What is the workup for syncope (fainting) and its differential diagnosis?

From the Guidelines

The workup for a patient who has passed out (syncope) should begin with a thorough history and physical examination, focusing on cardiac, neurological, and metabolic causes, as recommended by the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1. The initial evaluation should include vital signs, orthostatic measurements, ECG, and basic laboratory tests including complete blood count, electrolytes, glucose, and cardiac enzymes.

• The differential diagnosis includes:
  • Cardiac causes (arrhythmias, structural heart disease, valvular disorders)
  • Orthostatic hypotension
  • Vasovagal syncope
  • Neurological causes (seizures, TIA, stroke)
  • Metabolic disorders (hypoglycemia, electrolyte abnormalities)
  • Medication effects
• Situational factors like dehydration, prolonged standing, emotional stress, or pain can trigger vasovagal episodes, as noted in the guidelines for the diagnosis and management of syncope (version 2009) 1.
• Treatment depends on the underlying cause, ranging from cardiac interventions like pacemakers for bradyarrhythmias to medication adjustments for orthostatic hypotension.
• For recurrent vasovagal syncope, patients should be advised to maintain hydration, avoid triggers, and employ counterpressure maneuvers when feeling prodromal symptoms.
• Referral to cardiology or neurology may be necessary depending on suspected etiology, as suggested by the guidelines on management (diagnosis and treatment) of syncope-update 2004 1.

From the Research

Work-up for Passing Out and Differential Diagnosis

• The work-up for passing out, also known as syncope, involves a thorough history, physical examination, and electrocardiography 2, 3, 4, 5, 6
• The classification of syncope is based on the underlying pathophysiological mechanism causing the event, and includes:
  • Cardiac syncope: caused by cardiovascular diseases, such as arrhythmias or structural heart disease 2, 3, 4, 5
  • Reflex syncope (neurally mediated): caused by emotional or orthostatic stress, situational stressors, or carotid sinus pressure 2, 3, 4
  • Orthostatic hypotension: caused by an abnormal drop in systolic blood pressure upon standing, often due to autonomic nervous system failure or hypovolaemia 2, 3, 4, 5
• The initial assessment for all patients presenting with syncope includes:
  • Detailed history-taking to identify the precise cause and quantify the risk to the patient 2, 3, 4, 5, 6
  • Physical examination, including orthostatic blood pressure measurements 2, 3, 4, 5
  • Electrocardiography to diagnose cardiac causes of syncope 2, 3, 4, 5
• Laboratory testing and neuroimaging have a low diagnostic yield and should be ordered only if clinically indicated 3, 4, 5
• Risk stratification tools, such as the Canadian Syncope Risk Score, can be beneficial in determining the need for hospital admission 4
• The prognosis of patients with reflex and orthostatic syncope is generally good, while cardiac syncope is more likely to be associated with adverse outcomes 3, 4, 5