title: Paradoxical effect of isoprenaline infusion.
abstract: BACKGROUND
  Isoprenaline (isoproterenol) is a beta-adrenergic drug, used to increase the heart rate and, during electrophysiological study, to facilitate the induction of supraventricular (SVT) and ventricular tachycardias (VT). Decrease in heart rate during isoprenaline infusion is a rare phenomenon. The purpose of the study was to evaluate the incidence, the possible mechanisms, and the significance of a paradoxical bradycardia induced by isoprenaline infusion.
  
  
  METHODS
  Electrophysiological study was performed for the evaluation of tachycardias (n = 551) or dizziness/syncope (n = 214) in 765 patients aged from 15 to 85 years. The study was negative in the basal state, and was repeated after isoprenaline infusion (2-4 microg/min).
  
  
  RESULTS
  In 714 patients, this perfusion increased the heart rate to 100-140 bpm. A bradycardia was noted in 51 patients (7%). Two bradyarrhythmias were noted: (1) sinus or junctional bradycardia (cycle length - 10%) occurred in 43 patients, aged 15-70 years, generally studied for unexplained syncope (n = 37); a young age (40+/-16 years), syncope (n = 37) and absence of heart disease (n = 27) were more frequent than that in patients without isoprenaline-induced sinus or junctional bradycardia; another arrhythmia (SVT or VT) was induced in seven patients with syncope, five with heart disease and two without; six young patients (<50 years) had no syncope and were studied for SVT or VT; (2) eight patients, aged 65+/-11 years, developed second-degree atrioventricular (AV) block which was supraHisian (n = 4) or infraHisian (n = 4); they were studied for exercise-related syncope; they had no signs of myocardial ischaemia and AV block was reproduced by ajmaline testing: isoprenaline revealed organic conduction disturbance.
  
  
  CONCLUSIONS
  The occurrence of paradoxical bradycardia was a rare finding during isoprenaline infusion (7%); sinus or junctional bradycardia was a sign of hypervagotonia, but was without clinical significance in 35% of these patients. The development of second-degree AV block was always pathological and associated with AV conduction disturbances, which occurred spontaneously during exercise. Isoprenaline infusion appeared to be a simple means to detect organic AV conduction disturbance in patients complaining of exercise or stress-related dizziness/syncope and unable to perform exercise test.
authors.affiliation: Cardiology, CHU Brabois, Rue du Morvan 54511, 54500 Vandoeuvre-les-Nancy, France. b.brembilla-perrot@chu-nancy.fr
authors.forename: Béatrice
authors.initials: B
authors.lastname: Brembilla-Perrot
authors.forename: Ihad
authors.initials: I
authors.lastname: Muhanna
authors.forename: Marc
authors.initials: M
authors.lastname: Nippert
authors.forename: Batric
authors.initials: B
authors.lastname: Popovic
authors.forename: Daniel
authors.initials: D
authors.lastname: Beurrier
authors.forename: Pierre
authors.initials: P
authors.lastname: Houriez
authors.forename: Arnaud
authors.initials: A
authors.lastname: Terrier de la Chaise
authors.forename: Olivier
authors.initials: O
authors.lastname: Claudon
authors.forename: Pierre
authors.initials: P
authors.lastname: Louis
authors.forename: Ahmed
authors.initials: A
authors.lastname: Abdelaal
authors.forename: Simona
authors.initials: S
authors.lastname: State
authors.forename: Marius
authors.initials: M
authors.lastname: Andronache
authors.forename: Christine
authors.initials: C
authors.lastname: Suty-Selton
mesh_terms: D000293:Adolescent; D000318:Adrenergic beta-Agonists / Q000009:adverse effects*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001919:Bradycardia / Q000139:chemically induced*; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007262:Infusions, Intravenous; D007545:Isoproterenol / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013575:Syncope / Q000209:etiology; D013610:Tachycardia / Q000175:diagnosis / Q000209:etiology
chemical_list: D000318:Adrenergic beta-Agonists; D007545:Isoproterenol