Internal carotid artery occlusion: effect of contralateral flow reduction in inducing symptoms

Cerebral ischemic attacks ipsilateral to an occluded internal carotid artery (ICA) continue in more than 16% of patients. With common carotid artery compression on the side of ICA occlusion in 53 patients, the mean (+/- SEM) ophthalmic systolic pressure/brachial systolic pressure (OSP/BSP) ratio fell from 0.58 +/- 0.013 to 0.42 +/- 0.020 (p less than 0.001), without any cerebral ischemic symptoms. Compression of the contralateral patent common carotid artery resulted in the ophthalmic systolic pressure/brachial systolic pressure ratio dropping from 0.67 +/- 0.012 to 0.29 +/- 0.017 (p less than 0.001) on the patient side and from 0.58 +/- 0.013 to 0.48 +/- 0.018 (p less than 0.001). Twenty-six of 53 patients (49%) developed ischemic symptoms in response to compression of the remaining patent ICA system. In contrast, only 8 of 122 patients (6.5%) without ICA occlusion developed any symptoms of cerebral dysfunction (p less than 0.001). This study suggests embolic events rather than flow reduction may be of greater importance in the production of new symptoms and that contralateral flow is critical to normal cerebral function in half the population with ICA occlusion.