What is the appropriate workup for atypical syncope (fainting of unknown origin)?

From the Guidelines

Atypical syncope workup should begin with a thorough history, physical examination, and 12-lead ECG, as recommended by the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1.

Initial Evaluation

The initial evaluation should focus on identifying the cause of syncope, with a thorough history and physical examination being crucial in up to 50% of cases. The history should include circumstances surrounding the event, prodromal symptoms, position, exertion, and post-event symptoms.

• Initial testing should include orthostatic vital signs, complete blood count, basic metabolic panel, and cardiac biomarkers.
• A 12-lead ECG is essential in the initial evaluation, as it can help identify potential cardiac causes of syncope.

Further Cardiac Testing

If the initial evaluation is inconclusive, further cardiac testing is warranted, including:

• 24-48 hour Holter monitoring or 30-day event monitoring for suspected arrhythmias, as recommended by the 2017 ACC/AHA/HRS guideline 1.
• Echocardiography should be performed if structural heart disease is suspected.
• For recurrent unexplained syncope, consider tilt-table testing to evaluate for vasovagal syncope or orthostatic hypotension.

High-Risk Features

In cases with high-risk features, such as syncope with exertion, family history of sudden death, or abnormal ECG, electrophysiology studies may be indicated, as recommended by the 2004 European Heart Journal guidelines 1.

• Carotid sinus massage can be performed in patients over 40 without carotid bruits to evaluate for carotid sinus hypersensitivity.
• Neuroimaging (MRI or CT) is generally low-yield unless focal neurological findings are present.

Tailoring the Workup

The workup should be tailored to the patient's presentation, with the goal of identifying potentially life-threatening causes while avoiding unnecessary testing in cases of benign vasovagal syncope, as emphasized by the 2017 ACC/AHA/HRS guideline 1.

• The use of a leadless, self-applied monitor can be considered as an alternative to external loop recorder in patients with recurrent, infrequent, unexplained syncope, as it may be more comfortable and less cumbersome, potentially improving compliance 1.

From the Research

Atypical Syncope Workup

• The workup of atypical syncope involves a careful history, physical examination, electrocardiogram, risk stratification, and appropriately directed testing 2.
• A structured approach to the patient with syncope is required, with history-taking being the most important aspect of the clinical assessment 3.
• The classification of syncope is based on the underlying pathophysiological mechanism causing the event, and includes cardiac, orthostatic and reflex (neurally mediated) mechanisms, with atypical reflex syncope being a category of reflex syncope that cannot be attributed to a specific trigger or has an atypical presentation 3.

Diagnostic Tests

• The tilt table test is useful for evaluating predisposition to neurocardiogenic (vasovagal) syncope in patients with unexplained syncope and a normal heart 2.
• Electrophysiologic studies play a more important role in the setting of structural heart disease or an abnormal electrocardiogram 2.
• Noninvasive cardiac monitoring for symptom-rhythm correlation may be limited by infrequent symptoms, but external and implantable loop recorders can allow for prolonged periods of monitoring to increase diagnostic yield 2.
• Laboratory tests may be ordered based on history and physical examination findings, such as hemoglobin measurement if gastrointestinal bleeding is suspected 4.

Risk Stratification

• Risk stratification is crucial in the management of syncope, with the goal of identifying patients who are at high risk of adverse outcomes 5.
• The European Society of Cardiology syncope guidelines recommend an initial syncope workup based on detailed patient's history, physical examination, supine and standing blood pressure, resting ECG, and laboratory tests, including cardiac biomarkers, where appropriate 5.
• Patients can be stratified into high-, intermediate- and low-risk groups, with the high-risk group requiring immediate hospitalization and investigation, the intermediate group requiring systematic evaluation by syncope experts, and the low-risk group meriting education about the benign nature of the condition and discharge 5.
• Risk stratification tools, such as the Canadian Syncope Risk Score, may be beneficial in informing decisions regarding hospital admission 4.