Journal of Vascular Surgery
Volume 49, Issue 1 , Pages 133-139, January 2009

Duplex criteria for determination of in-stent stenosis after angioplasty and stenting of the superficial femoral artery

Presented at the Society for Vascular Surgery Annual meeting San Diego, Calif, June 5-8, 2008.

Division of Vascular Surgery, Department of Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pa

Received 10 June 2008; accepted 5 September 2008.

Article Outline

Objective

Endovascular intervention is considered first-line therapy for most superficial femoral artery (SFA) occlusive disease. Duplex ultrasound (DU) criteria for SFA in-stent stenosis and correlation with angiographic data remain poorly defined. This study evaluated SFA-specific DU criteria for the assessment of SFA in-stent stenosis.

Methods

From May 2003 to May 2008, 330 limbs underwent SFA angioplasty and stenting and were monitored by serial DU imaging. Suspected stenotic lesions underwent angiography and intervention when appropriate. Data pairs of DU and angiographically estimated stenosis ≤30 days of each other were analyzed. Seventy-eight limbs met these criteria, and 59 underwent reintervention. In-stent peak systolic velocity (PSV), the ratio of the stented SFA velocity/proximal SFA velocity, changes in ankle-brachial indices (ABIs), and the percentage of angiographic stenosis were examined. Linear regression and receiver operator characteristic (ROC) curve analyses were used to compare angiographic stenosis with PSV and velocity ratios (Vrs) to establish optimal criteria for determining significant in-stent stenosis.

Results

Mean follow-up was 16.9 ± 8.3 months. Of the 59 limbs that underwent reintervention, 37 (63%) were symptomatic, and 22 (37%) underwent reintervention based on DU findings alone. Linear regression models of PSV and Vr vs degree of angiographic stenosis showed strong adjusted correlation coefficients (R2 = 0.60, P < .001 and R2 = 0.55, P < 0.001, respectively). ROC curve analysis showed that to detect a ≥50% in-stent stenosis, a PSV ≥190 had 88% sensitivity, 95% specificity, a 98% positive predictive value (PPV), and a 72% negative predictive value (NPV); for Vr, a ratio of >1.50 had 93% sensitivity, 89% specificity, a 96% PPV, and a 81% NPV. To detect ≥80% in-stent stenosis, a PSV ≥275 had 97% sensitivity, 68% specificity, a 67% PPV, and a 97% NPV; a Vr ratio ≥3.50 had 74% sensitivity, 94% specificity, a 77% PPV, and a 88% NPV. Combining a PSV ≥275 and a Vr ≥3.50 to determine ≥80% in-stent stenosis had 74% sensitivity, 94% specificity, a 88% PPV, and a 85% NPV; odds ratio was 42.17 (95% confidence interval, 10.20-174.36, P < .001) to predict ≥80% in-stent stenosis. A significant drop in ABI (>0.15) correlated with a >62% in-stent stenosis, although the adjusted correlation coefficients was low (R2 = 0.31, P = .02).

Conclusion

PSV and Vr appear to have a significant role in predicting in-stent stenosis. To determine ≥80% stenosis, combining PSV ≥275 cm/s and Vr ≥3.50 is highly specific and predictive.

 

During the last decade, a paradigm shift has occurred in the treatment of superficial femoral artery (SFA) occlusive disease. Numerous reports have been published about the early technical and midterm clinical success of endoluminal therapies (particularly angioplasty and stenting) in the treatment of atherosclerotic SFA lesions.1, 2, 3, 4, 5, 6, 7 The publication of these data has culminated in the recommendation by the TransAtlantic InterSociety Consensus (TASC) II committee of angioplasty or stenting, or both, as first-line therapy in the treatment of most femoropopliteal occlusive lesions.8

The use of nitinol self-expanding stents has been associated with a reduction of periprocedural treatment failure and an improvement in short-term primary patency.3, 5 From our own experience, we have reported an 87% assisted primary-patency rate and a 94% secondary-patency rate at 2 years.7 Despite these promising results, the most common recognized mode of failure has been the development of in-stent stenosis in up to 40% of patients at 1 year.2, 4, 5, 9

