title: Impaired negative chronotropic response to adenosine in patients with inappropriate sinus tachycardia.
abstract: BACKGROUND
  Adenosine is an endogenous nucleoside that has an important role in the diagnosis and treatment of several cardiac arrhythmias. However, its effects on inappropriate sinus tachycardia (IST) are not well established.
  
  
  RESULTS
  In this study, the response to intravenous adenosine (0.1 to 0.15 mg/kg) was studied in 18 patients (age 46+/-15 years) with IST. In a subset of patients (n = 5), the direct effects of adenosine were assessed during pharmacologic beta-adrenergic and cholinergic blockade. Atrial cycle length (ACL) was measured before adenosine injection, at the time of the greatest cycle length prolongation, and during the maximum rebound acceleration of heart rate. Eighteen subjects (age 46+/-11 years) with normal sinus rhythm undergoing clinically indicated electrophysiologic study served as controls. Adenosine did not terminate IST in any patient. The maximum dose of adenosine prolonged the sinus interval significantly, from 780+/-128 msec to 985+/-225 msec (P < 0.001) in the control subjects. In contrast, adenosine caused no significant lengthening of atrial cycle length (527+/-69 msec vs 590+/-148 msec; P = NS) in the patients with IST. Similar difference in the response to adenosine was seen during the pharmacologic autonomic blockade. The reflex increase of the sinus rate (rebound effect) was greater in the control subjects than in the patients with IST (21.2%+/-9.7% vs 8.5%+/-8.8%; P < 0.001).
  
  
  CONCLUSIONS
  The usual negative chronotropic effect of adenosine was impaired in the patients with IST. This may have important diagnostic implications and provide new insight into the mechanism(s) of IST.
authors.affiliation: Department of Internal Medicine, University of Oulu, Finland.
authors.forename: Aino-Maija
authors.initials: AM
authors.lastname: Still
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
authors.forename: K E Juhani
authors.initials: KE
authors.lastname: Airaksinen
authors.forename: M Juhani
authors.initials: MJ
authors.lastname: Koistinen
authors.forename: Raimo
authors.initials: R
authors.lastname: Kettunen
authors.forename: Juha
authors.initials: J
authors.lastname: Hartikainen
authors.forename: Raul D
authors.initials: RD
authors.lastname: Mitrani
authors.forename: Agustin
authors.initials: A
authors.lastname: Castellanos
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Myerburg
authors.forename: M J Pekka
authors.initials: MJ
authors.lastname: Raatikainen
mesh_terms: D000241:Adenosine / Q000008:administration & dosage / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000328:Adult; D000889:Anti-Arrhythmia Agents / Q000008:administration & dosage / Q000494:pharmacology*; D003864:Depression, Chemical; D004305:Dose-Response Relationship, Drug; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D005387:Finland; D005431:Florida; D006325:Heart Atria / Q000187:drug effects; D006329:Heart Conduction System / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D008875:Middle Aged; D013616:Tachycardia, Sinus / Q000188:drug therapy*; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D000319:Adrenergic beta-Antagonists; D000889:Anti-Arrhythmia Agents; D000241:Adenosine