title: Sudden death in patients with implantable cardioverter defibrillators: the importance of post-shock electromechanical dissociation.
abstract: OBJECTIVE
  The purpose of this study was to determine the mechanisms of sudden death (SD) in patients with ventricular tachyarrhythmias (ventricular tachycardia/ventricular fibrillation [VT/VF]) treated with an implantable cardioverter defibrillator (ICD).
  
  
  BACKGROUND
  Despite ICD therapy, some patients with VT/VF still die suddenly. Optimal ICD use requires determination of the mechanisms of these residual SDs.
  
  
  METHODS
  We reviewed 320 patient deaths during trials of Medtronic transvenous ICD systems (Medtronic Inc., Minneapolis, Minnesota). Sudden deaths were further categorized according to mechanism. Post-shock electromechanical dissociation (EMD) describes a scenario where VT/VF was appropriately detected and treated by an ICD shock that restored a physiologic rhythm, but death still occurred immediately by EMD.
  
  
  RESULTS
  A mode of death could be ascribed for 317 patients-90 (28%) were sudden, 156 (49%) were non-sudden cardiac, and 71 (22%) were noncardiac. A mechanism of SD was proposed for 68 patients-20 (29%) had post-shock EMD, 17 (25%) had VT/VF uncorrected by shocks, 11 (16%) had primary electromechanical dissociation, 9 (13%) had incessant VT/VF, 5 (7%) had VT/VF after their ICD was deactivated or removed, and 6 (9%) had single instances of various other terminal events. Only New York Heart Association functional class independently predicted SD by post-shock EMD.
  
  
  CONCLUSIONS
  The most common mechanism of SD in patients with an ICD is VT/VF treated with an appropriate shock followed by EMD. As this mechanism accounted for 29% of the SDs to which a cause could be ascribed, this mechanism of SD warrants further investigation.
authors.affiliation: Foothills Hospital/University of Calgary, Calgary, Alberta, Canada. brent.mitchell@calgaryhealthregion.ca
authors.forename: L Brent
authors.initials: LB
authors.lastname: Mitchell
authors.forename: Edgar A
authors.initials: EA
authors.lastname: Pineda
authors.forename: Jack L
authors.initials: JL
authors.lastname: Titus
authors.forename: Paulette M
authors.initials: PM
authors.lastname: Bartosch
authors.forename: David G
authors.initials: DG
authors.lastname: Benditt
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002170:Canada / Q000453:epidemiology; D016757:Death, Sudden, Cardiac / Q000453:epidemiology* / Q000209:etiology*; D017147:Defibrillators, Implantable / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D013318:Stroke Volume / Q000502:physiology; D016019:Survival Analysis; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology