Hemodynamics and Wall Mechanics of Vascular Graft Failure

Blood vessels are subjected to complex biomechanical loads, primarily from pressure-driven blood flow. Abnormal loading associated with vascular grafts, arising from altered hemodynamics or wall mechanics, can cause acute and progressive vascular failure and end-organ dysfunction. Perturbations to mechanobiological stimuli experienced by vascular cells contribute to remodeling of the vascular wall via activation of mechanosensitive signaling pathways and subsequent changes in gene expression and associated turnover of cells and extracellular matrix. In this review, we outline experimental and computational tools used to quantify metrics of biomechanical loading in vascular grafts and highlight those that show potential in predicting graft failure for diverse disease contexts. We include metrics derived from both fluid and solid mechanics that drive feedback loops between mechanobiological processes and changes in the biomechanical state that govern the natural history of vascular grafts. As illustrative examples, we consider application-specific coronary artery bypass grafts, peripheral vascular grafts, and tissue-engineered vascular grafts for congenital heart surgery as each of these involves unique circulatory environments, loading magnitudes, and graft materials.

Integrating vascular access surveillance with clinical monitoring for stenosis prediction

BACKGROUND

Arteriovenous fistula and arteriovenous graft are the most common types of vascular access for dialysis; stenosis and thrombosis are major complications leading to access failure and to an incresed risk of mortality. The aim of the present study was to assess the results of integrating  strict vascular access blood flow surveillance with routine clinical monitoring for predicting vascular access stenosis in chronic hemodialysis patients.

METHODS

In this retrospective study, chronic dialysis patients with arteriovenous fistula or arteriovenous graft were included from a setting in which all patients underwent quarterly blood flow surveillance in 2017. The results of blood flow surveillance were confirmed by thorough physical examination. Predictive performance of blood flow surveillance models in detecting stenosis in patients with arteriovenous fistula or arteriovenous graft was evaluated. The predictive performance of the quarterly blood flow surveillance model was described by confusion matrix. Differences in accuracy, positive predictive value (PPV), and negative predictive value (NPV) between blood flow surveillance models with distinct blood flow thresholds were evaluated.

RESULTS

Of 397 included patients, 336 had an arteriovenous fistula and 61 had an arteriovenous graft. In 2017, 106 percutaneous transluminal angioplasty procedures were performed in patients with an arteriovenous fistula, and 63 in patients with an arteriovenous graft. The results revealed similar predictive performance of surveillance models using an absolute blood flow threshold of < 500 or < 400 mL/min in predicting stenosis in patients with arteriovenous fistula. Blood flow surveillance models for patients with an arteriovenous fistula had significantly higher accuracy than those for patients with an arteriovenous graft. Furthermore, the use of a relative threshold, defined as blood flow < 1000 mL/min and a 25% decline in blood flow, did not affect the predictive performance of blood flow surveillance models.

CONCLUSION

Blood flow surveillance models using thresholds of < 400 and < 600 mL/min, followed by thorough physical examination, showed an accuracy of 91.54% and 72.15% in predicting stenosis in patients with arteriovenous fistula and arteriovenous graft, respectively. These two blood flow surveillance models may be integrated with routine clinical monitoring to improve early detection and treatment of stenosis in hemodialysis patients.

Poor runoff and distal coverage below the knee are associated with poor long-term outcomes following endovascular popliteal aneurysm repair

OBJECTIVE

Reports of good short-term outcomes for endovascular repair of popliteal artery aneurysms have led to an increased use of the technique. However, data are lacking on long-term limb-related outcomes and factors associated with the failure of endovascular repair.

METHODS

All patients who underwent endovascular popliteal aneurysm repair (EPAR) at a single institution from January 2006 to December 2018 were included in the study. Demographics, indications, anatomic and operative details, and outcomes were reviewed. Long-term patency, major adverse limb event-free survival (MALE-FS) and graft loss/occlusion were analyzed with multivariable cox regression analysis and Kaplan-Meier curves.

