title: Significance of adenosine-induced atrioventricular block in patients with unexplained syncope.
abstract: OBJECTIVE
  The purpose of this study was to test whether a prolonged (>/=6 seconds) period of AV block in response to adenosine triphosphate (ATP) identifies additional patients at risk for bradycardia who may benefit from pacemaker implantation.
  
  
  BACKGROUND
  Bradycardia is a common etiology for syncope in patients without underlying structural heart disease. Conventional testing using electrophysiologic and tilt table studies often fail to identify patients prone to episodes of symptomatic bradycardia.
  
  
  METHODS
  Adenosine testing was performed in 92 consecutive patients (64 women, age 55 +/- 21 years) with syncope of uncertain origin referred for tilt table testing. The adenosine test measured the maximal R-R interval after bolus administration of intravenous adenosine 150 mug/kg to upright patients. A positive adenosine AV block response was defined as a maximal R-R interval > or =6 seconds.
  
  
  RESULTS
  A total of 21 patients (23%) had a positive response. During mean follow-up of 14.3 +/- 5.9 months, 14 patients (16%) had recurrent syncope. Among patients with a positive adenosine response, 3 patients (14%) had recurrent syncope. In comparison, 11 of 69 patients (16%) without adenosine-induced AV block had recurrent syncope (P = 1.00).
  
  
  CONCLUSIONS
  Prolonged adenosine-induced AV block in patients with unexplained syncope failed to predict recurrent syncopal episodes. These data do not support therapeutic interventions (e.g., pacemaker implantation) based on a positive adenosine AV block response alone.
authors.affiliation: Department of Medicine, Division of Cardiology, Cornell University Medical Center, New York, New York 10021, USA.
authors.forename: Jim W
authors.initials: JW
authors.lastname: Cheung
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Stein
authors.forename: Steven M
authors.initials: SM
authors.lastname: Markowitz
authors.forename: Sei
authors.initials: S
authors.lastname: Iwai
authors.forename: Amit B
authors.initials: AB
authors.lastname: Guttigoli
authors.forename: Bindi K
authors.initials: BK
authors.lastname: Shah
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Yarlagadda
authors.forename: Bruce B
authors.initials: BB
authors.lastname: Lerman
authors.forename: Suneet
authors.initials: S
authors.lastname: Mittal
mesh_terms: D000255:Adenosine Triphosphate; D000367:Age Factors; D005260:Female; D006327:Heart Block / Q000139:chemically induced; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012008:Recurrence; D013575:Syncope / Q000209:etiology*; D018667:Tilt-Table Test
chemical_list: D000255:Adenosine Triphosphate