Syncope

Definition

• Braunwald's Heart Disease, p. 1384

Epidemiology

• Accounts for 1% of hospital admissions and 3% of ED visits
• Up to 50% of young adults report a prior LOC episode (mostly isolated, never reaching medical attention)
• Peak prevalence: ages 10-20, with additional peaks at ~60 and ~80 years
• In adolescents, 80% of pediatric fainting is neurocardiogenic (vasovagal)
• 15-25% of adolescents experience at least one episode in their lifetime

Classification / Etiology

1. Neurally Mediated (Reflex) Syncope - Most Common

• Vasovagal (neurocardiogenic) syncope - triggered by orthostatic stress, pain, fear, blood phobia, emotional stimuli
• Situational syncope - triggered by cough, micturition, defecation, postprandial state, exercise
• Carotid sinus hypersensitivity (CSH) - pressure on carotid sinus causes reflex bradycardia/hypotension
• Mechanism: reflex combination of vasodilation (vasodepressor) and bradycardia (cardioinhibitory) causing reduced cerebral perfusion
• Recovery usually takes 1-5 minutes; nausea and fatigue can persist for hours

2. Orthostatic Hypotension

• Drop in BP on standing due to impaired autonomic compensation (dysautonomia, dehydration, medications, Parkinson disease, diabetes, prolonged bedrest)
• More common in elderly due to reduced baroreceptor responsiveness

3. Cardiac Syncope

• Arrhythmic (most common cardiac cause): AV block, sick sinus syndrome, VT, SVT, bradydysrhythmias
• Structural/obstructive: aortic stenosis, HCM, pulmonary embolism, cardiac tamponade, aortic dissection
• Rare but dangerous: long-QT syndrome, Brugada syndrome, ARVC, CPVT, short-QT syndrome

4. Neurologic Causes

• Vertebrobasilar insufficiency (usually accompanied by brainstem symptoms: diplopia, dysarthria, vertigo, focal weakness)
• Migraine-mediated syncope

5. Metabolic

• Hypoglycemia, hypoxia, hyperventilation (mechanistically distinct - not true syncope)

Key point: NMS and other reflex-mediated causes are the most frequent at any age and in any setting. Cardiac causes (especially tachyarrhythmias) are more common in older patients, with up to half of elderly ED patients with syncope having a cardiac condition.

• Braunwald's Heart Disease, pp. 1384-1390; Tintinalli's Emergency Medicine, p. 3828

Clinical Features & Differentiation

Vasovagal vs. Arrhythmic vs. Seizure - Key Distinguishing Features

• Braunwald's Heart Disease, p. 688 (Table 71.4)

Events Mistaken for Syncope

• Seizure: simultaneous motor activity + LOC, prolonged postictal phase
• Hypoglycemia: confusion progressing to LOC, requires glucose to terminate
• Vertigo: spinning sensation but no LOC
• Hysteria/psychogenic: no true LOC, indifference to event
• Basilar migraine: headache, rarely true LOC

Evaluation

Step 1: History, Physical Examination, ECG (cornerstone)

• Targeted history: circumstances of event, prodrome, recovery, medications, cardiac history, family history of sudden death
• Orthostatic vital signs: measure BP/HR supine then each minute after standing for 3-5 minutes
• Carotid sinus massage: if CSH is suspected (older patients)
• ECG: abnormal in 50% of cases, but yields a specific diagnosis in only ~5%

Step 2: Targeted Workup Based on Clinical Suspicion

• Braunwald's Heart Disease, pp. 1390-1394

Risk Stratification

• Syncope during exertion or while supine
• Preceded by palpitations
• Associated chest pain, dyspnea
• Structural or known heart disease
• Family history of sudden cardiac death
• Age >65 years
• Abnormal ECG (new bundle branch block, prolonged QT, Brugada pattern, delta waves)

• Young patient (<40 yr)
• Clear precipitating trigger (pain, fear, prolonged standing, blood phobia)
• Typical prodrome (nausea, warmth, diaphoresis)
• No structural heart disease
• Normal ECG

Management

Neurally Mediated / Vasovagal Syncope

• Education and reassurance - explain the benign nature
• Behavioral modification: avoid triggers, recognize prodrome and adopt supine position, avoid prolonged standing, increase fluid/salt intake
• Physical counterpressure maneuvers: leg crossing, arm tensing - effective when prodrome allows
• Increased salt and fluid intake in patients without contraindications
• Medications (for refractory cases): fludrocortisone, midodrine, beta-blockers (controversial), SSRIs
• Pacemaker (dual-chamber): in cardioinhibitory NMS with documented asystole (e.g., ISSUE-3 trial patients with pause >3 sec)
• Cardioneuroablation: emerging option for highly symptomatic patients with cardioinhibitory response

Orthostatic Hypotension

• Adequate hydration, compression stockings, elevating head of bed
• Reduce/eliminate offending medications
• Fludrocortisone, midodrine, droxidopa (for neurogenic orthostatic hypotension)

Arrhythmic Syncope

• Bradyarrhythmias (AV block, SSS): permanent pacemaker
• Ventricular tachyarrhythmias: ICD, antiarrhythmic drugs (beta-blockers, flecainide for CPVT), catheter ablation
• SVT: catheter ablation or rate/rhythm control medications
• ICD is recommended only for patients with cardiac arrest, recurrent syncope, or polymorphic/bidirectional VT in CPVT

Structural/Obstructive Syncope

• Treat the underlying cause (valve replacement for severe AS, septal reduction for HCM, anticoagulation/thrombolytics for PE)

Older Adults - Special Considerations

• Syncope is often multifactorial in the elderly
• 2-year mortality 25-30% in patients >75 years
• Detailed medication review (polypharmacy) is essential
• Consider syncope in any unexplained fall in the elderly
• Braunwald's Heart Disease, pp. 1394-1397; Braunwald's Heart Disease (Geriatrics), p. 2909

Prognosis

• Neurally mediated syncope in young patients: excellent prognosis
• Orthostatic hypotension syncope: twofold increase in mortality (reflects comorbidity burden)
• Cardiac syncope (structural heart disease or primary electrical disease): increased risk of SCD and overall mortality
• Syncope can be the only warning sign before sudden cardiac death