DEFINITION OF SUDDEN CARDIAC DEATH
Sudden cardiac death (SCD) describes an unexpected natural death resulting from a cardiac cause within a short time period after the onset of symptoms in a person without a prior condition that would appear imminently fatal. It is most often caused by a sustained ventricular tachyarrhythmia (ventricular tachycardia [VT] and ventricular fibrillation [VF]). Although many cardiovascular disorders increase the risk of SCD, the presence of preexisting cardiovascular disease is not necessary, and SCD may be the first manifestation of overt cardiac disease.1,2 Prodromal symptoms, such as palpitations, chest pain, or 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 between onset of symptoms and death, the unexpected nature of the event, and the specific cause of death which, unfortunately, can be difficult to verify in all cases. Recent definitions have focused on time intervals between symptom onset and death of 1 hour or less, which normally identify populations having a 90% or more proportion of arrhythmic death.3,4 However, because 80% of sudden deaths occur in the home environment and up to 40% are unwitnessed, the interval between symptom onset and death, and the cardiac rhythm that precipitated onset of symptoms, are frequently unknown. Therefore, precise measurement of SCD rates is difficult.5,6 For this reason, in some studies, time intervals of up to 24 hours have been used to allow capture of events in persons that were unexpectedly found dead but who were alive and well during the prior day 6,7
SCD accounts for between 180,000 and over 450,000 deaths yearly in the United States, with exact numbers depending on the data source and SCD definition used.1,8,9 When the definition of SCD is restricted to deaths less than 2 hours from onset of symptoms, 12% of all natural deaths are sudden and 88% of these are a result of cardiac disease. In autopsy-based studies, a cardiac etiology of sudden death has been reported in 60% to 70% of sudden death victims.5 More recent data from the United States, Europe, and Asia have demonstrated an incidence of approximately 40 to 100 SCDs per 100,000 persons,6,7,10,11,12,13 with significant geographical variation (Fig. 91–1). The majority of cardiac arrest victims are male, and the average age is > 60 years.6,7,14
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.
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