Proposed duplex velocity criteria for carotid restenosis following carotid endarterectomy with patch closure

Article Outline

• Abstract
• Patients and methods
  • Statistical analysis
• Results
  • Peak systolic velocities (PSV)
  • End diastolic velocities (EDV)
  • PSV of the ICA/CCA ratio
  • ROC curve analysis for sensitivity and specificity
• Discussion
• Conclusion
• Author contributions
• Tables, online only. 
• References
• Copyright

Background

Duplex ultrasound velocity criteria have been used to evaluate the severity of carotid stenosis, however, these standard velocities may not be applicable to carotid restenosis after carotid endarterectomy (CEA) with patch angioplasty. The purpose of this study is to determine if patch angioplasty closure alters velocities just distal to CEA and to define the optimal velocities for detecting ≥30%, ≥50%, and ≥70% restenosis.

Methods

This study includes 200 CEAs randomized into 100 with polytetrafluoroethylene (PTFE) ACUSEAL patch and 100 with Hemashield Finesse patch. All patients underwent immediate postoperative duplex ultrasounds, which were repeated at 1 month and every 6 months thereafter. Patients with a peak systolic velocity (PSV) of the internal carotid artery ([ICA], just distal to the patch) of ≥130 c/s underwent computed tomography angiogram (CTA). PSVs, end diastolic velocities (EDV), and internal carotid artery/common carotid artery (ICA/CCA) ratios were correlated to completion arteriograms/CTAs. Receiver operator characteristic curves analyses were used to determine optimal velocity criteria in detecting ≥30%, ≥50%, and ≥70% restenosis.

Results

One hundred ninety-five pairs of imagings (duplex ultrasound vs CTA/angiogram) were available for analysis. When standard velocity criteria for nonoperated arteries were applied, 37% and 10% of patients were believed to have ≥50% to <70% and ≥70% to 99% restenosis vs 11.3% and 11.3% on CTA/angiography, respectively (P < .001). The mean PSV for ≥30%, ≥50%, and ≥70% restenosis were 172, 249, and 389 c/s, respectively (P < .001). An ICA PSV of ≥155c/s was optimal for ≥30% restenosis with sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy (OA) of 98%, 98%, 98%, 98%, and 98%, respectively. A PSV of ≥213 c/s was optimal for ≥50% restenosis with sensitivity, specificity, PPV, NPV, and OA of 99%, 100%, 100%, 98%, and 99%, respectively. An ICA PSV of 274 c/s was optimal for ≥70% restenosis with sensitivity, specificity, PPV, NPV, and OA of 99%, 91%, 99%, 91%, and 98%, respectively. ROC analysis showed that the PSVs were significantly better than EDVs and ICA/CCA ratios in detecting ≥30% and ≥50% restenosis.

Conclusions

The mean PSVs of a normal ICA distal to CEA patching were higher than normal nonoperated ICAs, therefore, standard duplex velocities criteria should be revised after CEA with patch closure.

Carotid duplex ultrasound has become the method of choice for the initial noninvasive evaluation of extracranial carotid artery disease. The degree of carotid stenosis is largely based on analysis of the peak systolic velocity (PSV), the end diastolic velocity (EDV), and/or the internal carotid artery/common carotid artery (ICA/CCA) PSV ratio.¹, ², ³, ⁴, ⁵ Many laboratories, including our own, have proposed several duplex velocity criteria for threshold stenoses to be compatible with the threshold stenoses utilized in the carotid trials investigating symptomatic and asymptomatic carotid artery stenosis, North American Symptomatic Carotid Endarterectomy Trial (NASCET)⁶ and Asymptomatic Carotid Atherosclerosis Study (ACAS).¹, ², ³, ⁴, ⁵, ⁶, ⁷

Since these carotid duplex velocities have been tested on native (nonoperated) carotid arteries, these standard velocities may not be applicable to carotid restenosis after carotid endarterectomy (CEA) with patch angioplasty. Elevated velocities have been noted in the internal carotid artery distal to patching because of the relative narrowing of the normal internal carotid artery distal to the patch.⁸ Therefore, the purpose of this study was to determine if patch angioplasty closure alters velocities just distal to the CEA and to define optimal velocities for detecting ≥30%, ≥50%, and ≥70% restenosis. To our knowledge, this is the first study to analyze duplex velocity criteria of the internal carotid artery just distal to carotid patching.

