Upright tilt table testing in the evaluation of syncope

INTRODUCTION — The upright tilt table test is a component of the evaluation of selected patients with suspected vasovagal syncope (a type of reflex syncope) or orthostatic syncope, although the clinical utility of this test is limited.

Syncope is a clinical syndrome of self-limited transient loss of consciousness (LOC) caused by a period of inadequate cerebral nutrient flow, most often the result of an abrupt drop in systemic blood pressure. In evaluating a patient with suspected syncope, other causes of LOC and collapse should be excluded (algorithm 1). (See "Syncope in adults: Epidemiology, pathogenesis, and etiologies".)

Tilt table testing, including indications, protocol, interpretation, and complications, will be reviewed here. Related issues are discussed separately:

●(See "Syncope in adults: Clinical manifestations and initial diagnostic evaluation" and "Syncope in adults: Risk assessment and additional diagnostic evaluation" and "Syncope in adults: Epidemiology, pathogenesis, and etiologies".)

●(See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation".)

●(See "Mechanisms, causes, and evaluation of orthostatic hypotension".)

INDICATIONS — The upright tilt table test is a component of the evaluation of selected patients with syncope. However, the role for tilt table testing is limited since the initial diagnostic evaluation (without tilt testing) by experienced clinicians is often diagnostic in patients with vasovagal syncope, and tilt table testing has limited reproducibility and diagnostic accuracy (see 'Test performance' below). Interpretation of test results requires careful evaluation of the patient’s overall clinical presentation. Despite criticism of the test’s utility, a strong argument can be made for retaining it in the overall diagnostic toolkit [1]. In general, our approach to tilt table testing is consistent with the published major society guidelines and expert recommendations [2-6].

With the understanding that tilt table testing is an imperfect diagnostic test requiring experienced interpretation and that clinical practice varies, tilt table testing may be included as part of a comprehensive syncope evaluation for selected patients in the following settings [2,4]:

●Syncope of unknown cause – For patients with recurrent episodes of syncope (or a single episode of syncope with high risk for physical injury or occupational hazard should syncope recur) with unknown cause after initial evaluation, tilt table testing is recommended. If structural heart disease is present, cardiac causes of syncope (eg, arrhythmias) should be excluded before further evaluation including tilt table testing is performed. (See "Syncope in adults: Clinical manifestations and initial diagnostic evaluation" and "Syncope in adults: Risk assessment and additional diagnostic evaluation".)

For older adults with syncope who may have limited recollection of events and circumstances, the tilt table test may be helpful in assessing susceptibility to orthostatic and vasovagal syncope [5].

Tilt table testing may be helpful in distinguishing the following conditions:

•Convulsive syncope (syncope associated with convulsion-like muscular jerking movements) from epilepsy, especially if an electroencephalogram recording is obtained during the procedure. (See "Nonepileptic paroxysmal disorders in adolescents and adults", section on 'Syncope'.)

•Syncope from pseudosyncope or pseudoseizures (See "Psychogenic nonepileptic seizures: Etiology, clinical features, and diagnosis".)

●Suspected vasovagal or orthostatic syncope

•To confirm diagnosis – For patients with suspected vasovagal or orthostatic syncope with uncertain diagnosis after the initial evaluation, tilt table testing may help confirm the diagnosis. It is particularly useful if the faint is induced by testing and when patients are able to confirm verbally that this is what they experience during spontaneous spells. The latter not only helps to confirm the diagnosis but also gives patients the confidence that the clinician has witnessed a true symptom spell and are thereby better positioned to recommend appropriate treatment. (See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation", section on 'Upright tilt table test' and "Mechanisms, causes, and evaluation of orthostatic hypotension", section on 'Diagnostic evaluation'.)

•To identify the mechanism of syncope – In patients with suspected vasovagal syncope, tilt table testing is helpful to assess whether bradycardic and/or vasodepressor responses are occurring, as this influences therapy [7]. For example, an individual with a predominantly vasodepressor response would be unlikely to respond to permanent cardiac pacing. (See "Reflex syncope in adults and adolescents: Treatment", section on 'Pacemaker therapy'.)

●Evaluation of autonomic system function – As part of the overall evaluation of interactions between the autonomic nervous system and the cardiovascular system. The "active standing" test may also be used as part of the evaluation procedure but does not replace the head-up tilt test; these tests supplement each other, but active standing is less thoroughly studied. (See "Diabetic autonomic neuropathy" and "Hereditary sensory and autonomic neuropathies" and "Mechanisms, causes, and evaluation of orthostatic hypotension" and "Immune-mediated neuropathies".)

As an example, tilt table testing is often performed in patients undergoing assessment for postural tachycardia syndrome, although the diagnostic utility of tilt testing is not well established. (See "Postural tachycardia syndrome", section on 'Diagnostic approach'.)

In contrast, tilt table testing is generally not helpful to identify patients with situational vagal syncope (ie, syncope due to situations associated with enhanced vagal tone such as micturition, defecation, cough, or vomiting) [8]. (See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation", section on 'Situational syncope'.)

CONTRAINDICATIONS — Tilt table testing should not be performed in patients who have severe coronary or cerebrovascular disease in whom hypotension may cause myocardial or cerebral ischemia.

Similarly, tilt tests are usually avoided in pregnant patients as hypotension may potentially be harmful to the fetus.

Additional concerns apply to use of drug provocation, which is used only after a baseline drug-free tilt test is nondiagnostic, as discussed below (see 'Drug provocation phase' below). Although a controlled infusion of isoproterenol is generally safe in patients without heart disease, it must be used cautiously in patients with coronary artery disease and/or known arrhythmia, since angina and serious arrhythmia can be provoked [9,10]. Other contraindications to isoproterenol use include uncontrolled hypertension, left ventricular outflow tract obstruction, and significant aortic stenosis. Contraindications for nitrates include use of sildenafil or vardenafil within 24 hours or use of tadalafil within 48 hours. (See 'Drug provocation phase' below.)

TILT TABLE TESTING PROCEDURE — Upright tilt table testing is typically performed in an electrophysiology laboratory or dedicated procedure room using a special motorized tilt table that raises to 70 degrees above supine.

Patient preparation — Patient preparation includes the following measures.

●The patient should fast at least three to four hours before the test. Some clinicians recommend an overnight fast (ie, at least 8 hours) prior to testing.

●Depending upon the clinical circumstances, patients may be asked to take their usual meds or, alternatively, hold their usual drugs.

●The test should be performed in a quiet room with a comfortable temperature and minimal distractions for the patient.

●The patient should have an intravenous catheter placed prior to the procedure, allowing for administration of fluids and/or medications (eg, isoproterenol or nitroglycerin) if needed. This is best done at least 30 minutes prior to the test.

Equipment — The patient is placed on a motorized tilt table with a foot board and safety restraints. The table should be capable of smoothly and rapidly moving the patient passively from a supine position to a head-up position between 60 to 70 degrees and quickly (in <10 seconds) returning the patient to a horizontal supine position to minimize the duration of any precipitated asystole and/or hypotension [11].

Monitoring — Continuous electrocardiogram (ECG) and beat-to-beat blood pressure (BP) monitoring are employed throughout the test. Careful monitoring of both is required, because while many patients have a pronounced cardioinhibitory response detectable by ECG, many others have vasodepressor episodes (characterized by symptomatic hypotension without marked bradycardia), and some patients exhibit simultaneous cardioinhibitory and vasodepressor responses.

●Most tests are performed using either three or six ECG leads, although there is no defined consensus on this. Conventional limb leads are commonly used as they are convenient and offer more than adequate monitoring to assess for changes in heart rate (HR) and rhythm.

●Systemic BP and HR recording should be beat-to-beat and is typically noninvasive.

Invasive arterial monitoring is rarely used with tilt table tests, but it is acceptable as long as the line is placed at least an hour before the procedure to allow autonomic tone to return to baseline. Intermittent BP measurement via sphygmomanometer (such as an arm cuff) is not adequate, as the number of data points precludes identifying developing problems, and, even more importantly, the cuff disturbance may alter patient autonomics and thereby undermine the objective of the study.

●Electroencephalogram monitoring may be warranted in certain cases, especially if pseudosyncope/pseudoseizure or ictal asystole are suspected. In the case of suspected pseudosyncope/pseudoseizure, near-infrared spectroscopy (NIRS) may also be used to confirm that cerebral blood flow has not been diminished and that true syncope has not occurred [12]. However, NIRS is limited in terms of the depth of penetration of the cerebrum and, thus, the region in which blood flow can be monitored.

