Annals of Vascular Surgery
Volume 20, Issue 4 , Pages 478-481, July 2006

Duplex Ultrasound Verified by Angiography in Patients with Severe Primary and Restenosis of Internal Carotid Artery

Department of Neurology, Rambam Medical Center, Haifa, Israel

Article Outline

There are very limited data in the literature about the reliability of duplex ultrasound (DU) verified by angiography in patients with restenosis of the internal carotid artery (ICA) after carotid surgery compared with primary carotid artery stenosis patients. Our objective was to compare the reliability of DU verified by conventional angiography in the diagnosis of severe primary stenosis versus restenosis of ICA. One hundred thirty-four patients (238 arteries) were examined by both DU and angiography. Severe stenosis (>70%) was found in 47 primary stenotic arteries and in 70 restenotic arteries. Accuracy, specificity, sensitivity, positive predictive value (PPV), and negative predictive value were obtained for basic DU criteria after verification of ultrasound data by angiography. The best accuracy for detection of±70% stenosis by end diastolic velocity was found for the velocity of 70 cm/sec or more in both groups, but accuracy for the restenosis group was significantly higher (96.9% vs. 89.8%, p = 0.025). Additionally, specificity (p = 0.01) and PPV (p = 0.01) were significantly higher in the restenosis group. The best accuracy for detection of>70% stenosis by peak systolic velocity was found for the velocity of 220 cm/sec or more for restenoses and 200 cm/sec or more for primary stenoses. The accuracy of the ultrasound was significantly higher in the restenosis group (94.6% vs. 87%, p = 0.04), as were specificity (p = 0.01) and PPV (p = 0.02). The diagnosis of severe restenosis by DU is reliable and can be used for decision making regarding surgery or stenting without angiography. In patients with Doppler parameters pointing to borderline moderate/severe primary carotid stenosis and technically complicated cases, angiography in addition to sonography before surgery is recommended.

 

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INTRODUCTION 

Carotid restenosis during the first years after end-arterectomy appears mainly as a result of homogenous neointimal proliferation without calcified plaques.1, 2 In this study, we aimed to define the reliability of carotid duplex ultrasound (DU) in patients with primary internal carotid artery (ICA) stenosis and restenosis after carotid endarterectomy (CEA) compared with the gold standard of conventional angiography.

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MATERIALS AND METHODS 

Patients 

A total of 134 patients (48 female, 86 male, mean age 71.8 ± 7.6, range 52-85 years) with carotid stenosis by DU or computed tomography (CT) angiography performed elsewhere were referred for evaluation for carotid stenting. From these patients, 75 had restenosis after CEA and 59 had primary carotid stenosis. Of those patients with restenosis, 84% were less than 3 years post-CEA.

An additional DU was performed in our laboratory before selective angiography. The latter was performed before the ICA stenting. A total of 257 from 268 carotid arteries were evaluated by both DU and angiography (unilateral carotid angiography was performed in 11 patients). The results of angiography were as follows: occlusion was found in 19 carotid arteries, stenosis of 1-49% in 80 arteries, stenosis of 50-69% in 41 arteries, and stenosis of 70-99% in 117 arteries. The latter arteries were included in the final analysis (47 arteries were primary stenotic and 70 restenotic after CEA).

Duplex Ultrasound 

One operator (E.K.) performed all DU examinations and measurements with the Aloka (Tokyo, Japan) 1700 SSD Color Duplex System ultrasonic device. The common carotid artery, ICA, carotid bifurcation, and external carotid artery were examined by both B-mode and color flow modalities. The maximal peak systolic velocity (PSV) and end diastolic velocity (EDV) were recorded from each location. According to B-mode imaging, the different types of plaques were marked out as follows: (1) soft plaques with uniform, homogenous gray texture and a smooth surface; (2) dense plaques (homo- or heterogenous) with high echogenic echoes; and (3) calcified plaques with high echog-enicity and acoustic shadow. Additionally, spectral broadening was assessed in all arteries with stenosis>70%. The spectral broadening was defined as mild or moderate if there was no obliteration of the spectral window or severe if there was complete obliteration of the spectral window.

Angiography 

Percutaneous catheter angiography was performed with standard coronary angiography techniques immediately before percutaneous angioplasty and stenting of ICA with at least two selective projections with the best appearance of the lesion. The degree of stenosis was calculated according to the North American Symptomatic Carotid Endarterec-tomy Trial (NASCET) method:3

where d is the ICAdiameter at the most stenotic site and D is the ICA diameter of the intact segment. All measurements were performed on a printed hard copy by a special ruler with 0.5 mm increments (G.T. and E.K.).

Statistics 

Statistical analyses included correlations, determination of sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of ultrasound results in comparison with angiography. JMP (SAS Institute, Cary, NC) was employed for the analyses.