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Patients and methods 

This study includes 200 CEAs (done between August 20, 2003 and November 2, 2005) that were randomized into 100 with polytetrafluoroethylene ACUSEAL (W. L. Gore, Flagstaff, Ariz) patches and 100 with Hemashield Finesse patches. This study was approved by the Institutional Review Board at our institution. The results of the comparison of these two patch materials were presented previously.⁹ Both patches were 8 mm wide, manufacturer-designed, and with a similar tapering at the end towards the ICA, ie, there was not any discrepancy in the size of both patches, and the length of both patches were comparable.

The indications for CEA included: symptomatic ≥50% carotid artery stenosis and asymptomatic ≥70% carotid artery stenosis. All patients underwent preoperative duplex ultrasound using HDI 5000 Phillips systems (Phillips, Bellevue, Wash) in our Intersocietal Commission of Accreditation of Vascular Laboratories (ICAVL)-accredited vascular laboratory with or without magnetic resonance angiography/computed tomography angiography prior to CEA. All patients also underwent immediate postoperative duplex ultrasounds, which were repeated at 1 month, 6 months, and every 6 months thereafter.

The demographic and risk factors of all patients were tabulated, including smoking, hypertension, diabetes mellitus, hypercholesterolemia, and the presence of coronary artery disease.

All Doppler spectra were obtained using a Doppler sample volume of 1 to 1.5 mm and a Doppler angle of 60 degrees or less. The examination also included gray-scale B-mode and color imaging of the common carotid artery, carotid bifurcation, external carotid artery, proximal, middle, and distal portions of the ICA. The PSV and EDV of the internal and common carotid arteries, and the ICA/CCA PSV ratios were recorded. The highest PSVs and EDVs in the ICA just distal to the patch were used for analysis and comparison to other imaging modalities. Proximal common carotid endpoint restenoses and intra-patch restenoses were excluded from the analysis.

Patients with PSVs of the ICA (just distal to the patch) of ≥130 cm/s underwent carotid computed tomography angiography and/or conventional carotid arteriograms to verify the presence of restenosis. This number was selected from a previous study of a systemic review and meta-analysis of the sensitivity and specificity of color duplex ultrasound measurements and the estimation of ICA stenosis.¹⁰ The threshold of PSV of ≥130 cm/s in that study was associated with a sensitivity of 98% and a specificity of 88% in the identification of angiographic stenosis of ≥50%.¹⁰

Angiographic measurement of stenosis was calculated according to the North American Symptomatic Carotid Endarterectomy Trial,⁶ basically by comparing the narrowest segment of the carotid artery with the diameter of the distal normal ICA, where the wall becomes parallel.

An independent observer, who was blinded to the duplex ultrasound findings, was used for the interpretation of the computed tomographic (CT) angiography/carotid arteriography. It should be noted that we previously correlated conventional carotid arteriography and CTA findings in several patients with very good accuracy (Kappa = 0.81).¹¹

This study analyzes patients with concurrent duplex ultrasounds that were done within 24 hours of post completion carotid arteriograms, regardless of the PSV values, ie, patients with PSVs at completion of the procedure of <130 cm/s were included, and patients who had carotid duplex ultrasound and CT angiography and/or carotid arteriography at late follow-up, which were done within 30 days.

Our standard carotid duplex criteria for native carotid arteries, which we published previously,⁵ were: a PSV of the ICA of <120 cm/s was normal, a PSV of ≥120 to <140 cm/s was consistent with 30% to <50% stenosis, a PSV ≥140 cm/s was consistent with ≥50% stenosis, a PSV ≥150 cm/s with an EDV of ≥65 cm/s was consistent with ≥60% stenosis, and a PSV ≥150 cm/s and an EDV of ≥90 cm/s was consistent with ≥70% to 99% stenosis. The ultrasound consensus criteria for carotid stenosis were as follows: a PSV of the ICA of <125 cm/s was normal, a PSV of the ICA of 125 cm/s with <50% diameter reduction plaque were consistent with <50% stenosis, a PSV of >125 to 230 cm/s was consistent with 50% to <70% stenosis, and a PSV of >230 cm/s with an EDV of >100 cm/s was consistent with 70% to 99% stenosis.¹²

