retrograde conduction over the fast pathway. On rare occasions, anterograde AV node conduction occurs simultaneously through fast and slow pathways resulting in two ventricular beats in response to one atrial beat. We report a case of AVNRT where the tachycardia is always induced by the same mechanism described above. Successful ablation was achieved by slow pathway modification.

The practical approach to discerning between atrial lead displacement and reversal in dual chamber pacemakers.

We describe a 12-lead electrocardiogram image of a pacemaker malfunction due to atrial lead displacement. Facilitating the understanding of pacemaker timing cycles could explain the underlying mechanisms in this instance. This review utilizes the feature of the ventricular safety pacing interval to discern between atrial lead displacement and reversal.

The ECG role in identifying the etiology of tachycardia-induced cardiomyopathy (TIC).

Tachycardia-induced cardiomyopathy (TIC) is a well recognized entity of heart failure (HF) and various mechanisms due to tachyarrhythmias have been postulated to be responsible for impaired cardiac contractility. Previously reported cases showed reversibility of such disorders whenever stable cardiac rhythm is maintained adequately and we report on a 16-year-old boy who has been diagnosed to have TIC, which was misinterpreted initially as sinus tachycardia secondary to dilated cardiomyopathy and heart failure. A complete recovery of his left ventricular function was achieved by radiofrequency catheter ablation and highlights the importance of a 12-lead electrocardiogram (ECG) assessment in such patients.

The importance of utilizing 24-h Holter monitoring as a non-invasive method of predicting the mechanism of supraventricular tachycardia.

Despite the emergence of advanced invasive technology in identifying the various types of arrhythmia mechanisms, 24-h ambulatory electrocardiogram monitoring as a non-invasive method remains an invaluable informative tool in delineating such mechanisms. Furthermore, one observational study has supported the utilization of 24-h Holter monitoring in exploring AV Node (AVN) characteristics sufficiently in correlation with invasive studies when limited to patients without Wolf Parkinson White syndrome showing a positive predictive value of 98% in their supraventricular tachycardia (SVT) assessment (Fukuda et al., 2005). We describe in this report suspected tachycardia initiation mechanism in three SVT cases based on 24-h Holter recordings. Premature atrial contraction with subsequent AVN fast pathway conduction block initiated the common type AVN re-entrant tachycardia (AVNRT). Dual AVN physiology was documented during the electrophysiological studies in all three cases and a definitive therapy was achieved by the AVN slow pathway modification.