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RESULTS 

Mean degree of stenosis by angiography was 84.7 ± 7.1% in the stenosis group and 86 ± 7.5% in the restenosis group (not significant, NS). Mean PSV was 303.7 ± 80 cm/sec in the primary stenosis group and 331.6 ± 77.9 cm/sec in the restenosis group (NS). Mean EDV was 114.6 ± 27.4 and 117.3 ± 46.1 cm/sec (NS), respectively. There was no statistically significant difference in PSV or EDV in stenosed arteries (in both primary and restenosis groups) depending on the presence or absence of contralateral severe stenosis or occlusion. In patients with primary stenosis, the majority of plaques were calcified (80.8%), while in patients with restenoses the plaques were soft or dense and homogenous (72.9%). Mild or moderate spectral broadening was found in 56.3% of arteries with primary stenosis and in 66.7% of arteries with restenosis; severe spectral broadening was found in 43.7% and 33.3% (NS), respectively. Sensitivity, specificity, PPV, NPV, and accuracy for DU for both groups were calculated (Table I, Table II). The best accuracy for detection of ≥70% stenosis by EDV was found for the velocity of 70 cm/sec or more in both groups, but accuracy for the restenosis group was significantly higher (96.9% vs. 89.8% for primary stenosis group, p = 0.025). The velocity of 70 cm/sec or more also had good sensitivity, specificity, NPV, and PPV in both groups. All of these parameters were higher in the restenosis group, with significant differences for specificity (p = 0.01) and PPV (p = 0.01). The best accuracy for detection of >70% stenosis by PSV was found for the velocity of 220 cm/sec or more for restenosis and 200 cm/sec or more for primary stenosis. Accuracy in the restenosis group was significantly higher (94.6% vs. 87% for stenosis group, p = 0.04). The sensitivity, specificity, NPV, and PPV for the above-mentioned velocities were higher in the restenosis group, with statistically significant differences for specificity (p = 0.01) and PPV (p = 0.02).

Table I. Sensitivity, specificity, PPV, NPV, and accuracy of DU by EDV for severe primary stenosis and restenosis groups
EDV (cm/sec)
60708090
Sensitivity (%)
Stenosis95.693.580.471.9
Restenosis98.695.885.981.7
Specificity (%)
Stenosis77.487.190.391.9
Restenosis81.498.3*98.398.3
PPV (%)
Stenosis75.984.386.186.8
Restenosis86.498.5*98.498.3
NPV (%)
Stenosis9694.786.181.4
Restenosis9895.186.181.7
Accuracy (%)
Stenosis85.289.886.183.3
Restenosis90.896.9*86.189.2

* p < 0.05.

Table II. Sensitivity, specificity, PPV, NPV, and accuracy of DU by PSV for severe primary stenosis and restenosis groups
PSV (cm/sec)
210220230
Sensitivity (%)
Stenosis82.680.476.1
Restenosis939390.1
Specificity (%)
Stenosis82.383.985.5
Restenosis89.896.6*96.6
PPV (%)
Stenosis77.578.779.5
Restenosis91.797.1*97
NPV (%)
Stenosis86.485.282.8
Restenosis91.491.989.1
Accuracy (%)
Stenosis82.483.481.5
Restenosis91.594.6*93.1

* p < 0.05.

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DISCUSSION 

DU is a noninvasive, convenient, easily performed, and readily available tool for diagnosis of ICA stenosis. Consequently, the decision regarding surgical intervention in these patients is based solely on DU in many clinics.4, 5, 6 On the other hand, CEA, despite a significant improvement over recent years of surgical technique and brain protection, remains an interventional procedure carrying morbidity and mortality.7, 8, 9 Thus, selection of patients for the operation has to be strictly accurate. Many clinicians, therefore, use DU for screening with subsequent angiography or magnetic resonance angiography in cases appropriate for surgery.10, 11, 12

Reliability of DU can be hampered by size and contour of the neck, acoustic shadowing from calcified plaques, and low echogenicity of soft plaques. Our study evaluated the reliability of ultrasound diagnosis of severe primary carotid stenosis and of severe restenosis after CEA in comparison with angiographic data. Numerous reports can be found in the literature about the accuracy of DU compared with angiography in patients with primary carotid stenosis.13, 14, 15, 16, 17, 18, 19, 20 However, similar data about restenosis after surgery are very limited. In most cases, restenoses during the first years after end-arterectomy result from neointimal proliferation without calcified plaques. Thus, it seems that the simpler morphology and the more homogeneous and smooth contour of restenoses compared to primary atherosclerotic plaques may allow a better Doppler characterization of the stenotic segment by DU and subsequently more precise measurements of the degree of stenosis.

Our results confirm the above-mentioned supposition. Firstly, ultrasonic evaluation of vessel wall morphology showed a predominance of calcified plaques in the primary stenosis group, in contrast to soft or dense, noncalcified plaques in the restenosis group. Secondly, the accuracy of DU was significantly higher in patients with restenoses. The other important statistical index is PPV, which actually reflects the prevalence of false-positive results. This is especially important for patients with carotid stenoses who may be referred for surgery /angioplasty in cases of false-positive examination. The obtained PPV was significantly higher in patients with restenosis. Thus, these patients can be referred to surgery/angioplasty without angiography. This recommendation can be attributed to early restenoses resulting from myo-intimal hyperplasia. In patients with Doppler parameters pointing to borderline moderate/severe primary carotid stenosis and in technically complicated cases, angiography in addition to sonog-raphy before surgery should be recommended.

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REFERENCES 

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PII: S0890-5096(06)61465-9

doi:10.1007/s10016-006-9049-4

Annals of Vascular Surgery
Volume 20, Issue 4 , Pages 478-481, July 2006

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