What is the purpose and procedure of a tilt test for diagnosing syncope?

Tilt Test for Diagnosing Syncope

The tilt test is a crucial diagnostic tool for evaluating unexplained syncope by inducing reflex hypotension/bradycardia or orthostatic hypotension under controlled conditions, allowing physicians to identify the underlying mechanism of syncope and guide appropriate treatment. 1

Purpose of Tilt Testing

• Tilt testing is primarily indicated for diagnosing reflex syncope (vasovagal syncope) when initial evaluation is inconclusive, particularly in cases of unexplained single syncopal episodes in high-risk settings or recurrent episodes without evidence of organic heart disease 1
• It helps discriminate between different types of syncope, including reflex syncope and orthostatic hypotension 1
• Tilt testing can differentiate syncope with jerking movements from epilepsy, helping avoid misdiagnosis 1
• It's valuable for evaluating patients with recurrent unexplained falls, particularly in the elderly 1
• The test can demonstrate susceptibility to reflex syncope to patients, improving understanding and compliance with treatment 1

Procedure of Tilt Testing

Standard Protocol

• Preparation phase: Patient begins in a supine position for at least 5 minutes (when no venous cannulation is needed) or at least 20 minutes (when cannulation is undertaken) 1
• Tilt angle: The patient is tilted to an angle between 60-70 degrees on a motorized table with foot support 1
• Passive phase: The patient remains tilted for a minimum of 20 minutes and maximum of 45 minutes 1
• Provocation phase (if needed): Either nitroglycerine (300-400 μg sublingually) or isoproterenol (incremental infusion up to 3 μg/min) may be administered to increase sensitivity 1, 2
• Monitoring: Continuous beat-to-beat blood pressure and heart rate monitoring with ECG recording throughout the test 2, 3
• Documentation: Video recording may be used to capture clinical manifestations during the test 2

Safety Considerations

• Tilt testing is generally safe with no reported deaths during testing 1
• Resuscitation equipment should be available despite the low risk 1
• Isoproterenol is contraindicated in patients with ischemic heart disease, uncontrolled hypertension, left ventricular outflow tract obstruction, and significant aortic stenosis 1
• Minor side effects include palpitations with isoproterenol and headache with nitroglycerine 1
• Atrial fibrillation may occur during or after a positive test but is usually self-limited 1

Diagnostic Criteria and Interpretation

• Positive test: Induction of reflex hypotension/bradycardia with reproduction of syncope or pre-syncope symptoms 1
• Response types:
  • Cardioinhibitory: Predominant bradycardia
  • Vasodepressor: Predominant hypotension
  • Mixed: Both bradycardia and hypotension 1
• Orthostatic hypotension: Progressive BP fall with minimal heart rate change 2
• Psychogenic pseudosyncope: Apparent loss of consciousness without BP fall and with moderate heart rate rise 2

Clinical Utility and Limitations

• The diagnostic yield of tilt testing in patients with suspected vasovagal syncope is approximately 60% 3
• A negative tilt test does not exclude the diagnosis of reflex syncope 1
• A positive cardioinhibitory response predicts with high probability an asystolic spontaneous syncope, but other response types (vasodepressor, mixed, or negative) do not exclude asystole during spontaneous syncope 1
• Tilt testing is not recommended for assessment of treatment efficacy 1, 4
• The test may be less useful in younger patients due to lower specificity 5

Common Pitfalls and Caveats

• Unnecessary diagnostic tests are often performed before tilt testing; following European Syncope Guidelines can help avoid this 3
• Saddle support during testing may result in loss of specificity 5
• Tilting at angles less than 60 degrees results in loss of sensitivity 5
• Beta blockers may not significantly prevent syncope recurrence despite positive tilt test results 4
• In patients with structural heart disease, arrhythmia or other cardiovascular causes of syncope should be excluded before considering positive tilt test results as diagnostic 1