Carotid-to-subclavian bypass grafts are frequently employed to treat the subclavian steal syndrome. This laboratory study evaluated the effects on carotid blood flow of varying vascular resistance in the carotid and axillary arteries. In the presence of a functioning carotid-axillary bypass graft, distal carotid blood flow decreased whenever resistance to flow in the distal carotid artery was increased or when resistance in the axillary artery was decreased.
These observations explain the mechanism responsible for the occasional failure of a patient to improve following carotid-subclavian bypass grafting. As shown by these experiments, distal obstruction in the carotid artery can result in stealing of blood from the cerebral circulation by carotid-tosubclavian bypass. These studies indicate that obstructing lesions of the carotid artery must be repaired at the time of carotid-subclavian bypass.