Syncope
Differential Overview
Orthostatic/Autonomic
❑ Neurally mediated hypotension
❑ Volume depletion
❑ Cough syncope
❑ Anemia
❑ Autonomic insufficiency
Cardiac/Obstructive
❑ Myocardial infarction
❑ Pulmonary embolism
❑ Aortic stenosis
❑ Hypertrophic obstructive cardiomyopathy
❑ Aortic dissection
❑ Cardiac tamponade
❑ Left atrial myxoma
Cardiac/Dysrhythmic
❑ Complete heart block
❑ Sick sinus syndrome
❑ Tachyarrhythmia
❑ Carotid sinus hypersensitivity
Neurologic
❑ Vertebrobasilar ischemia
❑ Hypoglycemia
❑ Unwitnessed seizure
❑ Subclavian steal syndrome
Psychologic
❑ Hyperventilation
❑ Hysterical faint
Diagnostic Approach
The cause of syncope is usually evident after a careful history and physical exam. Identification of a cardiac cause is critical because it portends a poor prognosis (1-year mortality 18% to 33%). In patients with heart disease, the most specific predictors of a cardiac cause are syncope in the supine position or during effort, blurred vision, and convulsive syncope. In patients without heart disease, palpitations are the only significant predictor of a cardiac cause.
Focus on preceding events and witness description. Sudden loss of consciousness without warning is usually due to an arrhythmia. Syncope with chest pain mandates that aortic dissection, myocardial infarction, and pulmonary embolism be ruled out. Syncope with exertion suggests aortic stenosis, hypertrophic obstructive cardiomyopathy, or bradycardia. Events after the syncope, such as confusion, lethargy, or neurological symptoms suggest a seizure.
Consider syncope as the cause of unexplained trauma such as hip fracture or MVA.
Clinical Findings
Neurally mediated hypotension Also known as vasovagal syncope or common fainting, this phenomenon is autonomic, a paradoxical reflex initiated when ventricular preload is reduced by venous pooling. Syncope occurs when the patient is erect. Premonitory symptoms such as lightheadedness and queasiness usually precede the syncope, and persistent weakness usually follows. If observed, the patient is pale with beads of perspiration on the forehead, yawning, cold hands and feet, and a weak and slow radial pulse. There may be a few seizure-like movements at the time of the faint, but no loss of bowel or bladder function occurs. Syncope is often precipitated by perceived threat, fear, emotional stress, or pain, and may occur with micturition, cough, Valsalva, ocular stimulation, or heat-induced vasodilatation.
Volume depletion Lightheadedness or syncope occurs on arising to standing, due to diuretics, diarrhea, vomiting, or blood loss. Significant orthostatic vital sign changes will be present (20 mmHg fall in systolic pressure or 10 mmHg fall in diastolic pressure after 2 minutes of standing).
Cough syncope Syncope occurs following a severe or protracted cough.
Anemia Orthostatic lightheadedness, pallor, and absence of flushing of the palmar creases with extension of the hand are clues.
Autonomic insufficiency Syncope follows exertion. The heart rate fails to increase with a decrease in blood pressure. Other autonomic findings such as pupillary unreactiveness, urinary incontinence, diarrhea, and impotence may be present.
Myocardial infarction The episode is often preceded by an unstable angina pattern of increasing frequency of chest pressure and decreasing level of activity required to precipitate it. The pain is deep, heavy, and substernal with radiation into the left shoulder, neck, or arm. Lightheadedness and syncope are associated with diaphoresis and low blood pressure.
Pulmonary embolism Syncope may be a presenting sign of massive pulmonary embolism. Key clues are associated signs of pleuritic chest pain, acute dyspnea, hemoptysis, and leg swelling.
Aortic stenosis Signs of hemodynamic significance include a low volume and delayed carotid upstroke (pulsus parvus et tardus), absence of A2, and a long, loud murmur that travels through the second heart sound and is located at the upper right sternal border with radiation into the neck.
Hypertrophic obstructive cardiomyopathy A systolic murmur increases dramatically in intensity with standing.
Aortic dissection There is sudden onset of maximally severe tearing pain, which travels in location with the progression of the dissection and often radiates between the shoulder blades. The patient will often appear quite restless and be constantly in motion in an attempt to find a comfortable position. Asymmetry of pulses is a critical clue. Blood pressure may be normal in the presence of gray cyanosis. There is often a history of hypertension, blunt chest trauma, or Marfan syndrome.
Cardiac tamponade Tamponade is marked by muffled heart sounds or pericardial friction rub, pulsus paradoxus, and a narrow pulse pressure.
Left atrial myxoma A variable diastolic murmur and the presence of systemic emboli are clues to this rare condition.
Complete heart block This usually manifests as a slow yet strong pulse, with cannon A waves observed in the jugular veins. Survey for AV nodal blocking drugs.
Sick sinus syndrome Syncope usually occurs with prolonged sinus pauses of 8 to 10 seconds.
Tachyarrhythmia Syncope is precipitated by rates greater than 180 per minute, as seen in AV node reentry or bypass tract. Palpitations are often reported, and syncope may occur when the patient is supine.
Carotid sinus hypersensitivity With a hypersensitive carotid sinus, carotid massage will produce a long period of asystole. Symptoms may occur with wearing a tight collar or turning the head and may be aggravated by digoxin.
Vertebrobasilar ischemia Dizziness or vertigo, numbness of the ipsilateral face and contralateral limbs, diplopia, dysarthria, and dysphagia occur. Actual syncope is unusual.
Hypoglycemia Syncope is gradual in onset, with early restlessness, confusion, and anxiety. Low glucose tends to cause an altered level of consciousness rather than complete syncope.
Unwitnessed seizure Seizure can be recognized by an aura, tongue biting, incontinence, soft tissue injury at multiple sites (due to tonic-clonic seizure activity), and a protracted recovery phase.
Subclavian steal syndrome Syncope and basilar neurological symptoms begin following arm exercise. There will be a blood pressure differential between the arms and a subclavian bruit.
Hyperventilation There is a smothering feeling associated with perioral or acral paresthesias. Tetany occasionally occurs.
Hysterical faint A dramatic and graceful faint to the floor or couch occurs with an audience present, and the patient describes the episode in an emotionally detached manner (“la belle indifference”). Nausea, diaphoresis, and pallor will be absent.
Book Source Details
- Book Title: Field Guide to Bedside Diagnosis
- Author(s): David S. Smith
- Year of Publication: 2007
- Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2007 Lippincott Williams & Wilkins.
Other Book Chapters Related to Syncope
Read excerpts from these other book chapters related to Syncope:
Copyright Details: Field Guide to Bedside Diagnosis, Copyright © 2008 Williams & Wilkins.
More About Causes of Syncope
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More About This Book:
Title: Field Guide to Bedside Diagnosis
Authors: David S. Smith
Publisher: Lippincott Williams & Wilkins
Copyright: 2007
ISBN: 0-78178-165-5
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» Next page: Delirium/Hallucinations (Field Guide to Bedside Diagnosis)
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