Color-flow duplex criteria for grading stenosis in infrainguinal vein grafts

Asia-Pacific Consensus Statement on the Management of Peripheral Artery Disease: A Report from the Asian Pacific Society of Atherosclerosis and Vascular Disease Asia-Pacific Peripheral Artery Disease Consensus Statement Project Committee

BACKGROUND

Peripheral artery disease (PAD) is the most underdiagnosed, underestimated and undertreated of the atherosclerotic vascular diseases despite its poor prognosis. There may be racial or contextual differences in the Asia-Pacific region as to epidemiology, availability of diagnostic and therapeutic modalities, and even patient treatment response. The Asian Pacific Society of Atherosclerosis and Vascular Diseases (APSAVD) thus coordinated the development of an Asia-Pacific Consensus Statement (APCS) on the Management of PAD.

OBJECTIVES

The APSAVD aimed to accomplish the following: 1) determine the applicability of the 2016 AHA/ACC guidelines on the Management of Patients with Lower Extremity Peripheral Artery Disease to the Asia-Pacific region; 2) review Asia-Pacific literature; and 3) increase the awareness of PAD.

METHODOLOGY

A Steering Committee was organized to oversee development of the APCS, appoint a Technical Working Group (TWG) and Consensus Panel (CP). The TWG appraised the relevance of the 2016 AHA/ACC PAD Guideline and proposed recommendations which were reviewed by the CP using a modified Delphi technique.

RESULTS

A total of 91 recommendations were generated covering history and physical examination, diagnosis, and treatment of PAD-3 new recommendations, 31 adaptations and 57 adopted statements. This Asia-Pacific Consensus Statement on the Management of PAD constitutes the first for the Asia-Pacific Region. It is intended for use by health practitioners involved in preventing, diagnosing and treating patients with PAD and ultimately the patients and their families themselves.

Fast and Effective Nonsuture Anastomosis of Magnetic Artificial Blood Vessel Transplantation for Caval Reconstruction in Canines

BACKGROUND

The resection and reconstruction of the vena cava is frequently needed in tumor resection. The goal of this study was to evaluate the performance of the magnetic compression anastomosis (MCA) device for fast nonsuture anastomosis of caval reconstruction with artificial blood vessel transplantation after resection in canines.

METHODS

The MCA device consisted of paired neodymium-ferrum-boron (Nd-Fe-B) magnetic rings that were coated with titanium nitride and embedded in a polypropylene shell. Artificial blood vessel transplantation procedure was performed in sixteen canines and then they were divided into 2 groups: MCA group (n = 8), in which the novel magnetic pinned-ring device was used, and the traditional manual suture group (n = 8). In situ artificial blood vessel anastomoses were performed in the inferior vena cava (IVC). The anastomosis time and anastomotic patency and quality were investigated through ultrasonographic scans, angiographic, gross observation, histological staining, and scanning electron microscopy at 24 weeks postoperatively.

RESULTS

The IVC anastomoses were reconstructed successfully in all canines and all animals survived. In the MCA group, the operation time for IVC anastomosis with artificial blood vessel was significantly shorter than that in the tradition manual suture group (P < 0.05). Vena cava angiography and ultrasound showed good blood patency. The scanning electron microscope showed the re-endothelialization was smooth and endothelial cells were arranged regularly at the anastomotic site. Histological examination confirmed that the MCA group was associated with infiltration of inflammatory cells compared with the manual suture group.

CONCLUSIONS

The MCA device combined with artificial blood vessels is applicable in reconstruction of large vessels after resection. The magnetic pinned-ring device offers a simple, fast, reliable, and effective technique for nonsuture artificial blood vessel anastomosis of caval reconstruction in canines, and the anastomosis is functionally better than the traditional sutured anastomosis.

The Society for Vascular Surgery practice guidelines on follow-up after vascular surgery arterial procedures

Although follow-up after open surgical and endovascular procedures is generally regarded as an important part of the care provided by vascular surgeons, there are no detailed or comprehensive guidelines that specify the optimal approaches with regard to testing methods, indications for reintervention, and follow-up intervals. To provide guidance to the vascular surgeon, the Clinical Practice Council of the Society for Vascular Surgery appointed an expert panel and a methodologist to review the current clinical evidence and to develop recommendations for follow-up after vascular surgery procedures. For those procedures for which high-quality evidence was not available, recommendations were based on observational studies, committee consensus, and indirect evidence. Recognizing that there are numerous published reports on the role of duplex ultrasound for surveillance of infrainguinal vein bypass grafts, the Society commissioned a systematic review and meta-analysis on this topic. The panel classified the strength of each recommendation and the corresponding quality of evidence on the basis of the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system: recommendations were graded either strong or weak, and the quality of evidence was graded high, moderate, or low. The resulting recommendations represent a wide variety of open surgical and endovascular procedures involving the extracranial carotid artery, thoracic and abdominal aorta, mesenteric and renal arteries, and lower extremity arterial revascularization. The panel also identified many areas in which there was a lack of high-quality evidence to support their recommendations. This suggests that there are opportunities for further clinical research on testing methods, threshold criteria, and the role of surveillance as well as on the modes of failure and indications for reintervention after vascular surgery procedures.

Systematic review and meta-analysis of duplex ultrasound surveillance for infrainguinal vein bypass grafts

OBJECTIVE

Duplex ultrasound (DUS) surveillance of infrainguinal vein bypass grafts is widely practiced, but the evidence of its effectiveness compared with other methods of surveillance remains unclear.

METHODS

Following an a priori protocol developed by the guidelines committee from the Society for Vascular Surgery, this systematic review and meta-analysis included randomized and nonrandomized comparative studies that enrolled patients who underwent infrainguinal arterial reconstruction and received DUS surveillance for follow-up compared with any other method of surveillance. The search included MEDLINE, Embase, Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews, Cumulative Index to Nursing and Allied Health Literature, and Scopus through November 2016. Outcomes of interest included all-cause mortality, limb viability, and graft patency reports. Meta-analysis was performed using the random-effects model.

RESULTS

We included 15 studies. Compared with ankle-brachial index and clinical examination, DUS surveillance was not associated with a significant change in primary, secondary, or assisted primary patency or mortality. DUS surveillance was associated with a nonstatistically significant reduction in amputation rate (odds ratio, 0.70 [95% confidence interval, 0.23-2.13]). The quality of evidence was low because of imprecision (small number of events and wide confidence intervals) and high risk of bias in the primary literature.

