LAUSR

Some kind of infrahisian conduction disease is always present in patients with bundle branch reentry tachycardia, even with apparently normal ECG. These patients should undergo further investigations to look for the presence of an underlying structural heart disease. Introduction Bundle branch reentrant tachycardia (BBRT) is a form ofmacroreentrant tachycardia encompassing both the left and right bundle branches. It usually occurs in the context of dilated cardiomyopathy, previous valve surgery, or other cardiac conditions that affect the His-Purkinje system. The baseline electrocardiogram (ECG) in sinus rhythm generally shows a left bundle branch block (LBBB) or right bundle branch block (RBBB). This case is a very unusual presentation of BBRT in a patient with subclinical left ventricular noncompaction and bicuspid aortic valve. Despite a normal resting ECG, the intracardiac electrograms showed a significant infrahisian conduction delay. The BBRT initiated after development of phase 3 RBBB as a result of fast antegrade atrioventricular (AV) conduction, possibly over an AV nodal slow pathway or owing to atrioventricular nodal reentry tachycardia (AVNRT).