Curriculum in Cardiology
Long QT syndrome: Diagnosis and management

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Abstract

Background Long QT syndrome (LQT) is characterized by prolongation of the QT interval, causing torsade de pointes and sudden cardiac death. The LQT is a disorder of cardiac repolarization caused by alterations in the transmembrane potassium and sodium currents. Congenital LQT is a disease of transmembrane ion-channel proteins. Six genetic loci of the disease have been identified. Sporadic cases of the disease occur as a result of spontaneous mutations. The acquired causes of LQT include drugs, electrolyte imbalance, marked bradycardia, cocaine, organophosphorus compounds, subarachnoid hemorrhage, myocardial ischemia, protein sparing fasting, autonomic neuropathy, and human immunodeficiency virus disease. Methods Data on the diagnosis and management of LQT were thoroughly reviewed. Results and Conclusions The diagnosis of LQT primarily rests on clinical and electrocardiographic features and family history. The clinical presentations range from dizziness to syncope and sudden death. Genetic screening is available primarily as a research tool. Short-term treatment of LQT is aimed at preventing the recurrences of torsades and includes intravenous magnesium and potassium administration, temporary cardiac pacing, withdrawal of the offending agent, correction of electrolyte imbalance, and, rarely, intravenous isoproterenol administration. The long-term treatment is aimed at reducing the QT-interval duration and preventing the torsades and sudden death and includes use of oral β-adrenergic blockers, implantation of permanent pacemaker/cardioverter-defibrillator, and left thoracic sympathectomy. Sodium channel blockers are promising agents under investigation. Electrocardiograms are recorded for screening of family members. The data favor treating asymptomatic patients, if <40 years old at the time of diagnosis, with β-adrenergic blockers. (Am Heart J 2002;143:7-14.)

Section snippets

Diagnosis of LQT syndrome

The diagnosis of LQT primarily depends on the clinical features, the family history, and the ECG findings of the patient. Unexplained syncope or sudden cardiac death in a child or young adult should raise a high suspicion of the possibility of presence of LQT. Electrophysiologic testing is not helpful in making the diagnosis of LQT. Genetic testing has not become a routine part of the diagnostic workup in patients with LQT, although it could be of assistance in the borderline cases or in cases

Short-term treatment

Immediate cardioversion should be done in situations where torsades does not terminate spontaneously and results in hemodynamic compromise. The short-term treatment, which is aimed at prevention of the recurrences of torsades, includes withdrawal of the offending agents, correction of the underlying electrolyte abnormalities, and administration of magnesium, potassium, temporary transvenous cardiac pacing, and rarely intravenous isoproterenol. The magnesium, potassium, and temporary transvenous

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    Reprint requests: Ijaz A. Khan, MD, FACP, FACC, Creighton University Cardiac Center, 3006 Webster St, Omaha, NE 68131-2044. E-mail: [email protected]

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