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Home / Disability Medical Tests / Disability Medical Tests for Cardiovascular Impairments / Head-Up Tilt-Table Testing (HUTTT)

Head-Up Tilt-Table Testing (HUTTT)

Relevant Social Security Medical Listings

  • Listing 6.02 Chronic Kidney Disease (Adults)
  • Listing 106.02 Chronic Kidney Disease (Children)
  • Listing 4.05 Arrhythmias (Adults)
  • Listing 104.05 Arrhythmias (Children)
  • Listing 9.08 Diabetes Mellitus (Adults)
  • Listing 109.08 Diabetes Mellitus (Children)

Other Names

Head-Up Tilt Testing (HUTT), Tilt-Table Testing (TTT), Upright Tilt-Table Testing

Type

Objective/Physiological Test (Vascular)

Can SSA Purchase?

Yes, but purchase by the SSA would be very rare, and most physicians don’t have facilities for such testing. Also, protocols requiring the intravenous injection of drugs would not be purchased by the SSA. Test results should always be considered by the SSA if appearing in the evidence of record from a treating doctor.

Purpose

Diagnose and evaluate vasovagal (neurocardiogenic) syncope.

General

Vasovagal syncope refers to rapid fall in blood pressure (hypotension) that may be accompanied by nausea, sweating, slowed heart rate (bradycardia), pallor (paleness of skin) and loss of consciousness (syncope) if severe enough. Vasovagal syncope most often occurs during the process of attaining an upright posture.

Technique

Testing is done with the patient in a fasting state in a quiet room. All drugs that affect the heart or vascular system should have been stopped sufficiently far in advance as to prevent any interference with testing. Abstinence for 5 half-lives of a drug is sufficient for this purpose.

To be tested with HUTTT, the patient lies supine on a table capable of being tilted head-up at various degrees. Most protocols tilt the table head-up at a 60 angle, but some use angles as high as 80, after 10 – 15 minutes of supine rest. With the patient lying supine, the table is tilted head-up for a certain length of time, usually 40 minutes to 1 hour maximum. Blood pressure and heart rate and rhythm are continuously monitored, or at least every 3 – 5 minutes.

An intravenous (IV) line may be placed in a peripheral vein for injection of drugs or taking blood samples as appropriate to the testing protocol being used.

In some protocols, blood samples are taken for measurement of endothelin-1 in various body positions. Endothelin-1 is a natural chemical in the body, a neuropeptide, thought to help the body maintain normal blood pressure during postural changes by causing an increase in blood pressure. If endothelin-1 is being measured, blood samples are taken in the supine position and then at 5, 10, and 15 minute intervals after head-up tilting at 80. If the test is negative for symptoms at 30 minutes, the table is returned to the supine position and a last blood sample taken.

Other protocols involve injection of the patient with isoproterenol, which some authorities think increases the tendency to have vasovagal syncope. Isoproterenol may be given IV if there was a prior negative HUTTT with increasing provocative dose of 1 – 5 micrograms/min. In one typical protocol, the patient is infused with isoproterenol for 5 minutes in the supine position, then tilted up at an 80 angle. (The appearance of angina, severe headaches, nausea, shaking, tachycardia over 150 beats/min, ventricular arrhythmias, or emotional lability are drug side-effect reasons for terminating isoproterenol testing.) Nitrates (isosorbide dinitrate and nitroglycerin have also been used in testing).

Some protocols utilize simultaneous Transcranial Doppler (TCD), §11.34 (Chapter 11) monitoring. There is no standardization of HUTTT technique, and the tilt-table is placed head-up at various degrees from the horizontal and for various lengths of time depending on the testing facility.

Interpretation

Normally, when body posture is changed from a supine to upright position, arteries must contract142 to maintain blood pressure against the force of gravity. If blood pressure is not adequately maintained on becoming upright, decreased blood flow to the brain can cause syncope (loss of consciousness) or presyncope (dizziness or lightheadedness). Inadequate arterial constriction is known as a loss of vascular tone and is responsible for vasovagal syncope. Disorders that damage the autonomic nervous system, such as diabetes mellitus, are particularly prone to result in abnormal HUTTT testing.

Syncope or presyncope may occur at various angles of tilt and durations after the table is tilted head upward. The presence of vasovagal symptoms when accompanied by significant falls in blood pressure, i.e., falls of about 30 mm Hg from the supine to head-up position would be considered a positive (abnormal) HUTTT result. A symptomatic fall in systolic blood pressure to less than 80 mm Hg is defined by some authorities as a positive tilt table test. In contrast to a vasovagal response, some authorities also consider a vasodepressor response to be an abnormal response in which blood pressure falls in association with symptoms, but with no decrease in heart rate. An orthostatic response is one in which there is an immediate fall in flood pressure with the onset of upward tilt.

Some patients experience asystole (cardiac arrest) in change from the supine to upright position, i.e., their heart stops. Such asystole usually lasts less than a minute and probably averages about 10 seconds. A period of asystole does not suggest a poor prognosis in patients prone to syncope; in fact, asystole may be present in HUTTT in normal and otherwise asymptomatic people. Although bradycardia, nausea, sweating, and pallor may also be associated with hypotension and syncopal symptoms, it is presyncope or syncope accompanied by a significant fall in blood pressure that is most important in diagnosing a positive test result.

Some patients experience a fall in blood pressure and resulting syncope or presyncope after being tilted head-up for prolonged periods of 30 minutes to 1 hour. Others have symptoms within several minutes of head-up tilting, especially if they have received isoproterenol.
Some authorities think isoproterenol increases the patient’s sensitivity to syncope, and is therefore a valuable adjunct to testing. Other authorities question this conclusion, noting that results using isoproterenol are highly variable. Most authorities interpret HUTTT as negative if the patient has no symptoms or other abnormalities for as long as 45 minutes head-up; a few require an asymptomatic head-up tilt for as long as 1 hour before interpreting a negative result.
Patients with syncope tend to have a greater baseline (supine) level of endothelin-1 than normal patients and to lack the increase in endothelin-1 levels found in normal patients tilted into the head-up position. Endothelin-1 levels may therefore assist in prediction of what the results of HUTTT will be.

Transcranial Doppler monitoring (TCD) utilizes ultrasound to evaluate the velocity of blood flow through intracranial arteries. TCD may show increase in resistance to intracranial blood flow during positive HUTTT testing for vasovagal syncope, but is not generally used in HUTTT.

Authorities report different sensitivities and specificities for HUTTT. One study obtained a 61% sensitivity and a 93% specificity, as well as a reproducibility of test results in 86% of cases. Others report values as much as about 10 – 20% lower. The great variability in methodologies used in different HUTTT protocols is probably one of the factors responsible for variable results. Clinical judgment by the treating physician remains important. HUTTT is not a definitive diagnostic test for vasovagal syncope, but may be very helpful when positive.