2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope

Authors, Journal, Affiliations, Type, DOI

• Win-Kuang Shen (Chair), Robert S. Sheldon (Vice Chair), and 13 additional writing committee members
• Journal of the American College of Cardiology, Vol. 70, No. 5, 2017 (pp. e39–110); co-published in Circulation and HeartRhythm
• Multi-society guideline: ACC/AHA/HRS; developed with ACEP and SAEM; endorsed by PACES
• Type: Clinical practice guideline with independent systematic evidence review (ERC commissioned for pacing in reflex syncope)
• DOI: https://doi.org/10.1016/j.jacc.2017.03.003

Overview

The 2017 ACC/AHA/HRS Syncope Guideline is the primary US reference for evaluation and management of adult and pediatric patients with suspected syncope. It defines syncope as an abrupt, transient, complete loss of consciousness due to cerebral hypoperfusion with spontaneous recovery and establishes a structured evaluation framework beginning with a detailed history, physical examination, and 12-lead ECG. The guideline stratifies patients by short- and long-term risk, recommends selective (not routine) additional testing, and provides cause-specific management for reflex, cardiac, structural, and channelopathic etiologies. A key message is that cardiac syncope carries significantly worse prognosis than reflex syncope, and that most additional testing (neuroimaging, EEG, carotid ultrasound) provides negligible diagnostic yield in the absence of specific indications.

Keywords

Syncope, transient loss of consciousness, vasovagal syncope, orthostatic hypotension, risk stratification, cardiac syncope, implantable cardiac monitor, tilt-table testing, reflex syncope, electrophysiological study, pacemaker, carotid sinus syndrome, POTS, pseudosyncope

Key Takeaways

Definitions

• Syncope: Abrupt, transient, complete loss of consciousness + inability to maintain postural tone + rapid and spontaneous recovery; presumed mechanism = cerebral hypoperfusion; no clinical features of seizure, head trauma, or pseudosyncope
• Presyncope: Symptoms preceding syncope (extreme lightheadedness, tunnel vision, graying out, variable degrees of altered consciousness without complete LOC) — may or may not progress to syncope
• Vasovagal syncope (VVS): Most common reflex syncope; triggered by upright posture, emotional stress, pain, or medical settings; characteristic prodrome (diaphoresis, warmth, nausea, pallor); followed by fatigue; typical features may be absent in older patients
• Orthostatic hypotension (OH): Systolic BP drop ≥20 mmHg or diastolic drop ≥10 mmHg on assuming upright posture; classic OH = within 3 min; delayed OH = >3 min; initial OH = transient within 15s
• Neurogenic OH: OH caused by central or peripheral autonomic nervous system dysfunction; associated with neurodegenerative diseases (MSA, Parkinson's, Lewy body dementia) and peripheral neuropathies (diabetes, amyloidosis)
• Carotid sinus syndrome: Reflex syncope with carotid sinus hypersensitivity (pause ≥3s and/or systolic BP drop ≥50 mmHg on carotid massage); cardioinhibitory, vasodepressor, or mixed response
• POTS: Orthostatic HR increase ≥30 bpm within 10 min of standing (≥40 bpm in ages 12–19); absence of OH; accompanied by orthostatic symptoms
• Psychogenic pseudosyncope: Apparent but not true LOC; normal hemodynamics during event; no cardiac, reflex, neurological, or metabolic cause

Epidemiology

• Prevalence up to 41%; recurrent syncope in 13.5%; female predominance (22% vs 15%)
• Trimodal age distribution: first peak ~20yr, then ~60yr, then ~80yr; third peak 5–7yr earlier in males
• Etiology breakdown: reflex syncope 21%, cardiac syncope 9%, OH 9%, unknown 37%
• Older institutionalized patients: 7% annual incidence, 23% overall prevalence, 30% 2-year recurrence
• Syncope in NYHA Class III–IV HF: 12–14% of patients
• ED visits: 0.77% of all ED patients (National Hospital Ambulatory Medical Care Survey); 58% of patients >80yr are admitted to hospital