Widespread use of these techniques mandates the validation of noninvasive testing modalities designed to assist in the maintenance of clinical benefit. Criteria from duplex ultrasound (DU) imaging and other noninvasive methods for the diagnosis of in-stent stenosis have been generalized from established data concerning the detection of de novo lesions in previously untreated femoropopliteal vessels or in the detection of vein bypass graft stenosis.10, 11, 12, 13 Stent placement within an arterial segment results in a change in vessel compliance that may alter velocities as measured by DU imaging.14 This has specifically been shown in the carotid circulation where stent placement has been noted to alter the velocity thresholds for the detection of significant internal carotid artery re-stenosis.15

Currently, no data exist that correlate DU and angiographic data for the purpose of objectively defining SFA target vessel in-stent stenosis. The purpose of this study was to develop SFA-specific DU criteria with predictive power to serve as a benchmark for future investigations that will evaluate the success of such procedures and to assist in clinical management.

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Methods 

All patients undergoing endovascular interventions for femoropopliteal occlusive disease between May 2003 and May 2008 were retrospectively identified from prospectively maintained physician databases. During this time, 330 limbs underwent femoropopliteal angioplasty and stenting. Patients were seen in follow-up at 1, 3, and 6 months after their procedure. After this initial 6-month period, patients were then evaluated at 6-month intervals indefinitely. Follow-up consisted of an office visit with the treating physician and noninvasive studies, including ankle-brachial indices (ABIs), pulse volume recordings, and complete arterial DU examinations of the treated limb. Patients who had recurrent symptoms, evidence of recurrent or de novo (proximal or distal) stenoses on DU imaging, or significant ABI decreases (>0.15) underwent angiography and intervention when appropriate. Data pairs of DU and angiographically measured stenoses ≤30 days of each other were analyzed.

Ultrasound measurements 

All DU imaging was performed by registered vascular technologists at one of two laboratories approved by the Intersocietal Commission on Accreditation of Vascular Laboratories (ICAVL) using a LOGIQ 9 or a LOGIQ e (General Electric Healthcare, Piscataway, NJ) system. A 7-mHz linear probe was used at a 60° insonation angle, or when not possible, angle correction was used. The common femoral artery, the femoral bifurcation, and the length of the superficial femoral artery, as well as the popliteal artery were imaged. In particular, peak systolic velocities (PSV) were measured in a disease-free arterial segment 3 cm above the stented area and within the stent itself (Fig 1, A). If the SFA was significantly diseased at this level, the next most proximal area of normal vessel was used to determine the proximal velocity. The highest PSV within the stent was recorded. The velocity ratio (Vr) was calculated from the PSV within the stent to the PSV within the diseased free segment of proximal SFA.

  • View full-size image.
  • Fig 1. 

    A, Duplex ultrasound results demonstrate elevated velocity of 295 cm/s in the middle portion of a superficial femoral artery stent. B, Arteriogram demonstrates a superficial femoral artery midstent 70% stenosis.

Angiographic measurement 

Angiograms were obtained in anteroposterior and oblique views at the time of the initial and secondary or tertiary imaging. The magnified view of digitally archived images demonstrating the greatest degree of stenosis was used to determine the percentage of in-stent stenosis (Fig 1, B). The percentage of stenosis was calculated as [(stent diameter –narrowest in-stent lumen)/stent diameter × 100]. No distinction was made regarding the location of the stenoses with the stent. If the entire SFA was stented, then the control segment that was evaluated and measured against the in-stent stenosis was within a widely patent segment of the more proximal stent. Angiograms were reviewed independently from the DU findings.

Statistical analysis 

Linear regression analyses were performed and are presented as scatter plots, with the correlation coefficient (R2) adjusted for the number of samples. Receiver operator characteristic (ROC) curves were used to compare angiographic stenosis with PSV and Vr to establish optimal criteria for determining ≥50% and ≥80% stenosis. Threshold points were determined for each velocity parameter, and the C statistic was calculated. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for a range of thresholds. Combinations were also examined to determine if this improved diagnostic abilities. All advanced statistical analyses were performed by an independent statistician.

