When to use tilt table testing and findings regarding its sensitivity

Background

Tilt table testing (TTT) was introduced over 20 years ago for the evaluation of patients with unexplained syncope. Its use has spread unevenly in clinical practises, because initial enthusiasm has been hampered by the recognition of several limitations.
Tilt table testing is often negative in cases of typical vasovagal syncope (i.e., “low sensitivity”) and positive in patients without syncope (i.e., “low specificity”). Additionally, it has offered minimal or no value in assessing the efficacy of treatment with drugs or pacemakers. 
Thus, a number of physicians have concluded that management guided by careful clinical history was superior to TTT for identification of patients affected by reflex syncope, in particular. However, the latest ESC guidelines on syncope (2009) have provided new insights into the correct use of TTT, which in fact, should remain an important diagnostic tool in a number of clinical settings - provided that physicians learn its appropriate indications and the correct interpretations of results.

ESC Guidelines for the management of syncope

The ESC 2009 Guidelines for the management of syncope:

1. Offer precise criteria based on clinical presentation for diagnosis of reflex syncope: A) Vasovagal syncope can be diagnosed if syncope is precipitated by emotional distress (from fear, pain, instrumentation, venipuncture) and is associated with typical prodromes due to autonomic activation.
   B) Situational syncope can be diagnosed if syncope is triggered by specific circumstances (during or immediately after micturition, defecation, coughing, swallowing, laughing, eating or immediately after vigorous exercise) or by prolonged standing.
   When either type of syncope is established (both are “reflex” syncopes,)
   performing TTT is not necessary for confirmation, but it still useful to demonstrate susceptibility of the patient to reflex syncope, (e.g., training for syncope prevention).
2. Provide criteria for risk stratification and, specifically, for identification of patients with suspected cardiac syncope. In these patients, it is cardiac evaluation that is warranted. Tilt table testing, however, should not be performed as a first-choice test.
3. Define a syndrome of delayed orthostatic hypotension in which the standard active standing test is negative and diagnosis can be made only by means of TTT. Such cases should lead to the start of a specific therapy, e.g., elastic compression stocking of the legs which was proven to be effective in relieving symptoms of orthostatic intolerance (2).

Sensitivity and diagnostic yield

Prior to the 2009 guidelines, the sensitivity of TTT could not be calculated and was surrogated by the evaluation of a more general “positivity rate”, arousing some concern as to the real diagnostic yield of the test. In this respect the guidelines indicate that the specificity of TTT potentiated with nitroglycerin or clomipramine is approximately 10%. Thus, when TTT, performed for diagnostic purposes in patients affected by uncertain syncope, should in all likelihood provide a positive response. In a study conducted in our centre, we have thus been able to establish “true positive” cases in view of calculating the true sensitivity of TTT (3).

We have thus identified a group of patients affected by established reflex syncope based on clinical presentation. These patients - the “true positive group”- constituted a “gold standard” population that allowed us to calculate the sensitivity of TTT applied to our group (n=360). Sensitivity of TTT, when potentiated with nitroglycerin was found to be 71% and 75% in patients with vasovagal and situational forms of syncope respectively. The sensitivity of TTT potentiated with clomipramine was higher in patients with vasovagal forms (92%), but sub-optimal in patients with situational forms. Interestingly, sensitivity increased to 87% and 100% respectively, in patients with both vasovagal and situational syncopes, indicating a more complex and severe form of reflex syncope.
 
Our findings show that TTT supports a likely diagnosis of reflex syncope – reflex syncope was observed in 36% and 30% of cases with nitroglycerin TTT and clomipramine TTT respectively (3). We conclude that a negative response makes a diagnosis of reflex syncope less likely and suggests that other causes should be investigated (of which possible orthostatic or cardiac syncope).

More generally, the latest guidelines offer the following, current and appropriate indications for TTT:

When NOT to tilt-table test

• When diagnosis of vasovagal syncope is already certain
• When a cardiac syncope is likely (“cardiac evaluation first”)
• When syncope occurs in absence of emotional distress or orthostatic stress
• When a diagnosis is not necessary

When to tilt-table test – in establishing a diagnosis

• When reflex syncope is suspected, but clinical presentation is atypical
• When syncope is unexplained and an orthostatic trigger is present
• When delayed orthostatic hypotension is suspected

When to tilt-table test – in establishing therapy

• When differentiating reflex syncope from orthostatic hypotension as prerequisite for a specific therapy
• To demonstrate susceptibility of the patient to reflex syncope as part of the biofeedback training program for counter-pressure maneuvers. With this indication, a positivity rate approaching 100% is desirable. Nitroglycerin TTT should be performed in patients in whom a situational trigger is present, whereas clomipramine TTT should be undertaken in patients in whom an emotional trigger is present

*Not yet established: the indication of TTT for selecting cases of cardioinhibitory forms of syncope that would be candidates for pacing therapy.