title: Mechanism of syncope in patients with positive adenosine triphosphate tests.
abstract: OBJECTIVE
  We prospectively evaluated the mechanism of syncope in patients with positive adenosine triphosphate (ATP) tests (defined as the induction of atrioventricular [AV] block with a ventricular pause >/=6 s after an intravenous bolus of 20 mg ATP).
  
  
  BACKGROUND
  Patients with unexplained syncope tend to have more positive ATP tests results than those without syncope.
  
  
  METHODS
  An implantable loop recorder (ILR) was inserted in 36 ATP-positive patients (69 +/- 10 years; 22 women; median of 6 syncopal episodes); 15 of them also had a positive response to tilt testing.
  
  
  RESULTS
  During the follow-up of 18 +/- 9 months, 18 patients (50%) had syncopal recurrence and 16 (44%) had an electrocardiographically documented episode: AV block (n = 3: paroxysmal in 2 and permanent in 1), AV block followed by sinus arrest (n = 1), sinus arrest (n = 5), sinus bradycardia <40 beats/min (n = 2), normal sinus rhythm (n = 2), sinus tachycardia (n = 1), rapid atrial fibrillation (n = 1), and ectopic atrial tachycardia (n = 1). Bradycardia was documented in a total of 11 cases (69%), and a long ventricular pause (4 to 29 s) was present in eight cases (50%). All three patients with ILR-documented AV block had previously had a negative tilt test, whereas seven of eight with ILR-documented sinus bradycardia or sinus arrest had previously had a positive tilt test.
  
  
  CONCLUSIONS
  In patients with adenosine-sensitive syncope, the mechanism of syncope is heterogeneous, although bradycardia is the most frequent finding. Adenosine triphosphate-induced AV block predicts AV block as the mechanism of spontaneous syncope in only a few tilt-negative patients.
authors.affiliation: Department of Cardiology, Ospedali del Tigullio, Lavagna, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Donateo
authors.forename: Michele
authors.initials: M
authors.lastname: Brignole
authors.forename: Carlo
authors.initials: C
authors.lastname: Menozzi
authors.forename: Nicola
authors.initials: N
authors.lastname: Bottoni
authors.forename: Paolo
authors.initials: P
authors.lastname: Alboni
authors.forename: Maurizio
authors.initials: M
authors.lastname: Dinelli
authors.forename: Attilio
authors.initials: A
authors.lastname: Del Rosso
authors.forename: Francesco
authors.initials: F
authors.lastname: Croci
authors.forename: Daniele
authors.initials: D
authors.lastname: Oddone
authors.forename: Alberto
authors.initials: A
authors.lastname: Solano
authors.forename: Enrico
authors.initials: E
authors.lastname: Puggioni
mesh_terms: D000255:Adenosine Triphosphate / Q000008:administration & dosage; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001145:Arrhythmias, Cardiac / Q000150:complications / Q000503:physiopathology*; D003935:Diagnostic Techniques, Cardiovascular; D003943:Diagnostic Techniques, Neurological; D005260:Female; D006327:Heart Block / Q000150:complications / Q000503:physiopathology*; D006801:Humans; D020007:Implants, Experimental; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012008:Recurrence; D013575:Syncope / Q000209:etiology* / Q000503:physiopathology*
chemical_list: D000255:Adenosine Triphosphate