Journal of Vascular Surgery
Volume 37, Issue 3 , Pages 495-500, March 2003

Is early postoperative duplex scan surveillance of leg bypass grafts clinically important?☆☆☆★

Presented at the Fifty-sixth Annual Meeting of The Society for Vascular Surgery, Boston, Mass, Jun 9-12, 2002.

Division of Vascular Surgery, University of Arizona Health Sciences Center. Tucson, Ariz

Received 18 June 2002; accepted 15 October 2002.

Article Outline

Abstract 

Purpose: The typical leg bypass surveillance program begins with a duplex scan evaluation of the vein graft 3 months after surgery; studies are repeated every 3 months during the first year of follow-up and are fully reimbursed by our Medicare carrier. Some authors have recommended early (before discharge or first postoperative visit) duplex scanning to identify high-risk grafts. However, the natural history of velocity disturbances detected with early scans is unclear, and furthermore, such studies are not reimbursed by Medicare. Methods: We reviewed all infrainguinal vein bypass grafts prospectively entered into a surveillance protocol that included an early (<6 weeks) duplex scan study. Routine completion angiography was performed at the initial operation in all patients. Early duplex scan results, the need for graft revision, and detailed follow-up of these bypass grafts were analyzed. Results: Early duplex scans were performed in 224 bypass grafts placed in 204 patients. Early scans were abnormal (peak systolic velocity [PSV], >200 cm/s) in 58 grafts (26%). Six grafts of the 58 (10.3%; 2.7%) with an early abnormal duplex scan and unrepaired defects occluded during the follow-up period. Thirty grafts were revised on the basis of the initial early scan; 23 of these revisions were performed for critical or rapidly progressive lesions in the first 3 postoperative months. Seven lesions progressed more slowly and were repaired at a mean of 8 months after surgery. Interestingly, 22 flow abnormalities (37%) resolved or stabilized despite a PSV of more than 300 cm/s in six cases (27%). Clear duplex scan evidence of regression or progression of these early flow abnormalities occurred within 3 months in 51/58 cases (88%). A total of 68 grafts (30%) were revised during the entire study period; 30 of these (44%) were on the basis of the early abnormal scan. Conclusion: Despite normal completion arteriography, early graft velocity abnormalities are strikingly common and were detected in 26% of the 224 infrainguinal vein grafts in this series. These lesions were clinically important because 52% necessitated revision. Surprisingly, however, 38% of these early flow disturbances resolved, despite a PSV of more than 300 cm/s in 27% of cases. Early duplex scan surveillance singularly detects a clinically significant subgroup of grafts that need revision. The possible origin of these early lesions deserves further inquiry, but on the basis of its clinical yield, we recommend that early duplex scan surveillance of infrainguinal bypass grafts should be routine and should be considered for Medicare reimbursement. (J Vasc Surg 2003;37:495-500.)

 

Infrainguinal revascularization with autologous vein conduit is the preferred surgical method for treatment of critical lower extremity ischemia. Long-term success of such autologous vein bypasses can be significantly enhanced with the implementation of a routine postoperative clinical and duplex scan-directed graft surveillance protocol.1, 2, 3, 4, 5 Such protocols allow one to detect lesions within the graft that, unchecked, would subsequently lead to graft failure. The natural history of high-grade vein graft stenoses detected with surveillance is graft thrombosis.1, 3, 5, 6, 7, 8 In fact, intrinsic vein graft stenosis is the leading cause of vein graft failure in the first 2 postoperative years.9, 10, 11 Proposed inciting mechanisms leading to the development of such lesions include minor technical error, clamp injury, preexisting intrinsic graft abnormality, myointimal hyperplasia, incompletely divided valve leaflets in nonreversed grafts, and an abnormal response to arterialization. Vein graft surveillance protocols accurately detect these intrinsic graft lesions and those developing in the adjacent inflow and outflow arteries. Detection and timely repair of critical lesions help to maintain graft patency.