CONCLUSIONS

A recommendation for routine DUS surveillance of infrainguinal vein grafts remains dependent on low-quality evidence. Considering that DUS offers the opportunity of early intervention and because of its noninvasive nature and low cost, vascular surgeons may incorporate DUS as they individualize the follow-up of lower extremity vein grafts.

Actual Dose-Reduction Strategies in Cardiac Computed Tomography

Computed tomography (CT) in cardiac examination is a powerful imaging tool that has developed rapidly during the last decade and continues to increase its potential by bringing novel technologies. Due to its noninvasive character, cardiac CT became a largely used method in detecting coronary diseases or functional issues at the expense of conventional coronary angiography. The accuracy of images has also increased, especially since new generation dual-source multi-slice detectors were developed. Although there are continuous improvements that serve to gain better-quality images, thus increasing their diagnostic accuracy, there is an inconvenient that became a serious topic for debate in the current literature: exposure to higher doses of radiation during cardiac CT examinations. Fortunately, physicians and manufacturers are taking into consideration the need to apply new strategies for radiation dose-reduction. Thus, this objective can be achieved by using patient-tailored dose-reduction strategies and by modulating the technical features of the CT scanners in order to gather high-quality images with minimal radiation exposure. The aim of this manuscript was to review the current literature data on dose-reduction strategies that are used for cardiovascular computed tomography scans.

Duplex Features of Vein Graft Stenosis and the Success of Percutaneous Transluminal Angioplasty

Purpose:

To determine if criteria exist that are correlated to a successful outcome after balloon angioplasty for vein graft stenosis.

Methods:

During a 5-year period, duplex surveillance of 380 infrainguinal vein bypasses identified 76 hemodynamically failing grafts (87 stenoses) requiring intervention. Percutaneous transluminal angioplasty (PTA) was selected over surgical repair based on 3 criteria: time interval from primary grafting procedure, vein graft diameter, and stenosis length. The 28 (32%) stenoses (20 grafts) treated by PTA were used in a retrospective analysis to test if any variables favored a successful outcome. Patient and lesion characteristics, graft patency, and restenosis following PTA were correlated with duplex features of the stenosis recorded prior to, immediately after, and at 3- to 6-month intervals postprocedurally.

Results:

Lesion characteristics that correlated with a successful outcome were vein size ≥3.5 mm, lesion length < 2 cm, and appearance > 3 months after surgery. Conduit type, PTA site, patient demographics, and indication for bypass did not correlate with PTA durability. Nineteen lesions in 13 grafts met these criteria (group 1), while 9 stenoses in 7 grafts did not (group 2). Lesion severity based on duplex velocity measurements were similar in both groups before (p = 0.40) and after (p = 0.32) treatment. During the mean 21-month follow-up, group 1 grafts required less intervention (p = 0.035). At last follow-up, hemodynamic changes were durable in group 1 (p = 0.0068) but not in group 2 (p = 0.39).

Conclusions:

Selection of vein graft stenoses for treatment by PTA can be based on temporal and duplex data. PTA of short (< 2 cm) stenoses in good caliber veins (≥ 3.5 mm) appearing > 3 months after bypass placement was durable with a late intervention rate of approximately 10%. Direct surgical repair or replacement is recommended for early (< 3 months) and/or long segment stenoses that develop in small caliber conduits.

Stenosis of reverse great saphenous vein graft in infrainguinal arterial revascularization

OBJECTIVE

The aim of this study was to evaluate the prevalence of hemodynamically significant infrainguinal bypasses stenosis using reverse great saphenous vein graft.

METHODS

From March of 2008 to March of 2009, 56 infrainguinal bypasses were performed with reverse great saphenous vein graft in 56 patients. On the 30th post-operative day, 32 out of 56 patients were submitted to vascular ultrasonography. The prevalence of significant graft stenosis was determined. In addition, the diagnosis of stenosis was related to the clinical and surgical characteristics of the patients. The variables analyzed at the moment of diagnosis were the localization of the graft stenosis, the risk factors associated with stenosis and the association of vascular ultrasonography findings with ankle brachial pressure index (ABI).

RESULTS

The overall prevalence of significant graft stenosis was 48.4%. Out of the total number of observed stenosis, 19.4% were considered severe, and 29% mild or moderate. There was no significant association between the presence of significant stenosis and the following variables: gender, diabetes, hypertension, smoking, hipercholesterolemia, graft diameter, site of the distal anastomosis, and graft composition. There was a weak agreement between ABI and vascular ultrasonography in detecting stenosis in general (K = 0.30; CL95% 0.232 - 0.473; p = 0.018). However, there was a substantial agreement in detecting severe stenosis (K = 0.75; CL95% 0.655 - 0.811; p = 0.0001).

CONCLUSION

There was a high prevalence of stenosis on the 30th post-operative day, mostly localized in the proximal half of the vein graft. There was no significant association of stenosis with clinical and surgical factors analyzed. ABI and vascular ultrasonography had weak agreement with the diagnosis of stenosis in general and an important agreement for the diagnosis of severe stenosis.

Balloon angioplasty as a treatment of failing infrainguinal autologous vein bypass grafts

PURPOSE

The purpose of this study was to evaluate the role of balloon angioplasty in the treatment of failing infrainguinal vein bypass (IVB) grafts.

METHODS

A retrospective chart review of patients undergoing revision of a failing IVB graft by vascular surgeons at a tertiary care center from 1990 to 2001 was performed. Failing bypass grafts were identified by routine duplex scan surveillance and physical examination. The criteria for endovascular intervention varied on the basis of surgeon preferences and time period; factors considered when choosing balloon angioplasty included significant comorbidities that precluded operative intervention, the lack of adequate conduit for surgical revision, or poor accessibility of the stenotic lesion. Data recorded included demographic patient data, type of IVB graft, patency status, further procedures performed, and all complications and mortalities. Cumulative primary and assisted patency rates were calculated by using Kaplan-Meier life-table analysis.

RESULTS

A total of 45 balloon angioplasties were performed in 36 patients. There were 36 angioplasties of vein bypass grafts, and additional balloon angioplasties were performed on nine of these patients. Locations of IVB grafts included femoropopliteal (13 patients), femorodistal (13), and popliteal to distal (10). Initial success was achieved in 33 of 36 vein bypass grafts (91.7%). In these bypass grafts, the stenotic lesions were identified and treated at the proximal anastomosis (3 patients), mid-bypass graft (6 patients), and distal anastomosis (27 patients). Autogenous vein was used for all bypass grafts. Cumulative vein bypass graft (life-table analysis) primary patency rates (those free of occlusion or bypass graft threatening stenosis) were 74.2% at 6 months, 62.7% at 12 months, and 58.2% at 24 months. Repeat interventions included surgical thrombectomy with vein patch angioplasty or bypass graft revision, as well as repeat balloon angioplasty with or without thrombolysis. Cumulative assisted vein bypass graft patency rates (those free of occlusion or bypass graft threatening stenosis) were 87.0%, 83.2%, and 78.9% at 6, 12, and 24 months, respectively. Two patients (4%) developed thigh hematomas; no other procedure-related complications were noted, and there were no deaths in the perioperative period.

