Biphasic shocks compared with monophasic damped sine wave shocks for direct ventricular defibrillation during open heart surgery.
BACKGROUND
Biphasic waveform shocks are more effective than monophasic shocks for transchest ventricular defibrillation, atrial cardioversion, and defibrillation with implantable defibrillators but have not been studied for open chest, intraoperative defibrillation. This prospective, blinded, randomized clinical study compares biphasic and monophasic shock effectiveness and establishes intraoperative energy dose-response curves.


METHODS
Patients undergoing cardiothoracic surgery with bypass cardioplegia were randomly assigned to the monophasic or biphasic shock group. Ventricular fibrillation occurring after aortic clamp removal was treated with escalating energies of 2, 5, 7, 10, and 20 J until defibrillation occurred. If ventricular fibrillation persisted, a 20-J crossover shock of the other waveform was used.


RESULTS
Cumulative defibrillation success at 5 J, the primary end point of the study, was higher in the biphasic group than in the monophasic group (25 of 50 vs. 9 of 41 defibrillated; P = 0.011). In addition, the biphasic group required lower threshold energy (6.8 vs. 11.0 J; P = 0.003), less cumulative energy (12.6 vs. 23.4 J; P = 0.002), and fewer shocks (2.5 vs. 3.5; P = 0.002). Crossover-shock effectiveness did not differ between groups. Dose-response curves show biphasic shocks to have higher cumulative success rates at all energies tested.


CONCLUSIONS
Biphasic shocks are substantially more effective than monophasic shocks for direct defibrillation. The dose-response curve guides selection of first-shock energy for traditional step-up protocols. Starting at 5 J optimizes for lowest threshold and cumulative energy, whereas 10 or 20 J optimizes for more rapid defibrillation and fewer shocks.
Schwarz
Birgit
B
Department of Anesthesiology and Critical Care Medicine, University of Innsbruck, Austria. birgit.schwarz@uibk.ac.uk
Bowdle
T Andrew
TA
Jett
G Kimble
GK
Mair
Peter
P
Lindner
Karl H
KH
Aldea
Gabriel S
GS
Lazzara
Robert G
RG
O'Grady
Sharon G
SG
Schmitt
Paul W
PW
Walker
Robert G
RG
Chapman
Fred W
FW
Tacker
Willis A
WA
D000328:Adult; D000368:Aged; D006348:Cardiac Surgical Procedures; D001026:Coronary Artery Bypass / Q000379:methods*; D017548:Echocardiography, Transesophageal; D004554:Electric Countershock / Q000379:methods; D004573:Electrolytes / Q000097:blood; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011446:Prospective Studies; D014693:Ventricular Fibrillation / Q000601:surgery*
D004573:Electrolytes; D010100:Oxygen