Diagnosis of Right-to-Left Shunts by Transcranial Doppler in Patients With Insufficient Temporal Bone Window

To the Editor:I read with great interest the article entitled “Diagnosis of right-to-left shunt with transcranial Doppler and vertebrobasilar recording,”1 which appeared in Stroke . The authors studied use of vertebrobasilar circulation (VBC) monitoring for detection of right-to-left shunts (RLS) by contrast transcranial Doppler, so-called as “the bubble test.” In comparison with right middle cerebral artery (MCA) recordings, contrast transcranial Doppler with VBC monitoring missed 12 of 28 patients when the test was performed at rest, and 7 of 43 patients when Valsalva’s maneuver was performed during the bubble test. The authors were satisfied with these numbers because contrast transcranial Doppler with VBC recording caught all of the 22 patients with nonlow-grade RLS, which was defined as presence of at least 11 microbubbles (MBs). Based on these data, they suggest a possible use for VBC monitoring in subjects with insufficient sonic bone windows, in whom transesophageal echocardiography, according to the statement by the authors in the introduction section of the article, remains the only way to diagnose patent foramen ovale in …