How should I initially evaluate a patient with syncope?

Initial Evaluation of Syncope

Every patient presenting with syncope requires three mandatory components: a detailed history, physical examination with orthostatic blood pressure measurements, and a 12-lead ECG—this triad alone establishes the diagnosis in 23-50% of cases and determines whether hospital admission or outpatient management is appropriate. 1, 2

Critical History Components

Circumstances Before the Event

• Position during syncope: Supine onset strongly suggests cardiac etiology, whereas standing onset points toward reflex or orthostatic mechanisms 1, 2, 3
• Activity: Exertional syncope is a high-risk feature that mandates immediate cardiac evaluation and hospital admission 1, 2
• Specific triggers: Warm crowded places, prolonged standing, or emotional stress suggest vasovagal syncope; urination, defecation, or cough indicate situational syncope 1, 2, 3

Prodromal Symptoms

• Presence of warning symptoms: Nausea, diaphoresis, blurred vision, and dizziness favor vasovagal syncope 1, 2, 3
• Absence of prodrome: Brief or absent warning symptoms are high-risk features suggesting cardiac syncope, particularly arrhythmic causes 1, 2
• Palpitations before syncope: Strongly suggest an arrhythmic cause and require cardiac monitoring 1, 2, 3

Background Information

• Known structural heart disease or heart failure: Has 95% sensitivity for cardiac syncope and predicts 18-33% one-year mortality versus 3-4% for noncardiac causes 1, 4
• Family history: Sudden cardiac death or inherited arrhythmia syndromes (Long QT, Brugada, hypertrophic cardiomyopathy) are high-risk features 1, 2
• Medications: Review antihypertensives, diuretics, vasodilators, and QT-prolonging agents as common contributors 1, 3

Physical Examination Essentials

Orthostatic Vital Signs

• Measure blood pressure and heart rate in lying, sitting, and standing positions 1, 2
• Orthostatic hypotension is defined as systolic BP drop ≥20 mmHg or diastolic BP drop ≥10 mmHg, or drop to systolic BP <90 mmHg 1, 2
• Orthostatic tachycardia: Sustained heart rate increase ≥30 bpm within 10 minutes of standing (≥40 bpm in ages 12-19 years) 1

Cardiovascular Examination

• Assess for murmurs, gallops, or rubs that indicate structural heart disease 1, 2
• Evaluate heart rhythm for irregularity suggesting atrial fibrillation or other arrhythmias 2, 3
• Carotid sinus massage in patients >40 years old (contraindicated if history of TIA or carotid disease): positive test is asystole >3 seconds or systolic BP drop >50 mmHg 1, 2

12-Lead ECG Findings

High-Risk ECG Abnormalities Requiring Hospital Admission

• QT prolongation: Suggests Long QT syndrome 1, 2, 3
• Conduction abnormalities: Bundle branch blocks, bifascicular block, Mobitz II, or third-degree AV block 1, 2
• Signs of ischemia or prior myocardial infarction 1, 2, 3
• Brugada pattern, pre-excitation (WPW), or arrhythmogenic right ventricular cardiomyopathy findings 1, 2

Risk Stratification for Disposition

High-Risk Features Requiring Hospital Admission (Class I Recommendation)

• Age >60-65 years 1, 2
• Known structural heart disease or heart failure 1, 2
• Syncope during exertion or while supine 1, 2
• Brief or absent prodrome 1, 2
• Abnormal cardiac examination or ECG 1, 2
• Family history of sudden cardiac death or inherited cardiac conditions 1, 2
• Palpitations immediately before syncope 1, 2
• Systolic BP <90 mmHg 1, 3

Low-Risk Features Appropriate for Outpatient Management

• Younger age with no known cardiac disease 1, 2
• Normal ECG and cardiac examination 1, 2
• Syncope only when standing 1, 2
• Clear prodromal symptoms (nausea, diaphoresis, warmth) 1, 2
• Specific situational triggers (micturition, defecation, cough) 1, 2

Targeted Diagnostic Testing Based on Initial Evaluation

When to Order Echocardiography (Class IIa)

• Abnormal cardiac examination suggesting structural disease 1, 2
• Abnormal ECG findings 1, 2
• Syncope during or after exertion 1, 2
• Known or suspected structural heart disease 1, 2

When to Order Cardiac Monitoring

• Holter monitor (24-72 hours): For frequent symptoms likely to recur within monitoring period 1
• External loop recorder: For less frequent symptoms expected within 2-6 weeks 1
• Implantable loop recorder: For recurrent unexplained syncope with suspected arrhythmic etiology; provides 52% diagnostic yield versus 20% with conventional strategies 1, 2
• Continuous telemetry: Initiate immediately for patients with abnormal ECG, palpitations before syncope, or high-risk features 1, 2

When to Order Exercise Stress Testing (Class IIa)

• Syncope during or immediately after exertion 1, 2
• To uncover exercise-induced arrhythmias, catecholaminergic polymorphic VT, or dynamic outflow obstruction 1, 2

When to Order Tilt-Table Testing (Class IIb)

• Young patients without heart disease with recurrent unexplained syncope when reflex mechanism is suspected 1, 2
• Only after cardiac etiologies have been excluded 2

Tests NOT Routinely Recommended (Class III: No Benefit)

Laboratory Testing

• Routine comprehensive laboratory panels have low diagnostic yield and should not be ordered without specific clinical indication 1, 2
• Targeted blood tests are reasonable only when clinical assessment suggests specific causes: hematocrit if <30% suggests volume depletion; electrolytes if dehydration suspected 1, 2
• BNP and high-sensitivity troponin have uncertain usefulness even when cardiac cause is suspected 1

Neurological Testing

• Brain imaging (CT/MRI): Not recommended in routine evaluation; diagnostic yield only 0.24-1% 1, 2, 3
• EEG: Not recommended routinely; diagnostic yield only 0.7% 1, 2
• Carotid artery imaging: Not recommended routinely; diagnostic yield only 0.5% 1, 2

Common Pitfalls to Avoid

• Failing to distinguish true syncope from seizure (post-ictal confusion present), stroke (focal deficits persist), or metabolic causes 1, 3, 5
• Overlooking medication effects as contributors, especially antihypertensives, diuretics, and QT-prolonging agents 1, 3
• Ordering brain imaging without focal neurological findings wastes resources with <1% yield 1, 2, 3
• Using Holter monitoring for infrequent events when external or implantable loop recorders are more appropriate 1
• Missing exertional syncope as high-risk requiring immediate cardiac evaluation 1, 2
• Neglecting orthostatic vital signs in every patient, missing orthostatic hypotension as a treatable cause 1, 2

Management of Unexplained Syncope After Initial Evaluation

• Reappraise the entire work-up: Obtain additional history details, re-examine for subtle findings, review all test results 1, 2, 3
• Consider specialty consultation if unexplored clues to cardiac or neurological disease are apparent 1, 2
• Early implantable loop recorder should be considered when arrhythmic suspicion persists despite negative initial work-up 1, 2