EFFECT OF CAROTID ENDARTERECTOMY ON PATTERNS OF CEREBROVASCULAR REACTIVITY IN PATIENTS WITH UNILATERAL CAROTID-ARTERY STENOSIS

Background and Purpose Patients with unilateral significant carotid ar tery stenosis present with a variable intracranial hemodynamic status. In the majority of patients, hemodynamics are normal because of suffi cient collateral flow. One subgroup shows poor ipsilateral hemodynamic s because of a severely reduced blood supply, whereas in another subgr oup of patients a steal phenomenon from the contralateral to the ipsil ateral hemisphere can be observed during pharmacological provocation. The present study examined the effect of carotid endarterectomy (CEA) on these patterns of cerebrovascular hemodynamics in patients with car otid artery stenosis. Methods The CO2 reactivity of the cerebral resis tance index (CR(i)) was determined with transcranial Doppler sonograph y in 63 patients with unilateral high-grade to threadlike carotid arte ry stenosis before and 3 months after CEA and in 37 control subjects. The interhemispheric asymmetry of CR(i) reactivity of the control grou p was used to differentiate between normal and abnormal findings. Resu lts In patients with normal CR(i) asymmetry (comparable CR(i) reactivi ties at both hemispheres, n=41), CEA did not change hemispheric CR(i) reactivity. In patients in whom CR(i) reactivity was absent at the con tralateral hemisphere (intracerebral steal during hypercapnia, n=12), CEA abolished the steal phenomenon by significantly increasing CR(i) r eactivity at the contralateral hemisphere (preoperative, -1.0+/-2.1 %C R(i)/ vol%CO2; postoperative, 5.2+/-0.7 %CR(i)/vol%CO2; P<.01). Patien ts who showed severely diminished ipsilateral CR(i) reactivity, compat ible with a significantly reduced perfusion pressure at the poststenot ic hemisphere (n=10), demonstrated an improvement of ipsilateral CR(i) reactivity after surgery (preoperative, 0.6+/-0.8 %CR(i)/vol%CO2; pos toperative, 3.7+/-1.1 %CR(i)/vol%CO2; P<.01). Conclusions Most patient s do not respond significantly to CEA. One small subgroup of patients who presented with severely disturbed ipsilateral hemodynamics demonst rated postoperative improvement at the poststenotic hemisphere, wherea s in another small subgroup, who showed a steal phenomenon at the cont ralateral hemisphere, CEA improved contralateral hemodynamics. Determi nation of preoperative CR(i) reactivity allowed precise prediction of the effect of CEA on intracerebral hemodynamics.