What are the differential diagnoses for presyncope in young populations?

Differential Diagnoses for Presyncope in Young Populations

In young patients, presyncope is most commonly caused by benign reflex (vasovagal) syncope, but you must systematically exclude life-threatening cardiac causes including channelopathies, cardiomyopathies, and arrhythmias before attributing symptoms to benign etiologies. 1

Primary Differential Categories

Benign Reflex Causes (Most Common)

• Vasovagal (neurocardiogenic) syncope represents the vast majority of presyncope in young populations, triggered by emotional stress, prolonged standing, pain, or fear 1
• Orthostatic hypotension from dehydration, medications, or autonomic dysfunction 1
• Situational syncope triggered by micturition, defecation, coughing, or carotid sinus stimulation 2

Life-Threatening Cardiac Causes (Must Exclude First)

Channelopathies:

• Long QT syndrome - identifiable on surface ECG, can cause syncope with loud noise, fright, extreme emotional stress, or during swimming 1
• Brugada syndrome - distinctive ST elevation in V1-V2, may be intermittent or require provocative testing with procainamide 1
• Catecholaminergic polymorphic ventricular tachycardia - presents with syncope during high-intensity physical activity, requires exercise stress testing 1
• Wolff-Parkinson-White syndrome - delta wave on ECG indicating accessory pathway 1

Structural Heart Disease:

• Hypertrophic cardiomyopathy - most common cause of sudden death in young athletes, presents with exertional syncope 1
• Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) - syncope is an ominous finding; up to 20% of sudden cardiac deaths in patients <35 years 1
• Anomalous coronary artery - second most common cause of sudden death in young athletes 1
• Pulmonary arterial hypertension 1

Arrhythmias:

• Supraventricular tachycardia (SVT) - narrow complex tachycardia at 250-300 bpm in infants, represents hemodynamic compromise 3
• Arrhythmias after repaired congenital heart disease 1
• Myocarditis 1

Other Important Differentials

Neurological:

• Seizure disorders - distinguished by movements occurring before loss of consciousness, post-ictal confusion lasting >few minutes, tongue biting, and muscle pain lasting hours/days 1, 4
• Kearns-Sayre syndrome - external ophthalmoplegia with progressive heart block 1

Metabolic/Other:

• Breath-holding spells in early childhood (pallid or cyanotic types) 1
• Drug-induced from medications or over-the-counter supplements 1
• Psychogenic pseudosyncope - duration >5 minutes suggests this diagnosis 4

Critical Red Flags Requiring Cardiac Evaluation

History features that mandate aggressive cardiac workup: 1, 4

• Family history of premature sudden cardiac death (<30 years) or familial heart disease
• Known or suspected structural heart disease
• Syncope during exertion or swimming
• Syncope without prodrome, while supine, or during sleep
• Syncope preceded by chest pain or palpitations
• Event triggers: loud noise, fright, extreme emotional stress

Diagnostic Approach Algorithm

Step 1: Detailed History and Physical Examination

• Obtain exact circumstances: position (supine/standing), activity level, triggers, prodromal symptoms 1
• Measure orthostatic vital signs (supine and standing blood pressure/heart rate) 1
• Assess for cardiac examination abnormalities suggesting structural disease 1

Step 2: 12-Lead ECG (Mandatory for All Patients)

• Screen for prolonged QT interval, Brugada pattern, delta waves, bundle branch blocks, ventricular ectopy 1
• This is the single most important initial test beyond history and physical 1

Step 3: Risk Stratification

• Low risk (no red flags, normal ECG): Likely reflex syncope, education and reassurance sufficient 1
• High risk (any red flags or abnormal ECG): Proceed to echocardiogram and consider exercise stress testing 1

Step 4: Selective Advanced Testing Based on Clinical Suspicion

• Echocardiogram if structural heart disease suspected or any cardiac red flags present 1
• Exercise stress testing for exertional symptoms or to screen for catecholaminergic VT 1
• Cardiac MRI if ARVD/C suspected or to evaluate anomalous coronary arteries 1
• Tilt table testing has limited utility in young patients due to high false-positive rates; use cautiously 1

Common Pitfalls to Avoid

• Never assume benign vasovagal syncope in a young patient with documented tachycardia or any cardiac red flags - underlying heart disease makes presyncope potentially life-threatening 3
• Avoid brain CT/MRI in uncomplicated presyncope - yield is <1% for new neurological diagnosis and <6% for acute abnormality even with syncope 1
• Do not rely on tilt testing alone in adolescents - specificity may be as low as 85% with standard protocols, and 40% of healthy teenagers have near-fainting with IV placement 1
• Recognize that presyncope and syncope have similar 30-day serious outcomes (5.1% serious outcomes including 3.1% cardiovascular) and should be managed identically 1, 5
• Duration <30 seconds strongly favors syncope over epilepsy, but brief myoclonic jerks can occur with syncope and do not indicate seizure 1, 4