Tilt protocol — A variety of protocols have been described for the test that vary in the angle of tilt (60 to 70 degrees above horizontal supine), duration of tilt (generally 20 to 45 minutes), and the administration of isoproterenol or nitroglycerin. The most commonly used protocol is described here. (See 'Patient preparation' above.)

Other autonomic testing may be carried out during the tilt table test procedure, but sufficient time is needed between steps to allow the patient to return to basal state. These additional tests could include "active standing," Valsalva maneuver, carotid massage, respiratory sinus arrhythmia, and sweat testing.

Initial supine phase — To begin the test, the patient is monitored in an initial baseline horizontal supine position for 5 to 10 minutes to obtain baseline HR and BP measurements. If venous or arterial cannulation is performed just prior to the test, a longer initial supine time period of at least 20 minutes after venous cannulation and at least 60 minutes after arterial cannulation is recommended to allow any stimulated circulating catecholamines to return to baseline.

The patient should be instructed to report any symptoms that may develop during the test.

Passive phase — The first (and sometimes only) head-up tilt (angle between 60 and 70 degrees above horizontal) phase is a passive phase (ie, no provocation with isoproterenol or nitroglycerin) of ≥20 minutes (maximum of 45 minutes) [11]. If the patient develops complete loss of consciousness (LOC), the patient is rapidly (in <10 s) returned to a supine position.

HR and symptoms are recorded every three to five minutes, and the ECG is recorded continuously. The BP should be monitored noninvasively by beat-to-beat finger plethysmographic arterial monitoring. As noted above, an arm cuff should not be used during the test. (See 'Monitoring' above.)

Possible positive responses to the passive phase include a positive response for vasovagal syncope, a positive response for orthostatic hypotension (OH), or a positive response for psychogenic pseudosyncope. In patients exhibiting marked OH, testing may be repeated after hydration with intravenous saline. If no symptoms or ECG abnormalities consistent with the patient's history have developed after a period of 20 to 45 minutes of head tilt, the patient is returned to the supine position, and the passive test is considered nondiagnostic. Test interpretation is discussed further below. (See 'Test interpretation' below.)

Deciding whether to use drug provocation — The decision to proceed with a drug provocation phase after a nondiagnostic passive phase in a patient with suspected vasovagal syncope is up to the discretion of the clinician and is generally determined by the perceived clinical utility of inducing a response suggestive of vasovagal syncope. (See 'Test interpretation' below.)

It may be possible to reduce the time necessary for the tilt table test and avoid the need for isoproterenol infusion based upon the HR response early in the passive phase. In a study of 109 patients, an HR change ≤18 beats per minute during the first six minutes of the test prospectively predicted a negative tilt table test with a 96 percent specificity, 98 percent positive predictive accuracy, and 87 percent sensitivity, even with the subsequent use of isoproterenol [13]. However, this shortened procedure is not widely used and is not our recommended approach.

Drug provocation phase — If the patient has remained asymptomatic during the passive phase of tilt table testing, a second tilt table test is often performed with administration of a vasoactive medication (usually either isoproterenol or nitroglycerin). Either drug can be used for the drug provocation phase, with the choice of isoproterenol or nitroglycerin usually directed by local practice and clinician expertise. In many locations, the cost of isoproterenol has increased, and, consequently, nitroglycerin provocation (the so-called Italian protocol) is preferred.

Isoproterenol — If the passive phase is negative and isoproterenol infusion is chosen, the infusion is administered with the patient in the supine position, although some advocate for the infusion to be initiated with the patient already in the 60 to 70 degree head-up tilt position [4]. Isoproterenol is usually titrated from 1 to 3 mcg/minute to increase the HR by 20 to 25 percent above baseline. Once the desired HR has been achieved, the patient is placed in the 60 to 70 degree head-up tilt position for an additional 15 to 20 minutes while the infusion is continued. The infusion and tilt position are maintained until completion of the protocol or the patient develops complete LOC, whichever is sooner.

Generally, LOC during isoproterenol infusion is required to consider the test positive [4]. A modest decrease in BP with symptoms is common with isoproterenol and is nonspecific.

