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 duration as reflected by shortening of the rate-corrected QT interval on the ECG.
(See also Overview of Arrhythmias and Overview of Channelopathies.)
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.
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.
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
Genetic testing
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). 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.
Diagnosis reference
1. Gollob MH, Redpath CJ, Roberts JD: The short QT syndrome: proposed diagnostic criteria. J Am Coll Cardiol 57:802–812.2011. doi: 10.1016/j.jacc.2010.09.048
Treatment of SQTS
Treatment of any VT/VF
Usually an implantable cardioverter-defibrillator (ICD)
1).
Treatment reference
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
