Hemodynamics of in-tandem stenosis of the internal carotid artery: When iscarotid endarterectomy indicated?

BACKGROUND Recent publications have pointed out the importance of evaluating patients with in-tandem stenosis and in particular the association of moderate steno sis of the extracranial internal carotid artery (ICA) with moderate or seve re stenosis of the intracranial internal carotid artery. Such evaluations a re needed in symptomatic patients before planning carotid endarterectomies because observations have shown that in some cases the removal of an extrac ranial lesion does not necessarily improve these symptoms. This paper exami nes the hemodynamic effects of in-tandem stenosis in the internal carotid a rtery. METHODS Equations describing flow in arteries are modified to accommodate two regio ns of stenosis in tandem. An equivalent value of stenosis is derived such t hat two stenoses in tandem behave as a single stenosis with similar hemodyn amic properties. The solution to this problem is solved mathematically and this was used to analyze the observations made in five studies published on in-tandem stenosis of the internal carotid artery. RESULTS Equivalent stenoses for various values of extracranial and intracranial ste noses are presented. It was found that two stenotic lesions in tandem are n ot equivalent to a simple summation of both values. A graphical solution is presented to show the hemodynamic effects of both stenoses. CONCLUSIONS The most critical determinant of hemodynamic compromise when two lesions ar e in tandem is the larger one. Hence removal of a more proximal lesion may have little effect on a larger distal lesion if the symptoms are due to hyp operfusion. It is important that one distinguish between hypoperfusion and thromboembolic causes of the symptoms. No conclusions about the risk of thr omboembolic events after a carotid endarterectomy in the setting of a dista l stenosis can be made from this study. (C) 2000 by Elsevier Science Inc.