Potential impact of public access defibrillators on survival after out of hospital cardiopulmonary arrest: retrospective cohort study

OBJECTIVE: To estimate the potential impact of public access defibrillators on overall survival after out of hospital cardiac arrest. DESIGN: Retrospective cohort study using data from an electronic register. A statistical model was used to estimate the effect on survival of placing public access defibrillators at suitable or possibly suitable sites. SETTING: Scottish Ambulance Service. SUBJECTS: Records of all out of hospital cardiac arrests due to heart disease in Scotland in 1991-8. MAIN OUTCOME MEASURES: Observed and predicted survival to discharge from hospital. RESULTS: Of 15 189 arrests, 12 004 (79.0%) occurred in sites not suitable for the location of public access defibrillators, 453 (3.0%) in sites where they may be suitable, and 2732 (18.0%) in suitable sites. Defibrillation was given in 67.9% of arrests that occurred in possibly suitable sites for locating defibrillators and in 72.9% of arrests that occurred in suitable sites. Compared with an actual overall survival of 744 (5.0%), the predicted survival with public access defibrillators ranged from 942 (6.3%) to 959 (6.5%), depending on the assumptions made regarding defibrillator coverage. CONCLUSIONS: The predicted increase in survival from targeted provision of public access defibrillators is less than the increase achievable through expansion of first responder defibrillation to non-ambulance personnel, such as police or firefighters, or of bystander cardiopulmonary resuscitation. Additional resources for wide scale coverage of public access defibrillators are probably not justified by the marginal improvement in survival