Incidence of SCD SCA and its most common consequence, SCD, constitute major public health problems, account- ing for approximately 50% of all cardiovascular with at least 25% being first symp- tomatic cardiac events.S2.2.2-1,S2.2.2-40,S2.2.2-41 In addition, analyses of the magnitude of SCD are limited, in part because of the broad range of estimates of the risk based on different epidemiological methods.S2.2.2-42 During the past 20 to 30 years, SCD accounted for in the United States, with a range of <170 000 to >450 000, depending on epidemiological methods, data sources, and inclusion criteria.S2.2.2-41,S2.2.2-43 The lowest of these extremes came from national extrapo- lation of data from specific local programs, while the highest rates included noncardiac causes of sudden death such as pulmonary embolism or intracranial bleeding. The mid-range numbers were largely based CLINICAL STATEMENTS AND GUIDELINES on death certificate studies that required a code inclu- sive of ischemic heart disease. The 2017 update of cardiovascular statistics from the AHA estimated the total annual burden of out- of-hospital cardiac arrest at 356500.S2.2.2-44 An ad- ditional 209000 in-hospital cardiac arrests occur Among the out-of-hospital cardiac arrest group, approximately 357000 events trigger emergency rescue response, with 97% occurring in adults >18 years of age. The survival statistics for out-of-hospital cardiac ar- rest remain disappointing, with an estimated 10% overall survival rate.S2.2.2-44 Among the subgroup of 70% of out-of-hospital cardiac arrests that occur in the home, survival is 6%. 