Most reports, with slightly different duplex scan criteria for identification of graft-threatening lesions, cite a 20% to 30% incidence rate of revision, with most revisions occurring within 24 months of the index operation.3, 9, 10, 12, 13, 14, 15 Multiple investigators have provided critical information characterizing the natural history of infrainguinal vein bypass graft lesions to accurately correlate the findings of a duplex scan surveillance protocol and determine when intervention is necessary to preserve graft patency.1, 2, 3, 4, 5, 9, 10, 16 Most duplex scan surveillance protocols are not initiated until 3 months after graft implantation, and Medicare does not reimburse duplex scan surveillance studies performed before this time period. However, we and others have noted a surprisingly high incidence rate of vein graft lesions detected on early (<6 weeks) graft scans and concluded that such early scans may be worthwhile.7, 17, 18, 19

Over the past 4 years, we have routinely initiated duplex scan graft surveillance within the first 6 weeks, either before patient discharge from the hospital or at the time of the patient's first postoperative clinic visit. The purposes of this report were as follows: 1, to determine the incidence of early postoperative duplex scan-detected graft flow disturbances; 2, to determine the natural history of such early-appearing flow disturbances; 3, to develop and modify clinical criteria for intervention when such lesions are detected; and 4, to determine whether the initiation of a duplex scan surveillance protocol before the third postoperative month is clinically beneficial.

Current criteria for intervention with duplex scan measurements of peak systolic velocity (PSV) and velocity ratio (Vr) have been developed primarily on the basis of scans obtained 3 months or more after graft implantation. Several investigators have suggested that the natural history of early-appearing lesions may be more “malignant” (ie, rapidly progressive).7, 17 It is unclear whether standard criteria for intervention apply to early-appearing graft lesions.20, 21 In the current era of cost containment characterized by increasing economic pressures to define indications for clinical and laboratory studies and subsequent interventions on the basis of outcome data, a detailed analysis of the clinical utility of early postoperative duplex scanning would seem prudent and informative.22 A careful review of our experience with early graft surveillance forms the basis for this report.

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Methods 

All patients who underwent autologous infrainguinal bypass grafting between 1988 and 2001 at the University of Arizona Health Sciences Center were entered into a surveillance protocol consisting of routine history and physical examination, detailed duplex scan interrogation of the bypass graft, and ankle-brachial index measurement (ABI), or toe pressure measurement when the ABI was suprasystolic. Patients were studied every 3 months for the first year followed by twice yearly examinations for 2 years and annual surveillance thereafter. Over the past 4 years, most patients also received an early (<6 weeks) duplex scan surveillance examination. The analysis presented in this report was confined to the patients who underwent an early duplex scan.

Duplex scans were performed with an HDI 3000 machine or an Ultramark 8 or 9 machine (Advanced Technology Laboratories, Bothell, Wash) with a 5-MHz or 7.5-MHz transducer. Grafts were interrogated with the angle of insonation as close to 60 degrees as possible, beginning within the proximal target artery and continuing through the distal target artery. An abnormal duplex scan examination was defined by the findings of a focal PSV increase of more than 200 cm/s, a Vr exceeding 2.0, or global graft flow velocities of less than 45 cm/s. All surveillance scans were performed by experienced technologists and interpreted by a board-certified vascular surgeon in an Intersocietal Commission for the Accreditation of Vascular Laboratories—accredited vascular laboratory.

