Aortic stenosis or hypertrophic cardiomyopathy:
Exertional syncope
Systolic murmur on examination
Ventricular tachycardia:
No preceding symptoms
Cardiomyopathy or previous myocardial infarction
Sick sinus syndrome:
Preceding fatigue or dizziness
Sinus pauses on ECG
Advanced atrioventricular block:
Bifascicular block or ↑ PR interval on ECG
Dropped QRS complexes on ECG
Torsades de pointes
No preceding symptoms
Medications that prolong QT interval
Hypokalemia or hypomagnesemia