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ESSENTIALS OF DIAGNOSIS

  • Includes long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia.

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

  • Patients with long QT syndrome or catecholaminergic polymorphic ventricular tachycardia should be treated long term with an oral beta-blocker (nadolol or propranolol). 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 is an uncommon disease (1 in 2500 live births) that is characterized by a long QT interval (usually greater than 470 msec) and ventricular arrhythmia, typically polymorphic ventricular tachycardia. It may occur in the presence of congenital deafness (Jervell-Lange-Nielsen syndrome) with autosomal recessive inheritance. Acquired long QT syndrome is usually secondary to use of antiarrhythmic agents (sotalol, dofetilide), methadone, antidepressant medications, or certain antibiotics; electrolyte abnormalities; myocardial ischemia; or significant bradycardia (eFigures 10–90 and 10–91). Brugada syndrome accounts for up to 20% of sudden cardiac death in the absence of structural heart disease and is most often due to a defect in a sodium channel gene. Catecholaminergic polymorphic ventricular tachycardia is a rare but important cause of sudden cardiac death associated with exercise.

eFigure 10–90.

Quinidine effect. The rhythm is sinus; the PR interval is 0.2 s. The pattern of left ventricular hypertrophy with associated ST-T wave changes is present. The ST-T abnormalities in V2–3 may be contributed to by quinidine, since they are not expected to result from the ventricular hypertrophy alone. The QTU interval is prolonged to 0.6 s and represents an effect of quinidine. Since the QTU interval does not correlate directly with the serum level of the drug, prolongation of this interval does not predict the presence of quinidine toxicity. (Reproduced, with permission, from Goldschlager N, Goldman MJ. Principles of Clinical Electrocardiography, 13th ed. Originally published by Appleton & Lange. Copyright © 1989 by The McGraw-Hill Companies, Inc.)

eFigure 10–91.

Prolonged QT interval. Sinus bradycardia with deep T wave inversions is concerning for ischemia. Note markedly prolonged QT segment. (Used, with permission, from Jose Sanchez, MD.)

CLINICAL FINDINGS

Patients with an inherited arrhythmia syndrome have a variable clinical presentation; they 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. A 12-lead ECG should be performed with careful attention to any abnormality in the ST segment, T ...

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