Flow disturbances on the basis of measurements of PSV and Vr obtained from each postoperative duplex scan along with analysis of graft waveforms (such as resistance pattern and global flow velocity) and Doppler-derived ankle or toe pressure were used to place the patient in a risk-stratified group (Table).20

Risk stratification criteria for infrainguinal bypass grafts
CategoryHigh-velocity criteria Low-velocity criteria Δ ABI
I. Highest riskPSV > 300 cm/s or Vr > 3.5 or EDV > 100 cm/sandPSV < 45 cm/sor>0.15
II. High riskPSV > 300 cm/s or Vr > 3.5andPSV > 45 cm/sand<0.15
III. Intermediate risk300 cm/s > PSV > 200 cm/s or Vr > 2.0andPSV > 45 cm/sand<0.15
IV. Low riskPSV < 200 cm/s or Vr < 2.0andPSV > 45 cm/sand<0.15

EDV, End diastolic velocity.

These previously validated criteria then were prospectively applied to routine early scanning of grafts.16 Normal grafts with unchanged ABI or toe pressures were followed with the usual surveillance schedule as previously stated. Abnormal but low-risk examinations characterized by the findings of a PSV less than 300 cm/s and unchanged ABI or toe pressure led to the recommendation that another follow-up scan be performed within 6 weeks. Grafts with duplex scan-detected velocity disturbances more than 300 cm/s and normal distal velocities were recommended to undergo a repeat duplex scan examination within 4 weeks or arteriography and revision at the discretion of the attending vascular surgeon. High-risk examinations, indicated by the findings of a focal PSV exceeding 300 cm/s with decreased distal graft flow velocities less than 45 cm/s or decreased ABI more than 0.15, were followed by a recommendation for arteriography and revision if the lesion was confirmed.

Patient demographics, type of operation, conduit, and follow-up information were recorded and entered into a database (Microsoft Access and Excel, Redmond, Wash). Graft patency was determined with life-table analysis. Differences in patency were determined with two-tailed Student t test.

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Results 

Three hundred and eighteen bypasses were performed during the study period, of which early duplex scans (<6 weeks after surgery) were obtained on 224 autogenous infrainguinal bypass grafts performed in 204 patients, and these patients comprise the study group. The series consisted of 114 men (56%) and 90 women (44%) with a mean age of 68.5 years (range, 38 to 92 years). Cardiovascular risk factors in the study group included: hypertension (92%), diabetes mellitus (53%), smoking (59%), hyperlipidemia (25%), and hemodialysis-dependent renal failure (12%). The indications for revascularization were ischemic tissue loss (47%), ischemic rest pain (32%), disabling claudication (18%), and popliteal aneurysm (3%).

Proximal inflow sites for bypass grafts consisted of distal external iliac artery (0.5%), common femoral artery (54.7%), profunda femoris artery (4.7%), superficial femoral artery (25%), above-knee popliteal artery (3.5%), and below-knee popliteal artery (11.6%). Distal target outflow arteries for these grafts included: above-knee popliteal artery (16%), below-knee popliteal artery (25%), tibioperoneal trunk (3%), tibial or peroneal artery (45%), and pedal artery (11%). Reversed vein graft was used in 78% of cases, in situ saphenous vein technique in 14%, and nonreversed technique in 8%.

The most common graft conduit was greater saphenous vein (86%). Alternative vein, including spliced vein, lesser saphenous vein, and arm vein, was used in 14%. Completion arteriography, consisting of single-shot radiographic angiography or multiimage single plane c-arm fluoroscopy, was performed at the conclusion of all procedures.

With the previously defined criteria for abnormal scans (PSV > 200 cm/s or Vr > 2), 26% of vein grafts (58 of 224) were found to have an abnormal initial duplex scan examination. These lesions were characterized by a mean PSV of 309 cm/s (range, 201 to 642 cm/s). Risk stratification of these lesions is summarized in Fig 1.

The location of the duplex scan-detected velocity disturbance is summarized in Fig 2. After interpretation of the duplex scan examination and review by the patient's attending vascular surgeon, close follow-up or arteriography and operative repair were recommended. If the graft did not undergo immediate diagnostic angiography and operative revision, a repeat duplex scan examination was performed within 4 to 6 weeks. If follow-up documented progression of the graft flow velocity disturbance or a decrease in ABI or global distal graft flow velocity dropped to less than 45 cm/s, arteriography and revision were peformed. Otherwise, close follow-up with repeat examination was continued, generally every 6 weeks, until either resolution or progression to repair threshold was documented.

