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Key Features

Essentials of Diagnosis

  • Can be congenital or acquired

  • Genetic testing for patients with high suspicion of congenital cause based on family history, ECG or exercise testing, or severely prolonged QT interval (> 500 ms) on serial ECGs

  • Patients with congenital long QT syndrome should be managed long-term with an oral β-blocker (propranolol or nadolol)

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

General Considerations

  • Congenital long QT syndrome

    • An uncommon disease (1 in 2000 live births)

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

    • Caused by a genetic abnormality in ion channel activity

    • May be associated with increased cardiac sympathetic activity

    • May occur in the presence of congenital deafness (Jervell-Lange-Nielsen syndrome) with autosomal recessive inheritance

  • Acquired long QT interval

    • Usually secondary to

      • Use of antiarrhythmic agents, methadone, antidepressant medications, or certain antibiotics

      • Electrolyte abnormalities

      • Myocardial ischemia

      • Significant bradycardia

    • Notably, many antiarrhythmic medications that are effective for the treatment of atrial and ventricular arrhythmias may significantly prolong the QT interval (sotalol, dofetilide)

Clinical Findings

  • Clinical presentation is variable

    • Patients may be asymptomatic

    • Palpitations, sustained tachyarrhythmia, syncope, or sudden cardiac arrest may be present

  • In young patients with congenital long QT syndrome, syncopal episodes may be misdiagnosed as a primary seizure disorder

  • Thorough personal and family history should be obtained in all patients

Diagnosis

  • A 12-lead ECG should be performed as well as ambulatory ECG monitoring (Holter) to evaluate for ventricular arrhythmias as well as dynamic changes to the QT interval or T wave

  • Exercise ECG testing should be performed in all patients to assess for lack of appropriate QT interval shortening with exercise or during recovery

  • Genetic testing is appropriate for patients with

    • A high suspicion of congenital long QT syndrome based on the above findings

    • Severe (> 500 ms) prolongation of the QT interval on serial ECGs

Treatment

Pharmacologic

  • Intravenous β-blockers may be effective, especially in congenital forms of long QT syndrome

  • Intravenous magnesium should be given immediately

  • Increasing the heart rate, whether by infusion of β-agonist (dopamine or isoproterenol) or temporary atrial or ventricular pacing, is an effective approach that can both break and prevent the rhythm

  • Long-term management of acquired long QT syndrome generally involves withdrawal of the offending medication and/or correction of any electrolyte abnormalities

  • Long-term use of β-blockers (particularly propranolol or nadolol) is the mainstay treatment of congenital long QT syndrome

Surgery

  • Cervicothoracic sympathectomy should be considered for patients who do not respond to or are intolerant of β-blockers

  • ICD implantation

    • Recommended for patients in whom recurrent syncope, sustained ventricular arrhythmias, or sudden cardiac death occurs despite medical therapy

    • Should be considered as primary therapy in certain patients, such as ...

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