Forty percent of patients remain asymptomatic.
Ten percent of patients will have as first clinical sign, a cardiac arrest. Symptoms include syncope,
“epilepsy,” and palpitations precipitated by stressful events (intense
emotion or physical activity). Swimming appears to be a potent trigger.
Sudden death or cardiac arrest secondary to ventricular dysrhythmia can be the presentation. ECG
findings include long QTc interval (QTc = QT interval/square root of R-R
interval) calculated in lead II or V5 and abnormal T-wave morphology.
Ventricular dysrhythmias, torsades de pointes, and ventricular tachycardia
are common causes of collapse. Medical management includes beta blockade,
pacemaker insertion, implantable cardioverter-defibrillator placement, and
rarely left stellate ganglion excision/ablation. Genotyping may allow
targeting drugs at specific ion channels in the future.