Nine grafts (4.5%) occluded during the first 3 months despite early surveillance. Initial duplex scans were normal in three and abnormal in six of these grafts. Among the latter six patients, two refused further surgery despite a focal PSV more than 300 cm/s and one had no focal abnormal velocity increases but had low monophasic flow throughout the graft, and in the remaining three (PSV range, 280 to 316 cm/s), the attending surgeon had elected to closely follow the abnormality in question.

During the follow-up period, 22 of 58 graft flow abnormalities (38%) detected on early duplex scan examination were observed to completely resolve. The mean PSV in this patient subgroup was 292 cm/s (range, 203 to 450 cm/s), with a mean Vr of 3.29 (range, 1.8 to 6.2). Surprisingly, six grafts (27%) in which the initial graft velocity disturbance was noted to have resolved during close follow-up had an initial PSV more than 300 cm/s. This subset of grafts had a mean PSV of 363 cm/s (range, 307 to 423 cm/s) and a mean Vr of 4.3 (range, 2.2 to 6.2). During long-term follow-up, only one of these grafts occluded and new metachronous lesions subsequently developed in six of the remaining 21 grafts, yielding an overall revision rate of 19%.

Thirty of the initial 58 abnormal early duplex scan examinations (52%) led to arteriography and graft revision. Most of these early lesions, 23 of 30 (77%), were either high grade (risk category I or II) or rapidly progressed and were revised within 3 months of initial graft implantation. Evaluation of all follow-up studies revealed that evidence of regression or rapid progression was noted within 3 months of lesion detection in 45 of 52 instances. The remaining seven lesions progressed more slowly and were revised at a mean time of 8 months (range, 5 to 12 months) after surgery. The overall mean PSV and Vr in this group were 305 cm/s (range, 14 to 445 cm/s) and 4.01 (range, 1.8 to 8.7), respectively. There was no statistically significant difference in initial PSV and Vr between the group ultimately needing revision and the subset of grafts in which the early flow velocity disturbance resolved. A comparison of additional duplex scan-derived parameters and early surveillance examination data was performed to contrast these two groups of grafts. Analysis of duplex scan-derived spectral waveform morphology (biphasic versus triphasic), distal graft PSV, outflow artery PSV, and changes in ABI or toe pressure or development of symptoms did not reveal a significant difference between these two groups. The likelihood of progression or regression was not predictable on the basis of the initial scan but was only determined with close duplex scan follow-up examinations.

Kaplan-Meier life-table analysis revealed an overall primary assisted patency (PAP) rate of 82.6% at 60 months. The 5-year PAP rate was 86.1% for the subset of grafts with a normal early duplex scan examination compared with 77% for grafts with an abnormal early study, a difference that was statistically significant (P = .05).

During long-term follow-up, a total of 68 grafts (30%) underwent revision. Most grafts needed only a single revision (74%), but 17 grafts (25%) needed two revisions and one graft (1%) underwent three revisions. Of the grafts that underwent revision, 30 (45%) were predicted on the basis of the initial abnormal duplex scan examination. Twenty-three of 30 (77%) were performed within 3 months. The remaining seven had subsequent duplex scans that documented progression with an increase in velocity at the site of the previously identified flow abnormality.

