Most are asymptomatic
History may include:
Syncope
Cardiac arrest
Family history of long QT or sudden death
Medication history may include QT prolonging medications
Syncope
Cardiac arrest
Family history of long QT or sudden death
QT prolongation
Cardiovascular-mediated syncope
T wave changes
Dysrhythmias:
ST segment elevation
WPW 
ST segment depression
Long QT Syndrome/QT prolongation