Proximal Vein Segments Research Articles

Computational Analysis of Turbulent Hemodynamics in Radiocephalic Arteriovenous Fistulas to Determine the Best Anastomotic Angles

Hemodynamics has been known to play a major role in the development of intimal hyperplasia leading to arteriovenous fistula failure. The goal of our study is to investigate the influence of different angles of side-to-end radiocephalic anastomosis on the hemodynamic parameters that promote intimal dysfunction and therefore intimal hyperplasia. Realistic three-dimensional meshes were reconstructed using ultrasound measurements from distal side-to-end radiocephalic fistulas. The velocity at the proximal and distal radial inflows and at specific locations along the anastomosis and cephalic vein was measured through duplex ultrasound performed by a single examiner. A computational parametric study, virtually changing the inner angle of anastomosis, was performed. For this purpose, we used advanced computational models that include suitable tools to capture the pulsatile and turbulent nature of the blood flow found in arteriovenous fistulas. The results were analyzed in terms of velocity fields, wall shear stress distribution, and oscillatory shear index. Results show that the regions with high oscillatory shear index, which are more prone to the development of hyperplasia, are greater and progressively shift toward the anastomosis area and the proximal vein segment with the decrease of the inner angle of anastomosis. These results are specific to distal radiocephalic fistulas because they are subject to proximal and distal radial inflow. The results of this study show that inner anastomosis angles approaching 60-70° seem to yield the best hemodynamic conditions for maturation and long-term patency of distal radiocephalic fistulas. Inner angles greater than 90°, representing the smooth loop technique, did not show a clear hemodynamic advantage.

Management of Venous Thromboembolism (VTE) in Thrombocytopenic Patients Undergoing Induction Chemotherapy for Acute Leukemia

Introduction: Management of VTE in patients with hematological malignancies is challenging as these patients often have thrombocytopenia and are at increased risk for bleeding. The International Society of Thrombosis and Hemostasis (ISTH) guidance statement recommends adjusting anticoagulation based on the severity and acuity of VTE and considering platelet transfusion support to maintain platelet counts above >50K/µL to facilitate full-dose anticoagulation (AC) in patients with acute VTE with high-risk features. For acute VTE with low-risk features, a dose-modified strategy such as half- or prophylactic-dose AC, depending on platelet count, is recommended. While the risk of AC with supportive platelet transfusions may be justified in patients with severe VTE, lower-dose AC without platelet transfusion support may be adequate for patients with non-severe VTE and may reduce the risk for development of platelet alloantibodies. To better understand practice patterns at our institution, we reviewed the management of VTE in patients with acute leukemia over an 8-year period.Methods: We retrospectively reviewed all patients with acute leukemia who developed acute VTE during induction chemotherapy at Dartmouth-Hitchcock Medical Center for the 8-year period (2006-2013). Primary outcomes were 1) objectively confirmed, recurrent symptomatic VTE, and 2) clinically significant bleeding within 1 month after diagnosis of the index VTE. Secondary outcomes included IVC filter use and platelet alloantibody development within 3 months after diagnosis of VTE. We classified VTE events as acute or subacute/chronic and severe or non-severe. An acute event was defined as a new VTE diagnosed during the index hospitalization, while a subacute/chronic event was defined as a VTE that occurred prior to the index hospitalization for which the patient was being treated with AC during the hospitalization. A severe VTE was defined as a DVT involving femoral or more proximal vein segments, the SVC, cerebral veins or any PE. Non-severe events included UE DVT and distal DVT. We classified treatment at the time of diagnosis of VTE into one of the following categories: 1) full-dose AC with platelet transfusion to maintain platelet count >25-50K/µL, 2) half-dose AC with platelet transfusion to maintain platelet count >25-50K/µL, 3) prophylactic-dose AC without additional platelet transfusion beyond the standard of care, 4) no anticoagulation. We recorded the number of IVC filters inserted in each category. Descriptive statistics, including mean and standard deviation for continuous variables, and percentage and frequency for categorical variables, were calculated.Results: 40 subjects met entry criteria (55% male) with median age of 57.5 years. The majority (88%) had acute myeloid leukemia. Acute VTE was identified in 80% and VTE was severe in 55%. The degree of thrombocytopenia at the time of VTE diagnosis was <10K/µL (2.5%), 10-25K/µL (25%), 25-50K/µL (40%), and >50K/µL (32.5%). Subjects were initially treated with full-dose AC (60%), half-dose AC (5%), prophylactic-dose AC (12%) or no AC (22.5%). An IVC filter was inserted in 10 subjects (25%), and five subjects (12%) developed platelet alloantibodies. Seventeen subjects (42%) experienced bleeding complications within the first month of VTE diagnosis, six of which (35%) were clinically significant. Half of these were on full-dose AC, and half underwent insertion of an IVC filter. Two subjects (5%) had VTE recurrence within 1 month, and in both cases, AC had been discontinued prior to the recurrence due to bleeding complications.Conclusion: We found that management of VTE in patients with acute leukemia and thrombocytopenia varies and that the risk for bleeding complications was high irrespective of AC dose. We also uncovered the problem of VTE recurrence due to premature discontinuation of AC as a result of bleeding and observed a surprisingly high incidence of platelet alloimmunization. Dose-modified AC without platelet transfusion support may be an attractive alternative for treatment of VTE in this population, but further study is required to balance bleeding and thrombosis risk. DisclosuresNo relevant conflicts of interest to declare.