CONCLUSION

Balloon angioplasty of failing infrainguinal vein bypass grafts can be successfully performed with a low rate of complications. Acceptable short-term patency can be achieved. This procedure should be considered as an initial option in failing IVB grafts.

Altered expression of vascular endothelial growth factor and its receptors in normal saphenous vein and in arterialized and stenotic vein grafts

BACKGROUND

Myointimal thickening is a major cause saphenous vein graft failure. The prominence of medial and adventitial microvessels in stenotic vein grafts and the known angiogenic effects of vascular endothelial growth factor (VEGF) lead us to investigate the expression of VEGF and its receptors in vein graft arterialization and stenosis.

METHODS

Normal and arterialized vein graft segments were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) for expression of VEGF-R1 (flt), VEGF-R2 (KDR), and neuropilin-1. The cells expressing VEGF, VEGF-R1, VEGF-R2, and neuropilin-1 were identified in normal, stenotic, and arterialized vein graft segments by immunohistochemistry.

RESULTS

Vascular endothelial growth factor, detected in the wall in endothelial cells and adventitial microvessels in normal vein, localized to smooth muscle cells, endothelial cells and adventitial microvessels in arterialized and stenotic vein. VEGF-R1 and VEGF-R2 were expressed infrequently on endothelial cells, macrophages, and smooth muscle cells in arterialized and stenotic vein. Neuropilin-1 was detected in all specimens. RT-PCR demonstrated significantly greater expression of neuropilin-1 in normal vein compared with arterialized vein (P <0.05).

CONCLUSIONS

The differential expression of VEGF and its receptors in normal, arterialized, and stenotic vein grafts suggests that alterations in VEGF/VEGF-R2/neuropilin-1 interactions may be important determinants of the adaptive response of vein grafts to arterialization.

Evaluation of Peripheral Arterial Bypass Grafts with Multi–Detector Row CT Angiography: Comparison with Duplex US and Digital Subtraction Angiography

PURPOSE

To assess the technical feasibility of multi-detector row computed tomographic (CT) angiography in the assessment of peripheral arterial bypass grafts and to evaluate its accuracy and reliability in the detection of graft-related complications, including graft stenosis, aneurysmal changes, and arteriovenous fistulas.

MATERIALS AND METHODS

Four-channel multi-detector row CT angiography was performed in 65 consecutive patients with 85 peripheral arterial bypass grafts. Each bypass graft was divided into three segments (proximal anastomosis, course of the graft body, and distal anastomosis), resulting in 255 segments. Two readers evaluated all CT angiograms with regard to image quality and the presence of bypass graft-related abnormalities, including graft stenosis, aneurysmal changes, and arteriovenous fistulas. The results were compared with McNemar test with Bonferroni correction. CT attenuation values were recorded at five different locations from the inflow artery to the outflow artery of the bypass graft. These findings were compared with the findings at duplex ultrasonography (US) in 65 patients and the findings at conventional digital subtraction angiography (DSA) in 27.

RESULTS

Image quality was rated as good or excellent in 250 (98%) and in 252 (99%) of 255 bypass segments, respectively. There was excellent agreement both between readers and between CT angiography and duplex US in the detection of graft stenosis, aneurysmal changes, and arteriovenous fistulas (kappa = 0.86-0.99). CT angiography and duplex US were compared with conventional DSA, and there was no statistically significant difference (P >.25) in sensitivity or specificity between CT angiography and duplex US for both readers for detection of hemodynamically significant bypass stenosis or occlusion, aneurysmal changes, or arteriovenous fistulas. Mean CT attenuation values ranged from 232 HU in the inflow artery to 281 HU in the outflow artery of the bypass graft.

CONCLUSION

Multi-detector row CT angiography may be an accurate and reliable technique after duplex US in the assessment of peripheral arterial bypass grafts and detection of graft-related complications, including stenosis, aneurysmal changes, and arteriovenous fistulas.

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

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.

Repeat surgery without preoperative angiography in limbs with patent infrainguinal bypass grafts

The aim of this study was to assess the feasibility and results of repeat surgery without preoperative angiography in limbs with patent infrainguinal bypass grafts. Between January 1995 and December 1999, 73 surgical interventions were performed for correction of inflow, graft, or runoff-related lesions in limbs with patent infrainguinal bypass grafts. Fifty-six of the 73 cases were operated on based on the findings obtained from duplex scanning alone. There were 53 vein and 3 prosthetic grafts in the series. The indications for intervention without angiography were stenotic or occlusive lesions in 35, graft aneurysm in 7, and arteriovenous fistulae in 14. There were no deviations from the preoperatively planned surgical strategy in patients undergoing surgery without preoperative angiography. Cumulative life table primary, (stenosis free) and primary-assisted patency rates, at 12 months following graft revisions (excluding arteriovenous fistulae ligatures) without preoperative angiography, were 64% and 85%, respectively. The corresponding figures for revisions performed with preoperative angiography were 58% and 84%, respectively. There were no significant differences between patients undergoing surgery with or without preoperative diagnostic angiography with regard to patency rates. Surgical interventions for correction of infrainguinal graft-related stenotic or aneurysmal lesions can be safely performed based on findings obtained from duplex scanning.

