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Open Access Study protocol

Optimal cut-off criteria for duplex ultrasound for the diagnosis of restenosis in stented carotid arteries: Review and protocol for a diagnostic study

Paul J Nederkoorn* and Martin M Brown

BMC Neurology 2009, 9:36  doi:10.1186/1471-2377-9-36

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Ultrasound criteria for carotid In-stent restenosis.

Gert Jan de Borst   (2009-08-11 09:37)  UMC Utrecht email

Duplex ultrasound (US) velocity criteria have not been well-established for follow-up of patients with carotid artery stents. Stent placement alters the biomechanical properties (increased elastic modulus, decreased compliance) of the stented artery. This may cause an increase in duplex-acquired velocity measurements in the absence of technical error, residual stenotic disease, or myointimal thickening in the stent [1,2]. Therefore, the potential risk of using the generally accepted duplex criteria for follow-up after CEA is an overestimation of the degree of restenosis after CAS. As Nederkoorn and Brown correctly state, the magnitude and significance of these alterations are ill-defined and emphasize the need to develop customized velocity criteria for se in patients with implanted stents.
Only a few published studies so far addressed the application of duplex velocity criteria to assess stented carotid arteries. The main limitation of these studies was the small patient cohort and therefore very small cases with a real > 70% in-stent restenosis (ISR) confirmed by angiography [3]. In these series, most lesions were moderate in severity (40-70% stenosis) and only around 6% were haemodynamically significant (>70% stenosis) and required re-intervention.
What these papers however did prove, is that stent placement causes anatomical and hemodynamic alterations. Narrowing and associated increased velocities were objectified [4]. Such alterations, however, were laboratory and stent-type dependent and did not justify a general approach to new velocity criteria indiscriminately applied to all stents [1,4]. Stent type specific duplex US measurements were confirmed in a recent animal study [5]. Vascular laboratories therefore should realize that carotid stent placement itself leads to elevated duplex velocities, but that these alterations might well be highly stent type specific.
The trial design by Nederkoorn and Brown, focuses on patients 1 year after treatment, or the first ICSS follow-up thereafter. Their goal is 1) to validate the use of DUS for ISR during follow-up, and 2) to determine reliable cut-off criteria for different degrees of stenosis. The design brings several problems: Early registration of baseline velocities to compare with subsequent follow-up velocities of the stented carotid artery is ideal [6], but the proposed new sub-study set-up has only 1 measurement per patient relatively short following the procedure. Despite the obtained cohort of more than 300 inclusions, the total number of patients with a haemodynamic significant stenosis > 80% therefore still might be limited at 1 year, although this subgroup is indeed of most interest. Ideally, new criteria would reliably detect > 70% ISR, and identify >50% ISR that might become haemodynamic significant in the fiuture, to follow-up or re-intervene when symptomatic.
Furthermore, there is currently no way to predict which of the low-grade or moderate grade lesions will progress to need re-intervention [7] and it would be of interest to have more than 2 postoperative measurements with at least 12 months in between.
At last, as the authors state, because different centres participate, data will be derived from different CT machines. In fact, the problem is even larger than that, because duplex US data will also be derived from different laboratories with different duplex machines, collecting data on several different types of stents, at a different time interval from intervention.
It must be feared therefore, that based on the data that Nederkoorn will collect, he probably can conclude nothing more than already known: Arterial stent placement alters duplex velocity measurements. Clinicians should be aware of the limitations of duplex ultrasound when making management decisions. A mildly elevated PSV in carotid stented segments should be interpreted with caution. Most importantly, every Vascular Laboratory should develop their own specific velocity criteria for the evaluation of patients with carotid stents.

1. Lal BK, Hobson RW, Goldstein J, et al. carotid artery stenting: is there a need to revise the ultrasound velocity criteria ? J Vasc Surg 2004; 39: 58-66.
2. Ringer AJ, German JW, Guterman LR, et al. Follow-up of stented carotid arteries by Doppler ultrasound. Neurosurgery 2002; 51: 639-643.
3. Stanziale SF, Wholey MH, Boules TN, et al. Determining in-stent stenosis of carotid arteries by duplex ultrasound criteria. J Endovasc Ther 2005; 12: 346-353
4. Tanaka N, Martin JB, Tokunaga K, et al. Conformity of carotid stents with vascular anatomy: evaluation in carotid models. AJNR Am J Neuroradiol 2004;25:604-607.
5. De Borst GJ, Meijer R, Lo RH, Vosmeer HWG, Ackerstaff RGA, Moll FL. Effect of carotid angioplasty and stenting on duplex velocity measurements in a porcine model. J Endovasc Ther 2008; 15: 672-679.
6. Aburahma AF, Abu-Halimah S, Bensenhaver J, Scott dean L, Keiffer T, Emmett M, et al. optimal carotid duplex velocity criteria for defining the severity of carotid in-stent restenosis. J Vasc Surg 2008; 48: 589-594.
7. Lal BK, Kaperonis EA, Cuadra S, Kapadia I, Hobson RW. Patterns of in-stent restenosis after carotd artery stenting: Classification and implications for long term outcome. J Vasc Surg 2007; 46: 833-840.

Competing interests

None declared


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