Sudden cardiac death (SCD) generally refers to an unexpected death from a cardiovascular cause in a person with or without preexisting heart disease. The specificity of this definition varies depending on whether the event was witnessed; however, most studies include cases that are associated with a witnessed collapse, death occurring within 1 hour of an acute change in clinical status, or an unexpected death that occurred within the previous 24 hours. 1–3 Further, sudden cardiac arrest describes SCD cases with resuscitation records or aborted SCD cases in which the individual survived the cardiac arrest. The incidence of SCD in the United States ranges between 180000 and 450000 cases annually. 4 These estimates vary owing to differences in SCD definitions and surveillance methods for case ascertainment. 4, 5 In recent prospective studies using multiple sources in the United States, 6, 7 Netherlands, 8 Ireland, 9 and China, 10 SCD rates range from 50 to 100 per 100 000 in the general population. 3 Despite the need for multiple sources of surveillance to provide a more accurate estimate of SCD incidence, it is clear that the overall burden in the population remains high. Although improvements in primary and secondary prevention have resulted in substantial declines in overall coronary heart disease (CHD) mortality over the past 30 years, 11, 12 SCD rates specifically have declined to a lesser extent. 13–16 SCD still accounts for 50% of all CHD deaths and 15% to 20% of all deaths. 17, 18 For some segments of the population, rates are not decreasing19 and may actually be increasing. 14, 19 As a result, SCD prevention represents a major opportunity to further reduce mortality from CHD.

Despite major advances in cardiopulmonary resuscitation20 and postresuscitation care, survival to hospital discharge after cardiac arrest in major metropolitan centers remains poor. 21 Survival to hospital discharge was recently estimated to be only 7.9% among out-of-hospital cardiac arrests that were treated by emergency medical services personnel. 6 In addition, the majority of SCDs occur at home, often where the event is unwitnessed. 8, 22 As a result, automated external defibrillators, which improve resuscitation rates for witnessed arrests, 21 may have limited effectiveness on reducing overall mortality from SCD. Therefore, substantial reductions in SCD incidence will require effective primary preventive interventions. Since the majority of SCDs occur in the general population, an in-depth understanding of the epidemiology of SCD may lead to possible low-risk interventions that could be applied broadly to populations. In addition, recent data emerging related to the genetics of SCD