Recanalization Rates after Acute Deep Vein Thrombosis: A Single-center Experience Using a Newly Proposed Vein Diameter Variation Index

Duplex ultrasound scanning (DUS) is the method of choice for diagnosis of deep vein thrombosis (DVT). However, only a few studies have performed prospective serial DUS after an acute episode of DVT to assess its evolution. This study aimed to report our experience using DUS combined with a thrombosis score (TS) and a newly proposed vein diameter variation index (VDVI) to evaluate the rate of resolution of DVT by assessing and quantifying the early stages of vein recanalization in proximal vein segments within 6months after an episode of acute lower extremity DVT. Twelve patients with first episode of acute lower extremity DVT confirmed by DUS as occurring in ≤10days after the onset of venous thrombosis symptoms were followed up prospectively for 6months. TS and VDVI were calculated at 1, 3, and 6months to assess vein recanalization. Intra-thrombus arteriovenous fistula formation was also investigated and related to the recanalization process. Seven (58%) women were included, with a total cohort median age of 53.5±19years. The left lower extremity was affected in 7 (58%) patients. DVT was diagnosed in 55 proximal vein segments. All patients had proximal DVT, with involvement of the external iliac, femoral, and popliteal veins. After 6months, there was a significant decrease in TS and increase in VDVI (P<0.001) in all proximal vein segments assessed, indicating thrombus regression. The more distal the DVT was, the faster was the VDVI increase, with most popliteal veins being recanalized at 3months (P<0.001). Intra-thrombus arteriovenous fistula was identified in 50% of patients at 1month while on anticoagulation. The combined use of two different DUS-based assessment tools, TS and the proposed VDVI, provided an effective method to prospectively assess vein recanalization rates after an episode of acute lower extremity DVT in this series of patients and may allow a correct evaluation of DVT and its resolution or progression.

Stenting of coronary veins: a critical comment

Daniel Gras was the first to describe coronary venous stenting.1 Like other authors,2,3 he used a coronary stent to fixate a coronary vein (CV) lead in a proximal vein segment when more distal placement led to intractable phrenic nerve stimulation. At the Europace meeting in Lisboa in 2007 and at the 2008 Cardiostim conference in Nice, Szilagyi et al. presented their data on venous stenting in a larger cohort. The majority of … *Corresponding author. Tel: +49 5731 971913; fax: +49 5731 971820. E-mail address : bhansky{at}hdz-nrw.de

Varicose Veins Possess Greater Quantities of MMP-1 Than Normal Veins and Demonstrate Regional Variation in MMP-1 and MMP-13