The fact that isoproterenol may trigger vasovagal syncope may seem somewhat paradoxical. The mechanism is thought to be due to activation of central circulation mechanoreceptors, but the exact basis for the effect is not absolutely known. The potential efficacy of isoproterenol infusion was illustrated in a study in which a single-stage isoproterenol tilt table test more frequently induced syncope than a standard passive tilt table test (56 versus 32 percent) and reduced the time necessary for the procedure [14]. There was, however, a lower specificity (83 versus 91 percent for passive phase testing). (See 'Test performance' below.)

Nitroglycerin — If the passive phase is negative and nitroglycerin is chosen as the provocative agent, we administer a fixed dose of 300 to 400 mcg of sublingual nitroglycerin with the patient in the 60 to 70 degree upright position for 15 to 20 minutes [4]. The use of intravenously administered nitroglycerin has been described but is rarely used.

Generally, LOC following nitroglycerin administration is required to consider the test positive [4]. A modest decrease in BP with symptoms is common with nitroglycerin and is nonspecific. (See 'Test interpretation' below.)

Nitroglycerin likely increases susceptibility to vasovagal syncope by reducing venous return to the heart and thereby enhancing cardiac activity and activating the reflex via central cardiac mechanoreceptors [15]. Nitroglycerin causes venodilation, with consequent reduction in venous return and stroke volume, without impeding the sympathetic responses of increased HR and arterial vasoconstriction [16].

The addition of nitroglycerin to tilt table testing increases the frequency of hemodynamic changes and reproduction of symptoms and may shorten test duration but also increases the rate of false positive tests. In a study of 232 patients, including 149 with unexplained syncope and 83 asymptomatic controls, participants were randomly assigned to receive nitroglycerin (800 mcg metered spray) and a 20-minute tilt table test or no nitroglycerin and a standard 40-minute tilt table test [17]. Nitroglycerin increased the frequency of a positive tilt table test from 11 to 36 percent in all patients, although the results are nonspecific as the rate of positive tests increased in both patients with prior syncope and control patients.

Comparison of isoproterenol and nitroglycerin — Isoproterenol and nitroglycerin have been compared as adjuncts to tilt table testing [18,19]:

●In one study of 71 patients with unexplained syncope and 30 controls who underwent tilt table testing twice on separate days, with all patients receiving isoproterenol and nitroglycerin on separate days, rates of test positivity were similar in patients receiving nitroglycerin and isoproterenol (49 and 41 percent, respectively) [18]. However, sublingual nitroglycerin was simpler to use and better tolerated than isoproterenol.

●In a study of 96 patients with unexplained syncope who underwent three separate tilt table tests on the same day (passive, once with isoproterenol, once with nitroglycerin), sublingual nitroglycerin with tilt table testing led to a higher number of positive responses than isoproterenol (55 versus 42 percent), especially among patients with a positive tilt table test without pharmacologic agents (94 versus 67 percent) [19].

TILT TABLE TEST RESULTS

Test interpretation

General approach — The tilt table test findings should be interpreted in the context of all relevant clinical data, particularly information about the patient’s spontaneous events and other potential causes of events (eg, structural heart disease). On the other hand, while the tilt table test is frequently positive in patients with vasovagal syncope, it is not the gold standard for the diagnosis of vasovagal syncope, as it has limited sensitivity, specificity, and reproducibility.

Although isoproterenol and nitroglycerin increase the sensitivity of the test, these drug interventions also decrease test specificity (ie, increase the number of false positives). Thus, a positive test (with or without drug provocation) does not definitively establish that the patient’s clinical events were caused by the type of syncope induced by the test (eg, vasovagal syncope). After a positive test, the patient is asked if symptoms during the test were the same as those experienced during spontaneous events. It is crucial to interpret the test result in light of the patient’s spontaneous symptoms.