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Discussion 

The follow-up of infrainguinal bypass grafts utilizing autogenous vein with a close surveillance protocol including careful interrogation with duplex scanning has been widely accepted to identify, grade, and monitor graft stenosis for progression. Prophylactic repair of high-grade lesions has been shown by several investigators to improve overall graft patency.1, 2, 3, 4, 5, 6 Several series have confirmed that intrinisic graft stenoses are the most common cause of intermediate (1 to 24 month) vein graft failure and that appropriate and timely intervention leads to an overall improvement in patency.1, 2, 3, 4, 5, 8, 9, 15, 17

In the current era of cost containment and a progressive trend towards minimizing potentially expensive and unnecessary intervention, we sought to review the clinical utility of early duplex scan surveillance initiated earlier than 3 months of revascularization. Despite the routine application of completion arteriography, duplex scan surveillance identified a surprising 26% incidence rate of early graft flow disturbances that may have been from inherent limitations in angiography or the development of rapidly progressive, new lesions at the site of minor defects. Twenty-three of the 58 grafts (40%) with early abnormal scans necessitated graft revision within 3 months of the initial operation. Whether these lesions would have resulted in graft occlusion before detection on a 3-month scan is uncertain. However, on the basis of reported experience with velocity criteria for intervention developed by our group and other investigators, grafts harboring such lesions would be predicted to be at high risk for sudden graft occlusion in the absence of timely intervention.1, 2, 3, 4, 5, 9, 10, 16 Furthermore, many graft flow disturbances were found to progress on repeat duplex scan examinations performed before the end of the third postoperative month.

It is presently unclear, however, which specific criteria for revision should be used when an early-appearing flow disturbance is detected. After initial anecdotal experience with the natural history of duplex scan-detected graft flow velocity disturbances suggesting that some of these disturbances actually regress, we became interested in reviewing the more specific natural history of early-appearing lesions. We previously reported that duplex scan follow-up alone without arteriography was safe and effective for grafts harboring intermediate flow disturbances (PSV < 300 cm/s and Vr < 4.0); arteriography and revision were reserved only for documented progression or hemodynamic deterioration.8 These criteria, however, were not derived on the basis of early postoperative scans.

Our current review reveals a typical proportion, 68 of 224 (30%), of autogenous vein grafts are found to have a hemodynamically significant graft stenosis necessitating revision. Twenty-three revisions (34%) were performed within 3 months after revascularization (ie, before the first postoperative duplex scan would have been obtained in the usual surveillance protocol). Surprisingly, however, we identified numerous early graft flow disturbances that resolved during close, frequent duplex scan examinations at the discretion of the attending vascular surgeon. This approach, in our series, did not lead to a significant incidence of graft failure. Within the first 3 months after revascularization, nine grafts (4.5%) occluded despite surveillance and only six were known to have an abnormal duplex scan before graft thrombosis. We hypothesized that use of supplemental information derived from duplex scan data would help distinguish flow disturbances more likely to progress and need revision from those lesions that ultimately resolve. Our review included a qualitative duplex scan graft waveform analysis and measurements of distal graft flow velocity, PSV, Vr, and ABI. Unfortunately, we were unable to derive hemodynamic risk factors that would distinguish those early graft lesions prone to progress versus those that tend to resolve over time. The natural history of these early lesions is therefore incompletely understood. It should be emphasized that the origins of these early flow disturbances are likely to be heterogeneous and include turbulence associated with valve leaflets, minor flow disturbances at valve sites associated with increased velocities during the early postoperative hyperemic period, sites of platelet aggregation, rapidly developing myointimal hyperplasia, or even sampling error.11

The suggestion that some duplex scan-detected graft velocity disturbances will resolve is not entirely new. Only a limited number of previous reports have analyzed the results of early duplex scan surveillance and attempted to define the natural history of early graft lesions.7, 10, 17, 18, 19 Mills and associates10 previously reported a 33% incidence rate of early graft flow disturbances and documented resolution in 14/40 vein grafts (35%) in which such early graft flow disturbances had been detected with duplex scan. Vesti et al19 studied the behavior of valve sites in saphenous vein bypass grafts followed by serial duplex scan surveillance. These investigators closely examined a cohort of 69 infrainguinal vein grafts and identified 17 graft velocity disturbances (25%), with a Vr between 2.5 and 3.5 because of turbulence at valve sites. Of these grafts, 10 valve associated stenoses (59%) showed a regression to a Vr less than 2.0 during subsequent follow-up with duplex scan surveillance.

