Syncope is defined as a loss of consciousness that results from insufficient blood flow to the brain. Syncope accounts for more than 700,000 emergency department (ED) visits and 6% of hospital admissions each year in the United States. Though most etiologies are benign, a small portion of patients have a life-threatening cause of their syncope.
The history of present illness, physical examination, and 12-lead electrocardiogram (ECG) are fundamental to the ED evaluation of a patient with syncope. In fact, it is often the ECG that provides critical clues to the etiology of potentially life-threatening causes of syncope.
In the ED patient with syncope, the ECG should be scrutinized for signs of ischemia, bradydysrhythmias, tachydysrhythmias, and conduction delays.
![Abnormal Ecg Findings of Cardiac Syncope](https://manualofmedicine.com/wp-content/uploads/2021/11/Abnormal-Ecg-Findings-of-Cardiac-Syncope.png)
Additional critical diagnoses to consider that can be detected with the ECG include:
- Ventricular preexcitation syndromes
- Brugada syndrome
- Long or short QT syndromes
- Hypertrophic cardiomyopathy
- Arrhythmogenic right ventricular dysplasia
- Catecholaminergic polymorphic ventricular tachycardia
Ventricular Preexcitation (Wolff Parkinson White (WPW) Syndrome)
- PR segment < 120 ms
- QRS complex > 110 ms
- Slurred upstroke of the initial part of the R wave (delta wave)
- Type A: left-sided accessory pathway—delta wave in all precordial leads, R > S in lead V1
- Type B: right-sided accessory pathway—negative delta waves in leads V1 and V2
![Wolff Parkinson White (WPW) Syndrome - ECG Changes](https://manualofmedicine.com/wp-content/uploads/2021/11/Wolff-Parkinson-White-WPW-Syndrome-ECG-Changes.jpg)
![Wolff-Parkinson-White - Pathogenesis and clinical findings](https://manualofmedicine.com/wp-content/uploads/2021/08/Wolff-Parkinson-White-Pathogenesis-and-clinical-findings.png)
Brugada Syndrome
- Type 1
- Coved ST-segment elevation
- >2 mm of ST-segment elevation in 2 or more precordial leads (V1 to V3) followed by negative T wave
- Type 2
- Saddle back ST-segment elevation
- >2 mm of ST-segment elevation in 2 or more precordial leads (V1 to V3)
- Type 3
- Either type 1 or 2 with <2 mm ST-segment elevation
![Types of Brugada Syndrome](https://manualofmedicine.com/wp-content/uploads/2021/11/Types-of-Brugada-Syndrome.jpg)
Long QT Syndrome
- QTc = QT/√R-R interval
- Prolonged if QTc > 440 ms in men or >460 ms in females
- Increased risk of dysrhythmias when the QTc > 500 ms
- Potential for a “R on T” phenomenon, where a premature ventricular contraction at the end of T wave can induce polymorphic ventricular tachycardia or torsades de Pointes.
- Etiologies to consider include electrolyte deficiencies (potassium, magnesium, calcium), hypothermia, cardiac ischemia, increased intracranial pressure, and toxins.
![Long QT Syndrome](https://manualofmedicine.com/wp-content/uploads/2021/11/Long-QT-Syndrome.jpg)
Short QT Syndrome
- Shortened if QTc < 330 ms in males or <340 ms in females
- Short, or absent, ST-segment with peaked appearance of the T wave
- Etiologies to consider include congenital shortening, digoxin toxicity, and hypercalcemia.
Hypertrophic cardiomyopathy (HCM)
- Deep Q waves in the lateral (I, aVL, V5-V6) and inferior (II, III, aVF) leads
- Left ventricular hypertrophy (LVH)
- Left atrial enlargement
- Apical HCOM variant
- Localized hypertrophy of the LV apex
- LVH
- Giant T-wave inversions in the precordial leads
- Possibly inverted T waves in the inferior and lateral leads
![The ECG in Hypertrophic cardiomyopathy (HCM)](https://manualofmedicine.com/wp-content/uploads/2021/11/The-ECG-in-Hypertrophic-cardiomyopathy-HCM.jpg)
Arrhythmogenic Right Ventricular Dysplasia (ARVD)
- Epsilon wave (small positive deflection at end of QRS complex) is the most specific finding and found in ~30% of patients.
- T-wave inversions in leads V1 to V3
- Prolonged QRS in leads V1 to V3 (100 to 120 ms)
- Slurred S-wave upstroke in leads V1 to V3 (50 to 55 ms)
- Consider ARVD in patients with paroxysmal episodes of ventricular tachycardia.
![Epsilon Waves in Arrhythmogenic right ventricular dysplasia (ARVD)](https://manualofmedicine.com/wp-content/uploads/2021/11/Epsilon-Waves-in-Arrhythmogenic-right-ventricular-dysplasia-ARVD.png)
Catecholaminergic Polymorphic Ventricular Tachycardia
- ECG is typically normal at rest.
- Exercise classically induces ventricular tachycardia from adrenergic activation.
- Bidirectional tachycardia (alternating 180 degrees QRS axis beat to beat variation)
- Ventricular ectopy is often noted when the heart rate increases above 100 beats per minute.
Key Points
- An ECG should be performed on all ED patients with syncope.
- Scrutinize the ECG for signs of ischemia, conduction delay, tachydysrhythmias, and bradydysrhythmias.
- Be sure to look for signs of ventricular pre-excitation syndromes, Brugada syndrome, prolonged or short QT syndrome, ARVD, HOCM, and CPVT.
- Consider electrolyte abnormalities in the patient with QT interval abnormalities.
- The epsilon wave is the most specific finding for ARVD.
Suggested Readings
- Dovgalyuk J, Holstege C, Mattu A, et al. The electrocardiogram in the patient with syncope. Am J Emerg Med. 2007;25(6):688–701.
- Johnsrude CL. Current approach to pediatric syncope. Pediatr Cardiol. 2000;21(6): 522–531.
- Quinn J. Syncope and presyncope: Same mechanism, causes, and concern. Ann Emerg Med. 2015;65(3):277–278.
- Thiruganasambandamoorthy V, Stiell IG, Wells GA, et al. Outcomes in presyncope patients: A prospective cohort study. Ann Emerg Med. 2015;65(3):268–276.e6.