The vasovagal reflex seen on a tilt table test may reflect a given patient's predisposition to vasovagal syncope; however, the specific physiologic response to the tilt table test may differ from the physiology of clinical episodes. Also, the response to tilt table testing can be highly variable, and even the severity of cardioinhibitory versus vasodepressor components may differ from one test to another. Additionally, factors such as age and the use of medications during the protocol may affect the likelihood of a positive test. Older adults are less likely to have a cardioinhibitory response and more likely to have a vasodepressor response [20]. Ultimately, in all patients with syncope, obtaining a thorough history as part of the initial evaluation is the most important component of the diagnostic evaluation. In patients with structural heart disease, other causes of syncope should be evaluated before attributing the syncope to a vasovagal or orthostatic response. (See "Syncope in adults: Clinical manifestations and initial diagnostic evaluation", section on 'Approach to initial evaluation'.)

Patterns of response to head-up tilt include those with or without associated syncope [11]:

Patterns without syncope — The head-up tilt test is considered negative for syncope if the patient is able to maintain an upright position and/or does not experience complete loss of consciousness (LOC). The following hemodynamic responses to head-up tilt are observed:

●Normal result – In a normal response, there is no change or a slight increase (≤10 percent) in systemic blood pressure (BP) and slight increase (≤10 percent) in HR until the patient is returned to the baseline position [11].

●Postural tachycardia syndrome (POTS) – Tilt table testing may not be as useful as active standing for detection of POTS. Key features of POTS include symptoms of orthostatic intolerance (eg, lightheadedness or palpitations) with a sustained increase in heart rate (HR) ≥30 beats per minute (bpm; ≥40 bpm for individuals <20 years old) within 10 minutes after the start of head-up tilt with no decline in BP. However, other common clinical factors (eg, dehydration, concomitant inflammatory conditions, anemia, hyperthyroidism, etc) should generally be excluded before tilt table testing, and should be excluded before a POTS diagnosis is made. (See "Postural tachycardia syndrome", section on 'Diagnostic approach'.)

●Possible vasovagal response – If a patient experiences symptoms suggestive of presyncope without LOC with a significant fall in BP (≥40 mmHg decline in systolic BP) or HR (≥60 bpm decline in HR), the patient is returned to the baseline position, and the test is considered suggestive of vasovagal syncope. (See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation", section on 'Upright tilt table test'.)

●Nonspecific response – After a variable period of time after head-up tilt there is commonly a mild decrease in BP (generally <15 mmHg decline in systolic BP) and mild increase in HR (by ≤10 percent). The patient may or may not experience dizziness during this nondiagnostic response. The clinical significance of such responses without induction of syncope is not clear [2,4].

Patterns with syncope or apparent syncope — The head-up tilt response is considered positive for syncope if the patient experiences complete LOC and/or dizziness or lightheadedness with inability to maintain an upright posture.

Among patients experiencing syncope in response to head-up tilt, the associated physiologic features suggest the cause. Features of vasovagal syncope not present with orthostatic hypotension (OH) include latency (delay) in the BP fall after head-up tilt, an accelerating decline in BP, and a decline in HR.

●Vasovagal response – Key characteristics of the vasovagal response are a delayed accelerating fall in BP with mild to severe fall in HR. After a variable period of time after head-up tilt, there may be a gradual slight decline in BP and a gradual slight increase in HR. The rate of fall in BP then accelerates (convex curve), the rate of fall in HR also accelerates, and in some cases the HR falls to a period of asystole. LOC generally occurs within three minutes of onset of the vasovagal reaction [11]. After return to the baseline position, HR and BP quickly increase.

Variations in the vasovagal response include: only a mild HR decrease, an initial brief slight HR increase followed by a greater HR decrease, and minimal change in BP and HR before accelerating declines in BP and HR (figure 1). Responses to tilt table testing appear to vary with patient age. Younger subjects are more likely to have a bradycardic response, whereas older subjects are more likely to have a vasodepressive response (ie, minimal decline in HR) [21-23].

●Orthostatic hypotension – Key features of OH are either an immediate fall in BP with or without an increase in HR ("immediate OH") or a delayed ("classic") hypotensive response occurring within three to five minutes after assuming upright posture; some patients may exhibit both forms. Further, patients with severe autonomic failure syndromes (eg, pure autonomic failure, Parkinson disease) may exhibit an abrupt drop of pressure with upright posture that does not recover and may become sufficiently severe to necessitate test termination.

Immediately after head-up tilt, the BP declines at a decelerating rate (concave curve) [11]. After the first three minutes of head-up tilt, the BP may continue to decline considerably. The HR may increase in response to the fall in BP but if HR control is impaired there may be no or only slight increase in HR. The latter complicates prevention of OH, which typically demands therapies that further increase supine BP.

