From the Guidelines
Investigations for syncope should begin with a thorough history, physical examination, and 12-lead ECG, which together can identify the cause in up to 50% of cases. The history should focus on circumstances surrounding the event, prodromal symptoms, position, exertion, and family history of sudden death. Orthostatic vital signs should be measured, looking for a drop in systolic blood pressure ≥20 mmHg or diastolic blood pressure ≥10 mmHg within 3 minutes of standing. Laboratory tests should include complete blood count, electrolytes, glucose, renal function, and cardiac biomarkers if cardiac syncope is suspected.
Key Investigations
- A 12-lead ECG is recommended for all patients to detect arrhythmias or abnormality indicative of higher risk for arrhythmia 1
- Echocardiography is indicated when structural heart disease is suspected, as it can be useful in selected patients presenting with syncope if structural heart disease is suspected 1
- Additional tests may include:
- Exercise stress testing for exertional syncope
- Tilt-table testing for suspected vasovagal syncope
- Carotid sinus massage in patients over 40 with suggestive history
- Electroencephalogram if seizures are suspected
- Neuroimaging (CT or MRI) is only warranted when focal neurological signs are present, as syncope rarely has a primary neurological cause 1
- Ambulatory cardiac monitoring is recommended for unexplained syncope, with the duration determined by the frequency of symptoms: 24-48 hour Holter monitoring for frequent episodes, 7-30 day event monitors for less frequent episodes, and implantable loop recorders for rare episodes. These investigations help distinguish between cardiac syncope (which carries higher mortality), reflex syncope (vasovagal), orthostatic hypotension, and other non-syncopal causes of transient loss of consciousness.
From the Research
Investigations for Syncope
- The diagnostic workup for syncope often requires multiple and challenging investigations to determine whether the patient has a structural heart disease 2.
- Cardiac imaging tests, such as transthoracic echocardiography, should be used when baseline clinical findings raise the suspicion of a cardiac syncope 2.
- Advanced imaging techniques, including multidetector computed tomography and cardiac magnetic resonance imaging, should be reserved for selected cases when echocardiography is inconclusive 2.
- A 12-lead electrocardiogram (ECG) is the only instrumental test recommended for the initial evaluation of patients with suspected syncope 3.
- The ECG may disclose an arrhythmia associated with a high likelihood of syncope, avoiding further evaluations and permitting institution of specific treatment in some patients 3.
- ECG diagnostic criteria and findings suggestive of cardiac syncope can help identify patients with high likelihood of cardiac syncope due to arrhythmic or cardiopulmonary disorder 3.
Diagnostic Approach
- A thorough history and physical examination, including orthostatic assessment, are crucial for making the diagnosis of syncope 4.
- Short-term risk assessment should be performed to determine the need for admission 4.
- In patients with suspected cardiac syncope, monitoring is indicated until a diagnosis is made 4.
- In patients with suspected reflex syncope or orthostatic hypotension, outpatient evaluation with tilt-table testing is appropriate 4.
- Syncope units have been shown to improve the rate of diagnosis while reducing cost and are highly recommended 4.