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For further information, see CMDT Part 10-37: Ventricular Fibrillation & Sudden Death

Key Features

Essentials of Diagnosis

  • Most patients with sudden cardiac death (SCD) have underlying coronary heart disease (CHD)

  • In the absence of reversible cause, implantable cardioverter defibrillator (ICD) is recommended

General Considerations

  • Sudden cardiac arrest: defined as the successful resuscitation of ventricular fibrillation, either spontaneously or via intervention (defibrillation)

  • SCD: defined as unexpected nontraumatic death in clinically well or stable patients who die within 1 hour after onset of symptoms; the causative rhythm in most cases is ventricular fibrillation

  • A disproportionate number of sudden deaths occur in the early morning hours; this suggests that there is a strong interplay with the autonomic nervous system

  • Prompt evaluation to exclude reversible causes of sudden cardiac arrest should begin immediately following resuscitation

Clinical Findings

  • Underlying CHD

    • Cause of SCD in approximately 70% of cases

    • May be the initial manifestation of SCD in up to 40% of patients

  • Initiating arrhythmia in most patients is unknown, but is presumed to be

    • Sustained monomorphic ventricular tachycardia

    • Polymorphic ventricular tachycardia

    • Primary ventricular fibrillation (especially in the setting of acute ischemia)

  • Complete heart block and sinus node arrest may also cause sudden death

  • In patients < 35, most SCD is caused by inherited heart disease, such as

    • Long QT syndrome

    • Catecholaminergic polymorphic ventricular tachycardia

    • Brugada syndrome

    • Hypertrophic cardiomyopathy

    • Arrhythmogenic right ventricular cardiomyopathy

    • Dilated cardiomyopathy

  • In patients over the age of 35,

    • CHD is the most common cause of SCD

    • Inherited causes, though, are common up until the age of 50

  • Noninherited forms of heart disease can also lead to SCD, including

    • Valvular heart disease (aortic stenosis, pulmonic stenosis)

    • Congenital heart disease

    • Myocarditis


  • Laboratory testing

    • Should be performed to exclude severe electrolyte abnormalities (particularly hypokalemia and hypomagnesemia), acidosis, and to evaluate cardiac biomarkers

    • Abnormalities may be secondary to resuscitation and not causative of the event; use caution in attributing cardiac arrest solely to an electrolyte disturbance

  • A 12-lead ECG should be performed to evaluate for ongoing ischemia or conduction system disease

  • Echocardiography should be done to evaluate ventricular function

  • Coronary arteriography should be performed to exclude coronary disease as the underlying cause, since revascularization may prevent recurrence


  • Intervention is required unless ventricular fibrillation

    • Occurs shortly after myocardial infarction

    • Is associated with ischemia

    • Is seen with a correctable process (eg, electrolyte abnormality or medication toxicity)

  • Targeted temperature management protocol should be initiated rapidly and continued for 24–36 hours after cardiac arrest

  • ICD is generally indicated in patients who survive sudden cardiac arrest

  • Sudden cardiac arrest in the setting of acute ischemia or infarct should be managed with prompt coronary revascularization

  • Wearable defibrillator vest

    • Alternative to implantation of a prophylactic ICD in patients early after myocardial infarction

    • May be ...

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