Read more about this disease, some with Classification – Types – Signs and symptoms – Genetics – Pathophysiology – Diagnosis – Screening – Prevention – Treatment and management – Cures and much more, some including pictures and video when available.
The long QT syndrome (LQTS) is a rare congenital heart condition with delayed repolarization following depolarization (excitation) of the heart, associated with syncope (fainting) due to ventricular arrhythmias, possibly of type torsade de pointes, which can deteriorate into ventricular fibrillation and ultimately sudden death. Arrhythmia in individuals with LQTS are often associated with exercise or excitement.
Individuals with LQTS have a prolongation of the QT interval on the ECG. The QRS complex corresponds to ventricular depolarization while the T wave corresponds to ventricular repolarization. The QT interval is measured from the Q point to the end of the T wave. While many individuals with LQTS have persistent prolongation of the QT interval, some individuals do not always show the QT prolongation; in these individuals, the QT interval may prolong with the administration of certain medications.
The first documented case of Long QT syndrome was described in Leipzig by Meissner in 1856, where a deafmute girl died after her teacher yelled at her. When the parents were told about her death, they told that her older brother who also was deafmute died after a terible fright[1]. This was before the ECG was invented but is likely the first described case of Jervell and Lange-Nielsen syndrome. In 1957 the first case documented by ECG was described bý Anton Jervell and Fred Lange-Nielsen. Romano, in 1963, and Ward, in 1964, separately described the more common variant of Long QT syndrome with normal hearing, later called Romano-Ward syndrome.
Genetic LQTS can arise from mutation to one of several genes. These mutations tend to prolong the duration of the ventricular action potential (APD), thus lengthening the QT interval. LQTS can be inherited in an autosomal dominant or an autosomal recessive fashion. The autosomal recessive forms of LQTS tend to have a more severe phenotype, with some variants having associated syndactyly (LQT8) or congenital neural deafness (LQT1). A number of specific genes loci have been identified that are associated with LQTS. Genetic testing for LQTS is clinically available and may help to direct appropriate therapies (Overview of LQTS Genetic Testing). The most common causes of LQTS are mutations in the genes KCNQ1 (LQT1), KCNH2 (LQT2), and SCN5A (LQT3); the following is a list of all genes associated with LQTS:
Drug induced LQT is usually a result of treatment by anti-arrhythmic drugs such as amiodarone or a number of other drugs that have been reported to cause this problem (e.g. cisapride). Some anti-psychotic drugs, such as Haloperidol and Ziprasidone, have a prolonged QT interval as a rare side effect. Genetic mutations may make one more susceptible to drug induced LQT.
LQT1 is the most common type of long QT syndrome, making up about 30 to 35 percent of all cases. The LQT1 gene is KCNQ1 which has been isolated to chromosome 11p15.5. KCNQ1 codes for the voltage-gated potassium channel KvLQT1 that is highly expressed in the heart. It is believed that the product of the KCNQ1 gene produces an alpha subunit that interacts with other proteins (particularly the minK beta subunit) to create the IKs ion channel, which is responsible for the delayed potassium rectifier current of the cardiac action potential.
[tubepress mode=’tag’, tagValue=’Long QT syndrome’]