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Results 

Among the 78 limbs that met the criteria of having DU images and angiography ≤30 days of each other were 59 (76%) that underwent reintervention and 19 that were imaged angiographically at the time of an intervention on the contralateral limb or at a distinct anatomic location on the ipsilateral limb. Of the 59 limbs that underwent reintervention, 37 (63%) were symptomatic, and 22 (37%) underwent reintervention solely on the basis of DU criteria for a high-grade lesion in a native vessel (PSV >300 or Vr >3.5).10, 11, 16 The immediate technical success (<20% residual stenosis) for these reinterventions was 100%. Mean follow-up for this cohort was 16.9 ± 8.3 months.

Distribution of velocity measurements 

A linear regression model of PSV vs degree of angiographic stenosis showed a strong adjusted correlation coefficient (R2 = 0.60, P < .001; Fig 2, A). In addition, a linear regression model of Vr vs degree of angiographic stenosis showed a strong adjusted correlation coefficient (R2 = 0.55, P < .001; Fig 2, B). A linear regression model of decrease in ABI vs degree of angiographic stenosis showed a moderate adjusted correlation coefficient (R2 = 0.31, P = .02; Fig 2, C).

  • View full-size image.
  • Fig 2. 

    Scatter plots of the (A) peak systolic velocities (PSV), (B) in-stent PSV to proximal superficial femoral artery (SFA) PSV ratio, and (C) decrease in ankle-brachial index (ABI) correlate with angiographic stenosis in stented SFAs.

Thresholds to detect 50% and 80% in-stent stenosis 

Multiple potential thresholds for PSV and Vr were analyzed for sensitivity, specificity, PPV, and NPV to determine the optimal criteria for a ≥50% stenosis and a ≥80% stenosis. To distinguish <50% stenosis from ≥50% stenosis, the cut-point on the PSV ROC curve was 189 cm/s (Fig 3, A). This value corresponded with a sensitivity of 95%, a specificity of 92%, a PPV of 98%, and a NPV of 75%. Rounding this value to 190 cm/s was associated with a sensitivity of 88%, a specificity of 95%, a PPV of 98%, and a NPV of 72%. To distinguish a <50% stenosis from ≥50% stenosis, the cut-point on the Vr ROC curve was 1.55 (Fig 3. B). This value corresponded with a sensitivity of 93%, a specificity of 85%, a PPV of 98%, and a NPV of 82%. Rounding this value to 1.50 was associated with a sensitivity of 93%, a specificity of 89%, a PPV of 96%, and a NPV of 81%. Additional nearby values of both PSV and ratios were subsequently examined for sensitivity, specificity, PPV, and NPV (Table I).

  • View full-size image.
  • Fig 3. 

    Receiver operator characteristic (ROC) curves differentiate between ≥50% and <50% stenosis in stented arteries by (A) peak systolic velocity (PSV) and (B) velocity ratio. Differentiation between ≥80% and <80% stenosis in stented arteries is shown by (C) PSV and (D) velocity ratio.

Table I. Value of duplex ultrasound measurements for the identification of ≥50% stenosis in the stented superficial femoral artery
CriterionSensitivity, %Specificity, %PPV, %NPV, %
PSV
≥17590799371
≥18090799371
≥18995929875
≥19088959872
≥20085959867
Vr
≥1.251006791100
≥1.5093899681
≥1.5593859882
≥1.7585959867

NPV, Negative predictive value; PPV, positive predictive value; PSV, peak systolic velocity; Vr, velocity ratio.

Combining a PSV ≥190 and a Vr ≥1.50 to determine a ≥50% stenosis was associated with a sensitivity of 85%, a specificity of 95%, a PPV of 98%, and a NPV of 67%. In addition, the odds ratio (OR) for determining a ≥50% stenosis based on a PSV ≥190 and a Vr ≥1.50 was 99.99 (95% confidence interval [CI], 11.82-845.55, P < .001).

To distinguish <80% stenosis from ≥80% stenosis, the cut-point on the PSV ROC curve was 265 cm/s (Fig 3, C). This value corresponded with a sensitivity of 97%, a specificity of 68%, a PPV of 67%, and a NPV of 97%. Rounding this value to 275 cm/s was associated with a sensitivity of 97%, a specificity of 68%, a PPV of 67%, and a NPV of 97%. To distinguish a <80% stenosis from ≥80% stenosis, the cut-point on the Vr ROC curve was 3.50 (Fig 3, D). This value corresponded to a sensitivity of 74%, a specificity of 94%, a PPV of 77%, and a NPV 88%. As with the 50% stenosis data, additional nearby values of both PSV and Vr were subsequently examined for sensitivity, specificity, PPV, and NPV (Table II).

