Sudden death from cardiac arrest remains a major public health problem with generally dismal outcomes. Although early defibrillation plays a key role, it is difficult to further reduce the time from a patient’s collapse to defibrillation by emergency medical personnel, and so recent efforts have turned to increasing access to automatic external defibrillators (AEDs) in the community. However, it is unclear whether this strategy of dissemination will actually increase survival rates and in particular the rates of intact neurological survival.
To address this question the authors set-up the observational All-Japan Utstein Registry. This was a prospective, nationwide, population-based registry of out-of-hospital cardiac arrests which included all patients 18 years or older who, between 2005 and 2007, had an out-of-hospital cardiac arrest of cardiac origin, were subsequently treated by EMS personnel, and then transported to medical institutions. The primary outcome measure was the 1-month rate of survival with minimal neurologic impairment as assessed after hospital discharge by a study investigator using the Cerebral Performance Category scale where 1 is good cerebral performance and 4 is a vegetative state (5 is death). During this time period the cumulative number of public access AEDs increased nearly 10-fold in Japan, from 9906 to 88,265, moving from less than 1 per square kilometer of populated land, to 4 or more. The authors consequently divide the cohort longitudinally to try and assess the impact of greater AED availability over time.
During the study period, a total of 312,319 adults who had an out-of-hospital cardiac arrest were included. Of these, 12,631 had ventricular fibrillation (VF), an arrest that was of cardiac origin and that was witnessed by bystanders. In 462 of these patients (3.7%), shocks were administered by laypersons with the use of public-access AEDs, and during the study this proportion increased, from 1.2% to 6.2%, as the number of public-access AEDs increased (P<0.001 for trend). Among all patients who had a bystander-witnessed arrest of cardiac origin and who had VF, 14.4% were alive at 1 month with minimal neurologic impairment whilst among patients who received shocks from public-access AEDs, 31.6% were alive at 1 month with minimal neurologic impairment. With the greater availability of AEDs mean time to shock was reduced from 3.7 to 2.2 minutes, with early defibrillation, regardless of whether given by bystander or emergency-medical-services personnel, associated with a good neurologic outcome after a cardiac arrest with VF (adjusted odds ratio per 1-minute increase in the time to administration of shock, 0.91; 95% confidence interval, 0.89 to 0.92; P<0.001). Finally, survival with minimal neurologic impairment increased from 2.4 to 8.9 per 10 million population in areas where there was less than 1 AED per square kilometer as compared with areas in which there were 4 or more.
In this nationwide, population based study, the provision of AEDs led to tangible improvements in survival with a good functional status from a witnessed VF arrest, from only 0.3% of people at its outset, to over 2% by the end of the study. However in real terms these numbers equate to very few people (less than 150 over the three year period of the study out of a total population of 127 million) and cost-benefit concerns remain. Nonetheless, the study makes a persuasive argument that AEDs in the community are a successful intervention to improve outcomes in VF.