The ECG after Transient Loss of Consciousness
| ECG feature | Comment |
|---|---|
| Sinus bradycardia (rate <50/min) or sinus pauses | May reflect sinoatrial disorder. Pacing indicated for syncope with sinus bradycardia <40/min or sinus pauses >3s. |
| Sinus tachycardia | Many possible causes. Consider:
|
| First-degree AV block | Raises the possibility of intermittent second- or third-degree AV block, but as an isolated abnormality is usually of no significance. |
| Second-degree AV block | Likely to be the cause of syncope: indication for pacing. |
| Third-degree (complete) AV block | Likely to be the cause of syncope: indication for pacing. Arrange echocardiography to check for associated structural heart disease and assess left ventricular function. |
| Atrial fibrillation | May reflect sinoatrial disorder of underlying structural heart disease. Indication for echocardiography. |
| Paced rhythm | Pacemaker failure is rare but should be excluded. Arrange for interrogation of device to determine rhythm at the time of TLoC. |
| Short PR interval (<120ms) | Look for other features of Wolff-Parkinson-White (WPW) syndrome: delta wave, widened QRS complex. If WPW present, discuss management with a cardiologist. |
| Right-axis deviation (QRS predominantly negative in lead I and positive in lead II) | Consider pulmonary hypertension or pulmonary embolism. |
| Left-axis deviation (QRS predominantly positive in lead I and negative in lead II) | As an isolated abnormality, usually of no significance. |
| Right bundle branch block (RBBB) | Consider pulmonary hypertension or pulmonary embolism. Consider Brugada syndrome (ECG shows RBBB pattern with ST-elevation in leads V1–V3). |
| Left bundle branch block (LBBB) | May reflect structural heart disease or conducting system disease. Arrange echocardiography. |
| Bifascicular block (RBBB or LBBB with right-axis or left-axis deviation), with or without first-degree AV block | Significantly increases the likelihood that syncope was due to intermittent AV block. |
| Left ventricular hypertrophy | May be seen in:
|
| Pathological Q waves | Usually reflect previous myocardial infarction (with associated risk of ventricular tachycardia (Chapter 40)). May also be seen in hypertrophic cardiomyopathy or WPW syndrome (pseudoinfarct pattern). |
| Dominant R wave in V1 | May be seen in:
|
| Short QT interval | Short QT interval may reflect congenital channelopathy (short QT syndrome) or acquired disorder (e.g. due to acidosis, hyperkalaemia or hypercalcaemia), or a combination of the two. Short QT syndrome is associated with atrial and ventricular arrhythmias. |
| Long QT interval | Long QT interval may reflect congenital channelopathy (long QT syndrome) or acquired disorder (due to drugs (see http://www.sads.org.uk/drugs-to-avoid/), or metabolic disorder (e.g. hypokalaemia or hypocalcaemia)), or a combination of the two QT interval >500ms is associated with high risk of polymorphic ventricular tachycardia (torsade de pointes) (Chapter 41). |
| T wave inversion | May be seen in:
|