Common misconceptions and mistakes
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Believing that cough syncope is caused by coughing-induced vagal tone and bradycardia, leading to systemic hypotension and syncope (ie, vasovagal syncope as a result of cough)
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Believing that cough syncope is caused by decreased venous return secondary to the high intrathoracic pressure of forceful coughing, leading to systemic hypotension and syncope
Cough syncope
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The most common cause of syncope is cerebral hypoperfusion associated with transient systemic hypotension
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Forceful coughing may transiently decrease blood pressure by either:
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Causing increased vagal tone with subsequent symptomatic bradycardia, hypotension, and syncope (ie, vasovagal syncope as a result of cough) or
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Causing increased intrathoracic pressure, with subsequent decreased venous return, reflex tachycardia, hypotension, and syncope
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Patients with pulmonary hypertension and preexisting right-sided heart failure may be more vulnerable to a sudden decrease in preload, predisposing them to this physiology
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Cough syncope (originally known as laryngeal vertigo) describes a syndrome of syncope occurring with forceful coughing that is not associated with systemic hypotension
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Responsible for approximately 2% of all syncope cases
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Classic phenotype and presentation
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Most commonly affects stocky men (muscular and overweight) with abdominal obesity and chronic obstructive pulmonary disease (COPD)
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Episodes start with a forceful crescendo of coughing, leading to a transient loss of consciousness (seconds)
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Syncope occurs without systemic hypotension (and/or bradycardia)
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Often syncope occurs in the setting of tachycardia and hypertension driven by the adrenergic nature of forceful coughing
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Patients uniformly recall coughing before losing consciousness
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Often they report prior episodes and/or endorse frequent episodes of presyncope with coughing
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Over half of individuals experience jerking or rhythmic movements of the limbs with syncope (often erroneously interpreted as seizure activity)
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Pathophysiology of Cough Syncope
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Coughing increases intrathoracic pressure, which increases central venous pressure, which increases intracranial venous pressure
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The intracranial veins cannot absorb this pressure with distension (as occurs in other tissues in the body), because the brain is enclosed in the skull and surrounded by a noncompressible fluid
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Therefore a sudden increase in central venous pressure can cause a sudden increase in intracranial pressure (ICP)
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When ICP rises, cerebral perfusion pressure (CPP) drops, decreasing cerebral blood flow (CBF)
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CPP = mean arterial pressure (MAP) − intracranial pressure (ICP)
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In normal individuals, CBF flow decreases with forceful coughing, but never reaches zero
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In individuals with cough syncope, forceful coughing leads to transient cessation of cerebral blood flow
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As ICP exceeds diastolic blood pressure (BP), diastolic flow reversal occurs in the intracranial arteries
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CBF drops close to zero, and syncope ensues
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With syncope, coughing stops, intrathoracic pressure falls, ICP falls, perfusion returns, and consciousness is restored
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