title: Provocation of sudden heart rate oscillation with adenosine exposes abnormal QT responses in patients with long QT syndrome: a bedside test for diagnosing long QT syndrome.
abstract: OBJECTIVE
  As arrhythmias in the long QT syndrome (LQTS) are triggered by heart rate deceleration or acceleration, we speculated that the sudden bradycardia and subsequent tachycardia that follow adenosine injection would unravel QT changes of diagnostic value in patients with LQTS.
  
  
  RESULTS
  Patients (18 LQTS and 20 controls) received intravenous adenosine during sinus rhythm. Adenosine was injected at incremental doses until atrioventricular block or sinus pauses lasting 3 s occurred. The QT duration and morphology were studied at baseline and at the time of maximal bradycardia and subsequent tachycardia. Despite similar degree of adenosine-induced bradycardia (longest R-R 1.7+/-0.7 vs. 2.2+/-1.3 s for LQTS and controls, P=NS), the QT interval of LQT patients increased by 15.8+/-13.1%, whereas the QT of controls increased by only 1.5+/-6.7% (P<0.001). Similarly, despite similar reflex tachycardia (shortest R-R 0.58+/-0.07 vs. 0.55+/-0.07 s for LQT patients and controls, P=NS), LQTS patients developed greater QT prolongation (QTc=569+/-53 vs. 458+/-58 ms for LQT patients and controls, P<0.001). The best discriminator was the QTc during maximal bradycardia. Notched T-waves were observed in 72% of LQT patients but in only 5% of controls during adenosine-induced bradycardia (P<0.001).
  
  
  CONCLUSIONS
  By provoking transient bradycardia followed by sinus tachycardia, this adenosine challenge test triggers QT changes that appear to be useful in distinguishing patients with LQTS from healthy controls.
authors.affiliation: Department of Cardiology, Tel-Aviv Sourasky Medical Center, Sackler-School of Medicine, Tel Aviv University, Weizman 6, Tel Aviv 64239, Israel. saviskin@tasmc.health.gov.il
authors.forename: Sami
authors.initials: S
authors.lastname: Viskin
authors.forename: Raphael
authors.initials: R
authors.lastname: Rosso
authors.forename: Ori
authors.initials: O
authors.lastname: Rogowski
authors.forename: Bernard
authors.initials: B
authors.lastname: Belhassen
authors.forename: Aviva
authors.initials: A
authors.lastname: Levitas
authors.forename: Abraham
authors.initials: A
authors.lastname: Wagshal
authors.forename: Amos
authors.initials: A
authors.lastname: Katz
authors.forename: Dana
authors.initials: D
authors.lastname: Fourey
authors.forename: David
authors.initials: D
authors.lastname: Zeltser
authors.forename: Antonio
authors.initials: A
authors.lastname: Oliva
authors.forename: Guido D
authors.initials: GD
authors.lastname: Pollevick
authors.forename: Charles
authors.initials: C
authors.lastname: Antzelevitch
authors.forename: Uri
authors.initials: U
authors.lastname: Rozovski
mesh_terms: D000241:Adenosine; D000328:Adult; D000889:Anti-Arrhythmia Agents; D001919:Bradycardia / Q000139:chemically induced; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D019095:Point-of-Care Systems; D013610:Tachycardia / Q000139:chemically induced
chemical_list: D000889:Anti-Arrhythmia Agents; D000241:Adenosine