Early duplex-derived hemodynamic parameters after lower extremity bypass in diabetics: implications for mid-term outcomes

Early postoperative changes in the hemodynamic parameters of infrainguinal bypass grafts in diabetics have not been well defined. We undertook this study to better define such changes in duplex-derived velocities and waveforms, and correlate any observed changes with intermediate-term outcomes. A prospective study of 68 primary vein bypasses for limb salvage was carried out, with scans obtained intraoperatively, daily until discharge, and at 8- to 12-weeks intervals. During follow-up (12 +/- 6 months), 20 grafts developed stenoses, 17 occluded, and 8 limbs were amputated. Most grafts show a variant of a biphasic waveform intraoperatively at the mid-graft (MG) and distal graft (DG) levels (54% and 57%); 65% of waveforms remain unchanged during the first week, and 54% remain unchanged at 3 months. No duplex-derived factors were predictive of the development of stenoses. A number of parameters were predictive of ultimate graft thrombosis. Intraoperative MG velocity was higher in grafts that eventually remained patent (83 +/- 36 vs. 60 +/- 29 cm/sec; p <0.025). Grafts that remained patent also had a much lower decline in DG and distal native (DN) velocities from immediately postoperative to 8-12 weeks later, than grafts that eventually thrombosed (-3 +/- 35 vs. -44 +/- 43 cm/sec for DG, p <0.001; and -17 +/- 66 vs. -76 +/- 53 cm/sec for DN, p <0.04 respectively). In terms of limb salvage, when the MG or DG waveform worsened (from postoperation to 12 weeks later), amputation was more likely than when it remained unchanged or improved (MG 67% vs. 9% limb loss, p <0.04; DG 43% vs. 8% limb loss, p <0.04). We conclude that intensive graft duplex surveillance does not identify grafts likely to develop stenoses. However, a number of features allow the prediction of ultimate graft failure or limb loss.

Intraoperative flow predicts the development of stenosis in infrainguinal vein grafts

OBJECTIVE

There are data to suggest that the development of myointimal hyperplasia is affected by long-term alterations in blood flow. However, the clinical relevance of these findings has not been demonstrated.

METHODS

In this retrospective clinical study, intraoperative volume flow measurement with transit time flowmeter was performed in 257 infrainguinal vein grafts carried out in 241 patients. The patients were enrolled in an intensive duplex scanning-based surveillance program. The relationship between the intraoperative graft flow and subsequent occlusion or development of stenosis was evaluated and controlled for other pertinent risk factors.

RESULTS

The median follow-up time was 13.6 months. A graft stenosis was found in 58 grafts. The mean graft flow for event-free grafts was 98 mL/min, which was significantly higher compared with 78 mL/min for stenosed or 69 mL/min for occluded grafts. The patients were divided into four groups according to quartiles of the sample distribution of graft flow measurements. The respective 2-year primary and assisted primary patency rates in the lowest to the highest graft flow groups were 39%, 49%, 47%, and 72% (P =.003) and 55%, 67%, 71%, and 84% (P =.01). Analogous significant differences were observed for maximal flow capacity measurements. Female sex (P =.009) and low graft flow in maximal flow capacity measurements (P =.003) were independent predictors of stenosis development in the multiple regression model.

CONCLUSION

Intraoperative graft volume flow is a predictor of bypass occlusion after infrainguinal bypass. In addition, this study verifies an association between the development of clinically evident graft stenoses and low graft flow.

Current approach to peripheral arterial sonography

Color and pulsed Doppler imaging have assumed a prominent role for evaluating noninvasively lower-extremity arterial occlusive disease. In conjunction with indirect arterial tests, ultrasound imaging is recommended to screen for lower-extremity disease. It provides not only specific information regarding location, severity, and frequency of disease, but it can also determine the optimal therapeutic approach before more invasive procedures. Using ultrasound for graft surveillance is mandatory for identifying flow-reducing lesions that may lead to subsequent bypass failure. As new developments become perfected and clinically available, ultrasound contrast agents, three-dimensional imaging, and B-flow imaging each seem to have great potential for assessing peripheral arterial disease. In all likelihood, these additions will further improve the diagnostic capability of ultrasound and may also lead to the development of new vascular applications for this modality.

Transfer function index of pulse volume recordings: a new method for vein graft surveillance

OBJECTIVE

Color flow duplex scanning is currently the best method available for vein graft surveillance. However, it puts a considerable strain on the workload of a vascular unit and requires a highly trained operator. The aim of this study was to develop and validate a new, noninvasive tool for graft surveillance. The utility of transfer function index (TFI) of pulse volume recordings is tested for this purpose.

METHODS

The design of the study was a blind comparative study that involved 70 testing procedures that were performed on 58 different infrainguinal vein bypass grafts. The TFI was measured with a portable vascular laboratory multi-cuff unit. Ankle/brachial indexes were obtained with the same device. Color flow duplex scanning was used as a diagnostic standard. A graft was defined as at risk, according to duplex scanning, if a local stenosis with a V2/V1 more than 2 was found or if peak systolic velocity remained less than 45 cm/s throughout the graft. The repeatability of the method was tested on 30 grafts.

RESULTS

A total of 63 tests were available for analysis. Seven tests were excluded. Four were excluded because they had unreliable TFI measurement due to cardiac arrhythmias, and in three tests, the whole graft could not be visualized in the duplex scan. Forty normal and 22 at-risk grafts were found. One graft was occluded. The TFI was significantly lower for at-risk grafts (0.89) versus normal grafts (1.09; P =.005). A TFI of 1.02 or less correctly detected 21 of 22 at-risk grafts. The sensitivity, specificity, and accuracy were 96%, 65%, and 76%, respectively. The ability of the ankle/brachial index to detect the at-risk grafts was clearly inferior to the TFI. The repeatability of the method at proximal thigh, distal thigh, and proximal calf was +/- 0.21, +/- 0.07, and +/- 0.14, respectively.

CONCLUSION

The TFI is a sensitive and reliable method to detect an at-risk graft. The examination is noninvasive, simple, quick to perform, and well tolerated by the patients. We suggest that the TFI could be the first-line screening method in vein graft surveillance.

The natural history of intermediate and critical vein graft stenosis: recommendations for continued surveillance or repair

OBJECTIVE

Duplex ultrasound surveillance (DUS) after autogenous lower extremity bypass grafting is controversial. Specific criteria mandating graft revision are not uniform. It has been suggested that grafts harboring critical stenoses undergo revision, whereas those with intermediate stenoses undergo arteriography with selective repair. We sought to define the natural history and determine the risk of graft occlusion associated with unrepaired vein graft stenoses.

METHODS

We analyzed serial vascular laboratory and clinical data of 156 autogenous infrainguinal vein grafts in 142 patients. Grafts were categorized into three groups according to the first DUS-detected (index) lesion: (1) normal (peak systolic velocity [PSV] < 200 cm/s, velocity ratio [V(r)] < 2); (2) intermediate stenosis (200 cm/s < PSV < 300 cm/s, 2 < V(r) < 4); and (3) critical (PSV > 300 cm/s, V(r) > 4). Our policy was to repair grafts with critical lesions and monitor all others. The risks of stenosis progression, graft revision, and graft thrombosis for each group were compared.