Diagnosis of orthostatic hypotension by comparing supine and standing blood pressure is discussed separately. (See "Mechanisms, causes, and evaluation of orthostatic hypotension".)

●Pseudosyncope – During head-up tilt, if the patient appears to lose consciousness or is unable to maintain posture without a significant fall in BP or HR, the patient is returned to a horizontal supine position, and the test is considered positive for psychogenic pseudosyncope. Additional supportive observations include tightly closed eyes and a prolonged period of apparent LOC (typically >2 to 3 minutes even after return to supine posture). If an electroencephalogram is recorded during the test, it does not show the typical slowing that occurs in true syncope. (See "Psychogenic nonepileptic seizures: Etiology, clinical features, and diagnosis".)

It is important to be aware that many patients with pseudosyncope may also be experiencing true syncope, and the presence of pseudosyncope does not eliminate the need for a careful assessment of all symptoms.

Test performance — The sensitivity of tilt table testing is difficult to determine given the lack of a clinical gold standard as well as varying protocols and patient selection [4]. Using clinical diagnosis as the standard for comparison, reported sensitivity rates for passive phase testing have ranged from 13 to 75 percent [4,24]. Thus, the false negative rate may be ≥25 percent depending upon the protocol and patient population. For this reason, vasovagal syncope cannot be excluded by a negative tilt table test.

Although the specificity of passive phase tilt testing has been reported as greater than 90 percent in some studies of patients with syncope [24], high rates of passive tilt test positivity have been observed in patients with likely tachyarrhythmic syncope (45 percent) [25] and in healthy individuals with no history of syncope (13 percent) [26].

Drug provocation (with isoproterenol or nitroglycerin) yields higher sensitivity (eg, 42 to 87 percent) but this higher sensitivity is at the expense of lower specificity (70 to 94 percent) [24]. Among patients with cardiac syncope, 43 percent had a positive nitroglycerin tilt test [27]. Among healthy volunteers, a positive response is seen in as many as 45 percent who undergo a tilt table test with isoproterenol [28] and in as many as 28 percent who undergo tilt table test with nitroglycerin [17].

COMPLICATIONS AND SIDE EFFECTS — Complications of tilt table testing are rare, but prolonged asystole or symptomatic hypotension occasionally occurs. If either occurs, the patient should be placed in a horizontal supine position until recovery.

Atrial fibrillation is infrequently induced during or after a positive tilt table test with or without isoproterenol infusion [29]. While most cases spontaneously convert to sinus rhythm within 48 hours, atrial fibrillation commonly recurs during the next few years [29].

Ventricular fibrillation has been rarely reported in patients with ischemic heart disease or other structural heart disease undergoing tilt table testing with administration of isoproterenol [30]. (See 'Contraindications' above.)

Frequent minor side effects include palpitations in patients receiving isoproterenol and headache in patients treated with nitroglycerin [11].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Syncope".)

SUMMARY AND RECOMMENDATIONS

●Indications for tilt table testing – The upright tilt table test is a component of the evaluation of selected patients with syncope. The role for tilt table testing is limited since the initial diagnostic evaluation (without tilt testing) is often diagnostic in patients with vasovagal syncope, and tilt table testing has limited reproducibility and diagnostic accuracy. (See 'Test performance' above.)

However, a positive test that reproduces patient symptoms may not only be helpful diagnostically but may also increase patient confidence that an accurate diagnosis has been made.

With the understanding that tilt table testing is an imperfect diagnostic test requiring experienced interpretation and that clinical practice varies, tilt table testing may be included as part of the complete syncope evaluation for selected patients in the following settings:

•Syncope of unknown cause – For recurrent syncope (or a single episode with high risk of physical injury should syncope recur) with unknown cause after initial evaluation. If structural heart disease is present, cardiac causes of syncope should be excluded before tilt table testing is performed.

