Clot-Busting Ultrasound Gives Carotid Endarterectomy a Step Up

There were clinical benefits to putting patients under a steady ultrasound beam during carotid endarterectomy, the phase III sham-controlled SONOBIRDIE trial found.

Applied during the surgery for people averaging 80% internal carotid artery stenosis, sonolysis resulted in reductions in 30-day:

• Combined ischemic stroke, transient ischemic attack (TIA), and death (2.2% vs 7.6%; risk ratio [RR] 0.28, 95% CI 0.15-0.54)
• Ischemic stroke (1.4% vs 5.4%; RR 0.25, 95% CI 0.11-0.56)
• TIA (0.6% vs 2.6%; RR 0.23, 95% CI 0.07-0.73)

Although there were no significant between-group differences in mortality at 30 days or 1 year, the other clinical benefits were supported by the finding of fewer new ischemic lesions among study participants who had follow-up brain MRI (8.5% vs 17.4%, P=0.004), according to researchers led by David Školoudík, PhD, of the University of Ostrava in Czech Republic.

“The results of the SONOBIRDIE trial suggest that sonolysis should be used to reduce the risk of periprocedural cerebrovascular events during carotid endarterectomy in all patients with sufficient temporal bone window for transcranial Doppler,” they wrote in The BMJ. “It has the potential to make carotid endarterectomy safer with a higher benefit for patients with carotid stenosis compared with the best medical treatment, especially in patients with asymptomatic carotid stenosis.”

Notably, the SONOBIRDIE trial had been stopped early for effectiveness and its main results were previously reported at the European Stroke Organisation Conference in 2023.

As for safety in the trial, sonolysis did not result in any intracranial bleeds. Approximately 95% of patients in the sonolysis group were free from serious adverse events 30 days after the procedure; there was one reported case of intracerebral bleeding/subarachnoid hemorrhage in one sonolysis patient (0.2%) and none in the control group.

Sonolysis is the continuous application of a low-intensity pulsed wave ultrasound beam using a standard ultrasound machine and a transcranial Doppler probe. The procedure is thought to reduce thromboembolic risk by activating fibrinolytic enzymes in tandem with a direct mechanical breaking of existing clots — though the exact mechanism of benefit remains unknown.

For carotid endarterectomy in SONOBIRDIE, sonolysis was started before the first skin incision and stopped after the last suturing of the skin at the end of surgery (up to 2 hours).

“These findings represent a potentially significant innovation in the application of ultrasound from its historical diagnostic role to now also as a therapeutic intervention,” noted Jesse Columbo, MD, of Dartmouth Hitchcock Medical Center in Lebanon, New Hampshire, in an accompanying editorial. “Given the well documented low risk of stroke associated with asymptomatic carotid endarterectomy, the observed absolute risk reduction of 5.4% seems to represent a substantial additive advance in carotid endarterectomy care.”

However, Columbo laid out his concerns about the internal validity of the results, citing the whopping 6.9% incidence of the primary composite outcome in asymptomatic patients in the study and the fact that symptom status seemed to have no bearing on event rates.

“Resolution of the above concerns, along with a cost effectiveness calculation, can then inform whether this exciting new application of an established technology can improve care for patients undergoing carotid endarterectomy,” he wrote.

The SONOBIRDIE trial was conducted in Czech Republic, Slovakia, and Austria among 1,004 patients with ≥70% symptomatic or asymptomatic internal carotid artery stenosis who were randomized to sonolysis or a sham procedure.

Mean age was 68 years, 31% were women, and 45% had symptomatic carotid stenosis. Over 80% were on statins, about 90% were on antiplatelets, and over 10% were on anticoagulants.

Školoudík’s group reported that baseline characteristics were comparable between groups.

Based on the 45.8% of patients who underwent brain MRI before and 1 day after carotid endarterectomy, all ischemic lesions after surgery were ipsilateral to the intervened internal carotid artery.

The investigators acknowledged that the sonographer on each case was not blinded to the assigned treatment, but patients and the rest of their care team were blinded.

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