Transcranial Doppler ultrasonography of the basilar artery in patients with retrograde vertebral artery flow.

OBJECTIVE: Reversal of flow in the extracranial vertebral artery secondary to a proximal subclavian/innominate artery stenosis or occlusion is a frequent finding during carotid duplex ultrasonography. The characteristics of basilar artery flow are not well defined in these patients. The objective of this study is to evaluate basilar artery flow in patients with retrograde vertebral artery flow.

METHODS: From a transforaminal vice transforamen approach with the patient seated, pulsed Doppler scan spectral waveforms were obtained from the distal segment of each vertebral artery (depths of 66 mm and 70 mm) and throughout the basilar artery (depths of 80 mm up to 116 mm). The direction of flow and the peak flow velocity were recorded at each location. In the subset of patients with antegrade flow, we initiated a 5-minute period of arm ischemia (produced by brachial blood pressure cuff inflated to a suprasystolic pressure) and compared flow direction to baseline.

RESULTS: Twenty-five patients with retrograde vertebral artery flow on carotid duplex ultrasonography underwent transcranial Doppler (TCD) ultrasonography scan of the distal vertebral arteries and the basilar artery. There were 10 males (58-85-years-old; mean 70.7 years) and 15 females (47-85-years-old; mean 66.0 years). An additional 11 patients who had normal vertebral flow underwent TCD and served as a control group. Nineteen patients (76%) demonstrated antegrade basilar artery flow at rest. Six patients (24%) demonstrated abnormal basilar artery flow at rest. Five had complete reversal of flow; one had intermittent flow reversal which became retrograde throughout the cardiac cycle following a period of arm ischemia ipsilateral to the patient's retrograde vertebral artery flow. No patient with retrograde vertebral artery flow and antegrade basilar artery flow at rest demonstrated a change in basilar artery peak velocity or direction of flow following arm ischemia.

CONCLUSION: Less than 25% of patients with retrograde vertebral artery flow on carotid duplex ultrasonography scan demonstrated a corresponding reversal of flow in the basilar artery. The vast majority of patients do not develop flow reversal in the basilar artery. Provocative maneuvers to increase collateral flow to the arm ipsilateral to retrograde vertebral artery flow did not appear to alter basilar artery flow velocity or direction of flow. Transcranial Doppler ultrasonography is indicated in patients with retrograde vertebral artery flow to document basilar artery flow, especially prior to intervention in patients with symptoms suggestive of posterior cerebral circulation insufficiency.