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

Background and Purpose Patients with unilateral significant carotid artery stenosis present with a variable intracranial hemodynamic status. In the majority of patients, hemodynamics are normal because of sufficient collateral flow. One subgroup shows poor ipsilateral hemodynamics because of a severely reduced blood supply, whereas in another subgroup of patients a steal phenomenon from the contralateral to the ipsilateral 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 carotid artery stenosis. Methods The CO2 reactivity of the cerebral resistance index (CR(i)) was determined with transcranial Doppler sonography in 63 patients with unilateral high-grade to threadlike carotid artery stenosis before and 3 months after CEA and in 37 control subjects. The interhemispheric asymmetry of CR(i) reactivity of the control group was used to differentiate between normal and abnormal findings. Results In patients with normal CR(i) asymmetry (comparable CR(i) reactivities at both hemispheres, n=41), CEA did not change hemispheric CR(i) reactivity. In patients in whom CR(i) reactivity was absent at the contralateral hemisphere (intracerebral steal during hypercapnia, n=12), CEA abolished the steal phenomenon by significantly increasing CR(i) reactivity at the contralateral hemisphere (preoperative, -1.0+/-2.1 %CR(i)/ vol%CO2; postoperative, 5.2+/-0.7 %CR(i)/vol%CO2; P<.01). Patients who showed severely diminished ipsilateral CR(i) reactivity, compatible with a significantly reduced perfusion pressure at the poststenotic hemisphere (n=10), demonstrated an improvement of ipsilateral CR(i) reactivity after surgery (preoperative, 0.6+/-0.8 %CR(i)/vol%CO2; postoperative, 3.7+/-1.1 %CR(i)/vol%CO2; P<.01). Conclusions Most patients do not respond significantly to CEA. One small subgroup of patients who presented with severely disturbed ipsilateral hemodynamics demonstrated postoperative improvement at the poststenotic hemisphere, whereas in another small subgroup, who showed a steal phenomenon at the contralateral hemisphere, CEA improved contralateral hemodynamics. Determination of preoperative CR(i) reactivity allowed precise prediction of the effect of CEA on intracerebral hemodynamics.