title: Defibrillation threshold testing: is it really necessary at the time of implantable cardioverter-defibrillator insertion?
abstract: OBJECTIVE
  The purpose of this study was to (1) determine how often implantable cardioverter-defibrillator (ICD) system modifications were needed to obtain an adequate safety margin for defibrillation, (2) identify how often and for what indications defibrillation threshold (DFT) testing was not performed, and (3) identify factors predicting the need for modification.
  
  
  BACKGROUND
  Ventricular fibrillation (VF) typically is induced at the time of ICD insertion. Although DFT testing often is minimized, a safety margin of 10 J has been utilized as a standard of care. However, current devices offer technology such as biphasic waveforms and high outputs, and the need for testing has been questioned.
  
  
  METHODS
  We reviewed the records of the last 1,139 patients undergoing initial ICD placement, generator replacement, or revision.
  
  
  RESULTS
  Seventy-one patients (6.2%) were identified as having an unacceptably high DFT (<10 J safety margin) requiring intervention, and some required >1 modification. Use of a high-output device alone was not enough to obtain an adequate DFT in 48% (34/71) of patients who required modifications (3% of the total population). No arrhythmia inductions were performed in 54 patients (4.7%) because of well-defined clinical conditions. Patients who required system modification had a lower ejection fraction, were younger, were less likely to have coronary artery disease, were more likely to be undergoing upgrade/generator replacement, and were more likely to be taking amiodarone. Long-term mortality was not different between the group of patients who required modification compared with those who did not (17% vs 20%, P = NS).
  
  
  CONCLUSIONS
  Routine VF induction and documentation of effective defibrillation still remains a reasonable part of ICD placement because an inadequate safety margin may occur in >6% of patients. The incidence of patients who were inappropriate for testing based on well-defined clinical conditions is small (<5%) in this unselected large series. Although some clinical features may predict the need for system modification, additional studies are needed to better define "acceptable efficacy" of ICDs in preventing sudden death prior to altering these standards in selected patients.
authors.affiliation: University of Pennsylvania Health System, Philadelphia, Pennsylvania 19104, USA. andrea.russo@uphs.upenn.edu
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Russo
authors.forename: William
authors.initials: W
authors.lastname: Sauer
authors.forename: Edward P
authors.initials: EP
authors.lastname: Gerstenfeld
authors.forename: Henry H
authors.initials: HH
authors.lastname: Hsia
authors.forename: David
authors.initials: D
authors.lastname: Lin
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Cooper
authors.forename: Sanjay
authors.initials: S
authors.lastname: Dixit
authors.forename: Ralph J
authors.initials: RJ
authors.lastname: Verdino
authors.forename: Hemal M
authors.initials: HM
authors.lastname: Nayak
authors.forename: David J
authors.initials: DJ
authors.lastname: Callans
authors.forename: Vickas
authors.initials: V
authors.lastname: Patel
authors.forename: Francis E
authors.initials: FE
authors.lastname: Marchlinski
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial; D016757:Death, Sudden, Cardiac / Q000517:prevention & control; D017147:Defibrillators, Implantable / Q000592:standards*; D004554:Electric Countershock / Q000295:instrumentation; D005260:Female; D006331:Heart Diseases / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012189:Retrospective Studies; D012449:Safety; D012684:Sensory Thresholds; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000517:prevention & control*