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KEY FEATURES

ESSENTIALS OF DIAGNOSIS

  • Clinical constellation of congenital deafness, prolongation of the QT interval (QTc > 480 ms), syncope, and sudden death

  • Family history of sudden death

  • Characteristic arrhythmia is torsades de pointes

  • The fundamental abnormality is prolongation of action potential secondary to abnormality of transmembrane ion transport

  • Emotion seems to trigger cardiac events, particularly in patients with KvLQT1

GENERAL CONSIDERATIONS

  • Family history of sudden cardiac death (SCD), QT prolongation on the ECG, and bilateral neural deafness with autosomal recessive pattern of inheritance affecting several children in a family was first reported by Jervell and Lange-Nielsen

  • Family history of SCD, QT prolongation, and autosomal dominant pattern of inheritance was subsequently identified (Romano-Ward syndrome)

  • Romano-Ward syndrome is more common than Jervell and Lange-Nielsen syndrome

  • Deafness is not a manifestation of Romano-Ward syndrome

  • Mutations in 7 LQTS genes have thus far been identified

  • Repolarization (potassium) currents are affected in most of the disorders except in LQT3 and LQT4, where the sodium current is affected

  • Family members with identical gene mutations may experience wide variations in clinical symptoms (variable penetrance) from asymptomatic to recurrent syncope

  • SCDLQT1 (43%) and LQT2 (45%) account for most of the recognized patients

CLINICAL PRESENTATION

SYMPTOMS AND SIGNS

  • Resuscitated SCD or syncope

  • Incidental finding of prolonged QT interval or during family screening

  • Syncope with stress

  • Congenital deafness

  • Symptoms usually present during adolescence

  • Males are affected during adolescence and females during adulthood

  • LQT1 patients experience symptoms during exercise, and LQT2 patients during acute arousal

  • Once clinical symptoms occur, risk of recurrence is high

PHYSICAL EXAM FINDINGS

  • Bilateral nerve deafness

  • Otherwise, clinical examination is normal

DIFFERENTIAL DIAGNOSIS

  • Metabolic abnormalities with prolongation of QT

  • Drug-induced long QT

  • Idiopathic ventricular arrhythmia

  • Central nervous system disorder that prolongs QT

DIAGNOSTIC EVALUATION

LABORATORY TESTS

  • Metabolic panel to exclude hypokalemia and hypomagnesemia

  • Genetic testing is helpful and indicated, but the test results may take too long to influence clinical decision making and are commonly only performed in the outpatient clinic

    • – A negative test is not helpful unless testing is performed to identify a mutation that is already known within the family

ELECTROCARDIOGRAPHY

  • QTc > 480 ms

  • Outpatient cardiac monitoring may uncover asymptomatic torsades de pointes

  • Exercise ECG may be helpful if activity precipitates arrhythmia, or QT interval prolongation occurs during recovery if there is no prior diagnosis of long QT syndrome

  • Usefulness of outpatient cardiac monitoring and exercise stress test, although frequently used, is supported by very few studies

IMAGING STUDIES

  • Echocardiogram may be used to establish structurally normal heart

  • Depending on clinical situation, exclude central nervous system disorder with imaging

TREATMENT

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