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Timothy C. Hain, MD Page last modified: October 8, 2016
See also dysautonomia blue orthostatic hypotension blueTilt table testing blue Autoimmune autonomic neuropathy

Causes Evaluation Prognosis

Syncope and variants defined:

Syncope (faint) is a sudden fall of blood pressure resulting in loss of consciousness. About 3% of the population have syncope at some point in life (Savage, 1985).  Syncope also accounts for 3% of all emergency room visits and 6% of all hospital visits. Between 71 and 125 children and adolescents/100,000 population experience syncope each year. The incidence peaks in 15-19 year olds (Driscoll, 1997).

Presyncope consists of unsteadiness, weakness, or cognitive symptoms without loss of consciousness. It is often a symptom of orthostatic hypotension, and may also be a source of drop attacks (Dey et al, 1997).

Pseudosyncope is an apparent loss of consciousness unaccompanied by circulatory changes such as reduced blood pressure.

Causes of syncope:

Arrhythmia -- abnormal slowing or quickness of the heart.

hemodynamic -- obstruction to blood flow

Neurally mediated

In the differential diagnosis of syncope one must also consider non-cardiac causes of loss of consciousness:

Common drugs that are associated with an excess risk of syncope in the elderly include

(Source: adapted from Cherin et al, 1997)

Evaluation of Syncope:

Physical examination should include

If the syncope can be triggered by a particular maneuver, such as stretching or straining, it may be helpful to have the individual attempt to trigger the syncope in a controlled seeting, such as the medical office. Stretch syncope is a benign cause of fainting in young persons. (Mazzuca et al, 2007; Pelekanos et al, 1990).

Carotid sinus testing may also be helpful. Assessment of balance, such as with the tandem Romberg test, may be useful in excluding alternative causes of falls. According to Linzer and associates, a  careful history, physical examination combined with an ECG will yield a diagnosis in 50% of cases.

Routine Laboratory Testing:

The diagnostic yield of ambulatory event monitoring is 25-35% (Lanzer). The diagnostic yields of echo, stress testing, Holter monitoring and electrophysiological studies alone or in combination varies widely (5-35%). The routine ECG is often helpful in identifying abnormalities of rhythm, conduction or morphology of the heart electrical activity that give a clue as to the underlying etiology of the syncope. Recording the ECG during the spell can be achieved by using 24 hour ambulatory recording (also known as Holter monitoring), an event recorder, or a memory loop recorder. 24 hour monitoring is useful in persons who have frequent spells that can be expected to have an event during the 24 hours that they are monitored. Such individuals need to have a non-life threatening spell to make this modality safe. The event recorder and loop memory recorder are useful in persons whose events occure less frequently than every 24 or 48 hours. These devices require the patient or an accompanying person to activate the monitor at the time of symptoms. (Hammill, 1997). Recently implantable monitors have been made available for persons who need chronic monitoring of heart function (i.e Reveal device, made by Medtronic).

Additionally, there are now smartphone devices (e.g. Kardia, AliveCor), that can be used to monitor the EKG on demand, using a smartphone ap. These devices are far less expensive (and time consuming) than having ambulatory event monitoring. They do require one to be awake, and they do not go "back in time" as do the Holter or similar devices, but their low cost makes them very accessible.

In certain situations consider:

The diagnostic yield of EEG, CT scan, and doppler varies from 2-6%.  Obviously, this is very low.

The tilt table test procedure uses equipment to record blood pressure and pulse after a 70 degree tilt using a motorized table.

About 65% of patients with syncope but without structural heart disease have positive results on tilt-testing (Kapoor, 2003). Three types of responses to this procedure are considered abnormal:

The specificity of tilt table testing depends on the methodology. It is about 90% when used with a low-dose isoproterenol protocol or nitroglycerin, but lower when used with a high-dose isoproterenol protocol. The operators of tilt tables (usualy cardiologists) are usually unsophisticated about positional vertigo due to inner ear conditions, and can easily miss the single most common cause of positional vertigo -- BPPV.

The term "vasodepressor syncope" is used to describe syncope mediated by vasodilation. The term "cardioinhibitory syncope" is used for syncope mediated by slowing of the heart.

Persons with syncope are reported to have more MRI abnormalities called periventricular white matter lesions (Kruit et al, 2013). The reason for this is unknown. We have never noticed this association ourselves in our 18,000+ patients seen over the years with dizziness.


Pacing has been reported not helpful in treatment of recurrent vasovagal syncope (Connolly et al, 2003), but may be helpful in carotid sinus syndrome. More information about treatment of syncope can be found on the orthostatic hypotension page.


30% of people with one syncopal episode have recurrence. In children and adolescents, syncope is a benign event. For patients with cardiac causes, generally an older group, 50% die within 5 years, a third of which due to sudden death. For non-cardiac causes of syncope, excluding children and adolescents, 5-year mortality is 30%.



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