Factors modifying performance of a novel citizen text message alert system in improving survival of out-of-hospital cardiac arrest

Aims: Recently we found that the text message alert system increases survival of sudden out-of-hospital cardiac arrest. The aim of the present study is to explore the contribution of the system to survival specifically in resuscitation settings with prolonged delay of start of resuscitation. Methods and results: Data were used from consecutive patients resuscitated for out-of-hospital cardiac arrest during a two-year period in the Dutch province Limburg. Survival of 291 cases with out-of-hospital cardiac arrest where one or more volunteers attended (Scenario 2) was compared with survival of 131 cases with out-of-hospital cardiac arrest where no volunteers attended and only standard care was given (Scenario 1). Multivariable logistic regression models including terms for interaction between scenario and the covariate coding for resuscitation setting were used to test for effect modification. The highest impact on survival of the alert system was observed in cases of (a) witnessed arrests (odds ratio=2.25; 95% confidence interval: 1.27-4.00; p=0.005); (b) arrests that occurred in the home (odds ratio=2.28; 95% confidence interval: 1.21-4.28; p=0.011); (c) arrival of the ambulance with a delay of 7-10 min (odds ratio=2.63; 95% confidence interval: 1.09-6.35; p=0.032); and (d) arrests at evening/night (odds ratio=3.07; 95% confidence interval: 1.34-7.03; p=0.008). Due to the low sample size, p-values from tests for interaction were non-significant. Conclusion: The contribution of the alert system to survival is most substantial in cases of witnessed arrest, in the home situation, at slightly delayed arrival of the first ambulance and during the evening/night