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Figure 11. Survival rate by EMS response time and arrest witness status.
Figure 12. Survival rate by EMS response time and arrest witness status, among patients who received bystander CPR.
Figure 11 presents a bivariate analysis of survival to hospital discharge rate by EMS response time 
(measured from call receipt at dispatch center to arrival of the ambulance on scene) for all OHCA patients 
as well as three subsets: bystander witnessed, bystander witnessed VF/VT (Utstein), and unwitnessed. 
Patients with a witnessed VF/VT arrest experienced a significant decrease in survival with increasing EMS 
response time. In contrast, response time had minimal impact on survival among unwitnessed arrests. 
Figure 12 illustrates the interdependence between the links in the chain of survival, by highlighting how 
rapid 911 response and bystander CPR (bCPR) work in tandem to improve patient survival. Bystander CPR 
helps provide critical and timely intervention while 911 vehicles are en route to the scene. By comparing 
the same patient subgroups in Figure 11 and Figure 12, one can observe how survival is elevated when 
bystander CPR is performed.

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