Some investigators have suggested that early-appearing graft flow disturbances are more likely to be progressive and lead to graft thrombosis. Wilson and colleagues17 reported their findings obtained on 1-week and 6-week postoperative duplex scan surveillance studies obtained in 123 patients. Forty-six abnormalities (37%) were detected on the 1-week scan; revision was necessary in 26 cases (54%). Nielsen7 analyzed a series of 42 patients undergoing graft surveillance and reported a statistically significant adverse effect of an early-appearing graft stenosis on long-term graft patency. “Stenoses identified within 3 months of surgery were associated with an increased risk of thrombosis compared to stenoses identified at a later stage (12 month patency 51% versus 92%, p=0.03).”7 Our study also suggests that even with early graft surveillance, the long-term patency of grafts with early-appearing flow disturbances is inferior to grafts with normal scans (5-year PAP rate, 77% versus 83%; P = .05). In summary, available data strongly suggest that early duplex scans identify a clinically important subset of grafts at increased risk for failure. Despite satisfactory completion arteriography, 25% to 37% of such grafts harbor at implantation or develop soon thereafter significant focal flow abnormalities.

Gahtan et al21 have previously published prospectively derived criteria to determine which lesions can be followed on the basis of the duplex scan interrogation. With a mean follow-up period of 13 months, we determined that grafts with PSV more than 300 cm/s or Vr more than 3.5 would be more likely to progress and therefore need revision. Although this recommendation may also generally be applicable to early graft lesions, in this study, we documented resolution of early flow disturbances in 22 grafts, of which 6 (27%) had an initial PSV exceeding 300 cm/s. This information suggests to us that in the absence of low distal graft flow velocities or a fall in ABI it may be safe to follow selected early lesions and reserve intervention for documented progression or hemodynamic deterioration. In our experience, clear evidence of lesion regression or rapid progression occurs within 3 months of detection in nearly 90% of cases.

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Conclusion 

Early duplex scan surveillance detected velocity disturbances in a significant fraction (at least 25%) of infrainguinal bypass grafts. Early duplex scan surveillance also identified critical stenoses that necessitate revision within 3 months of the index operation in 10% of bypasses despite normal completion arteriography. Although most grafts met standard criteria for intervention, close follow-up with serial duplex scan-directed examinations also revealed that some disturbances resolve spontaneously. Therefore, until the natural history of graft velocity disturbances is further characterized and supplemental duplex scan criteria are developed to better categorize and stratify the risk for progression associated with these disturbances, we recommend that early surveillance become an integral part of the postoperative follow-up of infrainguinal vein bypass grafts.

