Effect of carotid endarterectomy on patterns of cerebrovascular reactivity in patients with unilateral carotid artery stenosis.

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Abstract
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. The CO2 reactivity of the cerebral resistance index (CRi) 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 CRi reactivity of the control group was used to differentiate between normal and abnormal findings. In patients with normal CRi asymmetry (comparable CRi reactivities at both hemispheres, n = 41), CEA did not change hemispheric CRi reactivity. In patients in whom CRi reactivity was absent at the contralateral hemisphere (intracerebral steal during hypercapnia, n = 12), CEA abolished the steal phenomenon by significantly increasing CRi reactivity at the contralateral hemisphere (preoperative, -1.0 +/- 2.1 %CRi/vol%CO2; postoperative, 5.2 +/- 0.7 %CRi/vol%CO2; P < .01). Patients who showed severely diminished ipsilateral CRi reactivity, compatible with a significantly reduced perfusion pressure at the poststenotic hemisphere (n = 10), demonstrated an improvement of ipsilateral CRi reactivity after surgery (preoperative, 0.6 +/- 0.8 %CRi/vol%CO2; postoperative, 3.7 +/- 1.1 %CRi/vol%CO2; P < .01). 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 CRi reactivity allowed precise prediction of the effect of CEA on intracerebral hemodynamics.