RESULTS

We included 117 limbs from 101 patients with a mean follow-up of 55.6 months (range, 0.43-158 months). The average age was 73 ± 9.3 years. Thirty-two patients (29.1%) were symptomatic (claudication, rest pain, tissue loss, or rupture). The stent grafts crossed the knee joint in 91.4% of cases. In all, 36.8% of procedures used one stent graft, 41.0% used two stent grafts, and 22.2% of procedures used more than two stent grafts. The median arterial length covered was 100 mm, with an average length of stent overlap of 25 mm. Tapered configurations were used in 43.8% of cases. The majority of limbs (62.8%) had a three-vessel runoff, 20.2% had a two-vessel runoff, and 17% has a one-vessel runoff. The Kaplan-Meier estimates of graft occlusion at 1 and 3 years were 6.3% and 16.2%, respectively. The 1- and 3-year primary patency rates were 88.2% and 72.6%, and the 1- and 3-year major adverse limb event-free survival (MALE-FS) rates were 82% and 57.4%. The 1- and 3-year survival rates were 92.9% and 76.2%, respectively. On multivariable Cox regression, aneurysm size, one-vessel runoff, and coverage below the knee were associated with a lower 3-year MALE-FS. Coverage below the knee was also associated with a lower 3-year MALE-FS. Other anatomic or technical details were not associated with limb-related events or patency.

CONCLUSIONS

This study is the largest single center analysis to describe the predictors of poor outcomes after EPAR. EPAR is a safe and effective way to treat popliteal artery aneurysms. Factors associated with poor MALE-FS after EPAR include single-vessel tibial runoff and coverage below the knee.

C-Reactive Protein to Albumin Ratio in Patients With Saphenous Vein Graft Disease

Atherosclerosis plays an important role in saphenous vein graft disease (SVGD). Previous studies showed that inflammatory blood cells play an active role in this process. C-reactive protein to albumin ratio (CAR) is considered as a novel predictor for cardiovascular risk and an indicator of inflammation. We aimed to assess the relationship between SVGD and CAR. A total of 711 participants with saphenous vein graft (SVG) were included; 348 patients had SVGD and 363 patients had patent (no stenosis) SVG. C-reactive protein to albumin ratio was higher in patients with SVGD (P < .001). There was a significant positive correlation between CAR and the age of SVG (r = 0.123; P = .001) and SYNTAX score (r = 0.568; P < .001). Multivariate logistic regression analyses showed that lymphocyte count, CAR, and SYNTAX score were independent predictors of SVGD (P < .05). C-reactive protein to albumin ratio may be a useful marker after bypass surgery to predict SVGD.

Long Term Results of Bypass Graft to the Right Atrium in the Management of Superior Vena Cava Syndrome in Dialysis Patients

BACKGROUND

Superior vena cava (SVC) occlusion in dialysis patients is a serious complication that can cause SVC syndrome and vascular access dysfunction. While endovascular therapy has advanced to become the first line of treatment, open surgical treatment may still be needed occasionally. However, no long term outcome data has been previously reported.

METHODS

We performed a retrospective review of 5 dialysis patients treated with bypass graft to the right atrium from 2012 to 2014. Four patients had severe dysfunction of their upper arm dialysis access as well as superior vena cava syndrome, and one patient with a femoral tunneled dialysis catheter (TDC) had SVC occlusion. None of the patients were candidates for lower extremity access creation or peritoneal dialysis (PD). Three patients underwent a left brachiocephalic-right atrial bypass and 2 underwent a bypass from the cephalic fistula to the right atrium.

RESULTS

All procedures were technically successful and maintained function of the arteriovenous fistulas or allowed creation of a new upper extremity dialysis graft. One-year secondary patency rate of the bypass was 100%. Longer follow up revealed that one patient died of leg sepsis and another one of a stroke within 14 months after the procedure. Another patient did well for 16 months when recurrent graft thrombosis occurred; and ultimately the graft failed after 31 months despite multiple interventions. Two patients maintained bypass graft patency during a follow up of 78 months; however, they underwent multiple endovascular interventions (23) and open vascular access procedures (4) to maintain hemodialysis function.

CONCLUSION

Bypass grafts to the right atrium in dialysis patients with SVC occlusion are successful in maintaining function of already existing vascular access or new ones. Long term secondary patency can be achieved but requires strict follow up and a proactive endovascular strategy to treat lesions in the access and or the bypass graft.

Relation between functional coronary artery stenosis and graft occlusion after coronary artery bypass grafting

OBJECTIVES

This study was conducted to evaluate graft patency rates during the 5 years after coronary artery bypass grafting according to the functional significance of the coronary artery stenosis, as determined by myocardial single-photon-emission computed tomography.

