title: Effect of shock polarity on biphasic defibrillation thresholds using an active pectoral lead system.
abstract: BACKGROUND
  The downsizing of implantable defibrillator pulse generators has made pectoral placement routine. A further reduction of defibrillation thresholds (DFTs) may simplify implantation defibrillation testing and allow for smaller, lower output pulse generators while maintaining an adequate defibrillation safety margin. One factor that may affect defibrillation efficacy is shock polarity.
  
  
  RESULTS
  Sixty consecutive patients undergoing dual-coil, active left pectoral defibrillator implantation were evaluated. Paired, biphasic DFTs were measured in normal (RV apex = cathode) and reverse (RV apex = anode) polarity with order of testing randomized. Reverse polarity conferred a 15% reduction of mean DFTs (8.5 +/- 5.0 J normal, 7.2 +/- 4.6 J reverse polarity, P = 0.02). The effect of polarity appeared most pronounced among the patients with a high DFT (> or = 15 J) resulting in a 31% reduction with reverse polarity (16.7 +/- 2.5 J normal, 11.5 +/- 5.9 J reverse, P = 0.03).
  
  
  CONCLUSIONS
  Reversing shock polarity results in significantly lower biphasic DFTs with an active pectoral lead system, particularly in the subgroup of patients with a high normal polarity threshold. Reversing polarity in these patients may simplify acute defibrillation testing and allow for lower output devices.
authors.affiliation: Department of Medicine, University of Maryland, Baltimore 21201, USA.
authors.forename: M R
authors.initials: MR
authors.lastname: Olsovsky
authors.forename: S R
authors.initials: SR
authors.lastname: Shorofsky
authors.forename: M R
authors.initials: MR
authors.lastname: Gold
mesh_terms: D001145:Arrhythmias, Cardiac / Q000517:prevention & control*; D017147:Defibrillators, Implantable; D004554:Electric Countershock / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies