2017 ACC/AHA/HRS Syncope Guidelines

What's New in This Guideline

Key Updates from 2017 ACC/AHA/HRS Syncope Guideline

• Expanded risk stratification: Refined definition of high-risk and low-risk features to guide hospital admission decisions
• Tilt-table testing clarification: Specific indications for tilt-table testing in vasovagal syncope, orthostatic intolerance, and pseudosyncope evaluation
• Implantable cardiac monitors: New evidence supporting implantable loop recorder (ILR) use in selected patients with syncope of undetermined origin
• Orthostatic hypotension management: Updated pharmacotherapy including midodrine and fludrocortisone dosing and indications
• Inherited arrhythmia syndromes: Comprehensive recommendations for Brugada, Long-QT, Short-QT, CPVT, and early repolarization patterns
• Structural heart disease: Management strategies for syncope in HCM, aortic stenosis, ARVC, and cardiac sarcoidosis
• Driving recommendations: Updated guidance on return-to-driving after syncope episodes
• Special populations: New sections on pediatric, geriatric, pregnant, and athlete populations

Classification of Syncope

Syncope is defined as a brief, sudden loss of consciousness with spontaneous recovery, caused by temporary cerebral hypoperfusion. Classification is based on underlying pathophysiology:

1. Reflex (Neurally-Mediated) Syncope

2. Orthostatic Hypotension (OH)

3. Cardiac Syncope

Initial Evaluation of Syncope

Class I recommendation (B-NR): A detailed history and physical examination should be performed in all patients with syncope.

History Key Elements

• Prodromes (palpitations, chest pain, dyspnea, diaphoresis, nausea)
• Circumstances and triggers (standing, emotional stress, exertion, specific situations)
• Positioning during event (sitting, standing, supine)
• Duration of loss of consciousness
• Presence of convulsive movements (may mimic seizure)
• Post-event confusion (absence suggests syncope, not seizure)
• Associated medical conditions and medication use
• Family history of syncope, SCD, or arrhythmia

Physical Examination

• Orthostatic vital signs: BP and HR lying, sitting, standing at 1, 3, and 5+ minutes
• Cardiac examination: Murmurs, clicks, irregular rhythm
• Neurological examination: Focal deficits, seizure activity
• Carotid palpation and massage (if no carotid bruits)

Baseline Electrocardiogram (ECG)

Class I recommendation (B-NR): A 12-lead ECG is useful and recommended in the initial evaluation of syncope.

ECG findings that suggest cardiac etiology:

• Sinus bradycardia, AV block, prolonged QRS
• Long QT or short QT interval
• Brugada pattern, early repolarization
• LVH, prior MI, ischemic changes
• Arrhythmogenic substrate (WPW, CPVT)

Risk Stratification

Risk stratification determines need for hospitalization and intensity of diagnostic workup.

High-Risk Features (Recommend Hospital Evaluation)

• Age >60 years
• Male sex
• Known cardiac disease (structural or arrhythmic)
• Abnormal ECG (arrhythmic substrate)
• Exertional syncope or syncope supine
• Family history of SCD
• Palpitations before syncope
• Reduced ejection fraction or HF
• Abnormal cardiac examination findings

Low-Risk Features (Often Suitable for Outpatient Management)

• Younger age without cardiac disease
• Clear prodrome (nausea, warmth, visual symptoms)
• Syncope only in standing position
• Identifiable trigger (emotional stress, pain, medical procedure)
• Normal ECG and cardiac examination
• No prior cardiac events
• No family history of SCD

Reflex Syncope Management

Vasovagal Syncope (VVS) Treatment Algorithm

Class I (C-EO): Patient education on diagnosis and prognosis of VVS is recommended.

