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Syncope ((syncope ⓘ), commonly known as fainting or passing out, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. [1] It is caused by a decrease in blood flow to the brain , typically from low blood pressure . [ 1 ]
Increased parasympathetic outflow prominently affects the heart, reducing the heart rate or, in extreme cases, completely halting heart beats.This is a common cause of fainting.
Complete heart block could be the cause of syncope that is otherwise unexplained if bifascicular block is seen on electrocardiography. [1] It is estimated that less than 50% of patients with bifascicular block have high-degree atrioventricular block , although the exact incidence is unknown.
Tilt table testing could provoke fainting or syncope. It is the purpose of the test to provoke these symptoms, in order to aid in diagnosis. [ 4 ] It may not be appropriate, or indeed even possible, to stop the test before fainting occurs, as the drop in blood pressure or pulse rate associated with fainting can come on in seconds.
Apart from treating underlying reversible causes (e.g., stopping or reducing certain medications, treating autoimmune causes), several measures can improve the symptoms of orthostatic hypotension and prevent episodes of syncope (fainting). Even small increases in the blood pressure may be sufficient to maintain blood flow to the brain on standing.
Reflex syncope can occur in otherwise healthy individuals, and has many possible causes, often trivial ones such as prolonged standing with the legs locked. [citation needed] The main danger of vasovagal syncope (or dizzy spells from vertigo) is the risk of injury by falling while unconscious.
The European Society of Cardiology recommends that, with or without symptoms or other investigations, LQTS can be diagnosed if the corrected QT interval is longer than 480ms. They recommend that a diagnosis can be considered in the presence of a QTc of greater than 460 ms if unexplained syncope has occurred. [ 4 ]
The San Francisco Syncope Rule (SFSR) is a rule for evaluating the risk of adverse outcomes in patients presenting with fainting or syncope. The mnemonic for features of the rule is CHESS: • C - History of congestive heart failure • H - Hematocrit < 30% • E - Abnormal ECG • S - Shortness of breath • S - Triage systolic blood pressure < 90