Background. Studies have reported that structural proteins such as elastin and collagen are decreased in varicose veins compared to normal controls. We hypothesized that the changes observed in varicose vein wall composition may be related to alterations in extracellular matrix remodeling proteins, such as the matrix metalloproteases and serine proteases. In addition we hypothesized that there may be regional variation in the expression of these enzymes within the leg. Patients and materials. One-centimeter segments of the proximal and distal greater saphenous vein (GSV) were obtained from patients undergoing ligation and stripping for venous insufficiency (vv) ( n = 15) or GSV harvest in conjunction with coronary artery bypass grafting (CABG) ( n = 7). All vv patients had incompetence of the GSV by color flow duplex. Vein specimens were examined for MMP-1, 3, and 13, tryptase, and GAPDH mRNA using semiquantitative RT–PCR analysis. Quantification of MMP-1 and 13 (active/latent forms) and tryptase was performed using Western blot analysis. Western blots were analyzed using scanning densitometry and standardized to normal controls and values expressed as the median densitometric index (D.I.). Nonparametric statistical methods (Wilcoxan signed rank test and Mann–Whitney U test) were used for analysis. Results. We were able to amplify MMP-1, MMP-13, and tryptase mRNA from both proximal and distal segments of all greater saphenous veins studied. MMP-3 mRNA, however, was not found in either segment of any of the veins examined. A semiquantitative analysis of RT–PCR products comparing the ratio of MMP-1, MMP-13, or tryptase mRNA to GAPDH mRNA showed no difference between cases and controls nor proximal vs distal vein segments. Western blot analysis revealed larger quantities of MMP-1 in varicose veins than in nondiseased veins from CABG patients (48.0 ± 36.7 D.I. vs 12.5 ± 6.8 D.I., P = 0.036). Investigation into the regional variation of proteases revealed lower amounts of MMP-1 in distal than in proximal vein segments (37.9 ± 35.0 D.I. vs 44.1 ± 41.6 D.I., P = 0.01). Similarly, we found significantly less MMP-13 in distal segments of varicose veins than in proximal segments (152.8 ± 130.0 D.I. vs 206.7 ± 173.3 D.I., P = 0.006). Conclusions. This study found that MMP-1 protein is increased in varicose veins when compared to controls despite no differences in mRNA expression. In addition we found that there is regional variation of MMP-1 and MMP-13 in diseased varicose veins. Lower leg veins have significantly reduced amounts of these proteolytic enzymes when compared to veins of the upper thigh. These data suggest that posttranscriptional regulatory controls could be responsible for the observed differences.

Venous duplex scanning of the leg: range, variability and reproducibility

Despite the many studies on venous haemodynamics using duplex, only a few evaluated the normal values, variability and reproducibility. Therefore, the range and variability of venous diameter, compressibility, flow and reflux were measured. To obtain normal values, 42 healthy individuals (42 limbs, 714 vein segments) with no history of venous disease were scanned by duplex. To determine the reproducibility the intra-observer variability was measured in 11 healthy individuals (187 vein segments) and the inter-observer variability in 15 healthy individuals (255 vein segments) and 13 patients (169 vein segments) previously diagnosed with deep venous thrombosis. Of the 714 normal vein segments, 708 (99%) were traceable, including the crural veins. Of the traceable vein segments, 675 (95%) were compressible and in 696 (98%) flow was present. Of the 42 common femoral vein segments, in 25 (60%) the reflux duration exceeded 1.0 s, but in the other proximal vein segments the reflux duration was less than 1.0 s (95% confidence interval 3.0-10.0). With the exception of the distal long saphenous vein, in the distal vein segments the reflux duration was less than 0.5 s (95% confidence interval 3.5-8.2). The coefficient of variation of the diameter measurements ranged from 14 to 50% and that of the reflux measurements from 28 to 60%. The kappa-coefficient of the inter-observer variability in the classification of compressibility measurements in the patients was 0. 77 and that of the reflux measurements was 0.86. This study shows that almost all veins were compressible in healthy individuals, except the distal femoral veins. In healthy individuals the duration of reflux of the proximal veins was less than 1.0 s and in the distal veins it was less than 0.5 s. The inter-observer variability of the reflux and compressibility measurements in the patients was good.

