Reduced frequency of embolic signals in severe carotid stenosis with poststenotic flow velocity reduction

Background: We aimed to investigate the effect of poststenotic low blood flow in patients with recently symptomatic severe carotid stenosis on arterio- arterial embolism. Methods: Analyses based on a series of 206 consecutive patients ( 155 men and 51 women, mean age 65.3 years) with a nondisabling ischemic event in the anterior circulation <= 30 days ( median 4.5) before presentation and diagnosis of ipsilateral carotid artery stenosis/ occlusion ( >= 30% local diameter reduction). All patients underwent Doppler/ duplex sonography, which included measurement of poststenotic flow velocity as an indicator for poststenotic blood flow as well as a 1-hour transcranial Doppler monitoring for the detection of embolic signals. Results: Thirty- seven of two hundred and six patients had very severe stenosis which was associated with reduced poststenotic flow velocity (< 20 cm/ s systolic) in 17 patients. Probability of embolic signals increased with increasing degree of stenosis and was maximal in patients with stenoses >= 90% local diameter reduction if poststenotic flow velocity was not reduced. Reduced poststenotic flow velocity in patients with very severe stenosis was associated with a significantly lower frequency of embolic signals compared to patients with the same degree of stenosis but no velocity reduction ( adjusted odds ratio 0.15, 95% confidence interval 0.025 - 0.897, p = 0.038, adjustment for antiplatelet medication and time since ischemia). Conclusions: Low poststenotic flow velocity behind very severe internal carotid stenosis reduces the otherwise high frequency of embolic signals in recently symptomatic patients corroborating the hypothesis that reduced blood flow across carotid stenosis causes reduced embolism.