METHODS

Two hundred ninety-five patients who underwent coronary artery bypass grafting using Y-composite grafts based on the in situ left internal thoracic artery, and in whom preoperative stress/rest myocardial single-photon-emission computed tomography and 1-year angiographies were available were enrolled. Seven hundred sixty-nine and 262 distal anastomoses were constructed to ischemic and nonischemic areas, respectively. One-year and 5-year angiographic occlusion rates were evaluated in all and 80.3% of study patients, respectively. Factors associated with graft occlusion were evaluated using generalized linear mixed-effects models.

RESULTS

Overall 1- and 5-year graft occlusion rates were 4.3% (44 of 1031 distal anastomoses) and 5.5% (45 out of 820), respectively. The occlusion rates of grafts bypassed to vessels with functionally significant and insignificant stenosis were 2.7% (21 out of 769) and 8.8% (23 out of 262) at 1 year and were 4.0% (25 out of 618) and 9.9% (20 out of 202) at 5 years, respectively. Graft occlusion during the 5 years after coronary artery bypass grafting was associated with the functional significance of coronary artery stenosis (odds ratio, 0.50; 95% confidence interval, 0.28-0.92). The odds ratio of the graft occlusion according to functional ischemia was lower and significant in grafts to arteries with intermediate stenosis (stenosis ≥70% but <90%; odds ratio, 0.34; 95% confidence interval, 0.13-0.93) whereas it was higher and insignificant in grafts to arteries with severe stenosis (≥90% stenosis; odds ratio, 0.76; 95% confidence interval, 0.33-1.72).

CONCLUSIONS

Graft occlusion during the 5 years after coronary artery bypass grafting was associated with the functional significance of coronary artery stenosis, particularly when the stenosis degree was not severe.

Considerations in the Development of Small-Diameter Vascular Graft as an Alternative for Bypass and Reconstructive Surgeries: A Review

BACKGROUND

Current design strategies for small diameter vascular grafts (< 6 mm internal diameter; ID) are focused on mimicking native vascular tissue because the commercially available grafts still fail at small diameters, notably due to development of intimal hyperplasia and thrombosis. To overcome these challenges, various design approaches, material selection, and surface modification strategies have been employed to improve the patency of small-diameter grafts.

REVIEW

The purpose of this review is to outline various considerations in the development of small-diameter vascular grafts, including material choice, surface modifications to enhance biocompatibility/endothelialization, and mechanical properties of the graft, that are currently being implanted. Additionally, we have taken into account the general vascular physiology, tissue engineering approaches, and collective achievements of the authors in this area. We reviewed both commercially available synthetic grafts (e-PTFE and PET), elastic polymers such as polyurethane and biodegradable and bioresorbable materials. We included naturally occurring materials by focusing on their potential application in the development of future vascular alternatives.

CONCLUSION

Until now, there are few comprehensive reviews regarding considerations in the design of small-diameter vascular grafts in the literature. Here-in, we have discussed in-depth the various strategies employed to generate engineered vascular graft due to their high demand for vascular surgeries. While some TEVG design strategies have shown greater potential in contrast to autologous or synthetic ePTFE conduits, many are still hindered by high production cost which prevents their widespread adoption. Nonetheless, as tissue engineers continue to develop on their strategies and procedures for improved TEVGs, soon, a reliable engineered graft will be available in the market. Hence, we anticipate a viable TEVG with resorbable property, fabricated via electrospinning approach to hold a greater potential that can overcome the challenges observed in both autologous and allogenic grafts. This is because they can be mechanically tuned, incorporated/surface-functionalized with bioactive molecules and mass-manufactured in a reproducible manner. It is also found that most of the success in engineered vascular graft approaching commercialization is for large vessels rather than small-diameter grafts used as cardiovascular bypass grafts. Consequently, the field of vascular engineering is still available for future innovators that can take up the challenge to create a functional arterial substitute.

In vitro hemo- and cytocompatibility of bacterial nanocelluose small diameter vascular grafts: Impact of fabrication and surface characteristics

Objective

There is an increasing need for small diameter vascular grafts with superior host hemo- and cytocompatibilities, such as low activation of platelets and leukocytes. Therefore, we aimed to investigate whether the preparation of bacterial nanocellulose grafts with different inner surfaces has an impact on in vitro host cytocompatibility.