RESULTS

Serial DUS was normal in 100 (64%) grafts. The incidence of graft thrombosis in the normal group was 3% per year (mean follow-up, 27.5 months). Intermediate lesions developed in 32 grafts (20%) and were followed. Among these 32 grafts with intermediate stenoses, 63% progressed to critical and were revised, and 32% resolved or stabilized (mean follow-up, 26 months). Only one graft occlusion occurred in grafts with intermediate lesions subjected to serial DUS monitoring (incidence 1.5% per year, P = not significant). In the third group, 16 of 25 grafts with critical lesions were successfully revised and remain patent. In nine cases, critical lesions were not repaired, resulting in seven (78%) occlusions, all within 4 months of DUS detection.

CONCLUSIONS

Serial surveillance is safe and effective for grafts with intermediate stenoses. The graft occlusion rate for such grafts with careful monitoring is no different from grafts without stenosis, and therefore, arteriography is not indicated in the absence of progression to critical stenosis. The short-term risk of graft occlusion in the presence of an unrevised critical stenosis is nearly 80%. These data have important clinical implications concerning the natural history of vein graft lesions.

Duplex scan surveillance during the first year after infrainguinal autologous vein bypass grafting surgery: costs and clinical outcomes compared with other surveillance programs

PURPOSE

In this study we assessed the costs and clinical outcomes of duplex scan surveillance during the first year after infrainguinal autologous vein bypass grafting surgery and compared duplex scan surveillance, ankle-brachial index surveillance, and clinical follow-up.

METHODS

In a clinical study, 293 patients (mean age, 70.1 years; 58.7% men) with peripheral arterial disease were observed in a duplex scan surveillance program after infrainguinal autologous vein bypass grafting surgery. Costs were calculated from the health care perspective for surveillance and subsequent interventions from 30 days to 1 year postoperatively. All costs are presented in 1995 US dollars per patient. In a simulation model, we estimated the costs and amputations of duplex scan surveillance, ankle-brachial index surveillance, and clinical follow-up conditional on the indication for surgery. The main outcome measure was the incremental cost per major amputation per patient avoided during the first postoperative year.

RESULTS

Duplex scan surveillance was the least expensive ($2823) and resulted in the fewest major amputations (17 per 1000 patients examined), compared with ankle-brachial index surveillance ($5411 and 77 amputations per 1000 patients) and clinical follow-up ($5072 and 77 amputations per 1000 patients). In patients treated for critical limb ischemia, duplex scan surveillance was the least expensive ($2974) and resulted in the fewest major amputations (19 per 1000 patients). Under all surveillance programs, 13 major amputations per 1000 patients treated for intermittent claudication were performed, and clinical follow-up had the lowest costs ($1577). In a sensitivity analysis that assumed that duplex scan surveillance could have avoided six major amputations per 1000 patients treated for intermittent claudication compared with the other programs, duplex scan surveillance had an incremental cost of $80,708 per major amputation per patient avoided compared with clinical follow-up.

CONCLUSION

Duplex scan surveillance is highly effective for patients treated for critical limb ischemia, leading to a reduction of major amputations and consequently to a reduction in costs compared with other surveillance programs. In patients treated for intermittent claudication, the evidence supporting duplex scan surveillance is less firm, but if duplex scan can avoid six major amputations per 1000 patients examined, the incremental costs are justified.

Abnormal duplex findings at the proximal anastomosis of infrainguinal bypass grafts: does revision enhance patency?

Using color duplex ultrasound (CDU) surveillance of autogenous infrainguinal bypasses, a peak systolic flow velocity (PSFV) ratio of greater than 3 to 1 within the graft relative to adjacent PSFV has been accepted as predicting significant stenosis mandating revision. At the proximal anastomosis, where significant vessel diameter differences and turbulent flow exist, the validity of these criteria is less clear. Our purpose was to review our experience with proximal anastomotic abnormalities in a CDU surveillance protocol. Routine CDU surveillance for all infrainguinal bypass gratis consisted of evaluation in an accredited vascular laboratory at 1 month postoperatively, every 3 months for the first year, every 6 months in the second year, and annually thereafter. Grafts with a PSFV ratio of >3 at the proximal anastomosis on any CDU study were included in this review. From our results we conclude that currently accepted CDU criteria for graft-threatening stenosis may not be valid for abnormalities at the proximal anastomosis of infrainguinal grafts. Regression of these abnormalities is common. Better CDU criteria are needed for predicting not only severity of proximal anastomotic stenosis but also likelihood of graft thrombosis.

An economic appraisal of lower extremity bypass graft maintenance

OBJECTIVE

Infrainguinal graft surveillance leads to intervention on the basis of duplex-identified stenoses. We have become increasingly concerned about the high frequency with which such revisions are required to maximize graft patency and limb salvage rates. The economic implications of these procedures have not been carefully analyzed or justified.

METHODS

We retrospectively reviewed 155 consecutive autogenous infrainguinal bypass grafts performed for chronic leg ischemia in 141 patients. All patients were enrolled in a prospective surveillance program using color flow duplex imaging. Full economic appraisal (cost analysis, cost-effect analysis, and cost-benefit analysis) was performed for all graft surveillance and limb salvage-related interventions through use of standard accounting and valuation techniques.

RESULTS

Mean follow-up was 27 months. Five-year assisted primary patency (72%) and limb salvage rates (91%) were calculated by means of life table analysis. A total of 61 grafts required 86 revisions. Within 1 year of implantation, 36% of the grafts required revision. During this first year, the mean cost per graft enrolled was $9417. Time intervals after the initial year demonstrated a reduced annual revision rate (6%) and cost ($1725 per graft). The mean 5-year cost of graft maintenance ($16,318) approached that of the initial bypass graft ($19,331). The sum of the initial cost of bypass graft and 5-year graft maintenance cost ($35,649) was similar to the cost of amputation ($36,273). Grafts revised for duplex-detected stenoses (n = 46), in comparison with those revised after thrombosis (n = 15), had an improved 1-year patency (93% vs 57%; P <.01), required fewer amputations (2% vs 33%; P <.01), less frequently required multiple graft revisions (P =.06), and generated fewer expenses (at 12 months after revision, $17,688 vs $45,252, P <.01).

CONCLUSION

The cost associated with graft maintenance is significant, particularly within the first year, and demands consideration. Revision of a duplex-identified stenosis was significantly less costly than revision after graft thrombosis. Compared with the cost of limb amputation, limb salvage-related expenses appear to be justified.

Interobserver agreement in duplex scanning for vein grafts

BACKGROUND

although the precision of duplex scanning is of utmost importance in vein-graft surveillance, it has not been properly assessed. This study aims to analyse interobserver agreement on duplex scanning.

