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  • Sudden cardiac death is near instantaneous death due to underlying cardiac cause and may include arrhythmic and non-arrhythmic causes.

  • Conventional definitions use death certificates, emergency medical systems records, or epidemiologic criteria to define sudden cardiac death, but these methods do not reliably exclude non-arrhythmic causes of sudden death.

  • More recent studies use postmortem investigation to more accurately define sudden arrhythmic death.

  • Sudden cardiac death is primarily intended to specify sudden deaths due to arrhythmic cause, that is, sudden arrhythmic death that is potentially rescuable with a defibrillator.

  • Common underlying etiologies and risk factors for sudden arrhythmic death include coronary artery disease, nonischemic cardiomyopathy, and other structural heart diseases such as left ventricular hypertrophy; primary electrical diseases are a rare cause.

  • Many noncardiac causes may underlie sudden cardiac arrest and sudden deaths, such as neurologic catastrophe, hemorrhage, occult overdose, and pulmonary embolism.


The effective study and prevention of sudden cardiac death is foremost dependent on understanding the pathophysiology of the condition it is intended to represent. As Hinkle and Thaler originally delineated in their classification of cardiac deaths in 1982, the primary mechanism presumed to underlie sudden cardiac deaths is lethal arrhythmia, most commonly ventricular tachycardia or fibrillation but also including heart block and bradyarrhythmias. These lethal arrhythmias usually occur in the setting of underlying chronic cardiovascular disease (eg, ischemic heart disease, cardiomyopathy). Although sudden cardiac death may also result from sudden hemodynamic collapse due to non-arrhythmic cardiac causes such as acute pump failure or tamponade, it is the arrhythmic phenotype that is the focus of interventions that include emergency medical systems resuscitation protocols, automated external defibrillators, or in high-risk populations, implantable cardioverter-defibrillators (ICD).

Investigators and clinicians have long sought an accurate and pragmatic definition that specifies arrhythmic and cardiac causes of instantaneous death. Broad consensus exists that the event is a sudden, unexpected, out-of-hospital death, but given its inherent sudden and unexpected nature, often limited diagnostic data are available to robustly exclude noncardiac causes which may also cause instantaneous death (eg, occult overdose, intracranial hemorrhage, aortic dissection, pulmonary embolism). Most definitions presume cardiac etiology or infer cardiac cause of death from limited pre-mortem and/or resuscitation records because these data are often the only records accessible and autopsies to verify cardiac cause are rarely performed. Moreover, due to variable investigative perspectives (emergency medicine, cardiology/electrophysiology, clinical trials, and pathology), data sources, and definitions (Table 15–1)—from death certificates to emergency medical services records to epidemiologic and societal definitions, to clinical trial definitions, and finally those based on pathology—incidence estimates of sudden cardiac death vary widely and sudden death due to primary arrhythmic cause is often presumed.

Table 15–1.Causes of Sudden Death

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