Sudden cardiac arrest (SCA) and sudden cardiac death (SCD) refer to the sudden cessation of cardiac activity with hemodynamic collapse, typically due to sustained pulseless ventricular tachycardia or ventricular fibrillation. The event is referred to as SCA (or aborted SCD) if an intervention (eg, defibrillation) or spontaneous reversion restores circulation. The event is called SCD if the patient dies. However, the use of SCD to describe both fatal and nonfatal cardiac arrest persists by convention. (See "Overview of sudden cardiac arrest and sudden cardiac death", section on 'Definitions'.)
SCA and SCD occur most commonly in patients with structural heart disease (including previously undiagnosed heart disease), particularly coronary heart disease. SCD in the apparently normal heart (at autopsy) is an uncommon occurrence that is responsible for only 10 to 15 percent of cases of SCD [1,2]. The majority of SCD patients without apparent structural heart disease likely do not actually have "normal" hearts, but our diagnostic tools limit identification of structural or functional derangement. In the past, the etiology of many of these deaths was unknown and deemed "idiopathic." However, more complete evaluation has identified the cause of death as a primary electrical disorder (ie, Long QT or Brugada Syndrome) in many of these patients [1-3]. (See "Pathophysiology and etiology of sudden cardiac arrest".)
SCD in the apparently normal heart will be reviewed here. SCD in patients with heart disease, and the evaluation and options for the management of survivors of SCD, are discussed separately. (See "Overview of sudden cardiac arrest and sudden cardiac death", section on 'Etiology' and "Pathophysiology and etiology of sudden cardiac arrest", section on 'Etiology of SCD' and "Incidence of and risk stratification for sudden cardiac death after acute myocardial infarction" and "Ventricular arrhythmias and sudden cardiac arrest in hypertrophic cardiomyopathy".)
In addition, sudden death may occur from noncardiac causes (eg, trauma, pulmonary embolism seizure), and these topics are discussed separately. (See "Overview of acute pulmonary embolism in adults" and "Sudden unexpected death in epilepsy".)
Based upon a review of death certificates in the United States during 1998 and 1999, sudden cardiac death (SCD) accounted for over 450,000 deaths, which represented 63 percent of cardiac deaths among adults ≥35 years of age . The incidence of SCD is increased six- to tenfold in the presence of clinically recognized heart disease (figure 1); it also increases with age and is two to three times more common in men than women (figure 2) .