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At a glance

Congenital or acquired adrenergic-induced ventricular arrhythmias. It is characterized by delayed repolarization with an increased risk of episodes of torsades de pointes. Clinically, affected individuals may present with fainting, syncope, and sudden death as a result of ventricular fibrillation. It can be triggered by hypokalemia and hypomagnesemia. The association between anorexia nervosa and sudden death is most possibly caused by severe electrolytes disturbances and Long QT Syndrome. Seizures have also been reported. Episodes may be provoked by various stimuli, depending on the subtype of the condition.

Synonyms

Romano-Ward Syndrome; Long QT Syndrome (1-2-3-4-5); Prolonged QT Interval Syndrome; Protracted QT; QT Interval Prolongation; QT Prolongation Syndrome; Ventricular Fibrillation Prolonged QT Interval Syndrome.

Classification

Fifteen types have been described on the basis of genetic variations. Of them, 12 present different genetic defects that have consequences either on potassium, sodium heart electrical transmission, or calcium homeostasis.

  • LQT1: Most common type. It corresponds to a defect of chromosome 11, encoding for the potassium channel.

  • LQT2: Second most common form of LQTS. It is reported to be a defect on chromosome 7, again encoding for the potassium channel. LQT1 and LQT2 are thought to represent 95% of all cases of LQTS. The standard treatment for LQT1 and LQT2 is β-adrenergic blockade, which has been confirmed to reduce mortality.

  • LQT3: Represents 3 to 4% of cases and corresponds to a defect on chromosome 3. It is encoding the sodium channel. β-Blockade is contraindicated in this type of LQTS because bradycardia can further prolong the QT interval and lead to ventricular arrhythmias. Therefore, it has been suggested that increasing the heart rate probably would be beneficial in LQT3.

  • LQT4: Involves defects in the potassium transmission and is located on chromosome 4, 21, and 24.

  • LQT5: Autosomal recessive medical condition that involves mutations in the gene KCNE1 that is responsible for the potassium channel beta subunit MinK. In its rare homozygous forms, it can lead to Jervell and Lange-Nielsen Syndrome (see “Other conditions to be considered”).

  • LQT6: Involve defects on the potassium transmission and are located on chromosomes 4, 21, and 21, respectively. They are very rare.

  • LQT7 (Andersen Tawil Syndrome; Andersen Cardiodysrhythmic Periodic Paralysis Syndrome): Discussed in Section A under this name. Further information on this medical condition can be found in “Other conditions to be considered” below.

  • LQT8: Caused by the alpha subunit of the calcium channel Cav1.2 encoded by the gene CACNA1c. It is associated with Timothy’s Syndrome (see “Other conditions to be considered”).

  • LQT9: Newly discovered variant caused by mutations in the membrane structural protein, caveolin-3. It is responsible for “late” sodium current that impairs cellular repolarization.

  • LQT10: Associated to gene SCN4B that is encoding the protein NaVβ4, a subunit controlling voltage-gated sodium channel of the heart. The mutation leads to a positive shift in inactivation of the sodium ...

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