Overview
This lecture covers the definition, evaluation, and treatment of syncope, emphasizing diagnostic modalities, risk stratification, and management approaches.
Definition and Epidemiology
- Syncope is a transient loss of consciousness due to cerebral hypoperfusion, characterized by rapid onset, short duration, and spontaneous recovery.
- The hallmark of syncope is complete loss of consciousness with amnesia for the event.
- Near-syncope means coming close to losing consciousness without actual loss.
- Syncope is common, costly, and can lead to injury, disability, or death, especially if cardiac in origin.
- Most common causes: neurally mediated (vasovagal) syncope (60%), orthostatic hypotension (15%), cardiac arrhythmia (10%), structural heart disease (5%), and undetermined causes (10%).
- Prognosis is generally benign for vasovagal syncope but worse for cardiac or neurologic etiologies.
Etiology and Physiology
- Vasovagal syncope involves blood pooling, decreased venous return, and an abnormal reflex causing hypotension and/or bradycardia.
- Orthostatic hypotension occurs from volume depletion, medications, or autonomic dysfunction.
- Cardiac causes include arrhythmias (brady- or tachyarrhythmias), structural disease (e.g., aortic stenosis, cardiomyopathies), and pulmonary embolism.
Initial Workup and Risk Stratification
- Initial evaluation: detailed history, physical exam, 12-lead ECG, and orthostatic blood pressure measurements (class 1 recommendations).
- Key questions: Was it a single episode? Is the etiology determined? Are high-risk features present (e.g., conduction disease, arrhythmia, structural heart disease)?
- High-risk ECG features: bundle branch block, prolonged/short QRS, AV block, bradycardia, arrhythmias, pre-excitation, long/short QT, Brugada/Epsilon waves, LVH.
Evaluative Modalities
- Carotid sinus massage: for patients >40 (after excluding carotid bruits) to diagnose carotid sinus hypersensitivity.
- Orthostatic challenge: significant BP drop within 3 minutes of standing indicates orthostatic hypotension.
- Tilt-table testing: used to evaluate reflex syncope, differentiate from epilepsy/pseudo-syncope, and assess orthostatic intolerance.
- External and implantable loop recorders: for correlating symptoms with arrhythmias, especially in recurrent or unexplained syncope.
- Hospital telemetry and Holter monitors: less useful than extended monitoring for infrequent episodes.
- Echocardiography: indicated for suspected structural heart disease.
- Exercise stress testing: for exertional syncope or suspicion of arrhythmogenic causes.
- Electrophysiology study (EPS): for patients with structural heart disease, conduction abnormalities, or suspected arrhythmias when noninvasive tests are inconclusive.
Management and Treatment
- Vasovagal syncope: education, reassurance, increased salt/fluids, counter-pressure maneuvers; consider midodrine for refractory cases.
- Orthostatic hypotension: address underlying causes (rehydration, medication adjustment), compression garments, midodrine, droxidopa.
- Cardiac causes: pacemaker or ICD for high-risk features (e.g., asystole, high-degree AV block, hypertrophic cardiomyopathy).
- Pacemakers benefit selected patients with recurrent, unpredictable syncope and documented asystole.
- Do not implant devices for unexplained syncope without evidence of conduction disease (class 3 recommendation).
Key Terms & Definitions
- Syncope — Temporary loss of consciousness from insufficient blood flow to the brain.
- Vasovagal syncope — A reflex cause of syncope from abnormal response to triggers.
- Orthostatic hypotension — BP drop upon standing causing syncope.
- Carotid sinus massage — Technique to evaluate carotid sinus sensitivity.
- Tilt-table test — Diagnostic tool to provoke syncope under monitored conditions.
- Implantable loop recorder (ILR) — Long-term device to monitor heart rhythm.
- EPS (Electrophysiology Study) — Invasive study to determine arrhythmia type and risk.
Action Items / Next Steps
- Review current guidelines and diagnostic algorithms for syncope.
- Practice identifying high-risk ECG features.
- Read up on the indications and interpretation of tilt-table testing and loop recorders.
- Familiarize yourself with classes of recommendations (1, 2a, 2b, 3).