What investigations should be sent for a patient presenting with syncope?

Initial Investigations for Syncope

Every patient presenting with syncope requires three mandatory initial investigations: 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 all subsequent testing. 1

Mandatory Initial Evaluation (All Patients)

History Taking

Focus on these specific elements that distinguish cardiac from non-cardiac causes:

• Position during syncope: Supine position suggests cardiac etiology; standing position suggests reflex or orthostatic causes 1, 2
• Activity: Exertional syncope is high-risk and mandates cardiac evaluation 3, 1
• Prodromal symptoms: Nausea, diaphoresis, blurred vision, and dizziness favor vasovagal syncope; absence of prodrome or brief prodrome suggests cardiac arrhythmia 3, 1
• Palpitations before syncope: Strongly suggests arrhythmic cause 1, 2
• Triggers: Warm crowded places, prolonged standing, emotional stress suggest vasovagal; urination, defecation, cough suggest situational syncope 1
• Recovery phase: Rapid, complete recovery without confusion confirms syncope; prolonged confusion suggests seizure 1
• Known structural heart disease or heart failure: 95% sensitivity for cardiac syncope 1, 2
• Medications: Review antihypertensives, diuretics, vasodilators, and QT-prolonging agents 1
• Family history: Sudden cardiac death <50 years or inherited arrhythmia syndromes 3, 1

Physical Examination

• Orthostatic vital signs: Measure blood pressure and heart rate in lying, sitting, and standing positions; orthostatic hypotension defined as systolic BP drop ≥20 mmHg or to <90 mmHg 1
• Cardiovascular examination: Assess for murmurs, gallops, rubs, and signs of heart failure that indicate structural heart disease 3, 1
• Carotid sinus massage (in patients >40 years): Positive if asystole >3 seconds or systolic BP drop >50 mmHg 1

12-Lead ECG

Assess for these specific abnormalities:

• QT prolongation (long QT syndrome) 1
• Conduction abnormalities: Bundle branch blocks, bifascicular block, sinus bradycardia, sinoatrial blocks, 2nd or 3rd degree AV block 3, 1
• Signs of ischemia or prior MI 1
• Any ECG abnormality is an independent predictor of cardiac syncope and increased mortality 1

Risk-Stratified Additional Testing

High-Risk Features Requiring Hospital Admission and Immediate Testing

Admit patients with any of these features for inpatient cardiac evaluation 3, 1:

• Age >60-65 years
• Known structural heart disease or heart failure
• Syncope during exertion or in supine position
• Brief or absent prodrome
• Abnormal cardiac examination or ECG
• Family history of sudden cardiac death or inherited conditions
• Palpitations before syncope

For high-risk patients, order immediately:

• Continuous cardiac telemetry monitoring: Initiate immediately for patients with abnormal ECG, palpitations before syncope, or high-risk features 1
• Transthoracic echocardiography: Order immediately when structural heart disease is suspected based on examination, ECG abnormalities, or high-risk history 3, 1
• Exercise stress testing: Mandatory for syncope during or immediately after exertion 3, 1

Low-Risk Features Allowing Outpatient Management

Patients with these features can be managed outpatient 3, 1:

• Younger age
• No known cardiac disease
• Normal ECG and cardiac examination
• Syncope only when standing
• Prodromal symptoms (nausea, diaphoresis, warmth)
• Specific triggers (dehydration, pain, medical environment)
• Situational triggers (cough, micturition, defecation)
• Frequent recurrence with similar characteristics

For low-risk patients with suspected vasovagal syncope:

• Tilt-table testing: Can confirm vasovagal syncope in young patients without heart disease when history is suggestive but not diagnostic 1

Targeted Laboratory Testing (Not Routine)

Order laboratory tests only based on specific clinical suspicion—routine comprehensive panels are not useful 3, 1:

• Hematocrit/CBC: Only if volume depletion or blood loss suspected 1
• Electrolytes, BUN, creatinine: Only if dehydration suspected 1
• Cardiac biomarkers (BNP, troponin): Only if cardiac cause suspected, but usefulness is uncertain 1

Cardiac Monitoring Selection (Based on Symptom Frequency)

Choose monitoring strategy based on frequency of syncope episodes 3:

• Holter monitor (24-48 hours): For frequent symptoms (daily to weekly) 3
• External loop recorder or patch recorder: For symptoms occurring every few weeks 3
• Implantable cardiac monitor: For infrequent symptoms (months apart) or recurrent unexplained syncope with high clinical suspicion for arrhythmic cause 3, 1

Tests That Should NOT Be Ordered Routinely

Avoid these tests without specific indications 1:

• Brain imaging (CT/MRI): Diagnostic yield only 0.24-1%; order only with focal neurological findings or head injury 1
• EEG: Diagnostic yield only 0.7%; order only with features suggesting seizure 1
• Carotid ultrasound: Diagnostic yield only 0.5%; not recommended routinely 1
• Routine cardiac imaging: Not useful unless cardiac etiology suspected on initial evaluation 3

Critical Pitfalls to Avoid

• Do not order comprehensive laboratory panels without specific clinical indication—this increases cost without improving diagnostic yield 1
• Do not overlook medication effects as contributors to syncope, particularly antihypertensives and QT-prolonging drugs 1
• Do not fail to distinguish true syncope from seizure, stroke, or metabolic causes—verify rapid, complete recovery without post-event confusion 1
• Do not miss cardiac syncope in patients with structural heart disease—one-year mortality is 18-33% for cardiac syncope versus 3-4% for non-cardiac causes 1