The effects of phase duration on defibrillation success of dual time constant biphasic waveforms.
OBJECTIVE
The effects of first and second phase duration of biphasic waveforms on defibrillation success were evaluated in a guinea pig model of ventricular fibrillation (VF). We hypothesized that waveform duration, and especially the first phase duration, played a main role on defibrillation efficacy in comparison to energy, current and voltage, when a dual time constant biphasic shock was employed.


METHODS
VF was induced and untreated for 5s in 30 male guinea pigs, prior to attempting a single defibrillatory shock with one of 5 defibrillation waveforms which had different durations of the first and second phase. A five step up-down protocol was utilized for determining the defibrillation efficacy. After a 3-min interval, the procedure was repeated. A total of 25 cardiac arrest events and defibrillations were investigated for each animal.


RESULTS
The defibrillation waveforms with an intermediate first phase of 5 ms, yielded the highest defibrillation success (p<0.05). These waveforms also presented significantly lower energy, current and voltage in comparison to waveforms with shorter or longer first phase durations (p<0.001). However, no differences on defibrillation success were observed among waveforms with different second phase durations varying from 1.5 ms to 3.5 ms.


CONCLUSIONS
For dual time constant biphasic waveforms, the first phase duration played a main role on defibrillation success. The intermediate first phase duration of 5 ms, yielded the best defibrillation efficacy compared with shorter or longer first phase durations. While the second phase duration did not affect defibrillation outcomes.
Shan
Yi
Y
Weil Institute of Critical Care Medicine, Rancho Mirage, CA 92270, USA.
Ristagno
Giuseppe
G
Fuller
Marc
M
Sun
Shijie
S
Li
Yongqin
Y
Weil
Max Harry
MH
Russell
James
J
Tang
Wanchun
W
D000818:Animals; D004554:Electric Countershock / Q000379:methods*; D006168:Guinea Pigs; D008297:Male; D013997:Time Factors; D014693:Ventricular Fibrillation / Q000628:therapy*