A new ECG sign of an accessory pathway in sinus rhythm: pseudo partial right bundle branch block

Abstract

It is clinically important to be able to detect the presence of an accessory pathway, as pre-excited atrial fibrillation is a well recognised cause of sudden cardiac death, for which there is a potential "cure" in the form of radiofrequency ablation of the pathway. The classic manifestations such as a shortened PR interval or delta waves may not always be present. In certain patients a pseudo partial right bundle block pattern-that is, an rSr' complex in lead V1- may be the sole manifestation of a left sided accessory pathway. An electrophysiological mechanism is proposed for this pattern and it is suggested that this pattern may be used as a new ECG sign for diagnosing an accessory pathway in sinus rhythm.

Figure 1

Pseudo partial right bundle block (rSr') pattern in lead V1 but no classic features of pre-excitation in a patient with a left sided accessory pathway.

Figure 2

Disappearance of the secondary r' wave in lead V1 during radiofrequency of a left sided accessory pathway.

Figure 3

Disappearance of pseudo partial bundle branch block pattern in lead V1 after the successful radiofrequency ablation of a left sided accessory pathway in the same patient as in fig 1.