ECG Features that suggest a potentially life-threatening arrhythmia as the cause for syncope.

Syncope is a risk factor for sudden cardiac death (SCD) in many conditions associated with structural heart disease as well as inherited heart disease. The ECG in patients with syncope should be examined carefully for signs of structural heart disease, such as myocardial infarction or cardiomyopathy; signs of conduction system disease, such as bundle branch block or atrioventricular block; and signs of primary electrical disease. Important forms of cardiomyopathy accompanied by ECG changes include hypertrophic cardiomyopathy (HCM), and arrhythmogenic right ventricular dysplasia (ARVD/C). Common ECG findings in HCM include left ventricular hypertrophy by voltage, repolarization abnormalities, QRS widening, pseudoinfarction patterns, and slurred QRS upstroke mimicking delta waves. Classical ECG findings of ARVD/C include T-wave inversions and epsilon waves in the right precordial leads (V₁-V₃). Important forms of primary electrical disease which may result in syncope include Wolff-Parkinson-White syndrome, long QT syndrome, and Brugada syndrome, which is characterized by coved ST-segments in the right precordial leads, associated with a history of syncope, ventricular arrhythmia, or sudden cardiac death in probands or family member. There are three Brugada ECG patterns; however, only type I (spontaneous or induced) is considered diagnostic. Recently, studies have suggested that patients with J-point elevation or early repolarization pattern on ECG are at elevated risk of SCD. The clinical significance of finding early repolarization in a patient with syncope is unknown and should be a subject of future research.