Transcarotid Artery Revascularization With the ENROUTE Transcarotid Neuroprotection System

Extracranial carotid artery occlusive disease is associated with the risk of stroke, disability, and death. The surgical treatment of carotid disease has undergone significant evolution from early attempts at carotid ligation to the first carotid endarterectomy by Michael Debakey in 1953. Over the following decades, carotid intervention was mostly limited for symptomatic patients. There was considerable research into the treatments of carotid disease and multiple randomized prospective trials were conducted, which demonstrated a definitive benefit to carotid endarterectomy in symptomatic patients with moderate to severe disease and asymptomatic patients with severe disease. Carotid endarterectomy became the treatment of choice for disease of the carotid bifurcation.

With the expansion of endovascular interventions in the 1990s, stenting for extracranial carotid disease with cerebral protection was explored as an alternative to endarterectomy in numerous trials. Several cerebral protection devices that were based upon distal cerebral occlusion balloons versus distal embolism filters were trialed, utilizing both open and closed cell stents. Interventions were performed both with and without devices to protect against embolization during interventions. Embolic protection included distal occlusive balloons and distal embolic filters. Multiple multicentered prospective randomized and nonrandom trials further explored transfemoral carotid stenting and established it as a viable treatment option for extracranial disease. These rigorous trials have also shed light on the nuances of this technique.

Based upon the results of these trials, the U.S. Food and Drug Administration granted approval for carotid artery stenting (CAS) with certain limitations. CAS from a transfemoral approach has been shown to have a significant increased risk of stroke compared with carotid endarterectomy. Factors that increase the risk include navigating tortuous anatomy, atheroma within the aortic arch, and crossing proximal common carotid lesions. The use of distal embolic protection devices improves outcome; however, these devices must be brought across the lesions in order to be deployed, which in itself can provoke embolization. Diffusion-weighted MRI studies of transfemoral CAS patients have shown an incidence of silent event as high as 40%. Many of these events were contralateral to the treated side, suggesting that navigation of the aortic arch may be a frequent cause of embolization. Transcarotid artery stenting (TCAR) with flow reversal was designed to mitigate many of these risks and to prevent stroke. Accessing the common carotid artery at the base of the neck allows the operator to avoid the complexities of challenging arch anatomy. Dynamic flow reversal is designed to prevent distal embolization beyond what is possible with distal filters.

The ENROUTE Transcarotid Neuroprotection System (Silk Road Medical, Sunnydale, California) is a flow reversal circuit that connects two 8-French sheaths through a flow modulator. One sheath is placed in the common carotid artery via arterial cutdown and the other is placed percutaneously into the femoral vein. The two sheaths are connected through a flow modulator, which can regulate the rate of flow reversal between high and low. The flow modulator can also temporarily stop flow reversal. When the common carotid artery is clamped proximal to the arterial sheath, the arterial–venous pressure gradient leads to flow reversal within the external and internal carotid arteries.

The ROADSTER trial was the pivotal trial for the ENROUTE system. It was a prospective, single arm, multicenter trial to assess the safety and efficacy of the flow reversal system in carotid artery stenting. The trial enrolled 141 patients, of whom 36 were symptomatic with stenoses >50%. The asymptomatic patients all had >70% stenosis. The enrolled patients were considered at high risk of endarterectomy based upon anatomic and physiologic criteria. The primary endpoint was major adverse events of death, stroke, and myocardial infarction. There were five major adverse events in the trial (two cerebrovascular accident, two deaths, and one myocardial infarction). There were also minor adverse events including eight arterial dissections, five hematomas, and one cranial nerve injury.