Methods

We have synthesized five different grafts in a bioreactor, namely open interface surface (OIS), inverted (INV), partially air dried (PAD), surface formed in air contact (SAC) and standard (STD) that were characterized by a different surface roughness. The grafts (length 55 mm, inner diameter 5 mm) were attached to heparinized polyvinyl chloride tubes, loaded with human blood and rotated at 37°C for 4 hours. Then, blood was analyzed for frequencies of cellular fractions, oxidative products, soluble complement and thrombin factors. The results were compared to clinically approved grafts made of polyethylene terephthalate and expanded polytetrafluoroethylene. Additionally, blood platelets were labelled with ¹¹¹Indium-oxine to visualize the distribution of adherent platelets in the loop by scintigraphy.

Results

SAC nanocellulose grafts with the lowest surface roughness exhibited superior performance with <10% leukocyte and <50% thrombocyte loss in contrast to other grafts that exhibited >65% leukocyte and >90% thrombocyte loss. Of note, SAC nanocellulose grafts showed lowest radioactivity with scintigraphy analyses, indicating reduced platelet adhesion. Although the levels of reactive oxygen species and cell free DNA did not differ significantly, the levels of thrombin-antithrombin complexes were lowest in SAC grafts. However, all nanocellulose grafts exhibited enhanced complement activation.

Conclusion

The systematic variation of the inner surfaces of BNC vascular grafts significantly improves biocompatibility. Especially, SAC grafts exhibited the lowest loss of platelets as well as leukocytes and additionally significantly diminished activation of the coagulation system. Further animal studies are needed to study in vivo biocompatibilities.

Drug-coated balloon versus conventional balloon angioplasty of hemodialysis arteriovenous fistula or graft: A systematic review and meta-analysis of randomized controlled trials

Background

Restenosis remains a significant problem in endovascular therapy for hemodialysis vascular access. Drug-coated balloon (DCB) angioplasty decreases restenosis in peripheral and coronary artery diseases. The aim of this systematic review and meta-analysis is to assess the patency outcomes following DCB angioplasty, as compared to conventional balloon (CB) angioplasty for the stenosis of hemodialysis vascular access.

Methods

A comprehensive search in the MEDLINE, EMBASE, and CENTRAL databases was conducted in order to identify eligible randomized controlled trials evaluating DCB angioplasty for hemodialysis vascular access dysfunction. The primary endpoint was the 6-month target lesion primary patency and the secondary endpoints were 12-month target lesion primary patency and procedure-related complications. Risk ratios (RR) were pooled and relevant subgroups were analyzed separately.

Results

Eleven randomized controlled trials comprised of 487 patients treated with DCB angioplasty and 489 patients treated with CB angioplasty were included. There were no significant differences in the target lesion primary patency at 6 months [RR, 0.75; 95% confidence interval (CI), 0.56, 1.01; p = 0.06] and at 12 months (RR 0.89; 95% CI, 0.79, 1.00; p = 0.06). The absence of benefit for the DCB group remained, even in the arteriovenous fistula subgroup or the subgroup of studies excluding central vein stenosis. The risk of procedure-related complication did not differ between the two groups (RR 1.00; 95% CI 0.98, 1.02; p = 0.95).

Conclusion

DCB angioplasty did not demonstrate significant patency benefit for the treatment of hemodialysis vascular access dysfunction. Wide variations in patency outcomes across studies were noted. Further studies focusing on specific types of access or lesions are warranted to clarify the value of DCB for hemodialysis vascular access. (PROSPERO Number CRD42019119938)

Unusual Cause of Heart Failure in a Patient with Marfan Syndrome: A Late Complication of Bioprosthetic Valved Graft Replacement

A high-velocity gradient across the left ventricular outflow tract is most often caused by aortic valve stenosis. We describe the unusual case of a high-velocity gradient caused by a kinked ascending aortic graft in a 69-year-old man who had Marfan syndrome. The patient had a history of ascending aortic aneurysm and had previously undergone replacement of the aortic root and ascending aorta with use of a bioprosthetic valved graft. The kinking was caused by dilation of the native aortic arch. The patient underwent successful hemi-arch replacement and repair of the kinked graft. Late complications and reoperation after proximal aortic surgery in patients with Marfan syndrome are rare, and a high-velocity left ventricular outflow tract gradient caused by the kinking of the aorta is unusual.