METHODS

a blinded comparative trial of 69 infrainguinal vein bypass reconstructions. Two consecutive duplex scans were performed by different examiners and duplex ultrasound machines on the same patient. The duplex examinations were also compared with angiography, when available, and clinical follow-up.

RESULTS

interobserver agreement in Kappa statistics was 0.69, signifying "good" agreement between the examinations in detecting haemodynamically significant changes in the grafts. The sensitivity, specificity and accuracy figures compared with a combination of angiography and follow-up data for the two scans were 80%, 91%, 88% and 85%, 93%, 91%, respectively. The limits of agreement were, however, wide for Doppler-derived velocity characteristics.

CONCLUSION

duplex scanning is an accurate and reproducible method for detecting haemodynamically significant changes in infrainguinal vein grafts.

The importance of revision of early restenosis after endovascular remote endarterectomy in SFA occlusive disease

OBJECTIVES

to investigate the results of revision of recurrent stenoses after superficial femoral artery (SFA) remote endarterectomy.

DESIGN

prospective, non-open, study.

MATERIALS

eighty-eight consecutive patients with long segmental SFA occlusive disease underwent 101 remote end-arterectomy procedures. All patients had chronic lower extremity ischaemia necessitating surgical intervention.

METHODS

clinical, haemodynamic, and duplex examinations were performed postoperatively at regular intervals, identifying 46 recurrent stenosed (PSV ratio >2.5) limbs, which formed the cohort for this study. The median follow-up was 25 months. Secondary revision was performed in 23 limbs, based on recurrent symptoms and individual preference of the attending vascular surgeon. Cumulative primary and primary assisted-patency rates were compared using the log-rank test of significance.

RESULTS

univariate analysis did not show any significant differences for other demographic and lesion characteristics apart from recurrent symptoms (all revised). Multivariate analysis revealed that revision "adjusted for time-of-onset" predicted reocclusion (p=0.007; HR 0. 21; 95% CI 0.06, 0.66). Among subjects in whom restenoses developed within 1 year, revision of recurrent stenoses improved primary patency rates from 47% to 77% at 30 months.

CONCLUSIONS

revision of early (<1 year) recurrent stenoses improves the mid-term patency rates of SFA remote endarterectomy.

Does a completely accomplished duplex-based surveillance prevent vein-graft failure?

OBJECTIVES

to assess the benefits of duplex-based vein-graft surveillance over clinical surveillance with distal pressure measurements.

DESIGN

prospective randomised comparative trial.

MATERIAL AND METHODS

three hundred and forty-four patients with 362 consecutive infrainguinal vein bypasses were prospectively randomised to a follow-up regime with or without duplex scanning (ABI group and DD group) at 1, 3, 6, 9, and 12 months postoperatively.

RESULTS

one hundred and eighty-three grafts were enrolled to the ABI group and 179 to the DD group. The primary assisted patency, secondary patency and limb salvage rates were 67%, 74%, 85% for the ABI group and 67%, 73%, 81% for the DD group. Ninety grafts in the ABI group and 57 in the DD group had surveillance that completely adhered to the protocol. The outcome was also similar for these groups at one year (77%, 87%, 94% and 77%, 83%, 93% respectively), although grafts were revised more frequently in the DD group.

CONCLUSIONS

intensive surveillance with duplex scanning did not improve the results of any outcome criteria examined. To demonstrate any potential benefit of duplex scanning for vein-graft surveillance a multicentre study with a large number of patients to ensure sufficient power is needed.

Do residual arteriovenous fistulae after in situ saphenous vein bypass grafting influence patency?

PURPOSE

The purpose of this study was to evaluate the influence on patency of residual arteriovenous fistulae (AVF) after in situ saphenous vein bypass grafting.

METHODS

Between January 1, 1994, and December 31, 1996, 98 in situ saphenous vein bypass grafting procedures were performed in 94 patients. Patency was evaluated with duplex scanning after operation and at 1, 3, 6, 9, and 12 months.

RESULTS

The indications for operation were intermittent claudication in two patients and critical leg ischemia in 92 patients. Two above-knee and 48 below-knee femoropopliteal and 48 femorocrural in situ saphenous vein bypass grafting procedures were performed. The median follow-up period was 9 months (range, 1.5 to 12.5 months). There were no residual AVF in 45 veins (44%; group 1), but 110 residual AVF were found in 53 veins (56%; group 2). In group 2, 36 AVF in 18 veins were surgically or radiologically occluded mainly as a result of a flow velocity decrease distal to the AVF, but the remaining 74 AVF were treated conservatively. The 1-year cumulative primary patency rates were 68% in group 1 and 74% in group 2 (log-rank test, 0.47; degree of freedom = 1; P =.52). The 1-year cumulative assisted primary patency rates were 68% in group 1 and 81% in group 2 (log-rank test, 2.19; degree of freedom = 1; P =. 14).

CONCLUSION

Residual AVF after in situ bypass grafting without influence on bypass graft hemodynamics do not compromise patency and thrombose spontaneously.

Duplex features of vein graft stenosis and the success of percutaneous transluminal angioplasty

PURPOSE

To determine if criteria exist that are correlated to a successful outcome after balloon angioplasty for vein graft stenosis.

METHODS

During a 5-year period, duplex surveillance of 380 infrainguinal vein bypasses identified 76 hemodynamically failing grafts (87 stenoses) requiring intervention. Percutaneous transluminal angioplasty (PTA) was selected over surgical repair based on 3 criteria: time interval from primary grafting procedure, vein graft diameter, and stenosis length. The 28 (32%) stenoses (20 grafts) treated by PTA were used in a retrospective analysis to test if any variables favored a successful outcome. Patient and lesion characteristics, graft patency, and restenosis following PTA were correlated with duplex features of the stenosis recorded prior to, immediately after, and at 3- to 6-month intervals postprocedurally.

RESULTS

Lesion characteristics that correlated with a successful outcome were vein size > or = 3.5 mm, lesion length < 2 cm, and appearance > 3 months after surgery. Conduit type, PTA site, patient demographics, and indication for bypass did not correlate with PTA durability. Nineteen lesions in 13 grafts met these criteria (group 1), while 9 stenoses in 7 grafts did not (group 2). Lesion severity based on duplex velocity measurements were similar in both groups before (p = 0.40) and after (p = 0.32) treatment. During the mean 21-month follow-up, group 1 grafts required less intervention (p = 0.035). At last follow-up, hemodynamic changes were durable in group 1 (p = 0.0068) but not in group 2 (p = 0.39).

