Синдром удлиненного интервала QT: диагностика, лечение и риски.

Management may include avoiding strenuous exercise, getting sufficient potassium in the diet, the use of beta blockers, or an implantable cardiac defibrillator. Long QT syndrome is estimated to affect 1 in 7,000 people.

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. Epilepsy is also associated with certain types of long QT syndrome. Some rare forms of long QT syndrome affect other parts of the body, leading to deafness in the Jervell and Lange Nielsen form of the condition, and periodic paralysis in the Andersen–Tawil (LQT7) form. The strongest predictor of whether someone will develop TdP is whether they have experienced this arrhythmia or another form of cardiac arrest in the past. Those with LQTS who have experienced syncope without an ECG having been recorded at the time are also at higher risk, as syncope in these cases is frequently due to an undocumented self terminating arrhythmia. While some have QT intervals that are very prolonged, others have only slight QT prolongation, or even a normal QT interval at rest (concealed LQTS). Those with the longest QT intervals are more likely to experience TdP, and a corrected QT interval of greater than 500 ms is thought to represent those at higher risk. Despite this, those with only subtle QT prolongation or concealed LQTS still have some risk of arrhythmias.

There are several subtypes of long QT syndrome. These can be broadly split into those caused by genetic mutations which those affected are born with, carry throughout their lives, and can pass on to their children (inherited or congenital long QT syndrome), and those caused by other factors which cannot be passed on and are often reversible (acquired long QT syndrome).

Inherited, or congenital long QT syndrome, is caused by genetic abnormalities. LQTS can arise from variants in several genes, leading in some cases to quite different features. The common thread linking these variants is that they affect one or more ion currents leading to prolongation of the ventricular action potential, thus lengthening the QT interval. A less commonly seen form is Jervell and Lange Nielsen syndrome, an autosomal recessive form of LQTS combining a prolonged QT interval with congenital deafness.

In cases of diagnostic uncertainty, other investigations may be helpful to unmask a prolonged QT. In addition to prolonging the resting QT interval, LQTS may affect how the QT changes in response to exercise and stimulation by catecholamines such as adrenaline. Provocation tests, in the form of exercise tolerance tests or direct infusion of adrenaline, can be used to detect these abnormal responses. These investigations are most useful for identifying those with concealed congenital Type 1 LQTS 1 (LQT1) who have a normal QT interval at rest. While in healthy persons the QT interval shortens during exercise, in those with concealed LQT1 exercise or adrenaline infusion may lead to paradoxical prolongation of the QT interval, revealing the underlying condition. Both sets of guidelines agree that LQTS can also be diagnosed if an individual has a Schwartz score of greater than 3 or if a pathogenic genetic variant associated with LQTS is identified, regardless of QT interval. In addition to this, two intervention options are known for individuals with LQTS: arrhythmia prevention and arrhythmia termination.

Arrhythmia suppression involves the use of medications or surgical procedures that attack the underlying cause of the arrhythmias associated with LQTS. Since the cause of arrhythmias in LQTS is early afterdepolarizations (EADs), and they are increased in states of adrenergic stimulation, steps can be taken to blunt adrenergic stimulation in these individuals. These include administration of beta receptor blocking agents, which decreases the risk of stress induced arrhythmias. Nadolol, a powerful non selective beta blocker, has been shown to reduce the arrhythmic risk in all three main genotypes (LQT1, LQT2, and LQT3). While the most compelling indication is for those whose long QT syndrome is caused by defective sodium channels producing a sustained late current (LQT3), 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. ICD implantation may be considered as a preventive step.

Genotype and QTc interval duration are the strongest predictors of outcome for patients with LQTS. have endorsed the use of independently validated risk score calculator, called 1 2 3 LQTS Risk Calculator, which allows to calculate individual 5 year risk of life threatening arrhythmic events. For people who experience cardiac arrest or fainting caused by LQTS and who are untreated, the risk of death within 15 years is around 50%.

Inherited LQTS is estimated to affect between one in 2,500 and 7,000 people. This was several decades before the ECG was invented, but is likely the first described case of Jervell and Lange Nielsen syndrome. In 1957, the first case documented by ECG was described by Anton Jervell and Fred Lange Nielsen, working in Tønsberg, Norway. Italian pediatrician Cesarino Romano, in 1963, and Irish pediatrician Owen Conor Ward, in 1964, separately described the more common variant of LQTS with normal hearing, later called Romano Ward syndrome. The establishment of the International Long QT Syndrome Registry in 1979 allowed numerous pedigrees to be evaluated in a comprehensive manner. This helped in detecting many of the numerous genes involved. Transgenic animal models of the LQTS helped define the roles of various genes and hormones involved, and recently experimental pharmacological therapies to normalize the abnormal repolarization in animals were published.