It is a relatively common cause of sudden death along with Brugada syndrome and arrhythmogenic right ventricular dysplasia. In the United States it results in about 3,500 deaths a year. The condition was first clearly described in 1957. Signs and symptoms
Many people with long QT syndrome have no signs or symptoms. When symptoms occur, they are generally caused by abnormal heart rhythms (arrhythmias), most commonly a form of ventricular tachycardia called Torsades de pointes (TdP). If the arrhythmia reverts to a normal rhythm spontaneously the affected person may experience lightheadedness (known as presyncope) or faint which may be preceded by a fluttering sensation in the chest. If the arrhythmia continues, the affected person may experience a cardiac arrest, which if untreated may lead to sudden death. Those with LQTS may also experience seizure-like activity (non-epileptic seizure) as a result of reduced blood flow to the brain during an arrhythmia. Epilepsy is also associated with certain types of long QT syndrome.The arrhythmias that lead to faints and sudden death are more likely to occur in specific circumstances, in part determined by which genetic variant is present.
Nadolol, a powerful non-selective beta blocker, has been shown to reduce the arrhythmic risk in all three main genotypes (LQT1, LQT2, and LQT3).Genotype and QT interval duration are independent predictors of recurrence of life-threatening events during beta-blocker therapy. To be specific, the presence of QTc >500 ms and LQT2 and LQT3 genotype are associated with the highest incidence of recurrence. In these patients, primary prevention with use of implantable cardioverter-defibrillators can be considered. Potassium supplementation: If the potassium content in the blood rises, the action potential shortens, so increasing potassium concentration could minimize the occurrence of arrhythmias. It should work best in LQT2, since the hERG channel is especially sensitive to potassium concentration, but the use is experimental and not evidence-based. Sodium channel blocking drugs such as mexiletine have been used to prevent arrhythmias in long QT syndrome. While the most compelling indication is for those whose long QT syndrome is caused by defective sodium channels producing a sustained late current (LQT3), mexiletine also shortens the QT interval in other forms of long QT syndrome including LQT1, LQT2 and LQT8. As the predominant action of mexiletine is on the early peak sodium current, there are theoretical reasons why drugs which preferentially suppress the late sodium current such as ranolazine may be more effective, although evidence that this is the case in practice is limited. Amputation of the cervical sympathetic chain (left stellectomy). This therapy is typically reserved for LQTS caused by JLNS, but may be used as an add-on therapy to beta blockers in certain cases.