Statistical analysis 

The velocity data were expressed as a mean plus or minus standard deviation. Analysis of variance (ANOVA) test was used to compare the means of PSV, EDV, and velocity ratio to the stenosis. Comparison of the duplex ultrasound velocity data with the CTA/angiography was done using the Fisher exact method, Kappa, and weighted Kappa statistic. Receiver operator characteristic curves (ROC) were used to compare angiographic data with velocity measurements to determine the optimum velocity criteria for detecting ≥30%, ≥50%, and ≥70% to 99% restenosis. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy (OA) were determined for specific PSV and EDV values and the ICA/CCA PSV ratios.

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Results 

This study includes 195 CEA patients, who had duplex ultrasound and CTA/angiography that were available for analysis. The mean follow-up was 25 months (range of 0-49 months). The demographic/clinical characteristics of these patients have been published previously.⁹ When our standard velocity criteria (for nonoperated arteries – PSV of ≥140 c/s was optimal in detecting ≥50% stenosis)⁵ were applied, 37% and 10% of patients were classified to have ≥50% to <70% and ≥70% to 99% restenosis vs 11.3% and 11.3% on CTA/angiography, respectively (P < .001, Kappa = 0.4829, weighted Kappa = 0.6334).

Similarly, when the ultrasound consensus criteria were applied,¹² 38.7% were classified to have ≥50% to <70% restenosis, and 9.8% had ≥70% to 99% restenosis (P < .001, Kappa = 0.4847, and weighted Kappa = 0.6238 [Table I]).

Table I. Correlation of CTA/angiography restenosis vs standard and ultrasound consensus criteria

	Restenosis by standard duplex velocity criteria
	<30%		≥30%-50%		≥50%-70%		≥70%-99%
	N	%	N	%	N	%	N	%
CTA/angio restenosis
0-<30%	84	100.0%	9	100.0%	19	24.4%	0	0.0%
≥30%-<50%	0	0.0%	0	0.0%	39	50.0%	0	0.0%
≥50%-<70%	0	0.0%	0	0.0%	20	25.6%	2	8.3%
≥70%-99%	0	0.0%	0	0.0%	0	0.0%	22	91.7%
Kappa = 0.4829
Weighted Kappa = 0.6334

	Restenosis by ultrasound consensus criteria
	<30%		<50%		50%-70%		70%-99%
	N	%	N	%	N	%	N	%
CTA/angio restenosis
0-<30%	83	100.0%	8	88.9%	21	25.9%	0	0.0%
≥30%-<50%	0	0.0%	1	11.1%	38	46.9%	0	0.0%
≥50%-<70%	0	0.0%	0	0.0%	21	25.9%	1	4.5%
≥70%-99%	0	0.0%	0	0.0%	1	1.2%	21	95.5%
Kappa = 0.4847
Weighted Kappa = 0.6238

CTA, Computed tomography angiogram.

It should also be noted that only 43% of those with ≥50% restenosis based on standard or consensus ultrasound criteria had ≥50% restenosis based on CTA/angiogram (P < .001, Kappa = 0.413 and 0.4198, respectively).

The mean PSV for patients with ≥30% to <50%, ≥50% to <70%, and ≥70% to <99% restenoses, based on CTA/angiography, were 172, 249, and 389 cm/s, respectively (P < .0001). Similarly, Table II summarizes the mean EDVs and the ICA/CCA ratios for various degrees of restenoses.

Table II. Mean velocities and ratio and degree of restenosis

PSV, Peak systolic velocity; EDV, end diastolic velocity.

Peak systolic velocities (PSV) 

As noted in Table III, online only, an ICA PSV of ≥155 cm/s was optimal for detecting ≥30% restenosis with a sensitivity, specificity, PPV, NPV, and an OA of 98%, 98%, 98%, 98%, and 98%, respectively. An ICA PSV of ≥213 cm/s was optimal for detecting ≥50% restenosis with sensitivity, specificity, PPV, NPV, and OA of 99%, 100%, 100%, 98%, and 99%, respectively. An ICA PSV of 274 cm/s was optimal for detecting ≥70% restenosis with sensitivity, specificity, PPV, NPV, and OA of 99%, 91%, 99%, 91%, and 98%, respectively.

