title: Implications of mechanism of bradycardia on response to pacing in patients with unexplained syncope.
abstract: OBJECTIVE
  Asystole >3 s or sinus bradycardia with a ventricular rate <40 in association with complete heart block or sinus node dysfunction are considered to be Class 1 indications for permanent cardiac pacing. Nevertheless, these phenomena may be observed in symptomatic patients with neurocardiogenic syncope, who may not respond to pacing therapy. We hypothesized that the pattern of spontaneous bradycardia in symptomatic patients would distinguish patients with sinus node dysfunction or conduction system disease who would benefit from pacing from patients with neurally-mediated syncope who would derive lesser benefit.
  
  
  RESULTS
  Patients with symptomatic spontaneous bradycardia during long-term monitoring for unexplained syncope who underwent pacemaker implantation were classified according to the ISSUE classification system and followed for recurrent syncope. Follow-up included review of medical records, pacemaker clinic visits, and telephone interviews. Loop recorder tracings were reviewed to identify characteristics potentially predicting a favourable response to pacing. Thirty-three patients (21 male; age, 70 +/- 14) were followed for 3.56 +/- 1.71 years. Six patients had a recurrence of syncope during the follow-up. All patients with recurrent syncope despite pacing demonstrated a Type 1A (n = 5) or 1B (n = 1) pattern with gradual onset of bradycardia at baseline, suggesting a neurocardiogenic mechanism. There was no difference in the severity of bradycardia or duration of asystole in baseline loop recorded events in responding and non-responding patients. Multivariate analysis using stepwise logistic regression revealed that the ISSUE classification and the absence of structural heart disease were the only independent predictors of treatment failure of cardiac pacing in patients with spontaneous symptomatic bradycardia.
  
  
  CONCLUSIONS
  Patients with syncope associated with abrupt bradycardia displayed a better response to cardiac pacing therapy than those with gradual onset bradycardia.
authors: Division of Cardiology, University of Western Ontario, London Health Sciences Centre, University Campus, C6-113 339 Windermere road, London, Ontario N6A 5A5, Canada.
authors: Sachin
authors: S
authors: Sud
authors: George J
authors: GJ
authors: Klein
authors: Allan C
authors: AC
authors: Skanes
authors: Lorne J
authors: LJ
authors: Gula
authors: Raymond
authors: R
authors: Yee
authors: Andrew D
authors: AD
authors: Krahn
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001919:Bradycardia / Q000150:complications* / Q000503:physiopathology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010138:Pacemaker, Artificial; D012008:Recurrence; D012189:Retrospective Studies; D019462:Syncope, Vasovagal / Q000209:etiology* / Q000503:physiopathology