title: Long-term evaluation of the ventricular defibrillation energy requirement.
abstract: BACKGROUND
  Defibrillation energy requirements in patients with nonthoracotomy defibrillators may increase within several months after implantation. However, the stability of the defibrillation energy requirement beyond 1 year has not been reported. The purpose of this study was to characterize the defibrillation energy requirement during 2 years of clinical follow-up.
  
  
  RESULTS
  Thirty-one consecutive patients with a biphasic nonthoracotomy defibrillation system underwent defibrillation energy requirement testing using a step-down technique (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, and 1 J) during defibrillator implantation, and then 24 hours, 2 months, 1 year, and 2 years after implantation. The mean defibrillation energy requirement during these evaluations was 10.9+/-5.5 J, 12.3+/-7.3 J, 11.7+/-5.6 J, 10.2+/-4.0 J, and 11.7+/-7.4 J, respectively (P = 0.4). The defibrillation energy requirement was noted to have increased by 10 J or more after 2 years of follow-up in five patients. In one of these patients, the defibrillation energy requirement was no longer associated with an adequate safety margin, necessitating revision of the defibrillation system. There were no identifiable clinical characteristics that distinguished patients who did and did not develop a 10-J or more increase in the defibrillation energy requirement.
  
  
  CONCLUSIONS
  The mean defibrillation energy requirement does not change significantly after 2 years of biphasic nonthoracotomy defibrillator system implantation. However, approximately 15% of patients develop a 10-J or greater elevation in the defibrillation energy requirement, and 3% may require a defibrillation system revision. Therefore, a yearly evaluation of the defibrillation energy requirement may be appropriate.
authors.affiliation: Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0022, USA.
authors.forename: T
authors.initials: T
authors.lastname: Tokano
authors.forename: F
authors.initials: F
authors.lastname: Pelosi
authors.forename: M
authors.initials: M
authors.lastname: Flemming
authors.forename: L
authors.initials: L
authors.lastname: Horwood
authors.forename: J J
authors.initials: JJ
authors.lastname: Souza
authors.forename: A
authors.initials: A
authors.lastname: Zivin
authors.forename: B P
authors.initials: BP
authors.lastname: Knight
authors.forename: R
authors.initials: R
authors.lastname: Goyal
authors.forename: K C
authors.initials: KC
authors.lastname: Man
authors.forename: F
authors.initials: F
authors.lastname: Morady
authors.forename: S A
authors.initials: SA
authors.lastname: Strickberger
mesh_terms: D017147:Defibrillators, Implantable / Q000592:standards*; D004554:Electric Countershock / Q000295:instrumentation; D004562:Electrocardiography; D004869:Equipment Safety; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D017180:Tachycardia, Ventricular / Q000503:physiopathology / Q000628:therapy*