CONCLUSIONS

Selection of vein graft stenoses for treatment by PTA can be based on temporal and duplex data. PTA of short (< 2 cm) stenoses in good caliber veins (> or = 3.5 mm) appearing > 3 months after bypass placement was durable with a late intervention rate of approximately 10%. Direct surgical repair or replacement is recommended for early (< 3 months) and/or long segment stenoses that develop in small caliber conduits.

Graft patency evaluation with colour-Doppler ultrasonography after bypass surgery in Takayasu's arteritis: a direct colour-flow lumen imaging method

OBJECTIVES

To assess the feasibility and potential diagnostic usefulness of colour-Doppler flow imaging (CDFI) to detect complications of supra-aortic vascular bypass grafts in Takayasu's arteritis (TA).

DESIGN

A prospective study.

MATERIALS

Nine supra-aortic grafts in six patients with Takayasu's arteritis.

METHODS

The minimal, maximal, and true colour-flow image diameters of the lumens of the grafts were measured and stenoses, occlusions, and dilatations were evaluated and compared with angiographic findings.

RESULTS

The sensitivity for detection in > 50% stenoses and in total occlusions was 75% while specificity was 100%. Only one 40% stenosis had been overlooked in whole. The maximal difference of stenosis by two methods was otherwise 20%.

CONCLUSIONS

CDFI was in general able to expose stenoses in supra-aortic grafts, but the lack of visibility of some grafts throughout their length cause the false results. It appears that some angiographies can be replaced by CDFI and that this is a suitable method for follow-up in symptom-free patients with grafts.

Revision of failing lower extremity bypass grafts

BACKGROUND

Color-duplex ultrasound (CDU) surveillance of arterial bypass grafts has been validated, but the natural history of "failing" grafts remains poorly defined. Our purpose was to compare failing grafts having prophylactic revision with those that did not.

METHODS

Postoperative duplex surveillance was performed in an accredited vascular laboratory for all lower extremity bypass grafts performed at a single institution. Eighty-five infrainguinal grafts (57 vein, 21 polytetrafluoroethylene (PTFE), and 7 composite grafts) in 83 patients were identified as failing by accepted criteria. Twenty-five grafts were revised early (early), 20 grafts revised more than 2 months after the initial CDU-abnormality (late), and 40 grafts were not prophylactically revised (no revision) at any time.

RESULTS

The three groups were not different (P > 0.10) with regard to gender, age, level of bypass, type of conduit, location of stenoses, or timing of abnormality after surgery. No revision patients more frequently had diffuse low peak systolic flow velocity (PSV) as the CDU abnormality (P = 0.013). Cumulative primary patency was significantly better at 12 months (P = 0.028) in the no revision group (78.9%) compared with early grafts (43.1%) or late grafts (63.8%), and this difference remained significant when low PSV grafts were excluded from analysis. However, assisted primary patency, secondary patency, and limb salvage rates did not differ between the three groups (P > 0.10).

CONCLUSIONS

Our experience in this retrospective study contradicts other reports supporting the efficacy of prophylactic graft revision for grafts identified as failing by currently accepted CDU criteria. Refinement of CDU criteria to more accurately predict graft thrombosis is needed.

The utility of duplex scanning in infrainguinal vein graft surveillance: results from a randomised controlled study

OBJECTIVES

To evaluate the utility and efficacy of colour-coded duplex scanning as an adjunct to clinical surveillance of infrainguinal vein bypass surgery.

DESIGN

Prospective controlled randomised trial.

METHODS

The trial included 179 consecutive patients undergoing 185 primary infrainguinal vein graft reconstructions during a 3-year period. Patients alive without amputation and with open graft at 1 month were randomised to a surveillance program based on clinical examination and ankle-brachial pressure index measurement (ABI group) or additional duplex scanning (DD group). All patients were scheduled for surveillance at 1, 3, 6, 9 and 12 months after operation.

RESULTS

Surveillance identified four failing grafts in the ABI group and 11 in the DD group which were revised. The number of occluded grafts was seven in ABI group and 12 in DD group. At 1-year overall cumulative assisted primary patency rates in the ABI group and in the DD group were 74% and 65% respectively (p = 0.21), corresponding secondary patency rates were 84% and 71% (p = 0.04) and limb salvage rates 88% versus 81% (p = 0.23) respectively.

CONCLUSIONS

This study failed to show any beneficial effect of duplex scanning in a surveillance program, which was difficult to accomplish as a part of routine clinical work. However, the main difference in outcome appeared during the first postoperative month before the commencement of the surveillance program.

The natural history of "failing" arterial bypass grafts in a duplex surveillance protocol

Though color duplex ultrasonography (CDU) can identify threatened arterial bypass grafts, the natural history of grafts predicted to fail is not known. We examined patency of "failing grafts" followed by CDU for prolonged periods without intervention. A graft was defined as failing if there was elevation of the peak systolic flow velocity (PSFV) to a ratio of three times the PSFV in the adjacent graft, or if PSFV was less than 45 cm/sec throughout the graft. Only patients followed with CDU abnormalities without intervention for more than 2 months were included. Forty-six CDU abnormalities were noted after construction or revision of lower extremity bypass grafts in 34 patients. Grafts were autogenous in 25 cases, prosthetic in 16, and composite in 5. Focal abnormalities were noted in 35 grafts (76.1%), low PSFV throughout the graft in 6 (13.0%), while both findings were present in 5 grafts (10.7%). For various reasons no intervention was performed during follow-up ranging from 2 to 50 (mean 10) months, during which time patients had a mean of 3.6 CDU studies. Abnormalities regressed in 10 grafts (21.7%), progressed to 5 (10.9%), and were stable in the remainder. Fourteen grafts (30.4%) were ultimately revised with surgery or angioplasty at a mean of 5 months after the first abnormal CDU. Only 3 grafts (6.5%) occluded while being followed. Two of the 3 were among the 5 grafts with both focal elevated PSFV ratio and low PSFV throughout the remaining graft, while all 3 were among the 7 grafts with PSFV ratio in excess of 7.0. Compared to grafts without these features, occlusion was significantly more likely (p = 0.03 and p = 0.001, respectively). Currently defined threshold CDU criteria for prediction of graft failure may be excessively sensitive.

At what peak velocity ratio value should duplex-detected infrainguinal vein graft stenoses be revised?

OBJECTIVES

To determine the peak velocity ratio (PVR) threshold at which to intervene and correct duplex detected vein graft stenoses.