Initial Evaluation

History and Physical Examination (Class I, B-NR)

• Goal: identify prognosis, diagnosis, reversible factors, comorbidities, medication use
• Focus on: situations in which syncope occurs, prodromal symptoms, bystander observations, post-event symptoms, family history (unexplained sudden death, drowning)
• Characteristics suggesting cardiac etiology: older age >60yr, male sex, known cardiac disease, brief/no prodrome, syncope during exertion or supine, abnormal cardiac exam, family history of premature SCD
• Characteristics suggesting noncardiac etiology: younger age, no cardiac disease, syncope only standing/positional, prodrome of nausea/vomiting/warmth, specific triggers, frequent recurrence

12-Lead ECG (Class I, B-NR)

• Mandatory in all patients; identifies arrhythmic substrates (WPW, BrS, LQTS, HCM, ARVC patterns)
• Abnormal ECG (AF, intraventricular conduction disturbance, LVH voltage, ventricular pacing) associated with increased 1-year all-cause mortality

Risk Assessment (Class I, B-NR)

Short-term risk factors (≤30 days):

• History: male sex, older age >60yr, no prodrome, palpitations preceding LOC, exertional syncope, structural heart disease, HF, cerebrovascular disease, family history of SCD, trauma
• Examination/labs: evidence of bleeding, persistent abnormal vital signs, abnormal ECG, positive troponin

Long-term risk factors (>30 days):

• Male sex, older age, structural heart disease, HF, cerebrovascular disease, VA, cancer, diabetes mellitus, high CHADS-2 score, abnormal ECG, lower GFR

Validated risk scores (OESIL, SFSR, STePS, ROSE, Boston Syncope Rule) — risk scores have NOT performed better than unstructured clinical judgment (Class IIb, B-NR)

Disposition After Initial Evaluation

• Hospital evaluation required (Class I, B-NR): serious medical condition identified — arrhythmic (sustained VT, Mobitz II/3°AV block, symptomatic bradycardia, inheritable arrhythmia), cardiac/vascular (cardiac ischemia, severe AS, HCM, cardiac tamponade, aortic dissection, acute HF, moderate-severe LV dysfunction, pulmonary embolism), noncardiac (severe anemia/GI bleeding, major trauma, persistent vital sign abnormalities)
• Outpatient management (Class IIa, C-LD): presumptive reflex-mediated syncope without serious conditions; VVS long-term mortality = same as matched controls
• Structured ED observation protocol (Class IIa, B-R): intermediate-risk patients with unclear cause; reduces hospitalization without adverse outcomes
• Selected outpatient management for suspected cardiac syncope (Class IIb, C-LD): in absence of serious identified conditions

Additional Testing: Blood Testing

• Targeted blood tests reasonable based on clinical assessment (Class IIa, B-NR)
• Routine comprehensive laboratory testing = NOT useful (Class III No Benefit, B-NR)
• BNP/high-sensitivity troponin: uncertain usefulness when cardiac cause suspected (Class IIb, C-LD)

Cardiovascular Testing

Cardiac Imaging

• Transthoracic echo: useful if structural heart disease suspected (Class IIa, B-NR); echocardiogram suggested cardiac syncope in 48% of patients with suspected cardiac disease
• CT or MRI: useful if cardiac structural abnormality suspected (Class IIb, B-NR); MRI preferred for ARVC or cardiac sarcoidosis
• Routine cardiac imaging: NOT useful (Class III No Benefit, B-NR)

Stress Testing

• Exercise stress testing: useful for exertional syncope or presyncope (Class IIa, C-LD); must be done with caution and ALS support

