Physio-Control LIFEPAK 20e - Manual (Page 173)

Append
ix B
Clinical Summaries
LIFEPAK 20e Defibrillator/Monitor Operating Instructions B-7
©2006-2013 Physio-Control, Inc.
INTRA-OPERATIVE VENTRICULAR DEFIBRILLATION
Overview
The defibrillation efficacy of the Physio-Control biphasic truncated exponential (BTE) waveform
was compared to the standard monophasic damped sine waveform (MDS) in a prospective,
randomized multi-center study of patients undergoing intra-operative, direct defibrillation for
ventricular fibrillation (VF). A total of 251 adult patients were enrolled in the study; 98 of these
developed VF that was treated with one or more study shocks. Seven patients who did not
satisfy all protocol criteria were excluded from analysis.
Subjects were randomized to receive BTE or MDS shocks from LIFEPAK 12 defibrillator/monitor.
Those who developed VF after removal of the aortic clamp received progressively stronger
shocks of 2, 5, 7, 10 and 20 joules (J) using 2-inch paddles until defibrillation occurred. A 20 J
crossover shock of the alternate waveform was given if VF persisted.
This study showed that these biphasic shocks have higher defibrillation efficacy, requiring fewer
shocks, less threshold energy and less cumulative energy than monophasic damped sine
shocks.
Objectives
The primary objective of the study was to compare the cumulative efficacy of BTE shocks to
MDS shocks at 5 J or less. A triangular sequential design was used to test for a difference
between waveform groups.
The secondary objective was to provide an estimation of the dose response relationship for the
two waveforms that would allow physicians to make well-informed selections of energy doses for
intra-operative defibrillation with biphasic shocks.
Results
Thirty-five male and 15 female subjects were randomized to the BTE group; 34 and 7 to the MDS
group. Mean age was 66 and 68 years, respectively. There were no significant differences
between BTE and MDS treatment groups for cardiac etiology, arrhythmia history, current cardiac
medications, American Society of Anesthesiology (ASA) risk class, left ventricular wall thickness,
cardiopulmonary bypass time, core temperature or blood chemistry values at the time of aortic
clamp removal.
Cumulative defibrillation success at 5 J or less, the primary endpoint of the study, was
significantly higher in the BTE group than in the MDS group (p=0.011). Two of the 91 patients
included in this primary endpoint analysis could not be included in more comprehensive analyses
due to protocol variances that occurred in the shock sequence after the 5 J shock. Thus, the
cumulative success rates for intra-operative defibrillation in the remaining 89 patients are
presented in
Table B-3 and Figure B-2 . These data provide a reasonable estimate of the
expected probability of defibrillation success for a single shock at any given energy level within
the range studied.
Compared to the MDS group, the BTE group required, on average, fewer shocks (2.5 vs. 3.5:
p=0.002), less threshold energy (6.8 J vs. 11.0 J: p=0.003) and less cumulative energy (12.6 J
vs. 23.4 J: p=0.002). There was no significant difference between success rates for BTE versus
MDS crossover shocks.