Physical Counter-Pressure Maneuvers

Class IIa (B-R): Useful in patients with prodrome allowing time for intervention

• Leg crossing with maximal isometric muscle contraction
• Squatting position (most effective, >70% of episodes prevented)
• Handgrip or abdominal straining
• Effective in preventing syncope in approximately 50-70% of patients with adequate prodrome

Pharmacotherapy for VVS

Midodrine (Class IIa, B-R) - Selective alpha-1 adrenergic agonist

• Dosing: 2.5-10 mg 2-3 times daily (caution in patients >42 years)
• Mechanism: Increases peripheral vascular resistance and blood pressure
• Use: For recurrent VVS unresponsive to physical maneuvers
• Side effects: Scalp tingling, piloerection, urinary retention

Fludrocortisone (Class IIb, B-R) - Mineralocorticoid

• Dosing: 0.1 mg once or twice daily
• Mechanism: Increases blood volume through sodium and water retention
• Onset: Requires 1-2 weeks for full effect
• Considerations: Monitor serum potassium; may worsen hypertension

Beta-blockers (Class IIb, B-R) - Limited evidence

• Mechanism: Reduce tachycardia and vasodilator response
• Evidence: Mixed results; effective in specific populations (older patients, postural VVS)
• Use with caution: May not prevent syncope in younger patients

Orthostatic Hypotension Management

Initial Evaluation

• Confirm diagnosis: Measure BP and HR in lying, sitting, standing positions at 1, 3, and 5+ minutes
• Differentiate neurogenic from non-neurogenic causes
• Review medications that may lower BP (antihypertensives, diuretics, vasodilators)
• Assess for dehydration and fluid status

Non-Pharmacological Management

Class I Recommendations:

• Acute water ingestion: 480 mL (16 oz) ingestion can increase blood pressure within 5-30 minutes
• Physical counter-pressure maneuvers: Leg crossing, squatting, abdominal bracing during prodrome
• Compression garments: High-waist and abdominal compression (at least thigh-high); can improve blood pressure by 15-20 mm Hg
• Salt and fluid loading: Increase dietary salt to 10-15 g/day and fluid intake to 2-3 L/day (if no contraindications)
• Recumbent position: Change position gradually (sit before standing, sit before lying)

Pharmacological Management

Midodrine (Class IIa, B-R)

• Dosing: 2.5-10 mg 2-3 times daily (contraindicated in ages >42 years with documented syncope due to increased SCD risk)
• Mechanism: Alpha-1 adrenergic agonist increasing peripheral vascular resistance
• Efficacy: Can increase standing systolic BP by 15-30 mm Hg

Fludrocortisone (Class IIb, B-R)

• Dosing: 0.1-0.2 mg once daily (monitor potassium and renal function)
• Onset: 1-2 weeks; requires monitoring for hypokalemia
• Use: For persistent OH despite salt and fluid loading

Other agents (Class IIb, C-LD)

• Pyridostigmine: 60 mg twice daily (cholinesterase inhibitor)
• NSAIDs: May help by reducing renal salt wasting
• Selective serotonin reuptake inhibitors: Limited evidence

Cardiac Syncope Management

Syncope due to cardiac cause carries significantly worse prognosis than reflex or orthostatic causes. Immediate cardiac evaluation is essential.

Arrhythmic Causes

Bradycardia

Sinus Node Dysfunction & AV Block: Class I (C-EO) - GDMT is recommended

• Mechanism: Inadequate HR increase with standing; prolonged asystole during arrhythmia
• Evaluation: ECG, Holter monitor, event recorder, EP study
• Management: Permanent pacemaker implantation; avoid nodal blocking agents

Tachycardia

Supraventricular Tachycardia (SVT) & Ventricular Tachycardia (VT): Class I (C-EO) - GDMT is recommended

• Evaluation: ECG, Holter, event recorder, EP study
• Management: Antiarrhythmic drugs, radiofrequency ablation, ICD (for VT with reduced EF)

Long QT Syndrome (LQTS): Class I (B-NR) - Beta-blocker therapy, ICD if high risk

• Diagnosis: QTc >500 ms or QTc 480-499 ms with risk factors
• Management: Beta-blockers (first-line); ICD for recurrent syncope despite beta-blockers
• Avoid QT-prolonging drugs; genetic testing in families

Brugada Syndrome: Class IIa (B-NR) - ICD in selected high-risk patients

• Diagnosis: Type 1 Brugada ECG pattern (spontaneous or drug-induced)
• Risk factors for SCD: Male, fever, syncope history, family history of SCD
• Management: ICD for symptomatic patients; avoid sodium channel blockers

Catecholaminergic Polymorphic VT (CPVT): Class I (C-LD) - ICD with beta-blockade

• Mechanism: Exercise or emotion-induced polymorphic VT
• Management: Beta-blockers (first-line), ICD, flecainide, LCSD (left cardiac sympathetic denervation)

