Long QT syndrome
Long QT syndrome is prolonged ventricular repolarization, congenital or acquired, that predisposes to torsades de pointes and sudden death. Diagnosis rests on a prolonged corrected QT with clinical and genetic features, and management centers on beta-blockade, avoiding QT-prolonging drugs, and an ICD for high-risk patients.
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What this article covers
- Overview
Definition: long QT syndrome (LQTS) is a disorder of prolonged ventricular repolarization, seen as a long corrected QT interval, that predisposes to torsades de pointes and sudden cardiac death.
- Epidemiology
Congenital LQTS is an important cause of sudden death in the young.
- Risk factors
Pathogenic ion-channel mutations (KCNQ1, KCNH2, SCN5A and others) and family history.
- Pathophysiology
Impaired repolarizing current or excess depolarizing current: loss-of-function potassium channel mutations (LQT1, LQT2) or gain-of-function sodium channel mutations (LQT3) prolong the action potential.
- Clinical features
Syncope or seizures from self-terminating torsades.
- Differential diagnosis
Acquired QT prolongation: QT prolongation from drugs, electrolytes, or bradycardia, distinguished from the congenital form by normalization once the offending drug is stopped or electrolytes…
- Diagnosis
Establish with a prolonged corrected QT plus clinical and genetic criteria: the diagnostic basis is a repeatedly prolonged QTc (generally over 460 to 480 ms, and clearly abnormal above 500 ms) on…
- Management
First-line, start a beta-blocker and remove QT-prolonging exposures: give a non-selective beta-blocker (nadolol 40 to 80 mg PO daily or propranolol 1 to 3 mg/kg/day PO in divided doses), both…
- Complications
Torsades de pointes and ventricular fibrillation.
- Prognosis
Good with beta-blockade and trigger avoidance in most patients.
- Prevention
Beta-blockade and avoidance of QT-prolonging drugs.
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- Torsades de pointes
Torsades de pointes is a polymorphic ventricular tachycardia occurring on a background of QT prolongation, with a characteristic twisting of QRS complexes around the baseline. Management is intravenous magnesium, correction of the underlying QT-prolonging cause, and rate acceleration by pacing or isoproterenol; unstable episodes are defibrillated.
- Sudden cardiac arrest
Sudden cardiac arrest is the abrupt cessation of cardiac function with loss of pulse and consciousness, most often from a ventricular tachyarrhythmia on a background of coronary disease. Survival depends on immediate CPR and defibrillation of shockable rhythms, followed by treatment of the cause and secondary prevention with an ICD.
- Brugada syndrome
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