Short QT syndrome
|Short QT syndrome|
|Schematic representation of normal ECG trace (sinus rhythm), with waves, segments, and intervals labeled.|
|Symptoms||Passing out, sudden cardiac death |
|Diagnostic method||Electrocardiogram (ECG) |
|Treatment||Medication, implantable cardioverter defibrillator (ICD) |
|Medication||Quinidine, Flecainide |
Short QT syndrome is a genetic disease of the electrical system of the heart. It consists of a constellation of signs and symptoms, consisting of a short QT interval on an EKG (≤ 370 ms) that does not significantly change with heart rate, tall and peaked T waves, and a structurally normal heart. Short QT syndrome appears to be inherited in an autosomal dominant pattern, and a few affected families have been identified.
Signs and symptoms
Some individuals with short QT syndrome frequently complain of palpitations and may have unexplained syncope (loss of consciousness). Mutations in the KCNH2, KCNJ2, and KCNQ1 genes cause short QT syndrome. These genes provide instructions for making proteins that act as channels across the cell membrane. These channels transport positively charged atoms (ions) of potassium into and out of cells. In cardiac muscle, these ion channels play critical roles in maintaining the heart's normal rhythm. Mutations in the KCNH2, KCNJ2, or KCNQ1 gene increase the activity of the channels, which changes the flow of potassium ions between cells. This disruption in ion transport alters the way the heart beats, leading to the abnormal heart rhythm characteristic of short QT syndrome. Short QT syndrome appears to have an autosomal dominant pattern of inheritance.
Short QT syndrome is associated with an increased risk of sudden cardiac death, most likely due to ventricular fibrillation.
Short QT syndrome is a genetic disorder caused by mutations in genes responsible for producing certain ion channels within heart cells. Some mutations cause an increased flow of potassium out of the cell, while others reduce the flow of calcium into the cell. The common effect of all these mutations is to shorten the cardiac action potential, reflected on the surface ECG as a shortening of the QT interval. A list of the genetic mutations associated with short QT syndrome can be found in the table below.
|SQT1||609620||KCNH2||Also known as hERG, encodes the potassium channel KV11.1 responsible for the delayed rectifier potassium current IKr |
|SQT2||609621||KCNQ1||Encodes the potassium channel responsible for the delayed rectifier potassium current IKs |
|SQT3||609622||KCNJ2||Encodes the potassium channel Kir2.1 responsible for the inward rectifying potassium current IK1 |
|SQT4||114205||CACNA1C||Encodes the alpha subunit of the L-type calcium channel carrying ICa(L) |
|SQT5||114204||CACNA2D1||Encodes the alpha2/delta subunit of the L-type calcium channel carrying ICa(L) |
|SQT6||106195||SLC4A3||Encodes a bicarbonate / chloride exchanger |
The Short QT Syndrome diagnostic criterion is based on a point system as follows:
QTc in milliseconds
<370 1 <350 2 <330 3
Sudden cardiac arrest 2 Polymorphic VT or VF 2 Unexplained syncope 1 Atrial fibrillation 1
1st or 2nd degree relative with SQTS 2 1st or 2nd degree relative with sudden death 1 Sudden infant death syndrome 1
Genotype positive 2 Mutation of undetermined significance 1 in a culprit gene
Patients are deemed high-probability (> or equal to 4 points), intermediate probability (3 points) or low probability (2 or less points).
Currently, some individuals with short QT syndrome have had implantation of an implantable cardioverter-defibrillator (ICD) as a preventive action, although it has not been demonstrated that heart problems have occurred before deciding to implant an ICD.
A recent study has suggested the use of certain antiarrhythmic agents, particularly quinidine, may be of benefit in individuals with short QT syndrome due to their effects on prolonging the action potential and by their action on the IK channels. Some trials are currently under way but do not show a longer QT statistically.
- Bjerregaard, Preben (2018-03-02). "The diagnosis and management of short QT syndrome". Heart Rhythm. doi:10.1016/j.hrthm.2018.02.034. ISSN 1556-3871. PMID 29501667.
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- Gaita F, Giustetto C, Bianchi F, Schimpf R, Haissaguerre M, Calo L, Brugada R, Antzelevitch C, Borggrefe M, Wolpert C (2004). "Short QT syndrome: pharmacological treatment". J Am Coll Cardiol. 43 (8): 1494–1499. doi:10.1016/j.jacc.2004.02.034. PMID 15093889.
- Maltret A, Wiener-VacherType S, et al. (2014). "short QT syndrome and vestibular dysfunction: Mirror of the Jervell and Lange-Nielsen syndrome ?". Int J Cardiol. 171.
- National Library of Medicine. Short QT syndrome