Objective: To determine whether survival following out-of-hospital cardiac arrest (OHCA) in Sydney, Australia, improved between 2004-2005 and 2009-2010, and whether there was a change in incidence of OHCA.

Design: Retrospective study using the Ambulance Service of New South Wales and NSW Registry of Births, Deaths and Marriages databases.

Participants and setting: All patients who had an OHCA in the Sydney metropolitan area and who used the Ambulance Service of NSW between June 2009 and May 2010 (2009-2010), and between June 2004 and May 2005 (2004-2005).

Main outcome measures: Survival to 90 days. Other outcome measures included the incidence of OHCA and survival to the day following OHCA, 28 days and 1 year following OHCA. Survival and incidence were also calculated according to initial electrocardiograph rhythm.

Results: Survival to 90 days was 12.3% in 2004-2005 and 10.2% in 2009-2010 (P = 0.015). In 2004-2005, the age-standardised incidence of OHCA was 52.6 events per 100 000 person-years (95% CI, 51.6-53.6 events per 100 000 person-years), and in 2009-2010 it was 48.4 events per 100 000 person-years (95% CI, 46.3-50.4 events per 100 000 person-years). In 2004-2005, the incidence of ventricular fibrillation (VF) was 31.3% (95% CI, 28.4%-33.9%) and in 2009-2010 it was 22.1% (95% CI, 20.0%-24.3%).

Conclusion: There was no improvement in survival following OHCA in Sydney between 2004-2005 and 2009-2010. There has been a decrease in overall survival from OHCA and a decrease in the overall age-standardised incidence of OHCA. The decrease in overall survival may be due to a decline in the incidence of VF.