Deep venous thrombosis: a prospective 3-month follow-up using duplex scanning and strain-gauge plethysmography.

1. The purpose of the study was to evaluate the degree of thrombus regression, development of valvular insufficiency, impaired calf muscle pump function and clinical symptoms after a period of acute deep venous thrombosis. 2. Seventy patients with acute deep venous thrombosis, diagnosed by duplex scanning or venography, received treatment with heparin and oral coumarin derivatives according to a standard protocol. All patients wore graduated compression stockings during the whole study period. Duplex scanning was performed at diagnosis and 1 and 3 months later to measure thrombus mass and reflux. The supine venous pump function test was used to assess calf muscle pump function. 3. Three months follow-up was completed in 60 patients. In total 218 (28%) out of 780 vein segments were initially thrombosed and 134 (17%) could not be traced. A statistically significant reduction of thrombus mass was recorded throughout the study period. Total resolution of thrombosis in all vein segments occurred in 25% of the patients within 1 month and in 40% in 3 months. There was no difference in regression between the various proximal vein segments. Distal segments showed more regression than proximal segments. Reflux occurred in 27% of the initially thrombosed veins and in 15% of the patent veins. Patients who showed total resolution after 1 month had a significantly higher calf muscle pump function than patients without total resolution (70%pf vs 61%pf, P < 0.05). Patients with reflux in two or more segments had a significantly lower calf muscle pump function than patients with reflux in less than two segments (58%pf vs 69%pf, P < 0.05). 4. Using duplex scanning and the supine venous pump function test 3 months after an acute deep venous thrombosis, overall haemodynamic abnormalities and local site of valve incompetence could readily be identified. Patients with haemodynamic abnormalities might be at risk to develop the post-thrombotic syndrome. There was no difference in thrombus regression between the various proximal vein segments. Reflux was significantly more often seen in initially thrombosed veins. Thirty-five percent of the patients developed an abnormal calf muscle pump function after 3 months. Patients with early resolution of thrombus had a higher calf muscle pump function after 3 months.

Duplex ultrasound in the hemodynamic evaluation of the late sequelae of deep venous thrombosis

Purpose:The use of duplex ultrasound scanning to evaluate the hemodynamic outcome of deep venous thrombosis 7 to 13 years after the original diagnosis. Methods: Duplex ultrasound was used to re-examine 1212 segments of vein from 72 patients (49 men, 23 women) with deep venous thrombosis previously diagnosed by means of phlebography to detect reflux and obstruction and evaluate flow; 611 segments were initially thrombosed and 601 segments were open. To define reflux, reversed flow in 31 healthy persons was measured. Results: In a review of all veins of the 72 patients, 8 patients (11%) had completely normal duplex results in all veins, 33 (46%) had reflux, 6 (8%) had at least one noncompressible vein segment, and 25 (35%) had a combination of both. In the proximal vein segments without initial thrombosis a higher percentage was normal (73%) than in segments with initial thrombosis (46%). There was a significantly higher frequency of reflux (46%, p = 0.05) and noncompressibility (12%, p < 0.01) in initially thrombosed proximal vein segments than in vein segments without initial thrombosis (reflux 25%, noncompressibility 3%). Distal to the knee 125 (17%) of 720 vein segments were not traceable. Significantly more initially thrombosed vein segments were not traceable ( p < 0.01). In distal vein segments there was no significant difference in reflux (7% versus 5%) and noncompressibility (10% versus 5%) between vein segments with and without initial thrombosis. Flow was present in 99% of the 611 previously thrombosed proximal and distal segments. Conclusions: Most patients with deep venous thrombosis still had venous abnormalities 7 to 13 years after the initial diagnosis. The most common abnormality was reflux. Significantly more abnormalities were found in initially thrombosed segments. The abnormalities were found in the proximal vein segments and in the distal vein segments, although less frequently in the latter. (J Vasc Surg 1998;27:472-8.)