Long-term changes in the incidence of out-of-hospital ventricular fibrillation

Aim of the studyTo report the long-term changes in the incidence of out-of-hospital ventricular fibrillation (VF), and also to report concurrent changes in the possible explanatory factors for the change.MethodsThis was a retrospective observational study. All bystander-witnessed out-of-hospital cardiac arrests (with a known initial rhythm) in Helsinki, Finland during 1.1.1994-31.12.2007 were included in the study. High (years 1994-1996) and low (2002-2004) incidence periods for VF were defined and compared.ResultsThere were 3131 bystander-witnessed out-of-hospital cardiac arrests of which 3118 (99.6%) had a known initial rhythm. During 2000-2007 the annual incidence of bystander witnessed ventricular fibrillation (VF) was 11.6 (95% CI 9.7-13.5) per 100,000 inhabitants. In 1994-1996 VF was 1.8 times more likely than in 2002-2004, after adjustment for several patient related factors and EMS related factors. Arrests with cardiac aetiology became less common, as 54.8% arrests had a cardiac cause in 1994-1996 compared to 45.2% in 2002-2004 (p < 0.001). Of cardiac arrests with cardiac aetiology, 60.6% presented with VF in 1994-1996 compared to 45.7% in 2002-2004 (p < 0.001). There were major changes in the possible explanatory factors during the study period.ConclusionThe decline in the incidence of out-of-hospital VF seems to have ended, and the annual incidence of VF has stabilised to 11.6 (95% CI 9.7-13.5) per 100,000 inhabitants. During the period of lower incidence of VF, cardiac aetiology caused fewer arrests, and these arrests did not present with VF as often as previously.