Cardiac Monitoring

• Selection based on frequency and nature of syncope events (Class I, C-EO)
• External monitors (Holter/transtelephonic/external loop recorder/patch/MCOT) useful in ambulatory suspected arrhythmic syncope (Class IIa, B-NR):
  • Holter: short monitoring window (24–72h)
  • External loop recorder: longer duration; higher yield than Holter; diagnostic yield 24.5% at 4 weeks
  • MCOT: highest diagnostic yield vs external loop recorder (89% vs 69%, p=0.008) in syncope/presyncope
• Implantable cardiac monitor (ICM): useful in recurrent infrequent unexplained syncope suspected arrhythmic (Class IIa, B-R); 55% diagnostic yield vs 19% conventional strategy (p=0.0014); cost per diagnosis lower despite higher upfront cost

In-Hospital Telemetry (Class I, B-NR)

• Continuous ECG monitoring for hospitalized patients with suspected cardiac etiology; diagnostic yield 5–18%; yield highest in older patients with HF

Electrophysiological Study (EPS)

• Useful in suspected arrhythmic syncope with structural heart disease (Class IIa, B-NR): 41% positive yield in cardiac disease patients (21% VT, 34% bradycardia); only 5% in those without structural disease
• NOT recommended when ECG normal and cardiac structure normal (Class III No Benefit, B-NR)
• EPS role has diminished — ICD is Class I for primary prevention in EF ≤35%; EPS no longer required before ICD

Tilt-Table Testing

• Suspected VVS (Class IIa, B-R): 70° for 30–40 min; adjunctive isoproterenol or sublingual nitrates improve sensitivity but reduce specificity; positive test ≠ causal proof; moderate sensitivity/specificity/reproducibility
• Suspected delayed OH (Class IIa, B-NR): up to 39% of patients with OH develop it only after >10 min of tilt
• Distinguishing convulsive syncope from epilepsy (Class IIa, B-NR): ~50% of drug-refractory "epilepsy" has positive tilt
• Establishing pseudosyncope diagnosis (Class IIa, B-NR): apparent LOC with normal hemodynamics + normal EEG = pseudosyncope
• NOT useful for predicting treatment response (Class III No Benefit, B-R)

Neurological Testing

• EEG simultaneous with tilt-table testing: useful to distinguish syncope/pseudosyncope/epilepsy (Class IIa, C-LD)
• Routine MRI/CT head: NOT recommended without focal neurological findings/head injury (Class III No Benefit, B-NR); diagnostic yield 0.24% (MRI) and 1% (CT) in syncope
• Routine carotid artery imaging: NOT recommended (Class III No Benefit, B-NR); diagnostic yield 0.5%
• Routine EEG: NOT recommended without neurological features of seizure (Class III No Benefit, B-NR); diagnostic yield 0.7%

Management: Cardiovascular Conditions

• Bradycardia (GDMT per device guidelines, Class I C-EO): permanent pacemaker reasonable for chronic bifascicular block + unexplained syncope when other causes excluded
• SVT including AF (GDMT, Class I C-EO): syncope from rapid ventricular response is uncommon; older patients more susceptible; WPW syncope requires EPS to characterize
• Ventricular arrhythmia (GDMT, Class I C-EO): VA ≥200 bpm → 65% syncope/presyncope; ICD for suspected lethal VA
• Ischemic/nonischemic cardiomyopathy (GDMT, Class I C-EO): ICD reasonable for unexplained syncope + significant EF reduction
• Valvular heart disease (GDMT, Class I C-EO): aortic stenosis exertional syncope → hemodynamic mechanism; AVR recommended after excluding other causes
• HCM (GDMT, Class I C-EO): ICD reasonable for ≥1 recent episode of syncope suspected arrhythmic; unexplained syncope = independent predictor of SCD and appropriate ICD discharge
• ARVC: ICD recommended for sustained VA (Class I, B-NR); ICD reasonable for suspected arrhythmic syncope (Class IIa, B-NR)
• Cardiac sarcoidosis: ICD recommended for sustained VA (Class I, B-NR); GDMT for conduction abnormalities (Class I, C-EO); ICD reasonable for suspected arrhythmic syncope + LV dysfunction/pacing indication (Class IIa, B-NR); EPS reasonable (Class IIa, B-NR)

