Abstract 243: Time-Dependent Benefit of Biphasic Defibrillators in Patients with Witnessed Out-of-Hospital Cardiac Arrest from VF/Pulseless VT

Background: Biphasic defibrillator is shown to be superior to monophasic one to terminate VF; however, it remains unclear whether biphasic defibrillator improves neurological outcome in patients of witnessed out-of-hospital cardiac arrest (OHCA) from shockable ventricular arrhythmia. Hence we examined that the superiority of biphasic defibrillator in association with the time from the onset to first shock in patients of witnessed OHCA. Methods and Results: We prospectively analyzed the data collected by Japanese official EMS at Ministry of Internal Affairs and Communications in Japan from April 1, 2006 to December 31, 2009. There were 15,040 patients of witnessed OHCA with VF or pulseless VT aged ≥18, and for whom shock was delivered within 30 minutes from the onset. We performed multivariate analysis and found that age, use of biphasic defibrillator, chest compression by bystander, and some other factors predicted better 1-month survival with Glasgow-Pittsburgh cerebral performance category 1 or 2. Shock was delivered using monophasic defibrillator in 3,242 patients (21.6%, monophasic group) and biphasic defibrillator in 11,798 patients (78.4%, biphasic group). The probability of 1-month survival with CPC 1 or 2 was higher in biphasic group than monophasic group when first shock was delivered 6 to 11 minutes after the onset (Figure, *P Conclusions: Biphasic defibrillator improved 1-month survival with favorable neurological outcome in witnessed OHCA from VF/pulseless VT. The beneficial effect was time-dependent and significant when the first shock is delivered 6 to 15 minutes after the witness.