Table II. Value of duplex ultrasound measurements for the identification of ≥80% stenosis in the stented superficial femoral artery
CriterionSensitivity, %Specificity, %PPV, %NPV, %
PSV
≥25097666597
≥26097686797
≥26597686797
≥27097686797
≥27597686797
≥30090686591
Vr
≥2.5090706792
≥3.0074817283
≥3.2574877984
≥3.5074947788
≥3.7568948494

NPV, Negative predictive value; PPV, positive predictive value; PSV, peak systolic velocity; Vr, velocity ratio.

Combining a PSV ≥275 and a Vr ≥3.50 to determine a ≥80% stenosis was associated with a sensitivity of 74%, a specificity of 94%, a PPV of 88%, and a NPV of 85%. The determination of a ≥80% stenosis by using PSV ≥275 and Vr ≥3.50 had an OR of 42.17 (95% CI, 10.20-174.36, P < .001).

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Discussion 

During the past decade, an increasing number of patients with femoropopliteal occlusive disease have been treated with endovascular techniques, specifically angioplasty and stenting. Although the long-term results of angioplasty and stenting of the femoropopliteal segment have not been fully elucidated, multiple studies have shown the safety of this technique and acceptable early and midterm patency rates.1, 2, 3, 4, 5, 6, 7, 9 Despite the large number of studies demonstrating the efficacy of endovascular techniques in the management of femoropopliteal occlusive disease, no noninvasive criteria have been established to evaluate recurrent disease and assist in the postprocedural management of these patients. In particular, little data have been published about DU evaluation of stented SFAs, and therefore, no adjudicated criteria are available on which to determine the presence of a significant in-stent stenosis.

DU imaging has been established as a sensitive, noninvasive means of detecting de novo lesions in the lower extremity arterial system as well as the primary means of surveillance of infrainguinal arterial bypass grafts.10, 11, 12, 13, 16, 17, 18, 19 For de novo lesions, DU imaging is the most accurate noninvasive study to evaluate the femoropopliteal segment,20, 21 which implies that the same modality should be accurate in imaging stented portions of the same segments. Vein bypass graft surveillance with DU is associated with higher assisted patency rates compared with the measurement of ABIs alone to avoid graft failure.22, 23

These criteria have been well established in the above scenarios, but the applicability of these criteria to the stented femoropopliteal segment has not been evaluated. The primary mode of stent failure has been in-stent stenosis, which occurs in up to 40% of treated lesions.1, 2, 3 Although patients with in-stent restenosis often do not present with recurrent symptoms, as evidenced by the current study, the implication exists that surveillance of these stented segments will result in higher assisted patency rates. Compared with the conventional criteria for vein bypass surveillance, our >80% stenosis data were similar to the PSV >300 and Vr >3.5, which has traditionally defined patients that are at the highest risk for graft thrombosis. Our laboratory uses a PSV >300 and a Vr >2.5 to determine a 50% stenosis in a native SFA. The application of these values to the stented vessels in our series would likely overestimate the degree of actual stenosis, a finding that has been previously demonstrated in the carotid circulation.24, 25

Scant data have been published on the subject of DU imaging after endovascular lower extremity arterial interventions, although there have been some reports of lower accuracy rates compared with DU evaluation of native arteries. Tato et al26 demonstrated that severe dissection is associated with a disproportionate rise in PSV compared with native lesions.26 In addition, Schlager et al27 demonstrated a lower degree of correlation between DU and angiography in stented SFAs compared with native SFA lesions, although both groups did demonstrate significant correlation.27 Our study found a strong correlation between both PSV and Vr vs angiographic stenosis, which formed the basis of our subsequent data analysis.