Management: Inheritable Arrhythmic Conditions

• Brugada syndrome: ICD reasonable for suspected arrhythmic syncope (Class IIa, B-NR); cardiac event rate 1.9%/yr with syncope vs 0.5% asymptomatic; ICD NOT recommended for reflex-mediated syncope (Class III No Benefit, B-NR); EPS may be considered (Class IIb, B-NR)
• Short-QT syndrome (QTc ≤340 ms): ICD may be considered for suspected arrhythmic syncope (Class IIb, C-EO); very rare condition; quinidine may provide some protection
• Long-QT syndrome: Beta-blockers = first-line (Class I, B-NR); syncope → 6–12× increased risk of fatal/near-fatal events; LQTS1 responds better to beta-blockers than LQTS2/3; ICD reasonable on beta-blocker or intolerant (Class IIa, B-NR); LCSD reasonable for recurrent syncope intolerant to or failing beta-blocker (Class IIa, C-LD)
• CPVT: Exercise restriction (Class I, C-LD); beta-blockers without ISA (Class I, C-LD); flecainide for breakthrough on beta-blocker (Class IIa, C-LD); ICD for refractory/optimal therapy or LCSD (Class IIa, B-NR); verapamil +/- beta-blocker may be considered (Class IIb, C-LD); LCSD may be reasonable for refractory (Class IIb, C-LD)
• Early repolarization pattern: ICD may be considered with FHx cardiac arrest (Class IIb, C-EO); EPS NOT recommended (Class III Harm, B-NR); absolute VF risk remains low despite population-based associations

Management: Vasovagal Syncope

• Patient education (Class I, C-EO): Explain diagnosis, identify/avoid triggers, reassure regarding benign nature
• Physical counter-pressure maneuvers (Class IIa, B-R): Leg crossing/limb contraction/squatting during prodrome; 43% relative risk reduction vs controls; first-line for all severity
• Midodrine (Class IIa, B-R): Reasonable for recurrent VVS without HTN, HF, or urinary retention; 43% reduction in syncope recurrence in meta-analysis of 5 RCTs; peripheral alpha-agonist
• Orthostatic training (Class IIb, B-R): Uncertain benefit; RCTs have not shown sustained reduction in syncope recurrence
• Fludrocortisone (Class IIb, B-R): Reasonable if inadequate response to salt/fluid; 31% risk reduction in adults (POST II; marginally insignificant); pediatric trial favored placebo
• Beta-blockers (Class IIb, B-NR): Reasonable only in patients ≥42 years; overall RCTs negative but age-stratified meta-analysis shows benefit ≥42yr
• Salt and fluid intake (Class IIb, C-LD): 2–3 L/day + 6–9 g salt/day in absence of contraindications (HTN, renal disease, HF)
• Reducing hypotensive medications (Class IIb, C-LD): Review and reduce cautiously with prescribing provider
• SSRIs (Class IIb, C-LD): May be considered for recurrent VVS; contradictory evidence from 3 small RCTs

Management: Pacemakers in VVS (Class IIb, B-R [SR])

• Dual-chamber pacing might be reasonable in patients ≥40yr with recurrent VVS and prolonged spontaneous pauses
• Based on independent systematic review; benefit limited to patients with documented asystole; positive tilt test (vasodepressor response) predicts non-response to pacing
• Earlier open-label trials uniformly positive; properly conducted double-blind RCTs had negative/mixed results

Management: Carotid Sinus Syndrome

• Permanent cardiac pacing (Class IIa, B-R): Reasonable for cardioinhibitory or mixed carotid sinus syndrome; 76% relative risk reduction vs untreated in 3 controlled open-label trials
• Dual-chamber pacemaker (Class IIb, B-R): May be reasonable when permanent pacing required; limited RCT evidence; dual-chamber may prevent hemodynamic compromise in older adults with concurrent sinus node dysfunction

Management: Orthostatic Hypotension

Neurogenic OH:

