title: Assessment of adequate safety margin using single coupling interval-upper limit of vulnerability test.
abstract: OBJECTIVE
  Upper limit of vulnerability (ULV) testing using T-wave scanning shocks at multiple coupling intervals correlates well with defibrillation threshold (DFT), but remains underutilized in clinical practice. We measured DFT and ULV at a single coupling interval (SCI), with the aim to identify adequate safety margin at a coupling interval that correlates best with DFT.
  
  
  METHODS
  Consecutive patients undergoing implantable cardioverter defibrillator implantation underwent simultaneous SCI-ULV and DFT assessment. Following a drive train of 400 ms, a T-wave-coupled shock was delivered. To minimize shocks, patients were randomized to programmed shock at 20 ms before peak (Group I), at peak (Group II), or 20 ms after peak (Group III) of T wave. An initial T-wave test shock at 9 J was followed by ±2 J shocks, until SCI-ULV was ascertained. Device rescue shocks were programmed at test shock +2 J and +4 J shocks followed by external rescue shock.
  
  
  RESULTS
  There were 200 patients: 66 patients in Group I, 67 patients each in Groups II and III; mean age was 68.9 ± 12.4 years; 75% of patients men, 66% with ischemic heart disease and mean ejection fraction of 27.1 ± 7.1%. Overall, the mean number of ventricular fibrillation induction was 1.39 ± 0.8, mean SCI-ULV energy was 7.97 ± 3.39 J, and mean DFT was 8.68 ± 3.19 J. The correlation between SCI-ULV and DFT improved from Group I to Group III and was best in Group III (r(2) = 0.689). There were no major adverse events.
  
  
  CONCLUSIONS
  SCI-ULV measured 20 ms after the peak of the T wave correlates well with DFT for assessment of adequate safety margin.
authors.affiliation: Sparrow Thoracic and Cardiovascular Institute, Division of Cardiology, Michigan State University, Lansing, Michigan.
authors.forename: Mehul B
authors.initials: MB
authors.lastname: Patel
authors.forename: Khyati
authors.initials: K
authors.lastname: Pandya
authors.forename: Ranjan K
authors.initials: RK
authors.lastname: Thakur
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable / Q000009:adverse effects*; D004056:Differential Threshold; D004869:Equipment Safety / Q000295:instrumentation* / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D018570:Risk Assessment / Q000379:methods*; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000209:etiology* / Q000503:physiopathology* / Q000517:prevention & control
keywords: defibrillation threshold; implantable cardioverter defibrillator; sudden cardiac death; upper limit of vulnerability; ventricular fibrillation