NEUROIMAGING / NEUROSONOLOGY

TCD/TCCD bubble test

Created 13/01/2023, last revision 26/01/2023

Indications

  • the TCD/TCCD bubble test is designed to detect right-left shunts, especially Patent Foramen Ovale (PFO)
  • an inexpensive, safe, and non-invasive imaging modality that is ideal for screening

Procedure

  • the test simulates paradoxical embolism
    • embolus (thrombus, gas, fat) passes intracardiac defect and enters systemic circulation
  • the patient is in the supine position, a blue cannula (22G) is inserted into the cubital vein and connected to a 3-way cock via a flexible tube
  • two 20 mL syringes are connected, one containing 8 mL of saline solution + 1 mL of blood, the other 1 mL of the air (the final mix = 8:1:1) (Zetola, 2019)
    • this dose of air is safe; in animal models, a threatening air dose is a bolus of > 20 ml or 11 mL/min [Tsivgoulis, 2010]
    • some authors mix NS with blood immediately, others mix at first NS + air  and finally draw 1 mL of blood to stabilize the mixed suspension
  • the contents of both syringes are mixed (perform at least 10 exchanges between the syringes)
  • inject the bolus of contrast agent (10 mL) while monitoring flow in the MCA (ideally in both MCA and ACA)
    • in case of an impenetrable temporal window, the terminal ICA can be examined transorbitally, or HITS can be detected in the extracranial portion of the ICA
    • bilateral monitoring using a fixation frame increases sensitivity
  • application of suspension is performed twice, first during normal breathing and then during the Valsalva maneuver (which increases the pressure in the right atrium and, thus, the functionality of the shunt)
    • the quality of the Valsalva maneuver should be checked beforehand (↓ PSV in ACM > 30% during the maneuver)
    • start Valsalva maneuver approx. 5s after suspension administration
    • repeated testing increases the sensitivity
TCD/TCCD bubble test

Definition of HITS

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Test evaluation

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Specificity and sensitivity

  • the sensitivity and specificity of both TCD and TCCD are reported to be over 90%
    • repeated/bilateral testing increases both
  • false-positive results:
    • the test is not PFO specific; it can be positive with any right-to-left communication (intraventricular septal defects, intrapulmonary AV shunt, etc.).
    • false-positive results can be obtained if the monitoring time is too long (some bubbles can be detected after they have passed through the pulmonary circulation) → see the timing of the HITS above
  • some modifications of the bubble test can increase sensitivity (such as above described suspension with blood to stabilize the microbubbles)
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TCD/TCCD bubble test
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