Syncope

Timothy C. Hain, MD Page last modified: November 23, 2008

Syncope defined Causes Evaluation Prognosis Index

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).

Causes of syncope:

Arrhythmia -- abnormal slowing or quickness of the heart.

• bradycardia (slowness of heart beat)
• sick-sinus (variable)
• supraventricular or ventricular tachycardia (abnormally fast)

hemodynamic -- obstruction to blood flow

• hypertrophic subaortic stenosis  (IHSS)
• aortic stenosis
• pulmonary embolism or hypertension

Neurally mediated

• vasovagal reaction (usually related to emotional stress)
• situational syncope (occurring after urination, defecation, swallow or cough)
• carotid sinus hypersensitivity
• postural hypotension (usually related to medication or dehydration)

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

• seizure
• stroke or TIA
• metabolic encephalopathy
• psychiatric conditions

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

• fluoxetine (Prozac)
• aceprometazine (Not available in the USA)
• haloperidol (Haldol)
• L-dopa (Sinemet)

(Source: Cherin et al, 1997)

Evaluation of Syncope:

Physical examination should include at a minimum

• blood pressure and pulse, standing and supine
• cardiac exam

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:

• ECG
• Exercise stress test
• Holter or ambulatory event monitoring

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).

In certain situations consider:

• Autonomic testing, including tilt-table testing, for orthostatic hypotension
• Carotid Doppler
• EEG
• Electrophysiological testing (catheterization)
• Psychiatric evaluation
• Tilt table testing

The diagnostic yield of EEG, CT scan, and doppler varies from 2-6%. 

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:

• Neurally mediated response, characterized by the sudden onset of hypotension, bradycardia, or both when the patient is kept in the upright position. This is the most common response.
• Positional orthostatic tachycardia
• Dysautonomia -- a gradual decrease in blood pressure with little or no change in heart rate during the procedure.

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.

Treatment

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.

Prognosis:

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%.

References:

• Cherin P, Colvez A, Deville G, Sereni D. Risk of syncope in the elderly and consumption of drugs: a case-control study. J. clinical epidem 50(3):313-20, 1997
• Connolly S and others. Pacemaker therapy for prevention of syncope in patients with recurrent severe vasovagal syncope. Jama 2003:289:2224-2229
• Dey Ab, Stout NR, Kenny RA. Cardiovasular syncope is the most common cause of drop attacks in the elderly. Pacing and clinical electrophysiology. 20:818-9, 1997
• Driscoll DJ, Jacobsen SJ, Porter CJ, Wollan PC. Syncope in children and adolescents. J Am College of Cardiology. 29(5):1039-45, 1997
• Hammill SC. Value and limitations of nonivasive assessment of syncope. Cardiologic Clinic 15(2):195-218, 1997
• Kapoor WN. Workup and management of patients with syncope. Med Clin North Am 79:1153, 1995
• Kapoor WN. Is there an effective treatment for neurally mediated syncope ? JAMA 289, 17, 2272-2275, 2003
• Linzer M, Yang EH, Estes NA, Wang P, Voperian VR, Kapoor WN.. Diagnosing syncope. Part 1. Annals Int Med. 126 (1) 986-96, 1997
• Miller JM. Syncope, Audiodigest family practice, 45, #30, 1997
• Savage DD, et al. Stroke 1985;16:626-629

Books (with links to Amazon.com)

• The Fainting Phenomenon: Understanding Why People Faint and What Can Be Done About It by Blair P. Grubb, Mary McMann

Links

• Tilt table testing