title: Differences in effects of electrical therapy type for ventricular arrhythmias on mortality in implantable cardioverter-defibrillator patients.
abstract: BACKGROUND
  Implantable cardioverter-defibrillator (ICD) shocks have been associated with an increased risk of death. It is unknown whether this is due to the ventricular arrhythmia (VA) or shocks and whether antitachycardia pacing (ATP) termination can reduce this risk.
  
  
  OBJECTIVE
  The purpose of this study was to determine whether mortality in ICD patients is influenced by the type of therapy (shocks of ATP) delivered.
  
  
  METHODS
  Cox models evaluated effects of baseline characteristics, ventricular tachycardia (VT; <188 bpm), fast VT (FVT; 188-250 bpm), ventricular fibrillation (VF; >250 bpm), and therapy type (shocks or ATP) on mortality among 2135 patients in four trials of ATP to reduce shocks.
  
  
  RESULTS
  Over 10.8 +/- 3.3 months, 24.3% patients received appropriate shocks (50.6%) or ATP only (49.4%), and 6.6% died. Mortality predictors were age (hazard ratio 1.07, 95% confidence interval 1.04-1.08, P <.0001), New York Heart Association class III/IV (3.50 [2.27-5.41]; P <.0001), coronary disease (3.08 [1.31-7.25]; P = .01), and cumulative VA (VT + FVT + VF) episodes shocked (1.20 [1.13, 1.29]; P <.0001). Beta-blockers (0.65, 0.46-0.92; P <.0001) and remote myocardial infarction (0.53, [0.38-0.76] P = .0004) predicted reduced risk. Since 92% of VT and all VF received a single therapy type (ATP and shocks, respectively), the effect of therapy on episode risk could not be established. For FVT (32% shocked, 68% ATP), episode and therapy effects could be uncoupled; ATP-terminated FVT did not increase episode mortality risk, whereas shocked FVT increased risk by 32%. Survival rates were highest among patients with no VA (93.8%) of ATP-only (94.7%) and lowest for shocked patients (88.4%). Monthly episode rates were 80% higher among shocked versus ATP-only patients.
  
  
  CONCLUSIONS
  Shocked VA episodes are associated with increased mortality risk. Shocked patients have substantially higher VA episode burden and poorer survival compared with ATP-only-treated patients.
authors.affiliation: Cardiac Arrhythmia Service, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA. mosweeney@partners.org
authors.forename: Michael O
authors.initials: MO
authors.lastname: Sweeney
authors.forename: Lou
authors.initials: L
authors.lastname: Sherfesee
authors.forename: Paul J
authors.initials: PJ
authors.lastname: DeGroot
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wathen
authors.forename: Bruce L
authors.initials: BL
authors.lastname: Wilkoff
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial / Q000379:methods* / Q000401:mortality; D017147:Defibrillators, Implantable; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D017180:Tachycardia, Ventricular / Q000401:mortality* / Q000628:therapy*; D014693:Ventricular Fibrillation / Q000401:mortality* / Q000628:therapy*