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.
In response to a triggering impulse, the waves of depolarisation will spread through regions with shorter action potentials but block in regions with longer action potentials. This allows the depolarising wavefront to bend around areas of block, potentially forming a complete loop and self-perpetuating. The twisting pattern on the ECG can be explained by movement of the core of the re-entrant circuit in the form of a meandering spiral wave. Diagnosis
Diagnosing long QT syndrome is challenging. Whilst the hallmark of LQTS is prolongation of the QT interval, the QT interval is highly variable among both those who are healthy and those who have LQTS. This leads to overlap between the QT intervals of those with and without LQTS. 2.5% of those with genetically proven LQTS have a QT interval within the normal range. Conversely, given the normal distribution of QT intervals, a proportion of healthy people will have a longer QT interval than any arbitrary cutoff. Other factors beyond the QT interval should therefore be taken into account when making a diagnosis, some of which have been incorporated into scoring systems. Electrocardiogram
Long QT syndrome is principally diagnosed by measuring the QT interval corrected for heart rate (QTc) on a 12-lead electrocardiogram (ECG). Long QT syndrome is associated with a prolonged QTc, although in some genetically proven cases of LQTS this prolongation can be hidden, known as concealed LQTS. The QTc is less than 450 ms in 95% of normal males, and less than 460 ms in 95% of normal females.