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The annual incidence of OHCA in the United States is estimated between 166,000 and 450,000 cases [59–10]. The reported incidence varies with the source of the data and definitions used. Precise epidemiological information is limited because the Centers for Disease Control and Prevention does not consider OHCA a reportable disease [11]. The rate of OHCA disability adjusted life years is 1347 per 100,000 population, which ranks third in the United States behind ischemic heart disease and low back and neck pain [12].

Many cardiac arrests are due to ventricular fibrillation (VF) or ventricular tachycardia (VT), but the proportion remaining in shockable rhythms on EMS arrival varies with the time from collapse to initial assessment. Studies based on patients who are hospitalized report shockable rhythms in about 75% of cases, whereas EMS studies report figures ranging from 24% to 60% [413–18]. EMS data suggest that the rate of out‐of‐hospital VF/VT may be decreasing, but the overall incidence of OHCA is not [19–22]. However, studies with rhythms recorded by on‐site defibrillators continue to identify VF/VT as the most common initial rhythm. VF/VT was the presenting rhythm in 61% of arrests in the casino trial and 59% of the patients in the PAD trial [23, 24].

Figure 12.1 Contributors to cardiac arrest survival. While the first links of cardiac arrest care (early 9‐1‐1, early bystander CPR, and early defibrillation) contribute to cardiac arrest survival, ALS care does not.

Source: Stiell IG, Wells GA, Field B, et al. Advanced cardiac life support in out‐of‐hospital cardiac arrest. N Engl J Med. 2004; 351:647–56. © 2004 Massachusetts Medical Society. All rights reserved.

The average survival to hospital discharge after OHCA is estimated to be between 5% and 10%, but reported OHCA survival rates also vary widely [4,25–29]. There are likely several reasons for this, including differing denominators, varying definitions of survival, and possibly true regional differences [24]. In CARES, which comprises more than 1,800 EMS agencies covering a catchment area of nearly 152 million people, an eight‐fold difference in survival (2.5–21.1%) was found between sites with at least 150 cardiac arrests annually. Cases witnessed by bystanders and presenting with shockable rhythms also had an eight‐fold difference in survival (7.7–64%), and rates of bystander CPR had a five‐fold difference (14.6–77.8%) [6].