23. What are the triggers for sudden cardiac death in patients with prolonged QT syndrome based on the different types of this disease?

Prolonged QT syndrome (aka Long QT Syndrome) consists of multiple different variations including long QT type 1-12, Romano-Ward syndrome and Jervell-Lange-Nielsen syndrome.

A prolonged QT interval increases the risk for polymorphic ventricular tachycardia (Torsades de Pointes), which can result in sudden cardiac death.

Long QT 1: The ECG shows broad-based T waves. A majority of arrhythmias in this group occur during exercise. Beta-blockers are effective treatment and an implantable cardioverter defibrillator (ICD) is not required unless syncope or cardiac arrest occurs. The risk for sudden cardiac death is 1% at 1 year in this group on beta-blocker therapy.

Long QT 2: The ECG shows low amplitude T waves frequently with a notch. Arrhythmias are more likely to occur during rest/sleep, especially with sudden awakening and/or auditory stimuli. Beta-blockers are somewhat effective. The risk for sudden cardiac death in this group is 7% at 1 year while on beta-blocker therapy.

Long QT 3: The ECG frequently shows an extended ST segment with a relatively narrow T wave, which can be peaked. This is also the finding when hypocalcemia prolongs the QT interval. Beta-blockers are not effective. Arrhythmias also occur during rest, similar to long QT 2. Sudden cardiac death risk is 14% at 1 year while on beta-blocker therapy.

Treatment includes beta-blockers and implantation of an ICD.