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  • Unexpected death occurring within an hour of onset of symptoms.
  • Primary electrical mechanisms include ventricular fibrillation, ventricular tachycardia, asystole, and pulseless electrical activity.

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Each year in the United States, more than 250,000 individuals die suddenly of some form of cardiovascular disease. Because of the many advances made during the past 30 years in clinicians’ ability to identify and modify the risk factors associated with sudden death, to resuscitate victims of cardiac arrest, and to prescribe specific antiarrhythmic therapy to prevent recurrences, age-adjusted sudden death mortality rates have declined dramatically. However, the number of elderly individuals in the population has increased, and sudden cardiac arrest remains an important problem.

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In a simplistic sense, any death can be considered sudden. For general clinical purposes, however, the term “sudden cardiac death” is usually reserved for those deaths in which the patient had stable cardiac function until the terminal event, with death occurring within a short time (often defined as less than 1 hour) of the onset of symptoms. Some experts prefer the term “instantaneous death,” namely, death with immediate collapse without preceding symptoms. Instantaneous death is usually assumed to be due to primary arrhythmia, but other catastrophic events, such as a massive pulmonary embolism, the rupture of an aortic aneurysm, or a stroke, can also cause instantaneous death. It is also important to note that not all arrhythmic deaths are sudden. For example, a patient who is resuscitated from a cardiac arrest may die days or weeks later from complications of the arrest. This death would be due to an arrhythmia but would not meet the standard definition for instantaneous or sudden death.

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Effective evaluation and treatment of patients at risk for cardiac arrest and sudden death require an understanding of the responsible pathophysiologic mechanisms, the strategies proposed for primary prevention, the techniques and results of resuscitation, and the treatment modalities for secondary prevention in survivors of an initial episode.

Rosamond W et al; American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Heart disease and stroke statistics—2008 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation. 2008 Jan 29;117(4):e25–146.  [PubMed: 18086926]

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A number of different electrophysiologic mechanisms may be responsible for sudden cardiac death. When ambulatory electrocardiographic (ECG) recordings from the time of an out-of-hospital cardiac arrest are examined, ventricular fibrillation and rapid ventricular tachycardia are the most commonly documented initial arrhythmias. Bradyarrhythmias, including atrioventricular block, asystole, or electromechanical dissociation, are also observed. The prevalence of these latter arrhythmias is higher in the setting of progressive and advanced underlying heart disease; in the elderly; and in patients whose sudden death is precipitated by an acute catastrophe, such as a pulmonary embolism, an acute myocardial infarction, rupture of a major vessel, or a major neurologic insult. The focus of this chapter will be principally those sudden deaths for which an arrhythmia was the primary cause.

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