Short QT syndrome: Difference between revisions
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===First Family with Short QT Syndrome=== | ===First Family with Short QT Syndrome=== | ||
The | The QT interval of her 21 year old brother was 240 msec, the QT interval of her 84 year old maternal grandfather was 240 msec, and the QT interval of her 51 year old mother was 230 msec. The EKG of here father was normal. | ||
He brother had no history of [[palpitations]], [[dizziness]] or [[syncope]]. August 13, 2003, he underwent a programmed electrical stimulation study with induction of ventricular fibrillation followed by implantation of an implantable cardioverter defibrillator. During follow-up he admited to occasional palpitations and interrogation of the ICD shows few brief episodes of atrial fibrillation with fast ventricular response. He has so far not received any shocks. | |||
Her mother is a 51 year old healthy white female with a QT interval of 230 ms and a history of 3 episodes of sustained palpitations and two of them documented as atrial fibrillation. On propafenone since April, 2003 she has been asymptomatic. She underwent programmed electrical stimulation study September 29, 2003 with induction of both atrial and ventricular fibrillation and received an implantable cardioverter defibrillator. She has so far not received any shocks. | Her mother is a 51 year old healthy white female with a QT interval of 230 ms and a history of 3 episodes of sustained palpitations and two of them documented as atrial fibrillation. On propafenone since April, 2003 she has been asymptomatic. She underwent programmed electrical stimulation study September 29, 2003 with induction of both atrial and ventricular fibrillation and received an implantable cardioverter defibrillator. She has so far not received any shocks. | ||
Revision as of 00:01, 3 September 2012
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Synonyms and keywords: SQTS; short QT; short QTc; QT interval shortening
Overview
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.
Historical Perspective
The syndrome was first described by Dr. Prebe Bjerregaard MD, DMSc in 1999.
First Patient with Short QT Syndrome
Shalon Hill, a 17 year old white female, underwent laparoscopic cholecystectomy at Anderson Hospital, Maryville, Illinois in 1999 which was complicated by atrial fibrillation with a rapid ventricular response (RVR) at 150-200 beats/min along with acute pulmonary edema[1]. The atrial fbrillation with RVR was treated with DC cardioversion and she was discharged to home in normal sinus rhythm on digoxin. The atrial fibrillation recurred 6 weeks later and she was found at that time to have a short QT interval of 225 mseconds which was treated with prophylactic therapy with propafenone. She then remained asymptomatic for 6 months and the propafenone was discontinued. However, the atrial fibrillation recurred 2 months after the propafenone was discontinued, and it was therefore resumed. She remained asymptomatic on propafenone, but an AICD was implanted given reports from around the world of sudden cardiac death.
First Family with Short QT Syndrome
The QT interval of her 21 year old brother was 240 msec, the QT interval of her 84 year old maternal grandfather was 240 msec, and the QT interval of her 51 year old mother was 230 msec. The EKG of here father was normal.
He brother had no history of palpitations, dizziness or syncope. August 13, 2003, he underwent a programmed electrical stimulation study with induction of ventricular fibrillation followed by implantation of an implantable cardioverter defibrillator. During follow-up he admited to occasional palpitations and interrogation of the ICD shows few brief episodes of atrial fibrillation with fast ventricular response. He has so far not received any shocks.
Her mother is a 51 year old healthy white female with a QT interval of 230 ms and a history of 3 episodes of sustained palpitations and two of them documented as atrial fibrillation. On propafenone since April, 2003 she has been asymptomatic. She underwent programmed electrical stimulation study September 29, 2003 with induction of both atrial and ventricular fibrillation and received an implantable cardioverter defibrillator. She has so far not received any shocks.
Her grandfather is an 84 year old white male (born in Italy) with chronic atrial fibrillation in the setting of coronary artery disease and arterial hypertension. Following an embolic stroke he dies. ECG’s taken on several occasions all show short QT interval (240 ms).
Pathophysiology
The etiology 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. In the families afflicted by short QT syndrome, two different missense mutations have been described in the human ether-a-go-go gene (HERG). These mutations result in expression of the same amino acid change in the cardiac IKr ion channel. This mutated IKr has increased activity compared to the normal ion channel, and would theoretically explain the above hypothesis.
Genetics
In the families afflicted by short QT syndrome, mutations have been described in three genes, KvLQT1, the human ether-a-go-go gene (HERG), and KCNJ2. 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.
Due to the autosomal dominant inheritance pattern, individuals may have family members with a history of unexplained or sudden death at a young age (even in infancy), palpitations, or atrial fibrillation.
Causes
Common Causes
Causes in Alphabetical Order
Epidemiology and Demographics
Since the syndrome was first described in 2000, < 30 cases have been identified.
Natural History, Complications, Prognosis
Short QT syndrome is associated with an increased risk of sudden cardiac death, most likely due to ventricular fibrillation.
Diagnosis
Diagnostic Criteria
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 criteria is based on a point system as follows:
- QTc in milliseconds
- <370 = 1 point
- <350 = 2 points
- <330 = 3 points
- J point - T peak interval in milliseconds
- <120 = 1 point
- Clinical History
- Sudden cardiac arrest = 2 points
- Polymorphic VT or VF = 2 points
- Unexplained syncope = 1 point
- Atrial fibrillation = 1 point
- Family History
- 1st or 2nd degree relative with SQTS = 2 points
- 1st or 2nd degree relative with sudden death = 1 point
- Sudden infant death syndrome = 1 point
- Genotype
- Genotype positive = 2 points
- Mutation of undetermined significance in a culprit gene = 1 point
The points are summed and interpreted as follows:
- > or equal to 4 points: High-probability of SQTS
- 3 Points: Intermediate probability of SQTS
- 2 points or less: Low probability of SQTS
Symptoms
Some individuals with short QT syndrome complain of frequent palpitations and may experience unexplained syncope (loss of consciousness).
Electrocardiogam
The characteristic findings of short QT syndrome on EKG are a short QT interval, typically ≤ 300 ms, that doesn't significantly change with the heart rate. Tall, peaked T waves may also be noted. Individuals may also have an underlying atrial rhythm of atrial fibrillation.
Electrophysiologic Studies
In the electrophysiology lab, individuals with short QT syndrome are noted to have short refractory periods, both in the atria as well as in the ventricles. Also, ventricular fibrillation is frequently induced on programmed stimulation.
Genetic Testing
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.
Treatment
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 cardiac 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]
See also
References
- ↑ http://www.shortqtsyndrome.org/short_qt_history.htm
- ↑ 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.
- ↑ 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.