A model of survival following pre-hospital cardiac arrest based on the Victorian Ambulance Cardiac Arrest Register

Summary

Aims

This study describes the epidemiology of sudden cardiac arrest patients in Victoria, Australia, as captured via the Victorian Ambulance Cardiac Arrest Register (VACAR). We used the VACAR data to construct a new model of out-of-hospital cardiac arrest (OHCA), which was specified in accordance with observed trends.

Patients

All cases of cardiac arrest in Victoria that were attended by Victorian ambulance services during the period of 2002–2005.

Results

Overall survival to hospital discharge was 3.8% among 18,827 cases of OHCA. Survival was 15.7% among 1726 bystander witnessed, adult cardiac arrests of presumed cardiac aetiology, presenting in ventricular fibrillation or ventricular tachycardia (VF/VT), where resuscitation was attempted. In multivariate logistic regression analysis, bystander CPR, cardiac arrest (CA) location, response time, age and sex were predictors of VF/VT, which, in turn, was a strong predictor of survival. The same factors that affected VF/VT made an additional contribution to survival. However, for bystander CPR, CA location and response time this additional contribution was limited to VF/VT patients only. There was no detectable association between survival and age younger than 60 years or response time over 15 min.

Conclusion

The new model accounts for relationships among predictors of survival. These relationships indicate that interventions such as reduced response times and bystander CPR act in multiple ways to improve survival.

Introduction

Cardiovascular disease is a major cause of death in Australia, where it accounts for 37.2% of all deaths.¹ The majority of these deaths occur outside the hospital and present as sudden cardiac arrest. Without medical intervention, out-of-hospital cardiac arrest (OHCA) has a grave prognosis. A rapid delivery of treatment by emergency medical services (EMS) leads to a marked improvement in survival. In a recent cardiocerebral resuscitation trial 57% of VF/VT patients survived to hospital discharge.² CA is the only clinical condition in which EMS interventions have been clearly documented to improve survival.3, 4 For this reason it has been used as a benchmark for comparing different EMS systems. In this article we describe Victorian survival outcomes for OHCA patients and compare them with recently reported outcomes from other EMS services.

In previous studies, a number of factors were found to be consistently associated with survival following OHCA. These included rapid ambulance response times, the provision of bystander CPR, an initial cardiac rhythm of VF/VT, a public CA location, and the patient's age and sex.5, 6, 7, 8, 9, 10, 11, 12, 13 Several studies quantified the contributions of predictive factors to survival using multivariate statistical analyses, however, no single statistical model accounted for the contributions of all these factors to survival or for relationships among them.

The Victorian Ambulance Cardiac Arrest Registry (VACAR) is one of the largest CA registries in the world. Information from every incident of OHCA, which was attended by ambulance, in the Australian state of Victoria, is kept in the Victorian Ambulance Cardiac Arrest Register (VACAR). Within the 4-year period of this study (2002–2005), there were 18,827 cases of OHCA in Victoria. The large size of the registry allowed sufficient statistical power to construct a model, which takes into account the effect of relationships among predictor variables on OHCA survival. The relatively short 4-year time frame was another strength of this study. It minimized the impact that demographic changes or changes in EMS procedure could have on CA outcomes over time.