title: Supernormal conduction in the left bundle branch.
abstract: This report describes a patient with tachycardia-dependent left bundle branch block (LBBB) and atrial extrasystoles, some of which were followed by an unexpectedly narrow QRS complex. His-bundle recordings and premature atrial stimulation were performed to analyze the mechanism underlying the normalized intraventricular conduction of some of the early atrial impulses. The results suggested the presence of supernormal conduction in the left bundle branch (LBB), because: (1) the HV interval was identical in LBBB complexes and in early narrow QRS complexes; (2) during single test stimulation using different paced atrial cycle lengths, there was a well-defined range of H1H2 intervals resulting in normalization of intraventricular conduction; and (3) atrial pacing with a cycle length of 500 msec resulted in alternation between wide and narrow QRS complexes. These findings rule out alternative mechanisms that could explain the unexpectedly normal intraventricular conduction of early impulses.
authors.affiliation: Department of Cardiology, Academic Hospital, Maastricht, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Oreto
authors.forename: J L
authors.initials: JL
authors.lastname: Smeets
authors.forename: L M
authors.initials: LM
authors.lastname: Rodriguez
authors.forename: C
authors.initials: C
authors.lastname: Timmermans
authors.forename: H J
authors.initials: HJ
authors.lastname: Wellens
mesh_terms: D002037:Bundle-Branch Block / Q000209:etiology / Q000503:physiopathology*; D005117:Cardiac Complexes, Premature / Q000150:complications; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D006325:Heart Atria; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D012016:Reference Values; D013610:Tachycardia / Q000150:complications