Short QT syndrome: Difference between revisions
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==Diagnosis== | ==Diagnosis== | ||
[[Short QT syndrome diagnostic criteria|Diagnostic Criteria]] | [[Short QT syndrome history and symptoms|History and Symptoms]] | [[Short QT syndrome physical examination|Physical Examination]] | [[Short QT syndrome electrocardiogram|Electrocardiogram]] | [[Short QT syndrome electrophysiologic studies|Electrophysiologic Studies]] | | [[Short QT syndrome diagnostic criteria|Diagnostic Criteria]] | [[Short QT syndrome history and symptoms|History and Symptoms]] | [[Short QT syndrome physical examination|Physical Examination]] | [[Short QT syndrome laboratory studies|Laboratory Studies]] | [[Short QT syndrome electrocardiogram|Electrocardiogram]] | [[Short QT syndrome electrophysiologic studies|Electrophysiologic Studies]] | | ||
===Genetic Testing=== | ===Genetic Testing=== | ||
Revision as of 18:51, 3 September 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [3]
Synonyms and keywords: SQTS; short QT; short QTc; QT interval shortening
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Triggers
Differentiating Short QT Syndrome from other Diseases
Epidemiology and Demographics
Screening
Natural History, Complications, Prognosis
Diagnosis
Diagnostic Criteria | History and Symptoms | Physical Examination | Laboratory Studies | Electrocardiogram | Electrophysiologic Studies |
Genetic Testing
Because new genetic variants of SQTS are still being identified, a negative genetic test for existing variants does not exclude the presence of SQTS. A negative genetic test for existing variants could mean that a patient with a short QT interval does not have a heretofore unidentified variant of SQTS.
However, among family members of an affected patient, genetic testing may identify the syndrome in an asymptomatic patient, and may also rule out the presence of the syndrome in asymptomatic patients.
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.
Centers Performing Genetic Testing for Short QT Syndrome
Treatment
Device Based Therapy
An implantable cardioverter-defibrillator (ICD) is indicated in[1]:
- Symptomatic patients
- Patients with a family history of sudden cardiac death
Generally accepted criteria for implantation of an AICD also include:
- Inducibility on electrophysiologic testing
- Positive genetic test, although a negative result does not exclude the presence of a previously unreported mutation or the occurrence of a future arrhythmic event
Complications of AICD Placement
Inappropriate shocks may be delivered due to[2]:
- The occurence of tachycardias such as sinus tachycardia and atrial fibrillation.
- Oversensing of the tall, narrow peaked T wave
Pharmacologic Therapy
Short QT Syndrome 1 (SQT1)
The efficacy of pharmacotherapy in preventing ventricular fibrillation has only been studies in patients with SQT1. Given the limited number of patients studied, and the limited duration of follow-up, pharmacotherapy as primary or secondary preventive therapy for patients with SQT1 cannot be recommended at this time. AICD implantation remains the mainstay of therapy in these patients. Pharmacotherapy may play an adjunctive role in reducing the risk of events in patients with an AICD as described below in the indications section.
Patients with Short QT Syndrome 1 (SQT1) have a mutation in KCNH2 (HERG). Class IC and III antiarrhythmic drugs do not produce any significant QT interval prolongation [3][4] . Flecainide has not been shown to consistently reduce the inducibility of ventricular fibrillation.[5] Although it does not prolong the QT interval in SQT1 patients, propafenone reduces the risk of recurrent atrial fibrillation in SQT1 patients.[6]
Quinidine in contrast may be effective in patients with SQT1 in so far as it blocks both potassium channels (IKr, IKs, Ito, IKATP and IK1) and the inward sodium and calcium channels. In four out of four patients, Quinidine prolonged the QT interval from 263 +/- 12 msec to 362 +/-25 msec, most likely due to its effects on prolonging the action potential and by virtue of its action on the IK channels. Although Quinidine was successful in preventing the inducibility of ventricular fibrillation in 4 out of 4 patients, it is unclear if the prolongation of the QT interval by quinidine would reduce the risk of sudden cardiac death.
Although pharmacotherapy can be used to suppress the occurrence of atrial fibrillation in patients with SQT1, AICD implantation is the mainstay of therapy, and pharmacotherapy to prevent sudden death should is only indicated if AICD implantation is not possible.
Among patients with SQT1, Qunidine also:
- Prolongs the ST segment and T wave durations
- Restores the heart rate dependent variability in the QT interval
- Decreases repolarization dispersion
Indications for Pharmacologic Therapy
The following are indications for pharmacologic therapy of SQTS[7]:
- In children as an alternate to AICD implantation
- In patients with a contraindications AICD implantation
- In patients who decline AICD implantation
- In patients with appropriate AICD discharges to reduce the frequency of discharges
- In patients with atrial fibrillation to reduce the frequency of symptomatic episodes
References
- ↑ Borggrefe M. FESC, Wolpert C, Veltmann C, Giustetto C, Gaita F, Schimpf R. Short QT Syndrome : A new primary electrical disease, ESC E journal, Vol 3 N°34, 10 May 2005. [1]
- ↑ Schimpf R, Wolpert C, Bianchi F, et al. Congenital Short QT Syndrome and Implantable Cardioverter Defibrillator Treatment: Inherent Risk for Inappropriate Shock Delivery. J Cardiovasc Electrophysiol 2003; 14: 1273-1277.
- ↑ 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.
- ↑ Wolpert C, Schimpf R, Giustetto C, Antzelevitch C, Cordeiro J, Dumaine R, Brugada R, Hong K, Bauersfeld U, Gaita F, Borggrefe M (2005). "Further insights into the effect of quinidine in short QT syndrome caused by a mutation in HERG". Journal of Cardiovascular Electrophysiology. 16 (1): 54–8. doi:10.1046/j.1540-8167.2005.04470.x. PMC 1474841. PMID 15673388. Retrieved 2012-09-03. Unknown parameter
|month=ignored (help) - ↑ Gaita F, Giustetto C, Bianchi F, Schimpf R, Haissaguerre M, Calò L, Brugada R, Antzelevitch C, Borggrefe M, Wolpert C (2004). "Short QT syndrome: pharmacological treatment". Journal of the American College of Cardiology. 43 (8): 1494–9. doi:10.1016/j.jacc.2004.02.034. PMID 15093889. Retrieved 2012-09-03. Unknown parameter
|month=ignored (help) - ↑ Bjerregaard P, Gussak I. Atrial fibrillation in the setting of familial short QT interval. Heart Rhythm 2004; 1: S165 (abstract).
- ↑ Moreno-Reviriego S, Merino JL.Short QT Syndrome. An article from the E-Journal of the ESC Council for Cardiology Practice. Vol9 N°2, 17 Sep 2010 [2]