Background-Current versions of automated external defibrillators (AEDs) require frequent stopping of chest compression for rhythm analyses and capacity charging. The present study was undertaken to evaluate the effects of these interruptions during the operation of AEDs. Methods and Results-Ventricular fibrillation was electrically induced in 20 male domestic swine weighing between 37. 5 and 43 kg that were untreated for 7 minutes before CPR was started. Defibrillation was attempted with up to 3 sequential 150-J biphasic shocks, but each was preceded by 3-, 10-, 15-, or 20-second interruptions of chest compression. The interruptions corresponded to those that were mandated by commercially marketed AEDs for rhythm analyses and capacitor charge. The sequence of up to 3 electrical shocks and delays were repeated at 1-minute intervals until the animals were successfully resuscitated or for a total of 15 minutes. Spontaneous circulation was restored in each of 5 animals in which precordial compression was delayed for 3 seconds before the delivery of the first and subsequent shocks but in none of the animals in which the delay was Ͼ15 seconds before the delivery of the first and subsequent shocks. Longer intervals of CPR interventions were required, and there was correspondingly greater failure of resuscitation in close relationship to increasing delays. The durations of interruptions were inversely related to the durations of subthreshold levels of coronary perfusion pressure. Postresuscitation arterial pressure and left ventricular ejection fraction were more severely impaired with increasing delays. Key Words: cardiopulmonary resuscitation Ⅲ fibrillation Ⅲ defibrillation Ⅲ compression Ⅲ myocardium A utomated external defibrillators (AEDs) provide the single best option for improving the currently poor outcomes of out-of-hospital cardiopulmonary resuscitation (CPR) performed by bystanders. Fundamental to the operation of AEDs is the capability of automated ECG rhythm analyses, during which CPR is interrupted. Previous experimental studies had demonstrated both decreased resuscitability and greater impairment of postresuscitation myocardial function and survival when precordial compression was interrupted for 20 seconds in small animals. 1-3 Because current versions of AEDs prompt "hands-off" intervals of Ͼ10 seconds for rhythm analyses before advising the rescuer to deliver an electrical shock, as documented below, we hypothesized that such interruptions would adversely affect the outcomes of CPR. Conclusions-InterruptionsThreshold levels of coronary perfusion pressure (CPP) are identified as major determinants of successful cardiac resuscitation. 4 -7 Interruptions in precordial compression predictably result in declines in CPP and therefore delays in restoring threshold values of CPP. 5,6 We therefore anticipated that increasing the length of intervals of interrupted chest compression results in corresponding decreases in the success of CPR and greater severity of postresuscitation myocardial dysfunction.These co...

Lower-energy biphasic waveform shocks were as effective as conventional higher energy monophasic waveform shocks for restoration of spontaneous circulation after 4 and 7 min of untreated VF. Significantly better postresuscitation myocardial function was observed after biphasic waveform defibrillation.

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Cardiac output and PetCO2 were highly related in diverse experimental models of circulatory shock in which cardiac output was reduced by >40% of baseline values. Therefore, measurement of PetCO2 is a noninvasive alternative for continuous assessment of cardiac output during low-flow circulatory shock states of diverse causes.