This is a secondary analysis of BUBL, a clinical trial (www.clinicaltrials.gov; NCT04604015), to ascertain the effects of transcranial Doppler (TCD) bubble study technique on results, including right to left shunt (RLS) presence and size.

A prospective, multicenter device clinical trial demonstrated robot-assisted TCD, run by health care professionals with no prior TCD training, was 3x more likely to diagnose any, including large, RLS as compared to TTE. Valsalva maneuver, body positioning and IV placement have been reported to affect results in observational studies but not in the setting of a clinical trial.

We conducted a prospective, single-arm device clinical trial of robot-assisted TCD (raTCD) versus TTE for RLS diagnosis at 6 clinical sites in patients who presented with an event suspicious for embolic cerebrovascular ischemia from October 6, 2020 to October 20, 2021. Robot-assisted TCD was performed with standard TCD bubble study technique, including runs with and without Valsalva, supine and at 45^o incline. IV location was tracked, acknowledging recommendations for right antecubital placement as technically ideal.

A total of 154 patients were enrolled, 129 evaluable (intent to scan) and 121 subjects had complete data per protocol. In the intent to scan cohort, mean age was 60±15 years, 47% were women, and all qualifying events were diagnosed as ischemic stroke or transient ischemic attack. Valsalva maneuver and bed positioning increased RLS grade in 28% and 19%, respectively, including patients from RLS absence to presence and “small” to “large” grades. Antecubital IV placement had a RLS positivity rate of 63.6% and “other location” had a RLS positivity rate of 63.2%.

Technical aspects of TCD bubble study performance matter, including Valsalva maneuver and upright positioning, increasing not only sensitivity but the size grade of the RLS. IV location does not affect rate of RLS detection.