TOC |  STAT Neuro

Syncope Differential  -  Outlines in Clinical Medicine on Physicians' Online 2001

A. Cardiovascular syncope  

1. Reflex - Vasovagal Syncope (Vasodepressor)
a.Carotid sinus cardioinhibitory, vasodepressor central
b.Vasovagal cough, micturition defecation, post-prandial valsalva, sneeze

2. Orthostatic
a.Dehydration / Blood Loss: Diuretic drugs: thiazides, furosemide, Zaroxolyn, etc.
b.Autonomic insufficiency :Autonomic nervous system dysfunction: diabetic, alcoholic, Shy Drager Syndrome (degenerative CNS)
c. Sympathetic nervous system blocker drugs: methyldopa, prazosin, guanethidine, phenothiazines, tricyclics
d. Adrenal Insufficiency
e. Vasodilator drugs
f. Idiopathic

3.Mechanical (Obstructive)
a.Aortic Stenosis
b.Hypertrophic cardiomyopathy
c.Pulmonary Embolism, HTN, Stenosis
d.Aortic Dissection
e.Myocardial Infarction

4. Electrical (arrhythmia cardiac syncope)
a. AV Block
b. Sick Sinus Syndrome
c. Arrhythmia (Ventricular vs. Supra-)
d. Long QT syndrome

B. Neurologic  syncope

  1. Transient Ischemic Attack (TIA)
  2. Seizure
  3. Takayatsu (Giant Cell) Arteritis
  4. Intermittent Pressure Hydrocephalus
  5. Psychiatric - panic disorders, depression , hysteria
  6. Subclavian Steel Syndrome
  7. Vertebrobasilar insufficiency

C.  Metabolic syncope  

  1. Hypoglycemia syncope
  2. Hypoxia syncope
  3. Shock
  4. Hyperventilation
  5. Anemia
  6. Alcoholic

D. Idiopathic /Unexplained  (~50%)


1.Manolis AS, Linzer M, Salem D, Estes NA 3d. 1990. Ann Intern Med. 112(11):850

Diagnosing Syncope

For heart rhythm-related causes, an electrocardiogram (ECG) recorded during the fainting episode is considered to be the "gold standard," that is, the best possible way to tell if the syncope is caused by a heart rhythm problem.

Tests for determining the cause of syncope

ECG: to check for arrhythmia, cardiac cause.

Holter monitor: used for continuous monitoring on an in-patient basis for 24 to 48 hours, or for slightly longer periods of time on an outpatient basis.

External loop recorder: A device that monitors heart rhythm and rate for up to one month. During this test, the patient wears a device on the wrist or around the waist. After waking from a fainting episode, the patient presses a button on the device to make a recording of the heart activity during the fainting episode. Because external loop recorders can be worn for longer periods of time (up to one month) than Holter monitors, they are somewhat more effective in diagnosing syncope.

Tilt table test: This procedure attempts to simulate conditions that may cause fainting. It enables a physician to gauge how blood pressure, heart rate and rhythm respond to a change in position from lying down to standing. The patient is positioned on a table, given medication, and the table is tilted by varying degrees. The patient typically is tilted for 20 to 45 minutes. If the patient does faint during this test, the simultaneous heart monitoring should show whether the faint was caused by an arrhythmia. If not, the patient may be returned to a flat position, injected with a drug that makes the heart's lower chambers contract, and then tilted again for up to 30 minutes. If this stage of the test induces a faint, again the heart monitor should indicate whether the faint is related to an abnormal heart rhythm.

Electrophysiology (EP) Study: Performed in a special lab in the hospital, this lengthy procedure attempts to reproduce an abnormal heart rhythm if it is the suspected cause of fainting. This is done by threading catheters into the heart to record the heart's own electrical impulses and to assess the response to pacing and extra beats.

Other tests: These may include an electroencephalogram (EEG), magnetic resonance imaging (MRI), an echocardiogram ("echo"), neurologic or psychiatric evaluations, depending on what the doctor suspects as the cause of the fainting.

Limitations of traditional diagnostic methods
While nearly half of patients with recurrent, unexplained fainting remain undiagnosed after undergoing these tests, these methods have been, until recently, the best tools available to physicians for diagnosing the causes of syncope. The heart-monitoring methods listed above are particularly useful in diagnosing syncope that is relatively frequent, and therefore more likely to occur during testing.

Where the traditional heart-monitoring tests fall short is that they only monitor the heart for a relatively limited amount of time. Since the most difficult forms of syncope to diagnose are those that occur infrequently, the best diagnostic tool would be one that continuously monitors the heart's rhythm and rate for long periods of time — on the order of several months or more.

Now there is a new diagnostic tool available that can monitor the heart for up to 14 continuous months, making a diagnosis for recurrent, infrequent syncope much more likely.   

The device is called the Medtronic Reveal® Insertable Loop Recorder. This new, state-of-the-art technology represents a breakthrough in the diagnosis of fainting. The Reveal Insertable Loop Recorder can determine if fainting is related to a heart rhythm problem in up to 94 percent of cases. Smaller than a pack of gum, the Reveal Insertable Loop Recorder is inserted just beneath the skin in the upper chest area in a brief outpatient procedure that typically takes 15 to 20 minutes.

To capture and store the electrocardiogram (ECG) as it occurred at the time of the fainting episode, a patient places a hand-held, pager-sized Activator over the Reveal Insertable Loop Recorder after waking from a fainting episode, and presses a button. A family member or friend also can be the one to place the Activator over the patient's device to save the information. It is important for the patient to keep the Activator handy at all times (clipped to the clothes or looped over a belt). Later, a physician analyzes the stored information and determines whether the fainting episode was caused by an abnormal heart rhythm. Once the physician determines this, the device is removed and either treatment is begun or the patient is referred to other specialists.

Ref: Medtronic site