(See also Overview of Arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more and Overview of Channelopathies Overview of Channelopathies Channelopathies are a group of genetic, autoimmune, or inflammatory conditions that alter cardiomyocyte ion channel function in a manner that predisposes to bradyarrhythmias or tachyarrhythmias... read more .)
The cardiac ion channel dysfunction may involve
Gain of function of repolarizing potassium current channels OR
Loss of function of depolarizing sodium or depolarizing calcium current channels
Note the changes in channel function (ie, gain or loss) are the opposite of those occurring in long QT interval syndrome Long QT Interval Syndromes The long QT interval syndromes (LQTS) result from any congenital or acquired disorder of cardiac ion channel function or regulation (channelopathy) that prolongs ventricular myocyte action potential... read more .
The shortening of the action potential duration is most marked in the ventricular epicardium and may lead to polymorphic ventricular tachycardia (VT) or ventricular fibrillation (VF) often leading to sudden death. The likelihood of ventricular tachyarrhythmias increases with the degree of QTc interval shortening. Some patients with SQTS are also prone to atrial fibrillation Atrial Fibrillation Atrial fibrillation is a rapid, irregularly irregular atrial rhythm. Symptoms include palpitations and sometimes weakness, effort intolerance, dyspnea, and presyncope. Atrial thrombi may form... read more .
Short QT interval syndromes are classified based on the specific gene that has mutated. Abnormal genes include KCNH2, KCNQ1, and KCNJ2.
Patients are asymptomatic unless atrial fibrillation or VT/VF occurs, which may cause palpitations, near syncope, syncope, or cardiac arrest.
Diagnosis of SQTS
Specific clinical and electrocardiographic criteria
Screening of first-degree family members
Diagnosis should be considered in patients with unexplained cardiac arrest or syncope or a family history of such when the affected people do not have structural heart disease. It should also be considered in people who are discovered to have a short QT interval when ECG is done for other reasons.
Diagnosis is by ECG showing shortening of the rate-corrected QT interval (QTc). The degree of shortening of the QTc required is debated but ranges from < 0.36 second to ≤ 0.33 second; the longer durations may be more appropriate when patients or family members have a known mutation, documented VT/VF, or unexplained cardiac arrest. Genetic testing has a low yield (approximately 20%). A set of diagnostic criteria have been proposed (1 Diagnosis reference The short QT interval syndromes (SQTS) are extremely rare congenital or very rarely acquired disorders of cardiac ion channel function or regulation that shorten ventricular myocyte action potential... read more ). Additional testing may include ambulatory cardiac rhythm monitoring and cardiac imaging.
First-degree family members of patients should have clinical evaluation (ie, to detect symptoms suggestive of arrhythmia) and ECG. Genetic testing of family members is done when the patient has an identified mutation.
Treatment of SQTS
Treatment of any VT/VF
Usually an implantable cardioverter-defibrillator (ICD)
Treatment with quinidine (which prolongs the QT interval) has been proposed, but most symptomatic patients receive an ICD. Expert consensus is that an ICD may be considered for asymptomatic patients with a family history of sudden death (1 Treatment reference The short QT interval syndromes (SQTS) are extremely rare congenital or very rarely acquired disorders of cardiac ion channel function or regulation that shorten ventricular myocyte action potential... read more ).
1. Priori SG, Wilde AA, Horie M, et al: HRS/EHRA/APHRS Expert Consensus Statement on the diagnosis and management of patients with inherited primary arrhythmia syndromes: : document endorsed by HRS, EHRA, and APHRS in May 2013 and by ACCF, AHA, PACES, and AEPC in June 2013. Heart Rhythm 10:1932–1963, 2013. doi: 10.1016/j.hrthm.2013.05.014
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