Short QT syndrome
|Short QT syndrome|
Schematic representation of normal ECG trace (sinus rhythm), with waves, segments, and intervals labeled.
|Classification and external resources|
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 (≤ 300 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.
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).
The cause of short QT syndrome is unclear at this time. A current hypothesis is that short QT syndrome is due to increased activity of outward potassium currents in phase 2 and 3 of the cardiac action potential. This would cause a shortening of the plateau phase of the action potential (phase 2), causing a shortening of the overall action potential, leading to an overall shortening of refractory periods and the QT interval.
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.
- Gollob M, Redpath C, Roberts J (2011). "The Short QT syndrome: Proposed Diagnostic Criteria". J Am Coll Cardiol. 57 (7): 802–812. doi:10.1016/j.jacc.2010.09.048. PMID 21310316.
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- 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