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For further information, see CMDT Part 10-38: Inherited Arrhythmia Syndromes

Key Features

Essentials of Diagnosis

  • Includes long QT syndrome, Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy, and catecholaminergic polymorphic ventricular tachycardia (VT)

  • Genetic testing for patients with suspected congenital long QT syndrome based on family history, ECG or exercise testing, or severely prolonged QT interval (> 500 ms) on serial ECGs

  • Patients with long QT syndrome or catecholaminergic polymorphic VT should be managed long-term with an oral beta-blocker (nadolol or propranolol)

  • Implantable cardioverter defibrillator (ICD) is indicated for patients with ventricular arrhythmia or syncope despite medical treatment

General Considerations

  • Inherited arrhythmia syndromes may result in life-threatening ventricular arrhythmias due to gene mutations in cardiac channels resulting in abnormal electrolyte regulation across the cardiac cell membrane

  • Congenital long QT syndrome

    • Uncommon (1 in 2500 live births)

    • Characterized by a long QT interval (usually > 470 ms) and ventricular arrhythmia, typically polymorphic VT

  • Acquired long QT syndrome is usually secondary to

    • Use of antiarrhythmic agents (sotalol, dofetilide), methadone, antidepressant medications, or certain antibiotics

    • Electrolyte abnormalities

    • Myocardial ischemia

    • Significant bradycardia

  • Brugada syndrome

    • Accounts for up to 20% of sudden cardiac death in the absence of structural heart disease

    • Most often due to a defect in a sodium channel gene

  • Arrhythmogenic right ventricular cardiomyopathy

    • Predominantly affects the right ventricle

    • Characterized by areas of myocardial replacement with fibrosis and adipose tissue that frequently causes ventricular arrhythmia

  • Catecholaminergic polymorphic VT is a rare but important cause of sudden cardiac death associated with exercise

Clinical Findings

  • Variable clinical presentation

  • Patients may be asymptomatic or have palpitations, sustained tachyarrhythmia, syncope, or sudden cardiac arrest

  • In young patients, syncopal episodes may be misdiagnosed as a primary seizure disorder

  • Personal and family history should be thoroughly reviewed in all patients

Diagnosis

  • A 12-lead ECG should be performed with careful attention to any abnormality in the ST segment, T wave, and QT interval

  • A corrected QT interval longer than 500 ms on serial ECGs in the absence of a secondary cause (medication or electrolyte abnormality) identifies a high-risk subset of patients with long QT syndrome

  • Ambulatory ECG monitoring may be used to evaluate for ventricular arrhythmias as well as dynamic changes to the QT interval or T wave

  • Exercise ECG testing may be performed in patients with suspected long QT syndrome to assess for lack of appropriate QT interval shortening with higher heart rates

Treatment

Medications

  • Inherited arrhythmia syndromes

    • Antiarrhythmic medications should be avoided, except when specific genetic abnormalities have been identified and under the direction of a specialist

    • Long-term management depends on the presence of high-risk features

  • Long QT syndrome or catecholaminergic polymorphic VT

    • Use of beta-blockers (particularly propranolol or nadolol) is the mainstay of treatment

      • Intravenous beta-blockers may be ...

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