title: Improved defibrillation efficacy with an ascending ramp waveform in humans.
abstract: OBJECTIVE
  The purpose of this study was to compare an ascending ramp waveform (RAMP) with a standard, clinically available biphasic truncated exponential waveform (BTE) for defibrillation in humans.
  
  
  BACKGROUND
  In animal studies, RAMP had a lower defibrillation threshold (DFT) than BTE.
  
  
  METHODS
  We studied 63 patients at implantable cardioverter-defibrillator placement using a dual-coil lead and left pectoral active can. The subjects were divided into two groups, one with a 12-ms ascending first phase and one with a 7-ms ascending first phase. Phase 2 of RAMP for both groups was a truncated exponential decay with 65% tilt and reversed polarity. The BTE had a 50% tilt in each phase. DFT and upper limit of vulnerability (ULV) were measured for both waveforms using a binary search protocol.
  
  
  RESULTS
  The patient population was 77% male, with a mean age of 63 +/- 10 years and ejection fraction of 33 +/- 13%. Delivered energy at DFT was lower with the 7-ms RAMP vs BTE (5.4 +/- 2.6 J vs 6.5 +/- 3.4 J; P < .01) but unchanged with the 12-ms RAMP (7.4 +/- 4.5 J vs 7.1 +/- 4.9 J). Maximal voltage at DFT was significantly lower with either RAMP compared to BTE (P < .01). There was a strong correlation between ULV and DFT for both RAMP and BTE (P < .01).
  
  
  CONCLUSIONS
  The 7-ms ascending ramp waveform significantly reduced delivered energy (18%) and voltage (24%) at DFT, whereas the 12-ms RAMP reduced only DFT voltage. This is the first report of a waveform that is superior to a BTE for defibrillation in humans. ULV correlates with DFT for RAMP, supporting the use of ULV testing for implantation of devices.
authors.affiliation: University of Maryland, Division of Cardiology, Baltimore, Maryland 21201, USA. sshorofs@medicine.umaryland.edu
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Shorofsky
authors.forename: Eric
authors.initials: E
authors.lastname: Rashba
authors.forename: William
authors.initials: W
authors.lastname: Havel
authors.forename: Paul
authors.initials: P
authors.lastname: Belk
authors.forename: Paul
authors.initials: P
authors.lastname: Degroot
authors.forename: Charles
authors.initials: C
authors.lastname: Swerdlow
authors.forename: Michael R
authors.initials: MR
authors.lastname: Gold
mesh_terms: D000465:Algorithms; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D017147:Defibrillators, Implantable; D022062:Electrophysiologic Techniques, Cardiac; D004867:Equipment Design; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*