Syncope

BASICS

Definition: Transient loss of consciousness (LOC) with unresponsiveness and loss of postural tone, followed by spontaneous, rapid, and complete recovery. Usually brief, caused by cerebral hypoperfusion.
Systems affected: Cardiovascular, nervous

Mechanism: Systemic hypotension → ↓ cardiac output and/or systemic vasodilation → ↓ cerebral perfusion
Cardiac causes:
Arrhythmias
Obstruction to outflow (PE, hypertrophic cardiomyopathy, aortic stenosis)
Non-cardiac causes:
Reflex-mediated vasovagal (neurally mediated syncope/NMS): inappropriate vasodilation (most common in adults/children); situational (micturition, defecation, cough, pain, emotion, hair combing)
Orthostatic hypotension (OHT): volume depletion, pregnancy, anemia, meds
Drug/alcohol induced
Primary autonomic failure (pure autonomic failure, Parkinson)
Secondary autonomic failure (diabetes, amyloidosis)
Carotid sinus hypersensitivity
Pediatric: Vast majority are benign, due to vasomotor tone alteration

Careful history, exam, ECG most important
Differentiate from vertigo, seizure, falls without LOC
Typical syncope: rapid onset, brief (<60 sec), rapid & complete recovery
Circumstances: prolonged standing, urination, coughing, postprandial, emotion (NMS); neck movement (carotid sinus); exertion (cardiac)
Prodromal symptoms: (NMS)
Elderly: often no prodrome
Palpitations/chest pain/dyspnea: (cardiac)
Position: supine (arrhythmia), erect (NMS), transition (OHT)
Delayed recovery: neurologic (postictal)
Family history: Long QT, Brugada, VT, hypertrophic cardiomyopathy, sudden cardiac death <50 yrs
High-risk: new chest pain, breathlessness, abdominal pain, headache, exertional or supine syncope, sudden palpitations with syncope

Orthostatic BP & pulse: drop in SBP ≥20 mmHg or DBP ≥10 mmHg (OHT)
Cardiac murmur or focal neuro abnormality
High-risk: unexplained SBP <90, GI bleed, bradycardia <40 bpm, new systolic murmur

Initial:
ECG (arrhythmia, ischemia, block, QTc, preexcitation)
CBC, electrolytes, BUN, Cr, glucose, BNP, cardiac enzymes, D-dimer, urine pregnancy, drug screen as indicated
Imaging if PE/MI suspected
Follow-up (history/physical guided):
Exercise stress test (exertional syncope)
Echocardiogram (ischemic/valvular/congenital suspicion)
ECG monitoring (Holter, event, implantable loop recorder)
Head imaging, carotid US, EEG only if neuro cause suspected
Tilt-table test (vasovagal syncope)—limited reproducibility, high false positives
Psychiatric eval if psychogenic

Hydration, normal salt intake, premonitory sign education
Most pediatric cases: nonpharmacologic only
NMS: reassurance, behavior modification
Admit elderly/new heart disease/possible cardiac etiology
Young/healthy: outpatient workup
Treat documented, symptomatic arrhythmias; no need to treat asymptomatic arrhythmias

Counterpressure maneuvers, exercise (improve vasovagal syncope)
Head-up tilt sleeping, abdominal binders/support stockings, increase fluid/salt for recurrent NMS

ICD placement: High-risk cardiac syncope (long QT, Brugada, VT, HCM)
Pacemaker: 2nd (Mobitz II) or 3rd-degree heart block, high risk for 3rd-degree block, sinus node recovery time ≥3 sec

No specific restriction unless cardiac/NMS; consider increased salt/fluid for NMS

Most cardiac causes are treatable; noncardiac generally have excellent prognosis
Teach avoidance of triggers, preventative maneuvers, and position changes
Advise about driving restrictions during evaluation per local laws

Shen WK, Sheldon RS, Benditt DG, et al. 2017 ACC/AHA/HRS guideline for syncope. Circulation. 2017;136(5):e60-e122.
Brignole M, Moya A, de Lange FJ, et al. 2018 ESC guidelines for syncope. Eur Heart J. 2018;39(21):1883-1948.
Albassam OT, Redelmeier RJ, Shadowitz S, et al. JAMA. 2019;321(24):2448-2457.