Using geographic information systems to evaluate cardiac arrest survival

Objective. To evaluate cardiac arrest survival using geographical information systems (GIS) methodology. Methods. Patient data were obtained from a fire district Utstein-style adult cardiac arrest registry that also included address data. All incident locations were geocoded and fire station first-due areas were mapped by using the new computer-aided dispatch geographic data. Retrospective assignment of first-due versus second-due fire response unit was done by using a GIS "point-in-polygon" algorithm Survival to hospital admission was the primary outcome measure for incidents responded to by first-due versus second-due apparatus controlling for other potential predictors of survival using logistic regression. Cluster analysis was also performed to evaluate potential areas of high or low rates of survival. Results. There were 461 eligible patients with an average age of 67 ± 17 years, 63% were male, 53% had a witnessed arrest, bystander cardiopulmonary resuscitation was performed in 38%, bystander automatic external defibrillator (AED) Page: 1 was used in 0.01%, ventricular fibrillation or ventricular tachycardia were the presenting rhythms in 44%, the average response time was 5.5 ± 2.1 minutes, and survival to hospital admission was 17%. There was no significant difference in response time between survivors (4.97 minutes) and non-survivors (5.52 minutes), (difference 0.55 minutes, 95%CI -0.08 to 1.18 min). The number of cardiac arrest calls varied from 1 to 49 for each station and the rate of second-due response varied from 0 to 19%. There was a nonsignificant association of survival to hospital admission for the first-due area cohort: odds ratio 0.70, 95% CI 0.38-1.29. Conclusion. GIS is a new methodology for analyzing EMS incident data. It adds a spatial component of analysis to traditional statistical techniques. No spatial difference was found on patient survival in this analysis.