• R J Brison, J R Davidson, J F Dreyer, G Jones, J Maloney, D P Munkley, H M O'Connor, and B H Rowe.
• Division of Emergency Medicine, Queen's University, Kingston, ON.
• CMAJ. 1992 Jul 15;147(2):191-9.

ObjectivesTo describe the patient characteristics, circumstances and community response in cases of out-of-hospital cardiac arrest; to evaluate the effect on survival of the introduction of prehospital defibrillation; and to identify factors that predict survival.DesignPopulation-based before-and-after clinical trial.SettingFive Ontario communities: London, Sudbury, the Greater Niagara region, Kingston and Ottawa.PatientsA consecutive sample of 1510 primary cardiac arrest patients who were transported to hospital by ambulance over 2 years.InterventionThe use of defibrillators by ambulance attendants.Main Outcome MeasuresPatient characteristics (sex and age), circumstances of arrest (place, whether arrest was witnessed and cardiac rhythm), citizen response (whether cardiopulmonary resuscitation [CPR] was started by a bystander, time to access to emergency medical services and time to initiation of CPR), emergency medical services response (ambulance response time, time to initiation of CPR and time to rhythm analysis with defibrillator) and survival rates.Main ResultsA total of 92.1% of the patients were 50 years of age or older, and 68.3% were men. Overall, 79.6% of the arrests occurred in the home. The average ambulance response time for witnessed cases was 7.8 minutes. The overall survival rate was 2.5%. The survival rates before and after defibrillators were introduced were similar, and the general functional outcome of the survivors did not differ significantly between the two phases. Factors predicting survival included patient's age, ambulance response time and whether CPR was started before the ambulance arrived.ConclusionsThe survival rate was lower than expected. The availability of prehospital defibrillation did not affect survival. To improve survival rates after cardiac arrest ambulance response times must be reduced and the frequency of bystander-initiated CPR increased. Once these changes are in place a beneficial effect from advanced manoeuvres such as prehospital defibrillation may be seen.

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