•Suspected vasovagal or orthostatic syncope – To help confirm the diagnosis if the diagnosis is uncertain after the initial evaluation and to identify the mechanism of syncope (eg, cardioinhibitory and/or vasodepressor) in selected patients with suspected vasovagal or orthostatic syncope, which influences therapy. (See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation", section on 'Upright tilt table test' and "Mechanisms, causes, and evaluation of orthostatic hypotension", section on 'Diagnostic evaluation' and "Reflex syncope in adults and adolescents: Treatment" and "Reflex syncope in adults and adolescents: Treatment", section on 'Additional measures'.)

•Evaluation of autonomic system function – Tilt table testing may be a component of evaluation of the autonomic system. (See "Diabetic autonomic neuropathy" and "Hereditary sensory and autonomic neuropathies" and "Mechanisms, causes, and evaluation of orthostatic hypotension" and "Immune-mediated neuropathies".)

●Contraindications – Tilt table testing should not be performed in patients who have severe coronary or cerebrovascular disease or are pregnant. (See 'Contraindications' above.)

●Equipment and procedure – Upright tilt table testing is typically performed in an electrophysiology laboratory or dedicated procedure room using a special motorized tilt table that raises to 60 to 70 degrees with rapid return to a horizontal position. The passive (drug-free) phase is 20 to 45 minutes long. If the initial passive phase is negative, a drug provocation phase using isoproterenol or nitroglycerin may be performed. (See 'Tilt table testing procedure' above.)

●Interpretation – The tilt table test findings should be interpreted in the context of all relevant clinical data, particularly information about the patient’s spontaneous events and other potential causes of events (eg, structural heart disease). Although the tilt table test is frequently positive in patients with vasovagal syncope, it is not the gold standard for the diagnosis of vasovagal syncope, as it has limited sensitivity, specificity, and reproducibility. (See 'Test interpretation' above and 'Test performance' above and "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation", section on 'Diagnosis'.)

●Symptomatic response without syncope (see 'Patterns without syncope' above):

•Postural tachycardia syndrome (POTS) – Key features include symptoms of orthostatic intolerance (lightheadedness, palpitations, fading vision, presyncope, difficulty concentrating, or headache) with a sustained increase in heart rate (HR) ≥30 beats per minute (bpm; ≥40 bpm for individuals <20 years old) within 10 minutes after the start of head-up tilt with no decline in blood pressure (BP). However, other factors such as dehydration should be excluded before tilt table testing. (See "Postural tachycardia syndrome", section on 'Diagnostic approach'.)

•Possible vasovagal response – If a patient experiences symptoms suggestive of presyncope without loss of consciousness (LOC) with a significant fall in BP (≥40 mmHg decline in systolic BP) or HR (≥60 bpm decline in HR), the patient is returned to the baseline position, and the test is considered suggestive of vasovagal syncope. (See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation", section on 'Upright tilt table test'.)

•Nonspecific response – After a variable period of time after head-up tilt there is commonly a mild decrease in BP (generally <10 mm Hg decline in systolic BP) and mild increase in HR (by ≤10 percent). The patient may or may not experience dizziness during this nondiagnostic response.

●Patterns with apparent syncope (see 'Patterns with syncope or apparent syncope' above):

•Vasovagal response – Key characteristics of the vasovagal response are an initial sinus tachycardia with onset of upright posture followed by a delayed accelerating fall in BP with mild to severe fall in HR (figure 1).

•Orthostatic hypotension – Key features of orthostatic hypotension (OH) are one or both of the following: an immediate fall in BP with or without an increase in HR [11] or a delayed hypotensive response at three to five minutes after onset of upright posture.

•Pseudosyncope – During head-up tilt, if the patient appears to lose consciousness or is unable to maintain posture without a significant fall in BP or HR, the test is considered positive for psychogenic pseudosyncope. (See "Psychogenic nonepileptic seizures: Etiology, clinical features, and diagnosis".)

●Test performance – The sensitivity and specificity of tilt table testing are uncertain given the lack of a clinical gold standard. Reported sensitivity rates for passive phase testing have ranged from 13 to 75 percent and specificity may be greater than 90 percent. Drug provocation yields higher sensitivity but at the expense of a lower specificity.

●Complications – Tilt table testing is rarely complicated by prolonged asystole or hypotension. Atrial fibrillation is infrequently induced. Ventricular fibrillation is a rare complication of isoproterenol administration in patients with heart disease. (See 'Complications and side effects' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Brian Olshansky, MD, who contributed to earlier versions of this topic review.