Completely reversed flow in the vertebral artery does not always indicate subclavian steal phenomenon.

We evaluated the causes, differential diagnosis and clinical significance of completely reversed flow (CRF) in the vertebral artery (VA). Twenty-three patients diagnosed with CRF in the VA by Doppler ultrasound were studied retrospectively. CRF was divided into intermittent CRF and continuous CRF. The peak reversed velocity (PRV) and ratio of time in intermittent CRF to one cardiac cycle (tICRF/CC) were calculated. Causes of CRF were determined on the basis of previous angiography results. The results indicated that subclavian steal phenomenon (SSP) caused all cases of continuous CRF (n = 8). Intermittent CRF was caused by SSP (n = 6) or proximal VA occlusion (n = 9). PRV and tICRF/CC were increased in SSP as compared with VA occlusion (p < 0.05). Using a cutoff of tICRF/CC = 0.30, we achieved excellent accuracy in predicting the cause of intermittent CRF (100%) and posterior circulatory infarction (91%). Thus, analysis of CRF patterns and measurements of VA parameters can be used in differential diagnosis of the causes of CRF and in prediction of posterior circulatory infarction.