End diastolic velocities (EDV) 

Table IV, online only, summarizes the sensitivity, specificity, PPV, NPV, and OA for various end diastolic values. As noted in this table, an EDV value of 41, 60, and 80 cm/s were the optimal values for detecting ≥30%, ≥50%, and ≥70% restenoses.

PSV of the ICA/CCA ratio 

Table V, online only, summarizes the velocity ratio values for detecting ≥30%, ≥50%, and ≥70% restenosis. As noted, a ratio of 1.64, 2.25, and 3.35 were optimal for detecting ≥30%, ≥50%, and ≥70% restenosis, respectively.

Table VI summarizes the optimal values of PSVs, EDVs, and ICA/CCA PSV ratios in detecting ≥30%, ≥50%, and ≥70% restenoses.

Table VI. Cutoff of PSVs, EDVs, and ICA/CCA ratios

Cutoffs	PSV		EDV		Velocity ratio
	Cutoff	AUC (95% CI)	Cutoff	AUC (95% CI)	Cutoff	AUC (95% CI)
>30	155	99.8(99.5-100)	41	90.3(86.1-94.4)	1.64	84.0(78.3-89.6)
>50	213	100(99.5-100)	60	95.3(92.1-98.6)	2.25	84.3(77.1-91.5)
>70	274	99.2(98.1-100)	80	97.3(93.9-100)	3.35	88.6(80.3-96.8)

PSV, Peak systolic velocity; EDV, end diastolic velocity; ICA, internal carotid artery; CCA, common carotid artery; AUC, area under curve.

ROC curve analysis for sensitivity and specificity 

A ROC analysis showed that PSVs were significantly better than EDVs and ICA/CCA ratios in detecting ≥30% restenosis, as noted in Fig 1 (P < .0001). The area under the curve for PSVs was 1, vs 0.90 for EDVs, and 0.84 for velocity ratios. Similarly, Fig 2 shows that PSVs were statistically significantly better than EDVs or velocity ratios in detecting ≥50% restenosis (P value = .005 and P <.0001, respectively). The area under the curve for PSVs was 1, vs 0.95 for EDVs, and 0.84 for velocity ratios. Fig 3 shows the >70% restenosis ROC curves, where the area under the curve for PSVs was 0.99, 0.97 for EDVs, and 0.89 for velocity ratios. As noted in this figure, PSVs were statistically better than velocity ratios in detecting ≥70% restenosis (P value = .0117).

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• Fig 1. 

  Receiver operator curve analysis for ≥30% restenosis.

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• Fig 2. 

  Receiver operator curve analysis for ≥50% restenosis.

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• Fig 3. 

  Receiver operator curve analysis for ≥70% restenosis.

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Discussion 

Carotid duplex ultrasound has been utilized for the diagnosis of carotid artery disease for over two decades. The severity of carotid artery stenosis has been defined using specific threshold velocities, including PSVs, EDVs, and/or ICA/CCA PSV ratios.¹, ², ³, ⁴, ⁵, ¹² However, these standard duplex velocities may not be applicable to carotid restenosis after CEA with patch angioplasty. At the present time, duplex ultrasound velocities have not been analyzed in the ICA just distal to carotid artery patching. However, in a previously published study,⁸ elevated PSVs were noted in the ICA just distal to carotid artery patching, which was believed to be caused by the relative size discrepancy between the patched carotid artery and the native ICA.⁸ This present study was conducted after our observation of several patients who underwent CEA with patching where abnormally elevated PSVs (>130 cm/s) were noted distal to the patching, in spite of normal intraoperative duplex ultrasound examinations/arteriography. This is the first study to analyze velocities obtained from the ICA just distal to patching and to define the optimal velocity criteria for detecting ≥30% to <50%, ≥50% to <70%, and ≥70% to 99% restenosis after CEA with patching. In our present study, and when we initially applied, our ICAVL-accredited vascular laboratory duplex PSV cutoff of ≥140 cm/s (which was developed for native nonoperated carotid arteries to distinguish between <50% to >50% stenosis), 37% were felt to have ≥50% to <70% restenosis vs 11.3% based on CTA/angiography (P < .001). Similar findings were noted, even if we applied the ultrasound consensus criteria, which were published previously.¹²

