in a new study.
Being far easier to perform than regular transcranial Doppler ultrasound, it’s hoped that use of the robotic device will enable many more patients to undergo the more sensitive transcranial screening modality and increase the number of shunts identified.
“I believe robot-assisted transcranial Doppler ultrasound can fill the gap between the gold standard transcranial Doppler and transthoracic echocardiography, which is the current standard of care,” said lead author Mark Rubin, MD.
Dr. Rubin, who is assistant professor of neurology at University of Tennessee Health Science Center, Memphis, presented results of the BUBL study at the International Stroke Conference (ISC) 2022, where they were greeted with applause from the floor.
An improvement in the current standard of care
Dr. Rubin explained that patients with suspected embolic stroke are routinely screened for shunts in the heart, such as patent foramen ovale (PFO), that allow blood to flow from the right chamber to the left chamber and can lead to clots from the venous system, accessing the arterial system, then traveling to the brain and causing a stroke.
The current standard of care in screening for such shunts is the use of transthoracic echocardiography (TTE), a widely available and easy to perform, non-invasive procedure. “But we have known for decades that TTE does not pick up these shunts very well. With a sensitivity of only around 45%, it identifies less than half of the patients affected,” Dr. Rubin noted.
The more sensitive transesophageal echocardiography (TEE) gives much better results, but it is an invasive and unpleasant procedure with the ultrasound probe being passed down the throat, and the patient needing to be sedated, so it’s not appropriate for everyone, he noted.
“Transcranial Doppler ultrasound (TCD) also gives excellent results, with a sensitivity of about 96% for detecting PFO, but this procedure is difficult to perform and requires a great deal of skill in placing the probes in the right position and interpreting the signal,” Dr. Rubin said. “TCD has been around for decades, but it hasn’t caught on, as it is too difficult to do. It takes a lot of time to learn the technique.”
“With the robotic-assisted transcranial Doppler device, we can achieve the sensitivity of TCD without needing expert operators. This should vastly improve accessibility to this technology,” he said. “With such technology we can make significant strides into more accurate diagnoses on the cause of stroke, which should lead to better preventive treatments in those found to have right-to-left shunts.”
Robotic detection of shunts
For the BUBL study, the robotic TCD technique was compared with the standard TTE in 129 patients who had a diagnosis of presumed embolic stroke or transient ischemic attack (TIA), with all patients undergoing both procedures.
The robotic TCD device resembles a giant pair of headphones containing the ultrasound probes, which are attached to a frame. In the study, it was operated by a health care professional without TCD skills. Each ultrasound probe independently scans the temporal area autonomously – with angling and positive pressure against the scalp akin to a sonographer – to find and optimize bilateral middle cerebral artery signals, Dr. Rubin explained.
The primary endpoint was the detection of a right-to-left shunt. This occurred in 82 of the 129 patients (63.6%) with the robotic TCD device but in only 27 patients (20.9%) when TTE was used. This gives an absolute difference of 42.6% (95% confidence interval, 28.6%-56.7%; P < .001), which Dr. Rubin described as “astounding.”
However, he said he was not surprised by these results.
“In my experience with transcranial Doppler, I find shunts in patients every day that have not been seen with transthoracic echo,” he commented.
He noted that a previous meta-analysis has suggested a similar difference between TCD and transthoracic echo, but the current study provides prospectively collected data produced in a clinical trial setting and is therefore more reliable.
“What I hope comes from this is that more patients will be able to undergo transcranial Doppler, which is a far superior screening technique for identifying right-to-left shunts. There is so much evidence to support the use of transcranial Doppler, but with this new artificial-intelligence robotic device, we don’t need an expert to use it,” Dr. Rubin said.
He explained that finding a right-to-left shunt in stroke patients is particularly important, as it can direct treatment strategies to reduce future risk of recurrent strokes.
“If a patient has a large shunt, then they have a high risk of having another stroke, and the PFO should be closed.”
In this study, the robotic-assisted TCD detected three times as many large shunts that were considered “intervenable,” compared with transthoracic echo, identifying these shunts in 35 patients (27%) compared to just 13 (10%) with TTE.
“Of the 35 patients with intervenable shunts detected with robotic transcranial Doppler, TTE was completely negative in 18 of them and only suggested a small shunt in the others. So, the standard of care (TTE) missed half the patients with intervenable PFOs,” Dr. Rubin reported.