, Volume 1, Issue 3, pp 203-208

Early Out-of-Hospital Experience with an Impedance-Compensating Low-Energy Biphasic Waveform Automatic External Defibrillator

Abstract

Impedance-compensating low-energy biphasic truncated exponential(BTE) waveforms are effective in transthoracic defibrillation ofshort-duration ventricular fibrillation (VF). However, the BTE waveform hasnot been examined in out-of-hospital cardiac arrest (OHCA) with patients inprolonged VF often associated with myocardial ischemia. The objective ofthis study was to evaluate the BTE waveform automatic externaldefibrillator (AED) in the out-of-hospital setting with long-duration VF.AEDs incorporating a 150-J BTE waveform were placed in 12 police squad carsand 4 paramedic-staffed advanced life support ambulances. AEDs were appliedto arrested patients by first-arriving personnel, whether police orparamedics. Data were obtained from PC Data Cards within the AED.Defibrillation was defined as at least transient termination of VF. Tenpatients, 64 ± 14 years, were treated for VF with BTE shocks.Another 8 patients were in nonshockable rhythms and the AEDs,appropriately, did not advise a shock. Five of the 10 VF arrests werewitnessed with a 911 call-to-shock time of 6.6 ± 1.7 minutes. VFdetection and defibrillation occurred in all 10 patients. Spontaneouscirculation was restored in 3 of 5 witnessed arrest patients and 1 survivedto discharge home. Fifty-one VF episodes were converted with 62 shocks. Presenting VF amplitude and rate were 0.43 ± 0.22 (0.13-0.86) mV and232 ± 62 (122-353) beats/min, respectively, and defibrillation wasachieved with the first shock in 7 of 10 patients. Including transientconversions, defibrillation occurred in 42 of 51 VF episodes (82%)with one BTE shock. Shock impedance was 85 ± 10 (39-138) ohms.Delivered energy and peak voltage were 152 ± 2 J and 1754 ±4 V, respectively. The average number of shocks per VF episode was 1.2± 0.5 (1-3). More than one shock was needed in only 9 episodes; nonerequired >3 shocks to defibrillate. Impedance-compensating low-energyBTE waveforms terminated VF in OHCA patients with a conversion rateexceeding that of higher energy monophasic waveforms. VF was terminated inall patients, including those with high impedance.