Sudden cardiac death (SCD) describes the unexpected natural death due to a cardiac cause within a short time period from the onset of symptoms in a person without any prior condition that would appear imminently fatal. It is most often due to a sustained ventricular tachyarrhythmia. Although many cardiovascular disorders increase the risk of SCD, the presence or absence of preexisting cardiovascular disease is not necessary.1 Prodromal symptoms such as palpitations, chest pain, and dyspnea may suggest a cardiovascular etiology such as arrhythmia, ischemia, or congestive heart failure but are not specific. The definition of SCD includes the time interval from onset of the symptoms leading to collapse and then to death, the unexpected nature of the event, and the specific cause of death. Recent definitions have focused on time intervals of 1 hour or less, which normally identify SCD populations having a 90% or more proportion of arrhythmic death.2,3 However, because 80% of sudden deaths occur in the home environment and up to 40% are unwitnessed, the interval between symptoms onset and death is frequently unknown, rendering precise measurement of SCD rates difficult.4,5
SCD accounts for more than 460,000 deaths yearly in the United States, with exact totals depending on the definition used.1,6 When the definition of SCD is restricted to death less than 2 hours from onset of symptoms, 12% of all natural deaths are sudden and 88% of these are due to cardiac disease. In autopsy-based studies, a cardiac etiology of sudden death has been reported in 60% to 70% of sudden death victims.5
The US Centers for Disease Control and Prevention has estimated the SCD incidence per 1000 persons in 1999 to be 2.1 in men and 1.4 in women, with SCD accounting for 63% of all deaths attributed to cardiac disease.6 The average age of cardiac arrest victims is approximately 65 years, and 70% to 80% are men.7 In the United States, several population-based studies have documented an age-adjusted decline in SCD rates of more than 8% over the last 15 years.1 SCD rates in other developed countries are comparable to those in the United States: The World Health Organization reported an annual incidence of SCD of 1.9 per 1000 persons in men and 0.6 in women.8 SCD rates in developing countries are considerably lower, paralleling the rates of ischemic heart disease, the most common substrate for SCD in developed nations (Fig. 49–1).
Sudden cardiac death (SCD) rates by sex and country, ages 35 to 74 years, compiled from death certificates by the World Health Organization, Geneva, 1986. Reproduced with permission from Manolio TA, Furberg CD. Epidemiology of SCD. In: Akhtar M, Myerburg RJ, Ruskin JN, eds. SCD. Baltimore, MD: Williams & Wilkins; 1994:3.