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Emergency and Acute Medicine – Syncope
Syncope is a transient loss of consciousness associated with loss of postural tone, caused by temporary cerebral hypoperfusion, particularly affecting the brainstem reticular activating system. It is most often due to a sudden drop in cardiac output, after which cerebral perfusion is restored through autonomic mechanisms and the supine position following collapse. Syncope accounts for approximately 3% of emergency department visits.
Syncope can occur in special populations with unique considerations. In pregnancy, presyncope and syncope are common due to decreased systemic vascular resistance from the placenta acting like an arteriovenous shunt, as well as compression of the inferior vena cava by the fetus. However, serious conditions such as pulmonary embolism, preeclampsia, and cardiac disease must always be excluded. In elderly patients, syncope is more frequent and often multifactorial, with higher morbidity and multiple contributing causes.
The causes of syncope are broadly categorized. Neurally mediated syncope, such as vasovagal syncope, is the most common and results from reflex vasodilation and bradycardia, often triggered by pain, fear, or emotional stress, and usually preceded by prodromal symptoms. Carotid sinus hypersensitivity may be triggered by actions such as coughing, sneezing, or micturition. Orthostatic syncope results from a sudden drop in venous return due to positional change and may be caused by dehydration, hemorrhage, autonomic dysfunction (such as diabetic neuropathy), or medications. Cardiac causes include arrhythmias, which often present suddenly without warning, and structural heart disease such as aortic stenosis, hypertrophic cardiomyopathy, myocardial infarction, pulmonary embolism, or aortic dissection. Neurologic causes are less common but include conditions such as subarachnoid hemorrhage or cerebrovascular insufficiency.
Patients often report prodromal symptoms such as lightheadedness, diaphoresis, nausea, dimming vision, and weakness. Features that suggest a life-threatening cause include sudden loss of consciousness without warning, chest pain, or palpitations. A structured history using the “6 Ps” (preprodrome, prodrome, predisposing factors, precipitating factors, passerby account, and postictal phase) can help determine the etiology. A postictal phase suggests seizure rather than syncope. Physical examination should include assessment for trauma, orthostatic vital signs, cardiovascular examination for murmurs or arrhythmias, neurologic evaluation, and screening for possible bleeding or pregnancy. In children, concerning features include syncope during exertion, events triggered by loud noise or stress, occurrence while supine, or a family history of sudden death.
Evaluation relies heavily on history and physical examination, which can determine the diagnosis in most cases. An ECG should be performed immediately to assess for ischemia, arrhythmias, conduction abnormalities, long QT syndrome, Brugada syndrome, or pre-excitation syndromes. Laboratory testing is guided by clinical suspicion and may include complete blood count for anemia or bleeding, electrolytes, cardiac enzymes, and pregnancy testing. Imaging such as chest radiography, CT angiography, or head CT is reserved for suspected cardiopulmonary or neurologic causes. Echocardiography is useful when structural heart disease is suspected.
Management begins with stabilization, including airway, breathing, and circulation, oxygen supplementation, cardiac monitoring, and intravenous access. Fluid resuscitation is indicated in suspected hypovolemia. In unstable patients, advanced cardiac life support protocols should be followed. Treatment is directed at the underlying cause, such as managing arrhythmias, treating myocardial infarction, controlling blood pressure in aortic dissection or subarachnoid hemorrhage, or administering thrombolytics for pulmonary embolism when appropriate. In cases of persistent altered mental status, a “coma cocktail” including dextrose, thiamine, and naloxone may be considered.
Disposition depends on risk stratification. High-risk patients, such as those identified by the San Francisco Syncope Rule (history of congestive heart failure, hematocrit <30%, abnormal ECG, shortness of breath, or systolic blood pressure <90 mm Hg), should be admitted for monitoring. Patients with suspected cardiac causes or significant comorbidities also require admission. Low-risk patients with vasovagal or orthostatic syncope may be discharged with close follow-up, provided they are reliable and have adequate support. Driving restrictions should be advised until evaluation is complete.
Syncope is frequently confused with seizure, but the presence of postictal confusion strongly favors seizure. Brief tonic movements or urinary incontinence may still occur in syncope. Clinicians should avoid assuming a benign vasovagal cause when syncope is associated with chest pain or headache, as these may indicate serious underlying conditions.
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