What is a Tilt Test?
The tilt test is a test that assesses someone’s response to orthostatic stress. Orthostatic stress is the fancy medical term for standing upright. The tilt test is also known as a tilt table test because it involves being basically strapped to a table that can tilt to different angles. A lot of the interest in tilt table tests originated from the air force. Years ago it was reported that up to 25% of those in the air force would pass out if they were in a straight upright standing position for a prolonged period of time. It was known that the tilt test could induce passing out in a subset of people and so it became a tool with which to assess people at risk for this. Nowadays the tilt test is used widely to diagnose syncope. Syncope is the medical term for passing out.
What Happens in the Tilt Test?
- In the tilt test, patients are strapped to a tilt table. It is basically a table capable of being swiveled to different angles. At 90 degrees a person would be upright and at 0 degrees they would be laying completely flat.
- The patient is awake and alert during the test. The angle of table tilt chosen is usually between 60 to 80 degrees, so upright but not all the way.
- The test involves basically laying there and not moving to see what happens. Heart rate and blood pressure are monitored closely throughout. Sometimes the angles are changed to assess the body’s response.
- Sometimes medicines will be administered during the tilt test to try and recreate stressful situations and provoke a response.
- The test typically last between 20-60 minutes, the patient is monitored throughout, and the test is of course terminated if there is a feeling of passing out, passing out, low blood pressure or too low a heart rate.
What Drugs May Be Given In The Tilt Test And Why?
Nitrates are a class of drug that cause dilation of the blood vessels and my provoke pooling of blood in the lower extremities in some people
Isoproterenol is a drug that speeds up the heart rate and is used to mimic the flight or fright stress response and the body’s reaction to it
Clomipramine is a drug that alters the levels of certain brain hormones such as serotonin thought to be central to the fainting reflex
Is Tilt Testing Safe?
- Tilt testing is generally safe, no deaths have been reported
- Some very long heart pauses have been reported, but the rhythm returns to normal when this happens
- Patient selection is important. The test should be avoided in those with significant heart disease
- Sometimes an irregular heart rhythm such as atrial fibrillation can occur but it usually spontaneously reverts to normal
How Often Are Tilt Tests Positive?
A positive tilt test is one that elicits a response, such as fainting, pre-fainting, low blood pressure, high or low heart rate.
Studies of tilt tests have shown that in those patients that have a history of fainting episodes, around half will have a positive test. If provocative drugs are given during the test then this number increases to two-thirds of patients.
What Information Are We Looking For In A Tilt Test
Two of the major causes of passing out are known as cardiogenic syncope and neurally mediated syncope. Cardiogenic syncope is related to underlying heart disorders such as heart failure and heart rhythm disorders. It’s important to identify those, because the underlying cause can often be treated. Neurally mediated syncope is related to brain causes. Sometimes there can be underlying structural brain disease that will initially be ruled out by the treating physician. Usually though no clear underlying cause is found and the syncope is thought to be due to a reflex within the brain that leads to passing out. The trigger for this is often orthostatic stress, the stress of standing for prolonged periods. Positive tilt tests are felt diagnostic of neurally mediated syncope.
Other information can be provided in the tilt test. In postural orthostatic tachycardia or P.O.T.S syndrome for example and other forms of dysautonomia or orthostatic intolerance, the heart rate response to standing can be important in diagnosis.
Are Tilt Tests Accurate?
The problem with neurally mediated syncope is that there is no clear definition of what it is! We basically label those with positive tilt tests as having neurogenic syncope. The big problem with this is that not all people with neurally mediated syncope will have a positive tilt test. In fact those with and without a positive test typically share the same symptoms. Scientifically speaking the sensitivity and the specificity of the test is not well known. Although having a positive tilt test can give a diagnosis of neurogenic syncope, a negative test doesn’t rule the diagnosis out.
Another problem with tilt tests is that the results recorded don’t correlate with clinical outcomes. For example, just because the heart rate may go low in the tilt test, doesn’t mean that a low heart rate is causing the syncopal event. This makes it hard to prescribe therapies based on the test findings. Tilt table tests should be used with care, and not be the sole basis for treatment decisions.