• Acute water ingestion (Class I, B-R): Temporary relief; peak effect 30 min after ≥240 mL; additional benefit with ≥480 mL; sympathetically driven pressor effect
• Physical counter-pressure maneuvers (Class IIa, C-LD): Leg crossing, squatting, muscle tensing increase BP
• Compression garments (Class IIa, C-LD): Thigh-high minimum; abdominal compression more effective; benefit proven in older adults and neurogenic OH
• Midodrine (Class IIa, B-R): Dose-dependent standing BP increase; limited by supine hypertension, scalp tingling, piloerection, urinary retention
• Droxidopa (Class IIa, B-R): Norepinephrine precursor; approved for neurogenic OH

Dehydration/drug-induced OH (Class IIb, C-LD): Withhold offending agents; adequate fluid intake

Special Populations

• Pediatric: VVS most common; tilt-table useful; pacing very limited; safety considerations in channelopathies
• Adult congenital heart disease: Complex arrhythmic substrate; refer to specialist
• Geriatric (>75yr): Greater hospitalization/death risk; falls overlap with syncope (1-yr fall rate 38% in fainters); more comorbidities; polypharmacy evaluation critical
• Drivers: Driving restrictions vary by jurisdiction; syncope of suspected cardiac etiology = risk; reflex syncope with prodrome = lower risk; patient counseling required
• Athletes: Exertional syncope warrants thorough cardiac evaluation; channelopathies and structural disease must be excluded before return to sport

Quality of Life and Healthcare Costs

• Syncope significantly impacts QoL (injury risk, driving restrictions, occupational impairment, anxiety)
• Substantial healthcare resource use; syncope units may reduce hospitalization and increase diagnostic rates but require further outcome evidence in North America

Limitations of the Document

• Most risk score data have inconsistent definitions, composite outcomes, small samples, and limited external validation; none outperform clinical judgment
• Evidence base for most VVS pharmacotherapy is weak (small RCTs, open-label, pediatric populations)
• Pacing for VVS evidence predominantly from open-label trials; blinded RCTs largely negative; strict patient selection required
• Older adults defined as >75yr in this guideline (age cutoff evolving)
• Limited data on syncope management units in North American health systems
• Several management sections rely on cross-referenced prior ACC/AHA disease-specific guidelines (device therapy, valvular disease, HCM, VT/SCD)
• Superseded by some subsequent data (e.g., further CPVT/LCSD evidence, evolution of pacing-for-VVS evidence with ISSUE-3 follow-up)

Key Concepts Mentioned

• concepts/Syncope — primary focus; definition, classification, evaluation, risk stratification
• concepts/Vasovagal-Syncope — most common etiology; detailed management section
• concepts/Orthostatic-Hypotension — neurogenic and non-neurogenic OH; management algorithm
• concepts/Carotid-Sinus-Syndrome — diagnosis and pacing recommendations
• concepts/POTS — definition, diagnostic criteria, differentiated from syncope
• concepts/Permanent-Pacing-Indications — bradycardia-related syncope; pacing for carotid sinus syndrome and VVS
• concepts/Atrioventricular-Block — bradycardic syncope evaluation
• entities/ICD — cardiac syncope in structural and inheritable conditions
• concepts/HCM-Risk-SCD — unexplained syncope as independent SCD predictor in HCM
• concepts/Arrhythmogenic-Cardiomyopathy — ARVC + syncope → ICD indication
• concepts/Sudden-Cardiac-Death — cardiac syncope risk stratification
• concepts/Sinus-Node-Dysfunction — bradycardic syncope

Key Entities Mentioned

• entities/ICD — central device for cardiac syncope management
• Implantable cardiac monitor (ICM) — gold-standard rhythm monitoring device for syncope

Wiki Pages Updated

• Created wiki/sources/syncope-aha-acc-hrs-2017.md
• Created wiki/concepts/Syncope.md
• Created wiki/concepts/Orthostatic-Hypotension.md
• Created wiki/concepts/Carotid-Sinus-Syndrome.md
• Updated wiki/concepts/Vasovagal-Syncope.md
• Updated wiki/concepts/POTS.md
• Updated wiki/sourceindex.md
• Updated wiki/wikiindex.md
• Appended wiki/log.md