DESIGN

Prospective study.

MATERIALS

Infrainguinal vein grafts in patients attending the vascular studies for routine postoperative surveillance.

METHODS

Colour duplex detected stenotic vein graft lesions with a peak velocity ratio (PVR) between 2.0 and 2.9 were identified and monitored by serial duplex scans performed monthly for 3 months and then at 3-monthly intervals thereafter. At the end of the study period, the outcome of these lesions were analysed.

RESULTS

Thirty-eight lesions were identified from 32 grafts. Of these lesions, sixteen (42%) resolved, 11 (29%) remained stable and 11 (29%) progressed to a PVR of > or = 3.0 and underwent angioplasty. There were no occlusions in any of the grafts during the period of study.

CONCLUSIONS

Colour duplex detected vein graft stenoses with a PVR of less than 3.0 can be treated expectantly if grafts with stenoses with a PVR 2.0-2.9 are scanned every month for at least 3 months after detection.

Prospective validation of threshold criteria for intervention in infrainguinal vein grafts undergoing duplex surveillance

Although color flow duplex surveillance (CFDS) of infrainguinal vein grafts has gained wide acceptance, definitive criteria mandating graft revision remain to be established. We prospectively evaluated 101 infrainguinal vein grafts undergoing CFDS in order to validate threshold duplex criteria for intervention which were derived from our previous experience and that reported by others. Complete CFDS of the bypass conduit and adjacent inflow and outflow arteries and Doppler-derived ankle brachial indices (ABI) were obtained every 3 months x 4 and every 6 months thereafter. The following threshold criteria mandating further evaluation and intervention to prevent graft occlusion were applied: high-velocity criteria (HVC) defined as peak systolic velocity (PSV) > 300 cm/sec and velocity ratio (Vr) > 3.5; low-velocity criteria (LVC) defined as PSV < 45 cm/sec; an ABI decrease > 0.15. Fifty-one grafts had normal serial CFDS and ABI; none subsequently occluded or required revision. Stenosis was detected by CFDS in 43 grafts (PSV > 180 cm/sec, Vr > 1.5). Within this subgroup, 54% of grafts subsequently required revision (20/43) or occluded (3/43). All grafts in this subgroup with stenoses progressed to PSV > 300 or Vr > 3.5 prior to revision or occlusion. Ten lesions (23%) regressed spontaneously without intervention (mean PSV 252 cm/sec, mean Vr 3.2); 10 lesions (23%) are stable, non-progressive, and remain under surveillance. Two grafts were abnormal by LVC; one was successfully revised, the other occluded prior to intervention. Five grafts had normal CFDS and ABI decrease > 0.15. Four were revised (three inflow lesions, one outflow lesion) and one occluded (missed lesion by CFDS). Only five graft occlusions occurred in the entire series: three grafts met HVC and occluded prior to intervention; one developed an ABI drop of 0.4 due to graft stenosis missed by CFDS and uncovered following thrombolysis, and the other graft met LVC and occluded prior to intervention. Infrainguinal vein grafts with normal serial CFDS and ABI are at minimal risk of spontaneous graft occlusion. When CFDS is abnormal (PSV > 180 cm/sec, Vr > 1.5), over 50% of grafts will ultimately require revision or progress to occlusion. Grafts with such lesions can be safely monitored by CFDS until progression to lesions meeting HVC occurs with minimal risk of graft occlusion. A decrease in ABI > 0.15 with normal CFDS mandates arteriography to identify inflow and outflow lesions or a missed graft stenosis. The present study prospectively validates threshold intervention criteria for graft lesions meeting HVC (PSV > 300 cm/sec, Vr > 3.5), LVC (PSV < 45 cm/sec throughout graft) or an ABI decrease > 0.15.

One-point measurement of the peak-to-peak pulsatility index as an indicator for evaluation of infrainguinal bypass procedures

While duplex scanning has been advocated as the most accurate modality for postoperative graft surveillance, it is time-consuming for evaluating the entire graft. The aim of the present study was to determine which parameter predicts graft failure most simply and precisely, by examining 62 men and 1 woman who collectively underwent 71 infrainguinal arterial bypasses. A total of 212 scannings were obtained using a duplex scanner, and the peak systolic velocity (PSV), PSV ratio, and peak-to-peak pulsatility index (PPI) were analyzed. This analysis revealed 7 occlusions, 9 stenoses, and 1 arteriovenous fistula. When a PSV < 45 cm/s and/or a PSV ratio > 2.0 was defined as graft failure the sensitivity was 84.0% and the specificity was 81.8%: however, a PPI < 7.0 at the midgraft, indicating graft failure, showed a sensitivity of 100% and a specificity of 83.3%. The PPI exhibited better sensitivity and specificity than the PSV, even though the PPI needs only to be measured at the midgraft whereas the PSV should be measured at at least two points. Thus, we believe that the PPI could be the most useful and simple parameter to assess infrainguinal bypass grafts.

Arteriovenous fistulas aggravate the hemodynamic effect of vein bypass stenoses: an in vitro study

PURPOSE

The purpose of this study was to assess the impact of arteriovenous fistulas combined with varying degrees of stenosis on distal bypass hemodynamics and Doppler spectral parameters.

METHODS

In an in vitro flow model bypass stenoses causing 30%, 55%, and 70% diameter reduction were induced 10 cm upstream of a fistula with low outflow resistance. Flow and intraluminal pressure were measured proximal to the stenosis and downstream of the fistula. The waveform parameters peak systolic velocity, end-diastolic velocity, pulsatility index, and pulse rise time were determined from midstream Doppler spectra obtained 10 cm downstream of the fistula. All measurements were carried out with open and clamped fistula.

RESULTS

At 30% diameter reducing stenosis opening of the fistula induced a 12% systolic pressure drop across the stenosis but had no adverse effect on the Doppler waveform parameters. At 55% stenosis the pressure drop increased from 16% to 31% after fistula opening. This increased pressure drop was associated with a further reduction in peak systolic velocity, a decrease in pulsatility index, and an enhanced pulse rise time prolongation. Fistula opening at 70% stenosis increased the systolic pressure drop from 31% to 48% and had significant impact on all waveform parameters.

CONCLUSIONS

Distal arteriovenous fistulas enhance pressure loss across stenoses and affect downstream velocity waveform configuration. The presence of a combined fistula and a stenosis mimics the distal hemodynamic conditions of a more severe stenosis. Assessment of the hemodynamic impact of fistulas must be undertaken in the evaluation of in situ vein bypass stenoses.