Tilt-table test

• a tilt table test may be used to investigate a patient with a history of episodes of unexplained syncope
  • tilt table testing not warranted in certain circumstances (1)
    • a single syncopal episode, without injury and not in a high risk setting with evident neurocardiogenic features
    • syncope where a specific cause has already been established and where demonstrating a neurocardiogenic component would not alter treatment plans
• tilt-table testing is a provocative test used to determine a patient’s susceptibility to vasovagal syncope (2)
  • an orthostatic stimulus causes blood to pool in the lower extremities - in susceptible individuals, vasovagal syncope often ensues within approximately 20 minutes
    • triggering mechanism in vasovagal syncope is believed to be caused by a relatively central hypovolemia - this occurs because of blood pooling in the lower extremities
    • afferent end of this reflex may be mediated by left ventricular or right atrial mechanoreceptors that are activated during vigorous contraction around underfilled chambers in a situation similar to severe hemorrhage
      • information from these mechanoreceptors travels along vagal afferent C fibers to the brain stem
        • this pathway mediates the efferent response consisting of withdrawal of sympathetic vasomotor tone and a vagally mediated bradycardia.
• observations suggest the provoked response during tilt-table testing is essentially equivalent to the response during a spontaneous vasovagal syncopal episode
  • patients often describe the symptoms produced by tilt-table testing as identical to those experienced during spontaneous episodes of syncope
• there are numerous variations in the methods used for tilt-table testing
  • tilt-table tests are often done in 2 stages: a prolonged period of head-up tilt in the drug-free state, followed by a shorter period of head-up tilt after administration of a provocative pharmaceutical agent e.g. sublingual glyceryl trinitrate
    • a typical protocol comprises:
      • 30 min of lying flat on the tilt-table, during which time baseline values of pulse-rate and blood pressure are measured
      • 40 min of lying at 60 degrees to the ground, during which time:
        • the pulse-rate and blood pressure are monitored
        • any symptoms are recorded
  • the sensitivity of the drug-free head-up tilt table test, i.e., weighed against a classical clinical presentation of vasovagal syncope, for establishing a diagnosis of vasovagal syncope has been reported to range between 30 and 85% (3)
• interpretation of results of tilt table test:
  • patients with vasovagal syncope have an abrupt decrease in blood pressure accompanied by some decrease in heart rate
  • patients with a dysautonomic response to head-up tilt demonstrate a gradual and progressive decrease in blood pressure, usually with only a small or insignificant change in heart rate
  • patients with postural orthostatic tachycardia syndrome demonstrate an early and sustained increase in heart rate, often associated with a progressive decrease in blood pressure, although it can be associated with frank hypotension and syncope

Reference:

1. Grubb BP, Kosinski D. Tilt table testing: concepts and limitations. Pacing Clin Electrophysiol. 1997 Mar;20(3 Pt 2):781-7.
2. Sutton R, Bloomfield DM. Indications, methodology, and classification of results of tilt-table testing. Am J Cardiol. 1999 Oct 21;84(8A):10Q-19Q.
3. American college of cardiology expert consensus document. Tilt table testing for assessing syncope. J Am Coll Cardiol 1996;28: 263–275.