Structural Causes

Aortic Stenosis: Class I (C-EO) - GDMT is recommended

• Mechanism: Fixed outflow obstruction; syncope on exertion
• Red flag: Exertional syncope warrants urgent evaluation
• Management: Aortic valve replacement (AVR); caution with vasodilators

Hypertrophic Cardiomyopathy (HCM): Class I (C-EO) - GDMT is recommended

• Mechanism: LVOT obstruction; arrhythmias; diastolic dysfunction
• Risk for SCD: Family history, syncope, abnormal BP response to exercise
• Management: Beta-blockers or calcium channel blockers; ICD for high-risk features

Pulmonary Embolism: Class I (C-EO) - GDMT is recommended

• Mechanism: Acute RV dysfunction; increased RV afterload
• Evaluation: D-dimer, CT angiography
• Management: Anticoagulation, thrombolytics (selected cases)

Acute Coronary Syndrome: Class I (C-EO) - GDMT is recommended

• Mechanism: Mechanical complications (VSD, papillary muscle rupture, free wall rupture); arrhythmia
• Management: Urgent reperfusion; mechanical support as needed

Additional Diagnostic Testing

Tilt-Table Testing

Class IIa (B-R): Tilt-table testing can be useful for patients with suspected VVS and recurrent episodes.

• Indications: Suspected vasovagal syncope with frequent recurrences; differentiate from POTS/orthostatic intolerance; assess for convulsive syncope
• Protocol: Passive tilt 60-80 degrees for 20-40 minutes (20-40 minute passive phase optimal)
• Positive response: Reproduces syncope with hypotension, bradycardia, or both
• Not recommended: Routine screening or response to pharmacotherapy assessment

Ambulatory Monitoring

Class I (C-EO): Choice of monitoring device depends on frequency and nature of syncope events.

Holter Monitor (24-48 hours)

• Use: Palpitations or high suspicion of arrhythmia
• Limitation: Low yield unless frequent symptoms

Event Recorder (External Loop Recorder, 30 days)

• Use: Sporadic symptoms; patient-activated or auto-triggered devices
• Advantage: Longer monitoring period captures arrhythmias

Implantable Loop Recorder (ILR, 2-3 year battery) - Class IIa (B-NR)

• Indications: Recurrent syncope of undetermined origin; high suspicion for arrhythmia despite normal workup
• Diagnostic yield: 50-80% in selected populations
• Advantage: Long-term continuous monitoring; identifies inducible abnormalities

Cardiac Imaging

Transthoracic Echocardiography (Class IIa, B-NR): Useful if structural heart disease suspected (murmur, family history, ECG abnormality)

• Not recommended routinely without signs/symptoms suggesting cardiac etiology

CT/MRI (Class IIb, B-NR): Selected patients with syncope of suspected cardiac etiology

Electrophysiological Study

Class IIa (B-NR): EP study can be useful for evaluation of selected ambulatory patients with syncope of suspected arrhythmic etiology.

• Indications: Abnormal ECG suggesting arrhythmia substrate; recurrent syncope with high suspicion for arrhythmia
• Diagnostic yield: 30-50% in carefully selected patients

Special Populations

Elderly Patients (>65 years)

• Higher risk for serious outcomes and mortality from syncope
• Multiple comorbidities and medications increase complexity
• Longer evaluation and monitoring warranted
• Falls risk higher; emphasis on prevention strategies
• Consider orthostatic hypotension, medication effects, cardiac disease

Athletes

Exertional syncope: Red flag for serious cardiac disease until proven otherwise

• Mandatory evaluation: ECG, echocardiography, stress test
• Restriction from competition until cause identified and managed
• High-risk conditions: HCM, ARVC, Long-QT, Brugada, Aortic stenosis

Pregnancy

• Syncope in pregnancy warrants careful evaluation
• Avoid unnecessary radiation; use echocardiography for imaging
• Orthostatic hypotension common; address with fluid, salt, positioning
• ICD placement safe if indicated for life-threatening arrhythmias

Pediatric Patients

• Vasovagal syncope most common (>80% of cases)
• Familial arrhythmia syndromes require genetic testing
• School/sports participation counseling important

Key Do's and Don'ts

Useful Calculators & Risk Tools

These tools help stratify risk, assess comorbidities, and guide management decisions in syncope patients: