Detection of Right-to-Left Shunt with Ultrasound Contrast Agent and Transcranial Doppler Sonography

Abstract

An international Consensus Meeting to determine a standard in the examination technique for the detection of right-to-left shunt (RLS) using contrast transcranial Doppler sonography (TCD) led to the following recommendations to standardize the examination procedure: The patient should be prepared with an 18-gauge needle inserted into the cubital vein and should be in the supine position. Insonation of at least one middle cerebral artery (MCA) using TCD is performed. The contrast agent is prepared using 9 ml isotonic saline solution and 1 ml air mixed with a three-way stopcock by exchange of saline/air mixture between the syringes and injected as a bolus. In case of little or no detection of microbubbles (MB) in the MCA under basal conditions, the examination will be repeated using the Valsalva maneuver (VM). Contrast agent will be injected 5 s before the start of the VM; the overall VM duration should be 10 s. The patient should start the VM on examiner's command. The strength of the VM can be controlled by peak flow velocity of the Doppler curve. The time when the first MB appears at the MCA level will be noted. A four-level categorization according to the MB count should be applied: (1) 0 MB (negative result); (2) 1-10 MB; (3) >10 MB and no curtain, and (4) curtain. ('Curtain' refers to a shower of MB, where a single bubble cannot be identified.) The results should be documented for basal condition and VM testing separately. The clinical significance of the diagnosis of a RLS in a particular patient is not fully evaluated and requires further studies. A minimum amount of MB suggestive of a clinical relevant RLS is not yet established. It probably depends on interindividual differences in hemodynamics that are currently not fully understood. Transesophageal echocardiography remains the gold standard for detection of a patent foramen ovale or an atrial septum defect. However, TCD with a contrast agent has been turned out as a potential method to diagnose a RLS in several studies which have been published during the last years, and a RLS other than at the atrial level may be detected only by this method. Furthermore, the VM can be applied more comfortably and more reliably during Doppler examination than during transesophageal echocardiography.