title: Subclinical atrial fibrillation and the risk of stroke.
abstract: BACKGROUND
  One quarter of strokes are of unknown cause, and subclinical atrial fibrillation may be a common etiologic factor. Pacemakers can detect subclinical episodes of rapid atrial rate, which correlate with electrocardiographically documented atrial fibrillation. We evaluated whether subclinical episodes of rapid atrial rate detected by implanted devices were associated with an increased risk of ischemic stroke in patients who did not have other evidence of atrial fibrillation.
  
  
  METHODS
  We enrolled 2580 patients, 65 years of age or older, with hypertension and no history of atrial fibrillation, in whom a pacemaker or defibrillator had recently been implanted. We monitored the patients for 3 months to detect subclinical atrial tachyarrhythmias (episodes of atrial rate >190 beats per minute for more than 6 minutes) and followed them for a mean of 2.5 years for the primary outcome of ischemic stroke or systemic embolism. Patients with pacemakers were randomly assigned to receive or not to receive continuous atrial overdrive pacing.
  
  
  RESULTS
  By 3 months, subclinical atrial tachyarrhythmias detected by implanted devices had occurred in 261 patients (10.1%). Subclinical atrial tachyarrhythmias were associated with an increased risk of clinical atrial fibrillation (hazard ratio, 5.56; 95% confidence interval [CI], 3.78 to 8.17; P<0.001) and of ischemic stroke or systemic embolism (hazard ratio, 2.49; 95% CI, 1.28 to 4.85; P=0.007). Of 51 patients who had a primary outcome event, 11 had had subclinical atrial tachyarrhythmias detected by 3 months, and none had had clinical atrial fibrillation by 3 months. The population attributable risk of stroke or systemic embolism associated with subclinical atrial tachyarrhythmias was 13%. Subclinical atrial tachyarrhythmias remained predictive of the primary outcome after adjustment for predictors of stroke (hazard ratio, 2.50; 95% CI, 1.28 to 4.89; P=0.008). Continuous atrial overdrive pacing did not prevent atrial fibrillation.
  
  
  CONCLUSIONS
  Subclinical atrial tachyarrhythmias, without clinical atrial fibrillation, occurred frequently in patients with pacemakers and were associated with a significantly increased risk of ischemic stroke or systemic embolism. (Funded by St. Jude Medical; ASSERT ClinicalTrials.gov number, NCT00256152.).
authors.affiliation: Population Health Research Institute, McMaster University, Hamilton, ON, Canada.
authors.forename: Jeff S
authors.initials: JS
authors.lastname: Healey
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Connolly
authors.forename: Michael R
authors.initials: MR
authors.lastname: Gold
authors.forename: Carsten W
authors.initials: CW
authors.lastname: Israel
authors.forename: Isabelle C
authors.initials: IC
authors.lastname: Van Gelder
authors.forename: Alessandro
authors.initials: A
authors.lastname: Capucci
authors.forename: C P
authors.initials: CP
authors.lastname: Lau
authors.forename: Eric
authors.initials: E
authors.lastname: Fain
authors.forename: Sean
authors.initials: S
authors.lastname: Yang
authors.forename: Christophe
authors.initials: C
authors.lastname: Bailleul
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Morillo
authors.forename: Mark
authors.initials: M
authors.lastname: Carlson
authors.forename: Ellison
authors.initials: E
authors.lastname: Themeles
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Kaufman
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Hohnloser
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000150:complications* / Q000628:therapy; D002304:Cardiac Pacing, Artificial / Q000379:methods; D017147:Defibrillators, Implantable; D004617:Embolism / Q000209:etiology*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000150:complications; D008297:Male; D010138:Pacemaker, Artificial; D011446:Prospective Studies; D012306:Risk; D020521:Stroke / Q000209:etiology*