In most cases, modern therapy favors ICD implantation if beta blocker therapy fails. In patients considered at high risk of life-threatening arrhythmic events, ICD implantation may be considered as a preventive step. Arrhythmia termination
Arrhythmia termination involves stopping a life-threatening arrhythmia once it has already occurred. One effective form of arrhythmia termination in individuals with LQTS is placement of an implantable cardioverter-defibrillator (ICD). Also, external defibrillation can be used to restore sinus rhythm. ICDs are commonly used in patients with fainting episodes despite beta blocker therapy, and in patients having experienced a cardiac arrest. As mentioned earlier, ICDs may be used also in patients considered at high risk of life-threatening arrhythmic events.With better knowledge of the genetics underlying LQTS, more precise treatments hopefully will become available. Outcomes
Genotype and QT interval duration are the strongest predictors of outcome for patients with LQTS. These have been combined to create an externally validated risk score calculator, estimating a 5-year risk for each individual patient, which can help physicians to identify patients at the highest 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%. With careful treatment this decreases to less than 1% over 20 years. Those who exhibit symptoms before the age of 18 are more likely to experience a cardiac arrest. Epidemiology
Inherited LQTS is estimated to affect between one in 2,500 and 7,000 people.
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.