ObjectivesTo identify a method for predicting the success or failure of a defibrillatory shock such as to avoid potentially detrimental interruptions of cardiopulmonary resuscitation (CPR). Such a method would also guide more optimal programming of automated external defibrillators.DesignProspective, observational animal study.SettingMedical research laboratory in a university-affiliated research and educational foundation.SubjectsDomestic pigs.InterventionsVentricular fibrillation (VF) was electrically induced in 66 domestic pigs. After an interval of between 3 and 5 mins of untreated VF, precordial compression was begun. Electrocardiographic lead 2 was monitored and artifacts produced during precordial compression were removed by digital filtering.Measurements and Main ResultsIn the derivation study, electrical defibrillation restored spontaneous circulation in 30 of the 66 animals. Successfully resuscitated animals had significantly greater coronary perfusion pressure, maximum VF amplitude, mean VF amplitude, and dominant VF frequency. No animals were resuscitated if the coronary perfusion pressure was <8 mm Hg, maximum amplitude was <0.48 mV, mean amplitude was <0.25 mV, or dominant frequency <9.9 Hz independently of the duration of untreated VF. When mean amplitude and dominant frequency were combined, the predictability was further improved. In an additional validation study of 14 animals, consecutive defibrillations were uniformly unsuccessful if the combination of mean amplitude and dominant frequency did not exceed the threshold values obtained in derivation study.ConclusionMean VF amplitude alone or in combination with dominant frequency of VF was expressed as a numerical score. It served as an objective noninvasive measurement on a par with that of coronary perfusion pressure for predicting the success of defibrillation. As such, it minimizes the detriment of repetitively interrupting mechanical interventions during CPR for electrical defibrillation when an electrical shock predictably fails to restore an effective rhythm. (Crit Care Med 1999; 27:708-714)