Our present study suggests that different carotid duplex ultrasound velocities should be used to detect restenosis after CEA with patching. As noted, an ICA PSV of ≥155 cm/s was optimal in detecting ≥30% restenosis with a sensitivity, specificity, PPV, NPV, and OA of 98%, 98%, 98%, 98%, and 98%, respectively. Similarly, a PSV ≥213 cm/s was optimal in detecting ≥50% restenosis with a sensitivity, specificity, PPV, NPV, and OA of 99%, 100%, 100%, 98%, and 99%, respectively. An ICA PSV of 274 cm/s was also optimal for detecting ≥70% restenosis with a sensitivity, specificity, PPV, NPV, and OA of 99%, 91%, 99%, 91%, and 98%, respectively. A ROC analysis also showed that PSVs were significantly better than EDVs and ICA/CCA PSV ratios in detecting ≥30% and ≥50% restenosis.

Hirschl et al⁸ conducted a study to show if patch angioplasty or direct closure of the ICA after CEA resulted in any hemodynamic or pathologic differences. This study included 18 patients who underwent carotid patching and 20 patients who underwent direct closure, with an average postoperative period of 26 months. All patients were examined using duplex ultrasound scanning. They concluded that patients with carotid patching with broadened lumen at the bulb resulted in statistically elevated turbulent flow disturbances with increased flow velocity in the ICA just distal to the patch; however, quantitative flow volume measurement did not reveal any differences between the two groups. Pantaloon effects of the endarterectomized artery, at the bifurcation and origin of the ICA, will lead to measurable increased turbulent flow disturbances. Functional stenosis is believed to be created distal to the CEA site, ie, wider at the patch site and narrower at the native artery distal to the patch, which will result in elevated PSVs. We believe this may explain the increased abnormal velocities noted in the ICA distal to patching, causing the false impression of stenoses. Obtaining an immediate postoperative duplex ultrasound after CEA with patching is critical and can be used as a baseline for further comparison.

This present study has a few limitations, including the use of CT angiography instead of conventional arteriography in some of our patients; however, several studies have compared the accuracy of CTA angiography with conventional arteriography and have found them to be comparable.¹³, ¹⁴ Similar findings were also noted previously by us, with close agreement between the two modalities (Kappa = 0.81).¹¹ Another limitation of this study is the fact that it is a retrospective analysis of prospectively collected data of a previously published randomized trial comparing two patch materials.⁹ Therefore, the proposed diagnostic criteria will need to be validated in a prospective trial. Other limitations include the use of PSV as a threshold for the CTA/angiogram, which may bias the findings towards the PSV as being the most accurate predictor for restenosis, in comparison to using the ICA/CCA ratio or the EDVs. However, we previously reported a better overall accuracy for the diagnosis of carotid stenosis using optimal PSVs.⁵

It is important to note that the data obtained by individual vascular labs will vary because of differences in equipment, abilities and consistencies of vascular technicians, and reader interpretation,⁵, ¹⁵ therefore, each vascular laboratory much adapt a method that employs the equipment they use and validates their method when using proposed new duplex criteria.

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Conclusion 

In conclusion, the mean PSVs of a normal and abnormal ICA (distal to CEA patching) were higher than normal and abnormal nonoperated ICAs, therefore, standard duplex velocity criteria should be revised after CEA using patching.

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Author contributions 

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Tables, online only 

Table III, online only. PSVs: Sensitivity and specificity for ≥30%, ≥50%, and ≥70% restenosis

PSV, Peak systolic velocity; PPV, positive predictive value; NPV, negative predictive value.

Table IV, online only. EDVs: Sensitivity and specificity for ≥30%, ≥50%, and ≥70% restenosis

EDV, End diastolic velocity; PPV, positive predictive value; NPV, negative predictive value.

Table V, online only. ICA/CCA ratios: Sensitivity and specificity for ≥30%, ≥50%, and ≥70% restenosis

ICA, Internal carotid artery; CCA, common carotid artery; PPV, positive predictive value; NPV, negative predictive value.

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