Utilization of Retrograde Right Bundle Branch Block to Differentiate Atrioventricular Nodal from Accessory Pathway Conduction

Catheter-induced right bundle branch block: Practical implications for the cardiac electrophysiologist

The right bundle branch (RBB), due to its endocardial course, is susceptible to traumatic block caused by "bumping" during right-heart catheterization. In the era of cardiac electrophysiology, catheter-induced RBB block (CI-RBBB) has become a common phenomenon observed during electrophysiological studies and catheter ablation procedures. While typically transient, it may persist for the entire procedure time. Compared to pre-existing RBBB, the transient nature of CI-RBBB allows for comparative analysis relative to the baseline rhythm. Furthermore, unlike functional RBBB, it occurs at similar heart rates, making the comparison of conduction intervals more reliable. While CI-RBBB can provide valuable diagnostic information in various conditions, it is often overlooked by cardiac electrophysiologists. Though it is usually a benign and self-limiting conduction defect, it may occasionally lead to diagnostic difficulties, pitfalls, or undesired consequences. Avoidance of CI-RBBB is advised in the presence of baseline complete left bundle branch block and when approaching arrhythmic substrates linked to the right His-Purkinje-System, such as fasciculo-ventricular pathways, bundle branch reentry, and right-Purkinje focal ventricular arrhythmias. This article aims to provide a comprehensive practical review of the electrophysiological phenomena related to CI-RBBB and its impact on the intrinsic conduction system and various arrhythmic substrates.

Retrograde ventriculoatrial jump-What is the mechanism?

During ventricular extra stimuli(VES) protocol a VA jump was noted. In upper panel with VES @ 500/270 ms (Fig A) the His signal appeared after the A-EGM, ruling out pure nodal VA conduction and confirming presence of an accessory pathway (AP). The H signal was delayed due to probable retrograde RBBB. The atrium was already depolarised via AP and the VA traversing via left bundle-His-node got blocked with a H signal. In the lower panel with VES of 500/260 ms the retrograde AP conduction reached the effective refractory period and pure nodal VA conduction took place along with retrograde RBBB. The retrograde VA jump was hence due to a jump from AP to AV node.

Interesting Response with the Delivery of Right Ventricular Extrastimulus of Increasing Prematurity

A 45-year-old man with no structural heart disease underwent an electrophysiology study for recurrent episodes of palpitation. There was no evidence of pre-excitation on the baseline electrocardiogram. Baseline intervals, including the A-H and H-V intervals, were within the normal limits and remained so during the electrophysiology study. An interesting response was observed with the delivery of ventricular extrastimuli with increasing prematurity from the right ventricular apex, triggering consideration of the possible mechanism.

A case of a "pseudo jump-up phenomenon" caused by retrograde ventricular-His prolongation

A 35-year-old woman was referred for treatment of a supraventricular tachycardia. The tachycardia was diagnosed as a slow-fast form of atrioventricular nodal reentrant tachycardia. Radiofrequency ablation targeting the antegrade slow pathway was performed at the posterior septum of the right atrium. After the radiofrequency ablation, ventricular extrastimulus pacing was performed to assess the retrograde slow pathway, which was suggested before the ablation. The prolongation of the VA interval with a 10 ms decrease in the S2 pacing interval was 60 ms and retrograde dual pathways were suspected. However, the HA interval did not change and a prolongation of the VA interval was caused by the prolongation of the VH interval and no additional ablation was required.

Classification, Electrophysiological Features and Therapy of Atrioventricular Nodal Reentrant Tachycardia

Atrioventricular nodal reentrant tachycardia (AVNRT) should be classified as typical or atypical. The term 'fast-slow AVNRT' is rather misleading. Retrograde atrial activation during tachycardia should not be relied upon as a diagnostic criterion. Both typical and atypical atrioventricular nodal reentrant tachycardia are compatible with varying retrograde atrial activation patterns. Attempts at establishing the presence of a 'lower common pathway' are probably of no practical significance. When the diagnosis of AVNRT is established, ablation should be only directed towards the anatomic position of the slow pathway. If right septal attempts are unsuccessful, the left septal side should be tried. Ablation targeting earliest atrial activation sites during typical atrioventricular nodal reentrant tachycardia or the fast pathway in general for any kind of typical or atypical atrioventricular nodal reentrant tachycardia, are not justified. In this review we discuss current concepts about the tachycardia circuit, electrophysiologic diagnosis, and ablation of this arrhythmia.