Cardiology · Arrhythmia and Hemodynamics
The facts most likely to be tested
Press 1–5 to rate · ↑↓ to navigate
Vasovagal syncope is a reflex-mediated condition typically preceded by a prodrome of nausea, warmth, or diaphoresis triggered by emotional stress or prolonged standing.
Exertional syncope is a red flag that mandates immediate evaluation for structural heart disease such as aortic stenosis or hypertrophic cardiomyopathy.
Carotid sinus hypersensitivity is diagnosed when carotid sinus massage induces a ventricular pause of greater than 3 seconds or a drop in systolic blood pressure of 50 mmHg.
Orthostatic hypotension is defined as a decrease in systolic blood pressure of at least 20 mmHg or diastolic blood pressure of at least 10 mmHg within 3 minutes of standing.
Syncope occurring in the setting of palpitations or a family history of sudden cardiac death is highly suggestive of a primary arrhythmia.
Electrocardiogram (ECG) is the mandatory initial diagnostic test for all patients presenting with syncope to rule out conduction abnormalities or ischemia.
Echocardiography is the gold standard diagnostic test to evaluate for structural heart disease in patients with abnormal ECG findings or suspected cardiac syncope.
Vignette unlocked
A 24-year-old male presents to the clinic after a syncopal episode while playing basketball. He reports feeling lightheaded immediately before losing consciousness, but he regained awareness within seconds. He denies chest pain, palpitations, or shortness of breath. Physical examination reveals a harsh systolic crescendo-decrescendo murmur at the left lower sternal border that increases in intensity with Valsalva maneuver. His ECG shows left ventricular hypertrophy.
What is the most likely underlying cause of this patient's syncope?
Hypertrophic cardiomyopathy
The patient's exertional syncope combined with a murmur that increases with decreased preload (Valsalva) is classic for hypertrophic cardiomyopathy, a structural cause of syncope that must be ruled out in young athletes.
Full handout
High yield triage
Etiology / Epidemiology
Transient global cerebral hypoperfusion. Cardiac causes carry highest mortality; vasovagal is most common.
Clinical Manifestations
Brief loss of consciousness with spontaneous recovery. Prodrome of warmth, nausea, or lightheadedness.
Diagnosis
ECG is mandatory for all patients. Echocardiogram if structural heart disease suspected.
Treatment
Treat underlying cause. Physical counter-pressure maneuvers for vasovagal. Avoid driving until cleared.
Prognosis
Cardiac syncope has 30% 1-year mortality. Recurrence is common in neurocardiogenic types.
Full handout
Epidemiology & Etiology
Syncope is categorized into neurally mediated, orthostatic, and cardiac. Elderly patients are at high risk for multifactorial syncope. Structural heart disease and arrhythmias are the most dangerous etiologies.
Pertinent Anatomy
Cerebral perfusion requires intact carotid sinus baroreceptors and cardiac output. Obstruction of outflow (e.g., aortic stenosis) or impaired venous return triggers hypoperfusion.
Pathophysiology
Sudden drop in systemic blood pressure leads to global cerebral ischemia. Neurally mediated syncope involves a Bezold-Jarisch reflex causing paradoxical bradycardia and vasodilation. Cardiac syncope results from mechanical obstruction or electrical failure.
Clinical Manifestations
Patients present with sudden collapse and rapid, complete recovery. Prodrome (diaphoresis, nausea) suggests vasovagal; absence of prodrome suggests arrhythmia. Red flags include syncope during exertion, family history of sudden death, or chest pain.
Diagnosis
Initial evaluation requires ECG and orthostatic vitals (drop of >20 mmHg systolic or >10 mmHg diastolic). Echocardiogram is the gold standard for structural assessment. Tilt table test is reserved for recurrent, unexplained cases.
Treatment
Management focuses on the underlying trigger. For vasovagal, use physical counter-pressure maneuvers (leg crossing, handgrip). Pacemaker is indicated for symptomatic bradycardia or Sick Sinus Syndrome. Avoid driving until the etiology is identified and treated.
Prognosis
Cardiac syncope carries a 30% 1-year mortality rate. Patients with unexplained syncope and abnormal ECG require Holter monitoring or an implantable loop recorder to rule out occult arrhythmias.
Differential Diagnosis
Vasovagal: triggered by emotional stress or prolonged standing
Orthostatic: drop in BP upon standing due to volume depletion or meds
Arrhythmic: sudden onset without prodrome, often during exertion
Structural: Aortic Stenosis presenting with exertional syncope
Seizure: post-ictal state and tongue biting distinguish from syncope