title: Characterization of the distal insertion of atriofascicular accessory pathways and mechanisms of QRS patterns in atriofascicular antidromic tachycardia.
abstract: BACKGROUND
  The distal insertion of right atriofascicular pathways remains a source of debate. Moreover, there are various morphologies of preexcited QRS complexes involving atriofascicular pathways that have been poorly characterized.
  
  
  OBJECTIVE
  To characterize the distal insertion of atriofascicular accessory pathways and to provide a mechanism for the change in QRS morphology observed between short and long ventriculo-His (V-H) antidromic atrioventricular reentrant tachycardias (AVRTs) in the same patient.
  
  
  METHODS
  Thirteen patients with atriofascicular pathways and preexcited AVRT with short V-H and long V-H intervals were studied. For each patient, the tachycardia cycle length, V-H interval, QRS width, and axis were compared. A baseline His-ventricular interval was also recorded.
  
  
  RESULTS
  The baseline His-ventricular interval was significantly longer than the V-H interval during antidromic AVRT (median 50 ms vs. 10 ms; P < .0001). Retrograde right bundle branch block increased the V-H interval (median 10 ms vs. 85 ms; P < .0001), the tachycardia cycle length (median of 302.5 ms vs. 350 ms; P < .0001), and the QRS width (median 120 ms vs. 140 ms; P < .0002). At least subtle changes in QRS morphology, axis, or QRS width were seen in all patients.
  
  
  CONCLUSIONS
  The distal insertion of right atriofascicular pathways fuses with the right bundle branch. The various QRS morphologies seen during the change from short V-H to long V-H antidromic AVRT can be explained by fusion, particularly over the left anterior fascicle.
authors.affiliation: The Everett Clinic, Everett, Washington, USA.
authors.forename: Maheer
authors.initials: M
authors.lastname: Gandhavadi
authors.forename: Eduardo B
authors.initials: EB
authors.lastname: Sternick
authors.forename: Warren M
authors.initials: WM
authors.lastname: Jackman
authors.forename: Hein J J
authors.initials: HJ
authors.lastname: Wellens
authors.forename: Mark E
authors.initials: ME
authors.lastname: Josephson
mesh_terms: D058606:Accessory Atrioventricular Bundle / Q000503:physiopathology* / Q000601:surgery; D002037:Bundle-Branch Block / Q000503:physiopathology*; D017115:Catheter Ablation; D006329:Heart Conduction System / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000503:physiopathology*
keywords: A; AV; AVRT; Antidromic; Atriofascicular; ECG; Fusion; H; H-V; His; His-ventricular; LBB; Mahaim; RBB; RBBB; RV; V-H; atrial; atrioventricular; atrioventricular reentrant tachycardia; electrocardiogram/electrocardiographic; left bundle branch; right bundle branch; right bundle branch block; right ventricle/ventricular; ventriculo-His