title: 2:1 atrioventricular block during atrioventricular node reentrant tachycardia.
abstract: OBJECTIVE
  The purpose of this study was to determine the incidence and to clarify the mechanism of 2:1 atrioventricular (AV) block during AV node reentrant tachycardia induced in the electrophysiology laboratory.
  
  
  BACKGROUND
  In patients with 2:1 AV block during AV node reentrant tachycardia, the absence of a His bundle potential in the blocked beats has been considered evidence of intranodal, lower common pathway block.
  
  
  METHODS
  In consecutive patients with AV node reentrant tachycardia, the incidence of 2:1 AV block and the response to atropine and a single ventricular extrastimulus was observed.
  
  
  RESULTS
  Persistent 2:1 AV block occurred in 13 of 139 patients with AV node reentrant tachycardia. A His bundle deflection was present in the blocked beats in eight patients and absent in five. Patients with 2:1 AV block had a shorter tachycardia cycle length than did patients without such block (mean +/- SD 312 +/- 32 vs. 353 +/- 55 ms, p < 0.01). Atropine did not alter the 2:1 block in any patient. In every patient, a single ventricular extrastimulus introduced during the tachycardia converted the 2:1 block to 1:1 conduction.
  
  
  CONCLUSIONS
  The incidence of induced 2:1 AV block during AV node reentrant tachycardia is approximately 10%. The lack of a response to atropine and the consistent conversion of 2:1 block to 1:1 conduction by a ventricular extrastimulus indicate that, regardless of the presence or absence of a His bundle potential in blocked beats, 2:1 block during AV node reentrant tachycardia is due to functional infranodal block.
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor 48109-0022, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: Man
authors.forename: K
authors.initials: K
authors.lastname: Brinkman
authors.forename: F
authors.initials: F
authors.lastname: Bogun
authors.forename: B
authors.initials: B
authors.lastname: Knight
authors.forename: M
authors.initials: M
authors.lastname: Bahu
authors.forename: R
authors.initials: R
authors.lastname: Weiss
authors.forename: R
authors.initials: R
authors.lastname: Goyal
authors.forename: M
authors.initials: M
authors.lastname: Harvey
authors.forename: E G
authors.initials: EG
authors.lastname: Daoud
authors.forename: S A
authors.initials: SA
authors.lastname: Strickberger
authors.forename: F
authors.initials: F
authors.lastname: Morady
mesh_terms: D000328:Adult; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001285:Atropine / Q000494:pharmacology; D002036:Bundle of His / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D005260:Female; D006327:Heart Block / Q000209:etiology* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000150:complications* / Q000503:physiopathology
chemical_list: D000889:Anti-Arrhythmia Agents; D001285:Atropine