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References 

  1. Moody P, Gould DA, Harris PL. Vein graft surveillance improves patency in femoro-popliteal bypass. Eur J Vasc Surg. 1990;4:117–121
  2. Mills JL, Harris EJ, Taylor LM, Beckett WC, Porter JM. The importance of routine surveillance of distal bypass grafts with duplex scanning: a study of 379 reverse vein grafts. J Vasc Surg. 1990;12:379–389
  3. Bergamini TM, George SM, Massey HT, Henke PK, Klamer TW, Lambert GE, et al.  Intensive surveillance of femoropopliteal-tibial autogenous vein bypasses improves long-term graft patency and limb salvage. Ann Surg. 1995;221:507–518
  4. Lundell A, Lindblad B, Berquist D, Hansen F. Femoropopliteal-crural graft patency is improved by ABI intensive surveillance program: a prospective randomized study. J Vasc Surg. 1995;21:26–34
  5. Visser K, Idu MM, Buth J, Engel GL, Hunink MG. Duplex scan surveillance during the first year after autologous vein bypass surgery: costs and clinical outcomes compared with other surveillance programs. J Vasc Surg. 2001;33:123–130
  6. Donaldson MC, Mannick JA, Whittemore AD. Causes of primary graft failure after in situ saphenous vein grafting. J Vasc Surg. 1992;15:113–120
  7. Nielsen TG. Natural history of infrainguinal vein bypass stenoses: early lesions increase the risk of thrombosis. Eur J Vasc Endovasc Surg. 1996;12:60–64
  8. Mills JL, Wixon CL, James DC, Devine J, Westerband A, Hughes JD. The natural history of intermediate and critical vein graft stenosis: recommendations for continued surveillance or repair. J Vasc Surg. 2001;33:273–280
  9. Mills JL, Fujitani RM, Taylor SM. The characteristics and anatomic distribution of lesions that cause reversed vein graft failure: a five-year prospective study. J Vasc Surg. 1993;17:195–206
  10. Mills JL, Bandyk DF, Gahtan V, Esses GE. The origin of infrainguinal vein graft stenosis: a prospective study based on duplex surveillance. J Vasc Surg. 1995;21:16–25
  11. Mills JL. Mechanisms of vein graft failure. Semin Vasc Surg. 1993;6:78–90
  12. Buth J, Disselhoff B, Sommeling C, Stam L. Color-flow duplex criteria for grading stenosis in infra-inguinal vein grafts. J Vasc Surg. 1991;14:716–728
  13. Bandyk DF. Essentials of graft surveillance. Semin Vasc Surg. 1993;6:92–102
  14. Grigg MJ, Nicolaides AN, Wolfe JHN. Detection and grading of femorodistal vein graft stenosis: duplex velocity measurements compared with angiography. J Vasc Surg. 1988;8:661–666
  15. Idu MM, Blankensteijn JD, de Gier Pm, Truyen E, Buth J. Impact of a color flow duplex surveillance on infrainguinal vein graft patencu: a five year experience. J Vasc Surg. 1993;17:42–53
  16. Westerband A, Mills JL, Kistler S, Berman SS, Hunter GC, Marek JM. Prospective validation of threshold criteria for intervention in infrainguinal vein grafts undergoing surveillance. Ann Vasc Surg. 1997;11:44–48
  17. Wilson YG, Davies AH, Carrie IC, McGrath C, Morgan M, Baird RN, et al.  The value of pre-discharge duplex scanning in infrainguinal graft surveillance. Eur J Endovasc Surg. 1995;10:237–242
  18. Caps MT, Cantwell-Gab K, Bergelin RO, Strandness DE. Vein graft lesions: time of onset and rate of progression. J Vasc Surg. 1995;22:466–475
  19. Vesti BR, Primozich J, Bergelin RO, Strandness E. Follow-up of valves in saphenous vein bypass grafts with duplex ultrasonography. J Vasc Surg. 2001;33:369–374
  20. Mills JM. Infrainguinal vein graft surveillance: how and when. Semin Vasc Surg. 2001;14:169–176
  21. Gahtan V, Payne LP, Roper LD, Mills JL, Jackson MM, Bandyk DF. Duplex criteria for predicting progression of vein graft lesions: which stenoses can be followed?. J Vasc Technol. 1995;19:211–215
  22. Wixon CL, Mills JL, Westerband A, Hughes JD, Ihnat DM. An economic appraisal of lower extremity bypass maintenance. J Vasc Surg. 2000;32:1–12

☆ Competition of interest: none.

☆☆ Reprint requests: Joseph L. Mills, Sr, MD, Professor of Surgery, Chief, Division of Vascular Surgery, 1501 N Campbell Ave, POB 245072, Tucson, AR 85724 (e-mail: jmills@u.arizona.edu).

★ 0741-5214/2003/$30.00 + 0

PII: S0741-5214(02)75256-7

doi:10.1067/mva.2003.115

Journal of Vascular Surgery
Volume 37, Issue 3 , Pages 495-500, March 2003

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