Congenital or acquired adrenergic-induced ventricular
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
Seven different genetic defects have been
identified, all involving potassium and sodium transmission.
LQT1 is the most common type. It corresponds to a defect of chromosome 11,
encoding for the potassium channel.
LQT2 is the 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
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, LQT5, and LQT6 all involve defects on the potassium transmission and are located on
chromosomes 4, 21, and 21, respectively. They are very rare.
LQT7 (Andersen Cardiodysrhythmic Periodic Paralysis Syndrome) is discussed in
Section A under this name.
All types are characterized by a corrected QT interval of at least 440 ms on
the electrocardiogram. The manifestation is recurrent syncope associated
with documented ventricular arrhythmia and sudden death.
1:10,000 in the general population (= 90% of
Romano-Ward by autosomal dominant inheritance.
LQT1 has been mapped to chromosome 11. Other mutated genes located on
chromosomes 3, 6, and 11 may contribute to or cause LQTS.
Long QT syndrome results from structural of
acquired/transient (therapeutic) abnormalities in the potassium channels of
Acquired LQTS may be caused by the following:
- Drugs: A list of drugs known or suspected to prolong the QT interval is given
in Table L-4. A more extensive list of drugs that prolong the QT interval
can be found on the web site of either The University of Arizona Center for
Education and Research on Therapeutics at http://qtdrugs.org or http://www.torsades.org
- Electrolyte Disturbances: Acute or chronic hypokalemia, chronic hypocalcemia, and chronic
- Associated Medical Conditions: Atrioventricular block, sick sinus syndrome, myocarditis,
hyperparathyroidism, hypothyroidism, subarachnoid hemorrhage, encephalitis,
head trauma, starvation, and anorexia nervosa.
Table L-4 Drugs Known or Suspected to Prolong the QT Interval ||Download (.pdf)
Table L-4 Drugs Known or Suspected to Prolong the QT Interval