Purpose: This open single-center prospective study aimed to determine the redistribution of blood flow within the circle of Willis and through collateral pathways after carotid endarterectomy. Blood flow velocity and flow direction in the major cerebral arteries were determined, both at rest and during CO(2) inhalation.
Methods: Carotid endarterectomy was performed in 148 patients with a 70% or greater diameter stenosis of the internal carotid artery while patients were under general anesthesia. Arteriotomy closure was done with a venous patch. Selective shunting was performed with an electroencephalogram. Baseline blood flow velocity of the basal cerebral arteries was measured by means of transcranial Doppler sonography preoperatively (within 1 week before surgery) and 3 months postoperatively. At the same times, cerebrovascular reactivity was calculated during CO(2) inhalation insonating both middle cerebral arteries.
Results: Baseline blood flow velocity in the ipsilateral middle cerebral artery hardly changed 3 months postoperatively, but there was a considerable redistribution of flow in the circle of Willis. This was characterized by a decrease in contribution from the contralateral hemisphere through the anterior communicating artery, reduced cerebropetal flow rates in the ophthalmic artery, and smaller contribution of the posterior collateral sources. The CO(2) reactivity on the side of surgery increased in all patients. In patients with a contralateral occlusion, CO(2) reactivity increased on both sides. The redistribution of flow was most pronounced in patients who needed intraoperative shunting and in patients with a contralateral internal carotid artery occlusion.
Conclusion: After carotid endarterectomy, flow redistribution, as expressed by changes in blood flow velocity values, occurs in the circle of Willis. The contribution of collateral sources is diminished, and the CO(2) reactivity increases, both of which reflect improvement of the hemodynamic condition. The most improvement occurs in patients with contralateral occlusion.