The 12-lead ECG is crucial for establishing many cardiac diagnoses (see table Interpretation of Abnormal ECGs), including Arrhythmias Atrial enlargement Conditions that predispose to syncope or sudden death (eg, Brugada syndrome, long QT syndrome, Wolff-Parkinson-White syndrome) Myocardial ischemia Ventricular hypertrophy (see table Criteria for ECG Diagnosis of Left Ventricular Hypertrophy) For more information on ECG interpretation, see Overview of Arrhythmias and ECG in Acute Coronary Syndromes.