Revascularization of Collaterals for Hemodynamic Stroke

Abstract

Carotid atherosclerosis accounts for up to 15% of all strokes1 and approximately 15 000 to 20 000 have symptomatic carotid occlusions in the United States each year.2 Furthermore, recurrent ipsilateral stroke in unselected patients with carotid occlusion affects 2.1% to 3.8% on an annual basis.3–5 The pathophysiology of stroke due to atherosclerotic plaque of the internal carotid artery may be distinct once the stenotic or narrowed vessel progresses to occlusion. Various mechanisms for cerebral ischemia in carotid occlusion have been described, including downstream clot propagation and stump embolism6,7; however, impaired perfusion plays a major role, particularly once the distal stump of the occlusion develops mature endothelium. A combined effect of hypoperfusion and poor clearance of embolic material has also been described.8 Perfusion through collaterals to downstream territories of the brain is therefore pivotal. In fact, collaterals largely determine recurrence of symptomatic ischemia after hemodynamic stroke in carotid occlusion. The clinical observation of stereotypical events and those that occur with hypotension and initiation of antihypertensive agents, after a hot bath, or even with the upright position, support a hemodynamic process. Imaging reveals a hemodynamic pattern of ischemia with border zone infarcts as an initial presentation of carotid occlusion in 5% to 13% and in 44% to 72% of recurrent strokes.4,9 As perfusion pressure is reduced, cerebral blood flow determined by collaterals is maintained by dilatation of the resistance arterioles (Stage 1 hemodynamic impairment). Further reduction of perfusion pressure may exhaust this autoregulatory capacity and blood flow decreases proportionally to the perfusion pressure. Initially, increased oxygen extraction fraction (OEF) will maintain tissue metabolism (Stage 2 hemodynamic impairment). Thereafter, insufficient flow and oxygen delivery may result in energetic failure and infarction.10 The Carotid Occlusion Surgery Study (COSS)11 provides …