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The chain of survival refers to a series of actions intended to maximize the chances of survival following 
cardiac arrest. The six links in the chain of survival are activation of the emergency response system, 
early CPR, early defibrillation, rapid delivery of EMS care, post-resuscitative care, and recovery. For every 
minute of cardiac arrest without CPR or defibrillation, a patient’s chance of survival falls by 7-10%.2 This 
means that the community and bystander response are integral to survival from OHCA. 
Chain of Survival
The first step in the chain of survival is recognition of cardiac arrest and activation of the emergency 
response system by calling 911. The next crucial time period is the interval between call receipt at the 
dispatch center to arrival on scene, or “response time”. The distribution of First Responder and EMS 
response times are presented in Figure 10.
Response and treatment times are supplemental elements in CARES; however, participants are 
encouraged to track response times to identify local improvement opportunities. Records with missing 
response times (15.2%) as well as those that were witnessed by a 911 Responder (12.6%), have been 
excluded from response time analyses.
In 2025, median response time by First Responders was 6.4 minutes (interquartile range [IQR]: 4.9 - 8.3 
minutes) and median response time by EMS was 7.6 minutes (IQR: 5.6 - 10.4 minutes). First Responders 
arrived on scene in ≤ 5 minutes for 27.5% of arrests, while EMS arrived on scene in ≤ 9 minutes for 64.9% 
of arrests.
Activation of the Emergency Response System
2. Larsen MP, Eisenberg MS, Cummins RO, Hallstrom AP. Predicting survival from out-of-hospital cardiac arrest: a graphic model. 
Ann Emerg Med. 22:1652–1658.
Figure 10. Distribution of First Responder and EMS response times (time interval from 911 call to arrival on scene).

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