Syncope is a neurobehavioral manifestation that is a "transient loss of consciousness and postural tone caused by diminished blood flow to the brain (i.e., brain ischemia). Presyncope refers to the sensation of lightheadedness and loss of strength that precedes a syncopal event or accompanies an incomplete syncope."
- No diagnosis was made in one third of patients
- "The most frequent diagnosis was 'situational, orthostatic or vasavagal syncope'" 29%
- Bradyarrhythmia, 5%
- Tachyarrhythmia 3%
About 25% of patients have a cardiac cause, 15% are vasovagal and 10% are due to orthostatic hypotension. About 3% are from myocardial infarction, 91% having normal ST-segments. In octogenarians, 10% are from arrhythmias.
2% have a cerebrovascular cause. Generally, this is consider when there is basilar artery or bilateral vertebral or bilateral carotid stenoses severe stenoses. However, there are case reports suggesting unilateral carotid stenoses can cause syncope. However, it is not clear if these patients also had focal neurological symptoms.
2% are due to seizures.
Vasovagal syncope (also called neurocardiogenic syncope, neurogenic syncope, or vasodepressor syncope is the cause of syncope in about 15% of patients. Vasovagal syncope is "loss of consciousness due to a reduction in blood pressure that is associated with an increase in vagal tone and peripheral vasodilation". Vasovagal syncope includes vasodepressor syncope which is syncope during fright or stress. Sometimes asystole occurs and a pacemaker is needed.
Some authors use neurocardiogenic syncope or neurally mediated syncope as the broad term, and within this category are the parasympathetic mediated syncopes: 1) vasovagal syncope (syncope during fright or stress), 2) situational syncope (syncope following cough, micturition, or defecation), and 3) carotid sinus syncope (also called carotid sinus hypersensitivity).
History and physical
An evaluation based on the initial history and physical examination will correctly diagnose the underlying cause in 63% of patients according to one case series. Interviewing witnesses must be carefully done. Allowing observers to answer "I do not know" may be important.
"Palpitations before syncope, syncope during effort or in supine position, absence of autonomic prodromes and absence of predisposing and/or precipitating factors were found to be predictors of cardiac syncope."
Testing or carotid sinus hypersensitivity may be best done with the patients standing.
"Abnormal ECG and/or heart disease... found to be predictors of cardiac syncope."
A clinical practice guideline by the American College of Physicians recommends "neurologic testing, including electroencephalography, computed tomography, and carotid and transcranial Doppler ultrasonography, should be reserved for patients who have neurologic signs or symptoms or carotid bruits".
Clinical prediction rule
|Cause of syncope||1 year||5 years|
|mortality||sudden death||mortality||sudden death|
- Sensitivity 87% (most likely to miss cardiac arrhythmias)
- Specificity 52%
- Substantial between-study heterogeneity
- Regarding missed diagnoses, "the probability was 2% or lower when the rule was applied only to patients for whom no cause of syncope was identified after initial evaluation in the emergency department."
The ROSE (Risk Stratification of Syncope in the Emergency Department) prediction rule contains:
- brain natriuretic peptide > 300 pg/ml
- positive fecal occult blood
- hemoglobin < 90 g/dl
- oxygen saturation < 94% (OR: 3.0)
- Q-wave on the electrocardiogram
For patients who have syncope while driving, recurrence rates are:
- 20% rate during any activity. About 50% occurred within the first 6 months.
- 7% rate during driving. About 70% occurred more than one year after the initial event
Alternative scores, including the Boston criteria 21421292, are available.
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