Multiple prospective randomized studies have been conducted to evaluate the efficacy and durability of stents in the SFA.2, 3, 5, 9 These trials by design included primary restenosis (50% stenosis) as an end point for treatment failure. This degree of stenosis was determined by DU criteria that had been established for vein bypass graft surveillance. The goal of our study was to evaluate criteria to determine both 50% and an 80% in-stent stenoses. Our data showed that the PSV criteria that we have determined for a 50% in-stent stenosis are more specific but less sensitive than the criteria for an 80% in-stent stenosis. Conversely, the Vr criteria for a 50% in-stent stenosis are more sensitive but less specific than the criteria for an 80% in-stent stenosis.

By combining PSV and Vr data, however, we have developed criteria that are very specific and predictive for both 50% and 80% in-stent stenoses within the SFA. Thus, the PSV and the Vr should be used together to determine the degree of stenosis. Although these criteria are not markedly different from conventional criteria for native vessels and vein graft bypasses, the Vr does appear to be higher for higher-grade lesions (ie, ≥80%) than previously reported in native vessels or vein graft bypasses. In addition, the set points that discriminate between 50% and 80% stenoses are very distinct. Thus, these criteria should help guide physicians in determining optimal clinical management; that is, which patients will benefit from angiography and possible reintervention, even if asymptomatic.

Our data suggest that a significant decrease in ABI (>0.15) may not be present until a >60% stenosis exists. Patients in our cohort with recurrent symptoms had a mean PSV of 360 ± 120 cm/s and a mean Vr of 3.60 ± 1.41. These data indicate that patients who are asymptomatic and have minimal changes in ABIs may harbor significant high-grade stenoses that can be detected on routine DU imaging and successfully treated before occlusion. We believe that early reintervention may decrease the need for intervention on complete occlusions, which is associated with a lower technical success and an increased risk for distal embolization when mechanical thrombectomy techniques are used.28, 29 In particular, medically fit patients who meet the outlined DU criteria for a ≥80% in-stent stenosis should undergo angiography to further evaluate and possibly treat these lesions.

Although to our knowledge this is the largest reported series of DU data after SFA angioplasty and stenting, this study is limited by sample size and a number of additional factors. In particular, these data were collected from a prospectively maintained database, but the review was done in a retrospective fashion.

All DU imaging for this study was performed by registered vascular technologists at two laboratories approved by the ICAVL. Despite this, the technique remains operator- and patient-dependent. In select patients, accurately imaging the entire length of the femoropopliteal segment may prove difficult secondary to body habitus, prior operations, or dense arterial calcifications.

A number of different stents were used during the period reviewed, and the different stent configurations may have had some effect on the applicability of the DU criteria that we have outlined, as has been seen in the stented carotid artery.25 In addition, given the retrospective nature in which imaging studies were reviewed and the diffuse nature of some of these stenotic lesions, it is possible that the area of highest measured PSV did not correlate exactly with the area of greatest angiographic stenosis. This study made no distinction between in-stent vs marginal stenoses, which may affect these criteria. Despite these limitations these DU criteria are sensitive, specific, and accurate in the identification of significant restenoses either within the stent itself or at its proximal or distal margin.

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Conclusion 

In-stent stenosis after SFA angioplasty and stenting can be predicted by both PSV and Vr data as measured by DU imaging. To determine a ≥80% in-stent stenosis, combining a PSV ≥275 and a Vr ≥3.50 is highly specific and predictive. These criteria should help to guide future studies in evaluating the efficacy and durability of stents in the treatment of femoropopliteal occlusive disease and assist in the determination of which patients should undergo angiography to optimize assisted patency rates. This may ultimately lead to improved long-term clinical success and patient satisfaction.

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Author contributions 


Conception and design: DB, RR, LM

Analysis and interpretation: DB, RR, MM, RC, LR

Data collection: DB, JK, LM

Writing the article: DB, RR, LM

Critical revision of the article: DB, RR, JK, MM, RC, LM

Final approval of the article: DB, RR, JK, MM, RC, LM

Statistical analysis: DB, LM

Obtained funding: Not applicable

Overall responsibility: LM

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We would like to thank Faith Selzer, PhD, Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh Medical Center, for her assistance with statistical analysis.

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References 

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 Competition of interest: none.

PII: S0741-5214(08)01629-7

doi:10.1016/j.jvs.2008.09.046

Journal of Vascular Surgery
Volume 49, Issue 1 , Pages 133-139, January 2009

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