PHILADELPHIA — The current standards for diagnosing carotid artery stenosis by ultrasound velocity are too low once a stent is placed in the vessel, according to the results of a study of 80 patients presented at the Vascular Annual Meeting.
The standard ultrasound threshold for diagnosing carotid stenosis of 50% or more is a peak systolic velocity (PSV) of at least 125 cm/s. But after a carotid artery is stented, its biomechanical properties change and the PSV rises.
In stented patients, the flag for carotid stenosis of 50% or more should be a PSV of at least 217 cm/s, Dr. Sam A. Zakhary said at the meeting, which was sponsored by the Society for Vascular Surgery.
Another marker of stenosis is the ratio of the PSV in the internal carotid artery to that in the common carotid artery (ICA/CCA). The standard threshold for flagging stenosis of 50% or more is a ratio of at least 2.0, but in the study, the best threshold was found to be a ratio of at least 2.98, said Dr. Zakhary, a vascular surgeon at Baylor University Medical Center in Dallas.
In the 80-patient series, carotid angiography was done within 30 days of stenting, and ultrasounds were taken within 30 days of angiography. The 28 patients with less than 50% carotid stenosis after stenting were followed for 6 years, during which 5 developed stenosis of 50% or more.
Of the 80 patients, 40 were misdiagnosed with a residual carotid stenosis of 50% or more after stenting because their PSV was at least 125 cm/s. But none had this high a level of carotid stenosis when assessed with carotid angiography.
In contrast, a PSV of at least 217 cm/s showed high sensitivity and specificity for diagnosing 50% or more stenosis in the 80 patients (see box), Dr. Zakhary said.
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