Systematic review of embolic activity and cerebral hemodynamics in transcarotid artery revascularization using transcranial Doppler ultrasound

Background: Transcarotid artery revascularization (TCAR) is a safer alternative to transfemoral carotid artery stenting (tfCAS) for patients with carotid artery stenosis, using flow reversal to reduce embolic risk from wire manipulation. Intraoperative transcranial Doppler (TCD) enables real-time monitoring of cerebral hemodynamics and embolic events during TCAR. This review evaluates TCD's findings in enhancing the safety and outcomes of TCAR. Methods: We conducted a systematic review following the PRISMA guidelines. A comprehensive search of PubMed, Embase, and Scopus was conducted to identify relevant studies from the earliest available records through January 2025. Eligible studies were original research articles, including case series, case-control studies, retrospective or prospective cohort studies, and randomized controlled trials, reporting intraoperative TCD findings during TCAR, or compared them with findings from other revascularization methods, such as carotid endarterectomy (CEA) and tfCAS. Outcomes extracted focused on embolic burden (measured by high-intensity transient signals [HITS]) and mean flow velocity (MFV) of the middle cerebral artery (MCA), both overall and at specific procedural stages. A meta-analysis was not feasible owing to heterogeneity in study designs, outcome measures, and TCD protocols among the included studies. Results: Thirteen studies were included. Earlier TCD assessments during TCAR reported no embolic events, whereas more recent studies found mean embolic counts ranging from 0 to 29, indicating a generally low embolic burden. Larger embolic showers, with counts between 117 and 184 HITS, were also reported. The greatest embolic activity occurred during stent deployment and after flow reversal cessation, with median HITS counts across studies ranging from 8 to 16 and 34 to 56, respectively. Across the included studies, TCAR was associated with a lower embolic burden than tfCAS, with reported median HITS values ranging from 0 to 184 for TCAR, compared with 197 to 584 for tfCAS, particularly during lesion crossing and the predilation and postdilation phases. Comparisons with CEA were mixed: one study showed lower HITS in CEA, whereas another found no difference. Consistently, studies reported a significant MCA MFV decrease during flow reversal, particularly in patients with an incomplete circle of Willis. MFV returned to or exceeded baseline after flow reversal, indicating effective restoration of cerebral perfusion. Although the literature does not consistently link intraoperative TCD findings with postoperative stroke outcomes, one study found that patients with fewer than 20 HITS had significantly greater improvement in postoperative Glasgow Coma Scale scores (P = .028), suggesting a potential cognitive benefit from a lower embolic burden. Conclusions: These findings demonstrate the capability of intraoperative TCD examination to detect embolic and hemodynamic changes during TCAR, particularly in identifying high-risk procedural phases. Although TCAR shows a lower embolic burden than tfCAS, further research is needed to comprehensively compare its outcomes with those of CEA.