title: Ventricular tachyarrhythmias in patients receiving an implantable cardioverter-defibrillator for primary versus secondary prophylaxis indications.
abstract: BACKGROUND
  Data on the mechanisms of sudden cardiac death are limited and may be biased by delays in rhythm recording and selection bias in survivors. As a result, the relative contributions of monomorphic ventricular tachycardia (VT) (cycle length [CL] > 260 ms), monomorphic fast VT (FVT) (CL ≤ 260 ms), and polymorphic VT (PMVT)/ventricular fibrillation (VF) have not been well characterized nor compared in patients with and without prior arrhythmic events.
  
  
  METHODS
  A retrospective cohort study of implantable cardioverter-defibrillator (ICD) recipients with primary or secondary implant indications was used to evaluate intracardiac electrograms (EGMs) for the first spontaneous VT/VF resulting in appropriate ICD therapy. EGMs were categorized into VT, FVT, and PMVT/VF based on CL and morphologic criteria.
  
  
  RESULTS
  Of 616 implants, 145 patients (58 [40%] primary indications) received appropriate ICD therapy for VT/VF over mean follow-up of 3.8 ± 3.2 years. Primary implants had more diabetes (28% vs 12%; P = 0.02) and less antiarrhythmic use (15% vs 33%; P = 0.02). In those patients with spontaneous arrhythmia, PMVT/VF occurred in 20.7% of primary versus 21.8% of secondary implants, FVT in 19.0% versus 21.8%, and VT in 60.3% versus 56.4%, respectively (P = 0.88). Spontaneous VT CL was similar regardless of implant indication (284 ± 56 [primary] vs 286 ± 67 ms [secondary]; P = 0.92).
  
  
  CONCLUSIONS
  Monomorphic VT is the most common cause of appropriate ICD therapy regardless of implant indication. These results provide insight into the mechanisms of sudden cardiac death and have implications for the use of interventions designed to limit ICD shocks.
authors.affiliation: Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
authors.forename: Amin
authors.initials: A
authors.lastname: Manuchehry
authors.forename: Kartik
authors.initials: K
authors.lastname: Agusala
authors.forename: Mauro
authors.initials: M
authors.lastname: Montevecchi
authors.forename: Alan
authors.initials: A
authors.lastname: Kadish
authors.forename: Rod
authors.initials: R
authors.lastname: Passman
mesh_terms: D016009:Chi-Square Distribution; D015897:Comorbidity; D016757:Death, Sudden, Cardiac / Q000517:prevention & control*; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011322:Primary Prevention; D012008:Recurrence; D012189:Retrospective Studies; D055502:Secondary Prevention; D017180:Tachycardia, Ventricular / Q000503:physiopathology*; D014693:Ventricular Fibrillation / Q000503:physiopathology*