Find information on thousands of medical conditions and prescription drugs.

Long QT Syndrome

The long QT syndrome (LQTS) is a heart disease in which there is an abnormally long delay between the electrical excitation (or depolarization) and relaxation (repolarization) of the ventricles of the heart. It is associated with syncope (loss of consciousness) and with sudden death due to ventricular arrhythmias. Arrhythmias in individuals with LQTS are often associated with exercise or excitement. The cause of sudden cardiac death in individuals with LQTS is ventricular fibrillation. more...

Home
Diseases
A
B
C
D
E
F
G
H
I
J
K
L
Amyotrophic lateral...
Bardet-Biedl syndrome
Labyrinthitis
Lafora disease
Landau-Kleffner syndrome
Langer-Giedion syndrome
Laryngeal papillomatosis
Laryngomalacia
Lassa fever
LCHAD deficiency
Leber optic atrophy
Ledderhose disease
Legg-Calvé-Perthes syndrome
Legionellosis
Legionnaire's disease
Leiomyoma
Leiomyosarcoma
Leishmaniasis
Lemierre's syndrome
Lennox-Gastaut syndrome
Leprechaunism
Leprophobia
Leprosy
Leptospirosis
Lesch-Nyhan syndrome
Leukemia
Leukocyte adhesion...
Leukodystrophy
Leukomalacia
Leukoplakia
LGS
Li-Fraumeni syndrome
Lichen planus
Ligyrophobia
Limb-girdle muscular...
Limnophobia
Linonophobia
Lipodystrophy
Lipoid congenital adrenal...
Liposarcoma
Lissencephaly
Lissencephaly syndrome...
Listeriosis
Liticaphobia
Liver cirrhosis
Lobster hand
Locked-In syndrome
Loiasis
Long QT Syndrome
Long QT syndrome type 1
Long QT syndrome type 2
Long QT syndrome type 3
LSA
Lung cancer
Lupus erythematosus
Lyell's syndrome
Lygophobia
Lyme disease
Lymphangioleiomyomatosis
Lymphedema
Lymphoma
Lymphosarcoma
Lysinuric protein...
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
Medicines

Individuals with LQTS have a prolongation of the QT interval on the ECG. The Q point on the ECG corresponds to the beginning of ventricular depolarization while the T point corresponds to the beginning of 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.

Genetics

The two most common types of LQTS are genetic and drug-induced. 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 or congenital neural deafness. A number of specific genes loci have been identified that are associated with LQTS. Following is a list of the most common mutations:

  • LQT1 - mutations to the alpha subunit of the slow delayed rectifier potassium channel (KvLQT1 or KCNQ1). The current through the heteromeric channel (KvLQT1+minK) is known as IKs. This mutation is thought to cause LQT by reducing the amount of repolarizing action potential current that prolongs action potential duration (APD). These mutations tend to be the most common yet least severe.
  • LQT2 - mutations to the alpha subunit of the fast delayed rectifier potassium channel (HERG + miRP). Current through this channel is known as IKr. This phenotype is also probably caused by a reduction in repolarizing current.
  • LQT3 - mutations to the alpha subunit of the sodium channel (SCN5A). Current through is channel is commonly referred to as INa. Depolarizing current through the channel late in the action potential is thought to prolong APD. The late current is due to failure of the channel to remain inactivated and hence enter a bursting mode in which significant current can enter when it should not. These mutations are more lethal but less common.
  • LQT4 - mutations in an anchor protein Ankyrin B which anchors the ion channels in the cell. Very rare.
  • LQT5 - mutations in the beta subunit MinK which coassembles with KvLQT1.
  • LQT6 - mutations in the beta subunit MiRP1 which coassembles with HERG.
  • LQT7 - mutations in the potassium channel KCNJ2 which leads to Andersen-Tawil syndrome.
  • LQT8 - mutations in the calcium channel Cav1.2 encoded by the gene CACNA1c leading to Timothy's syndrome

Other mutations affect the beta subunits ion channels. For example LQT6 affects minK (aka KCNE1) which is the beta subunit that coassembles with KCNQ1 to form IKs channels.

Read more at Wikipedia.org


[List your site here Free!]


Long QT Syndrome
From Nurse Practitioner, 9/1/03 by Risser, Nancy

Long QT Syndrome Priori SG, Schwartz PJ, Napolitano C, et al.: Risk stratification in the long-QT syndrome. N Engl J Med 2003;348(19):1866-74.

Vincent GM: The long-QT syndrome-bedside to bench to bedside. N Engl J Med 2003;348(19):1837-38.

Moss AJ: Long QT syndrome. JAMA 2003;289(16):2041-44.

Al-Khatib SM, LaPointe NM, Kramer JM, et al.: What clinicians should know about the QT interval. JAMA 2003;289(16):2120-27.

Mutations in six genes can produce abnormal cardiac sodium or potassium channels and result in QT interval prolongation. These changes increase the risk of fatal ventricular arrhythmia. However, sudden death only occurs in about 4% of affected persons; 50% of carriers never have symptoms. The QTc (QT interval, adjusted for heart rate) is considered prolonged when it is more than 0.45 seconds in men and more than 0.46 seconds in women and children (top 1% of normal distribution).

Al-Khatib and coauthors reviewed registries and case series, focusing on outcomes associated with prolonged QT intervals and medication errors that may have predisposed for prolonged QT interval. Patients at risk or taking other QT prolonging drugs should avoid quinolone antibiotics.

Priori and coauthors studied 647 at-risk patients and reported that sex, genotype, and QTc duration independently predict risk. For certain genotypes, strenuous exercise can trigger symptoms; for others, emotions or loud noises are more likely triggers. Although beta-blocking drugs have little effect on QT duration, they are the treatment of choice for asymptomatic and symptomatic patients with long QT syndrome. Complete compliance is essential when on a beta-blocker regimen. Life-threatening arrhythmias can occur when these medicines are stopped due to rebound receptor catecholamine hypersensitivity.

Copyright Springhouse Corporation Sep 2003
Provided by ProQuest Information and Learning Company. All rights Reserved

Return to Long QT Syndrome
Home Contact Resources Exchange Links ebay