Long QT syndrome is a congenital disorder characterized by a prolongation of the QT interval on electrocardiograms and a propensity to ventricular tachyarrhythmias, which may lead to syncope, cardiac arrest, or sudden death.
symptoms Long QT syndrome is usually diagnosed after a person has a cardiac event (eg, syncope, cardiac arrest). In some situations, this condition is diagnosed after a family member suddenly dies. In some individuals, the diagnosis is made when an electrocardiogram shows QT prolongation.
Treatment All patients with long QT syndrome (LQTS) should avoid drugs that prolong the QT interval or that reduce their serum potassium or magnesium level. Potassium and magnesium deficiency should be corrected. Although treating asymptomatic patients is somewhat controversial, a safe approach is to treat all patients with congenital LQTS because sudden cardiac death can be the first manifestation of LQTS. Beta-blockers are drugs of choice for patients with LQTS. The protective effect of beta-blockers is related to their adrenergic blockade, which diminishes the risk of cardiac arrhythmias. They may also reduce the QT interval in some patients.
Research The first member of a family to be identified with LQTS, the proband, was usually brought to medical attention because of a syncopal episode during childhood or teenage years. Probands (n = 328) were younger at first contact (age 21 +/- 15 years), more likely to be female (69%), and had a higher frequency of preenrollment syncope or cardiac arrest with resuscitation (80%), congenital deafness (7%), a resting heart rate less than 60 beats/min (31%), QTc greater than or equal to 0.50 sec1/2 (52%), and a history of ventricular tachyarrhythmia (47%) than other affected (n = 688) and unaffected (n = 1,004) family members. Arrhythmogenic syncope often occurred in association with acute physical, emotional, or auditory arousal. The syncopal episodes were frequently misinterpreted as a seizure disorder. By age 12 years, 50% of the probands had experienced at least one syncopal episode or death. The rates of postenrollment syncope (one or more episodes) and probable LQTS-related death (before age 50 years) for probands (n = 235; average follow-up 54 months per patient) were 5.0% per year and 0.9% per year, respectively; these event rates were considerably higher than those observed among affected and unaffected family members.
33 identified cases, 55 % presented with TdP with the need of resuscitation and 45 % showed nonsustained VT, respectively. In the total cohort the mean corrected QT interval (QTc) was 532 ± 29 ms, with 530 ± 31 ms (n = 14) in men and 533 ± 28 ms (n = 19) in women (p = 0.80), respectively. Cardiac drugs with QTc interval prolonging effect were reported in 24 % of cases, and the other 76 % involved noncardiac medications. Although hypokalemia is the most common risk factor for drug-induced malignant arrhythmias, a QTc interval of at least 500 ms seems to be the major determinant of the risk of drug-induced proarrhythmias. Interestingly, patients with TdP exhibit more bradycardia as such with VT.