• Valerie J De Maio, Ian G Stiell, George A Wells, Daniel W Spaite, and OPALS Study Group.
• Department of Epidemiology and Community Medicine; Ottawa Hospital Loeb Health Research Institute.
• Ann Emerg Med. 2000 Feb 1; 35 (2): 138-146.

Study ObjectiveThe Utstein guidelines recommend that emergency medical services (EMS)-witnessed cardiac arrests be considered separately from other out-of-hospital cardiac arrest cases. The objective of this study was to assess EMS-witnessed cardiac arrest and to determine predictors of survival in this group.MethodsThis prospective cohort included all adults with an EMS-witnessed cardiac arrest in the 21 communities of the Ontario Prehospital Advanced Life Support (OPALS) study. Systems provided a basic life support with defibrillation (BLS-D) level of care. Case and survival definitions followed the Utstein style. Descriptive and univariate methods (χ2 and t test) were used to characterize EMS-witnessed cardiac arrest. Multivariate logistic regression was undertaken to assess predictors of survival to hospital discharge.ResultsFrom January 1, 1991, to December 31, 1996, there were 9,072 cardiac arrest cases in the study communities. Of these, 610 (6.7%) were EMS-witnessed. The majority had preexisting cardiac or respiratory disease (81.5%) and experienced prodromal symptoms before EMS personnel arrived (91.4%). An initial rhythm of pulseless electrical activity was present in 50.1% of the patients, ventricular fibrillation/ventricular tachycardia in 34.2%, and asystole in 15.7%. Survival to discharge was 12.6%. Multivariate analysis identified the following as independent predictors of survival (odds ratio with 95% confidence intervals [CIs]): nitroglycerin use before EMS arrival: 2.3 (95% CI 1.2 to 4.5), prodromal symptoms of chest pain: 2.5 (95% CI 1.4 to 4.5) or dyspnea: 0.5 (95% CI 0.3 to 1.0), and unconsciousness on EMS arrival: 0.5 (95% CI 0.2 to 0.9). Patients with chest pain were more likely than dyspneic patients to experience ventricular fibrillation/ventricular tachycardia (62% versus 17%, P <.0001), and were 5 times more likely to survive (30.6% versus 6.3%, P <.0001).ConclusionEMS-witnessed cases are clearly an important subset of out-of-hospital cardiac arrest and are characterized by 2 distinct symptom groups: chest pain and dyspnea. These symptoms are important predictors of survival and may also help determine underlying mechanisms before patient collapse. A later phase of the OPALS study will prospectively evaluate the impact of out-of-hospital advanced life support on the survival of victims of EMS-witnessed cardiac arrest. [De Maio VJ, Stiell IG, Wells GA, Spaite DW, for the OPALS Study Group. Cardiac arrest witnessed by emergency medical services personnel: descriptive epidemiology, prodromal symptoms, and predictors of survival. Ann Emerg Med. February 2000;35:138-146.].Copyright © 2000 American College of Emergency Physicians. Published by Elsevier Inc. All rights reserved.

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