Generally, the ECG of individuals with syncope is normal. However, ECG may be remarkable for an arrhythmia. The arrhythmia may be seen on the EKG include sinus bradycardia <40 beats/min or repetitive sinoatrial blocks or sinus pauses > 3s, Mobitz II 2nd or 3rd-degree atrioventricular block, alternating left and right bundle branch block, rapid paroxysmal supraventricular tachycardia, ventricular tachycardia, and pacemaker malfunction with cardiac pauses.

Generally, the ECG of individuals with syncope is normal. However, ECG may be remarkable for an arrhythmia. The following arrhythmia may be seen on the EKG:^[1][2]

• Sinus bradycardia <40 beats/min or repetitive sinoatrial blocks or sinus pauses > 3s
• Mobitz II 2nd or 3rd-degree atrioventricular block
• Alternating left and right bundle branch block
• Rapid paroxysmal supraventricular tachycardia
• Ventricular tachycardia
• Pacemaker malfunction with cardiac pauses

An ECG may be helpful in the diagnosis of syncope. Findings on an ECG suggestive of cardiovascular syncope include:

• Bifascicular block (defined as either left bundle branch block or right bundle branch block combined with left anterior or left posterior fascicular block)
• Other intraventricular conduction abnormalities (QRS duration > 0.12 s)
• Mobitz I second degree atrioventricular block
• Asymptomatic sinus bradycardia (<50 beats/min) in the absence of negatively chronotropic medications use
• Pre-excited QRS complexes
• QT prolongation
• Right bundle branch block pattern with ST elevation in leads V1-V3 (Brugada syndrome)
• Negative T waves in right precordial leads, epsilon waves and ventricular late potentials suggestive of arrhythmogenic right ventricular dysplasia
• Q waves suggesting previous myocardial infarction

Shown below is an EKG of an elderly man with syncope.

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