Short QT syndrome

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Short QT syndrome
SinusRhythmLabels.svg
Schematic representation of normal ECG trace (sinus rhythm), with waves, segments, and intervals labeled.
Specialty Cardiology
Symptoms Passing out, sudden cardiac death [1]
Causes Genetic
Diagnostic method Electrocardiogram (ECG) [1]
Treatment Medication, implantable cardioverter defibrillator (ICD) [1]
Medication Quinidine, Flecainide [1]

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[edit]

Short QT syndrome is inherited in an autosomal dominant pattern.

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.

Cause[edit]

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.

Type OMIM Gene Notes
SQT1 609620 KCNH2 Also known as hERG, encodes the potassium channel KV11.1 responsible for the delayed rectifier potassium current IKr [1]
SQT2 609621 KCNQ1 Encodes the potassium channel responsible for the delayed rectifier potassium current IKs [1]
SQT3 609622 KCNJ2 Encodes the potassium channel Kir2.1 responsible for the inward rectifying potassium current IK1 [1]
SQT4 114205 CACNA1C Encodes the alpha subunit of the L-type calcium channel carrying ICa(L) [1]
SQT5 114204 CACNA2D1 Encodes the alpha2/delta subunit of the L-type calcium channel carrying ICa(L) [1]
SQT6 106195 SLC4A3 Encodes a bicarbonate / chloride exchanger [1]

Diagnosis[edit]

Recent diagnostic criteria have been published out of the Arrhythmia Research Laboratory at the University of Ottawa Heart Institute from Drs. Michael H Gollob and Jason D Roberts.[2]

The Short QT Syndrome diagnostic criterion is based on a point system as follows:

QTc in milliseconds

   <370                                              1
   <350                                              2
   <330                                              3

Jpoint-Tpeak interval

   <120                                              1

Clinical History

   Sudden cardiac arrest                             2
   Polymorphic VT or VF                              2
   Unexplained syncope                               1
   Atrial fibrillation                               1

Family History

   1st or 2nd degree relative with SQTS              2
   1st or 2nd degree relative with sudden death      1
   Sudden infant death syndrome                      1

Genotype

   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).

Treatment[edit]

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.[3] Some trials are currently under way but do not show a longer QT statistically.[4]

See also[edit]

References[edit]

  1. ^ a b c d e f g h i j 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. 
  2. ^ 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. 
  3. ^ 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. 
  4. ^ 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. 

External links[edit]

Classification