Atrial Flutter with 2:1 A-V Conduction and Mobitz Type II-Like Block in the Left Bundle Branch

This article presents the data of a patient who manifested the phenomenon of intermittent and transient left bundle branch block (LBBB) and subsequently Mobitz type II-like block in the left bundle branch (LBB). The assumption is made that this uncommon tachyarrhythmia occurs only in hearts with latent localized organic His-Purkinje system disturbance and made evident by the effect of supraventricular tachycardia. The regularity of the R-R interval, occurrence of two consecutive aberrant QRS complexes of similar duration without altering the R-R interval, and the conversion of the tachycardia to normal sinus rhythm with normal QRS complexes by application of carotid massage, all lend support to a unifocal, supraventricular origin of tachycardias with alternant QRS complexes. The constant and stable duration of all the ventricular beats with LBBB pattern, preceded and followed by normal ventricular complexes along with changing conduction ratios of 3:1 and 2:1 LBBB suggested Mobitz type II-like response in the LBB.