title: High atrial antitachycardia pacing therapy efficacy is associated with a reduction in atrial tachyarrhythmia burden in a subset of patients with sinus node dysfunction and paroxysmal atrial fibrillation.
abstract: BACKGROUND
  Atrial tachycardia (AT) and atrial flutter that occur in association with paroxysmal atrial fibrillation (AF) can be successfully terminated by antitachycardia pacing (ATP) therapy. We hypothesized that atrial ATP therapy reduces AT/AF burden in a subset of patients with symptomatic bradycardia and frequent paroxysmal AT/AF.
  
  
  OBJECTIVE
  This study evaluated the effect of atrial ATP therapy on AT/AF burden in a pacemaker population with paroxysmal AF.
  
  
  METHODS
  We compared AT/AF burden in 261 patients who received a Medtronic AT500 pacemaker for treatment of AT/AF in the setting of symptomatic bradycardia based on device-classified atrial ATP efficacy < 60% and > or = 60%. Patients with > or = 10 device-detected episodes of AT/AF before and after atrial ATP therapy initiation were identified from four clinical studies performed in 72 centers worldwide.
  
  
  RESULTS
  The high efficacy group comprised 75 patients with atrial ATP efficacy > or = 60%. The low efficacy group comprised 186 patients with atrial ATP efficacy < 60%. AT/AF episode frequency was similar in both groups prior to ATP activation and decreased in the low efficacy group following ATP activation. Following atrial ATP initiation, total AT/AF burden increased slightly in the low ATP efficacy group (median 2.77 [25th-75th percentiles 0.84-5.86] hours/day vs 2.92 [0.59-8.12] hours/day, P = .01). In contrast, total AT/AF burden decreased significantly in the high efficacy group (median 2.46 [0.29-8.88] hours/day vs 0.68 [0.13-2.97] hours/day, P < .001).
  
  
  CONCLUSIONS
  Up to 30% of patients with frequent episodes of paroxysmal AF and symptomatic bradycardia experience a reduction in AT/AF burden from atrial ATP therapy over time.
authors.affiliation: Libin Cardiovascular Institute of Alberta and Department of Cardiovascular Sciences, University of Calgary and Calgary Health Region, Calgary, Alberta, Canada. amgillis@ucalgary.ca
authors.forename: Anne M
authors.initials: AM
authors.lastname: Gillis
authors.forename: Jodi
authors.initials: J
authors.lastname: Koehler
authors.forename: Margaret
authors.initials: M
authors.lastname: Morck
authors.forename: Rahul
authors.initials: R
authors.lastname: Mehra
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Hettrick
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000503:physiopathology / Q000628:therapy*; D001919:Bradycardia / Q000628:therapy*; D002304:Cardiac Pacing, Artificial; D002986:Clinical Trials as Topic; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D011446:Prospective Studies; D012849:Sinoatrial Node / Q000473:pathology; D013612:Tachycardia, Ectopic Atrial / Q000628:therapy*; D016896:Treatment Outcome