Rapid Review·Cardiovascular
Select any text to highlight it or add a note.
PATHOLOGY
T2High yieldSyncope
FA P318
Focus on
Three routes to a brief loss of consciousness, and the one category that can kill.
Key takeaways
Three routes to a brief loss of consciousness
Syncope
transient loss of consciousness from a period of reduced cerebral blood flow, in three categories.Reflex, the most common
vasovagal (prodrome of warmth, pallor, nausea; brief, with rapid recovery), situational (coughing, swallowing, defecation, micturition), and carotid sinus hypersensitivity (a tight collar).Orthostatic
hypovolemia, drugs such as antihypertensives, autonomic dysfunction. Defined as a fall in systolic BP of 20 or more, or diastolic of 10 or more, within 3 minutes of standing.Cardiac
arrhythmias, or structural disease such as aortic stenosis and hypertrophic cardiomyopathy. This is the dangerous category, and syncope during exertion points here.| Category | Cause | Clues |
|---|---|---|
| Reflex | Vasovagal | A trigger (emotional stress, prolonged standing) and a prodrome (nausea, sweating, warmth) |
| Reflex | Situational | With micturition, defecation, swallowing, or coughing |
| Reflex | Carotid hypersensitivity | Pressure on the carotid sinus while standing (tight collar); older age, carotid atherosclerosis |
| Orthostatic | Medications | Vasodilators (alpha-1 blockers, antihypertensives, muscarinic agonists) or inotropic and chronotropic blockade (beta-blockers) |
| Orthostatic | Hypovolemia | A history of volume loss |
| Orthostatic | Autonomic dysfunction | Older age, diabetes, Parkinson disease |
| Cardiac | LV outflow obstruction | Syncope with exertion, systolic ejection murmur |
| Cardiac | Ventricular tachycardia | No warning; cardiomyopathy or ischemic disease (monomorphic), long QT (polymorphic) |
| Cardiac | Conduction impairment (sick sinus, AV block) | Preceding fatigue or light-headedness; sinus pauses or dropped QRS on ECG |
Vasovagal and situational syncope
Triggers
pain, anxiety, emotional stress, heat, prolonged standing (watching a baseball game) for vasovagal; cough, micturition, or defecation for situational.Mechanism
emotion heightens the brain's sensitivity to afferent signals, or mechanoreceptors in the lung, gut, or bladder fire; either way the reflex has two arms.- Cardioinhibitory: parasympathetic tone rises, so heart rate and contractility fall.
- Vasodepressor: sympathetic tone falls, so the vessels dilate and preload drops.
- Cardiac output falls, cerebral perfusion falls, and the patient faints.
Presentation
a prodrome (warmth, pallor, nausea, diaphoresis) and rapid recovery of consciousness, within 1 to 2 minutes.Diagnosis
mainly the history and examination; upright tilt-table testing when the picture is uncertain.Carotid sinus syndrome
Mechanism
an exaggerated baroreceptor response: parasympathetic output surges into a prolonged sinus pause (3 to 5 seconds) while sympathetic outflow collapses, so the periphery dilates, blood pressure plunges, and cerebral perfusion transiently fails.Risk factors
coronary atherosclerosis, previous neck surgery or irradiation, age over 50.Diagnosis
carotid sinus massage reproduces it: a pause of 3 seconds or more and/or a systolic fall of 50 mm Hg or more.Treatment
teach the patient to avoid the triggers, such as tight collars.Exercise-associated collapse
Mechanism
during hard exercise the leg muscles squeeze the veins and drive venous return; the moment exercise stops, that pump stops too and venous return drops.Presentation
the athlete collapses right after finishing, with dizziness or syncope and a normal or only slightly raised core temperature.Management
Trendelenburg positioning (feet above the head) and oral hydration.A 17-year-old faints while sprinting; a 70-year-old faints while shaving. Which category is each?
The sprinter is cardiac (think aortic stenosis, HCM, or an arrhythmia) until proven otherwise. The shaver is reflex: carotid sinus hypersensitivity.
How it's tested
Syncope during exertion is cardiac until proven otherwise, and that single rule decides most questions on this page: it points to aortic stenosis or hypertrophic cardiomyopathy if there is a murmur, and to an arrhythmia if there is not. Contrast that with vasovagal syncope, which has a prodrome of warmth, pallor and nausea and a rapid, complete recovery, and with orthostatic syncope, defined by a fall of 20 systolic or 10 diastolic within 3 minutes of standing and usually explained by hypovolemia or the antihypertensive the stem just mentioned.
Go deeper
First Aid 2026 — CV/Pathology (p.318) · B&B — Syncope · Mehlman — HY Cardio (exertional syncope, carotid sinus hypersensitivity)
Flashcards for this page
Card 1 of 5 · try-out only, nothing is saved
(...) syncope
You just read one page of 944
The rest of Step 1, written exactly like this.
Rapid Review is the reading layer of a full Step 1 platform: a schedule fitted to your exam date, flashcards for every page, and a mentor a message away.
Every Step 1 system
Written the same way: what to know, how it’s tested, where to go deeper.
A plan built to your exam date
Tell us when you sit, and the schedule fits the whole library and your question bank to it.
Flashcards for every page
Ready-made spaced-repetition decks linked to each topic, so nothing you read gets forgotten.
