title: Shortening the second phase duration of biphasic shocks: effects of class III antiarrhythmic drugs on defibrillation efficacy in humans.
abstract: BACKGROUND
  The specific waveform providing optimal defibrillation threshold (DFT) is unknown. We compared the defibrillation efficacy of biphasic pulses with second phases (P2) of 2 and 5 msec in a randomized prospective clinical study.
  
  
  RESULTS
  Intraoperative DFTs of 62 patients (age 54 +/- 13 years; ejection fraction 43% +/- 17%; amiodarone 47%, d,l-sotalol 13%) were determined in random order using a binary search protocol. Anodal shocks of 60% tilt first phases (P1) and P2 of 2 msec/5 msec were delivered from two 100-microF capacitors between the right ventricular electrode and the test housing of a Phylax 06/XM device. Mean DFT was significantly lower using the shorter P2 (9.5 +/- 4.5 J vs 11.3 +/- 5.2 J; P < 0.0001). According to subgroup analysis, the effect of changing P2 duration was only influenced by antiarrhythmic treatment. DFT decreased markedly using the shorter P2 in patients treated with amiodarone (10.7 +/- 4.9 J vs 13.4 +/- 5.6 J; P < 0.00001) or d,l-sotalol (6.1 +/- 3.3 J vs 9.1 +/- 4.6 J; P < 0.05). The difference in patients not treated with Class III drugs was found to be insignificant. Chronic amiodarone treatment increased DFT only when the longer P2 was used.
  
  
  CONCLUSIONS
  Biphasic shocks with shorter P2 should be used in patients undergoing Class III antiarrhythmic treatment.
authors.affiliation: Department of Cardiovascular Surgery, Semmelweis University Budapest, Hungary. merkbel@hermes.sote.hu
authors.forename: B
authors.initials: B
authors.lastname: Merkely
authors.forename: A
authors.initials: A
authors.lastname: Lubiński
authors.forename: O
authors.initials: O
authors.lastname: Kiss
authors.forename: F
authors.initials: F
authors.lastname: Horkay
authors.forename: E
authors.initials: E
authors.lastname: Lewicka-Nowak
authors.forename: M
authors.initials: M
authors.lastname: Kempa
authors.forename: Z
authors.initials: Z
authors.lastname: Szabolcs
authors.forename: G
authors.initials: G
authors.lastname: Nyikos
authors.forename: E
authors.initials: E
authors.lastname: Zima
authors.forename: G
authors.initials: G
authors.lastname: Swiatecka
authors.forename: L
authors.initials: L
authors.lastname: Gellér
mesh_terms: D000328:Adult; D000368:Aged; D000638:Amiodarone / Q000627:therapeutic use*; D000889:Anti-Arrhythmia Agents / Q000145:classification / Q000627:therapeutic use*; D004554:Electric Countershock / Q000379:methods / Q000592:standards; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013015:Sotalol / Q000627:therapeutic use*; D013997:Time Factors
chemical_list: D000889:Anti-Arrhythmia Agents; D013015:Sotalol; D000638:Amiodarone