Evaluation of a Novel Spun Polytetrafluoroethylene Stent Graft in an Ovine External Iliac Artery Model

PURPOSE

To evaluate the patency, cellular response, and thrombogenicity of a novel vascular stent graft.

MATERIALS AND METHODS

Test stent grafts, incorporating luminal spun polytetrafluoroethylene and a nonpermeable fluoropolymer layer, and control stent grafts, constructed of permeable expanded polytetrafluoroethylene, were implanted in the external iliac arteries of 14 adult sheep with a median weight of 73.4 kg ranging from 60.6-86.8 kg for 30 (n = 4), 90 (n = 4), and 180 (n = 6) days. Angiographic patency and percent diameter stenosis (%DS) were assessed at termination. Excised stent grafts were fixed and stained for histopathologic analysis, including neointimal coverage (NC) assessment.

RESULTS

Test and control device migration occurred in 1 animal, resulting in test device thrombosis. Both devices were excluded from analysis. Mean %DS in test and control implants was 4.6% and 8.2% (P = .563), 2.0% and 10.9% (P = .363), and 2.1% and 10.3% (P = .009) at 30, 90, and 180 days, respectively. Median NC scores at 30, 90, and 180 days were significantly lower in middle test device sections (P < .05). Proximal and distal test and control sections exhibited similar median NC scores at all time periods (P > .05). When present, test and control devices exhibited no neointimal detachment from the graft surface. Except for the migrated test device, no thrombus was observed. Transgraft cellular migration was absent in test devices but present in control devices with tissue accumulation around the stent struts.

CONCLUSIONS

Test and control devices demonstrated excellent patency in an ovine model. Compared to the control, test devices exhibited significantly lower %DS values at 180 days and significantly lower mid-device NC scores at 30, 90, and 180 days.

[Invasive functional assessment of coronary artery stenosis using fractional flow reserve]

The presence of myocardial ischemia significantly affects prognosis of patients with coronary artery disease. The fractional flow reserve (FFR) allows interventional cardiologists to evaluate whether an equivocal coronary artery stenosis is associated or not with myocardial ischemia, and therefore deserve to be properly treated. The present article has the purpose to provide the readers with an overview about the role of FFR in the diagnosis and management of coronary artery disease, as well as the potential related controversies. The coronary physiology on the basis of this tool is also provided together with all the procedural aspects useful in the catheterization laboratory. In addition, the landmark trials on the basis of the FFR application in different clinical settings and coronary anatomies will be described, together with the main improvements aiming at favoring a more extensive use of this invasive tool.

Asymptomatic, Multiple Stent Fractures of a Superficial Femoral Artery

Certain factors like ostial disease, chronic total occlusion, and long, multiple stents are the main causes of multiple stent fractures, as were present in this case. Such stent fractures are usually associated with significant in-stent restenosis; however, this patient had a patent lumen despite multiple fractures.

Effects of aspirin resistance and mean platelet volume on vascular access failure in hemodialysis patients

BACKGROUND/AIMS

Maintaining the patency of vascular access (VA) in hemodialysis (HD) patients is important and can be life-saving. We investigated the effects of aspirin resistance and mean platelet volume (MPV) on VA failure in HD patients.

METHODS

We enrolled 163 patients on maintenance HD. VA failure was defined as thrombosis or a decrease of > 50% of the normal vessel diameter, as revealed by angiography.

RESULTS

Aspirin resistance was observed in 17 of 109 patients in whom this parameter was measured, and was not significantly associated with VA failure (p = 0.051). The mean MPV was 9.15 ± 0.05 fL. The 163 patients were grouped by the median MPV value (9.08 fL) at baseline; patients with higher MPVs (n = 82) had lower platelet counts (p = 0.002) and albumin levels (p = 0.009). During 34 months of follow-up, 65 VA failures (39.9%) occurred. The Kaplan-Meier curve revealed significant differences between the two groups in terms of cumulative VA failure (54.1% vs. 35.3%, p = 0.018). On multivariate analysis, the MPV (hazard ratio [HR], 1.794; 95% confidence interval [CI], 1.066 to 3.020; p = 0.028), platelet count (HR, 1.003; 95% CI, 1.001 to 1.006; p = 0.01), and smoking status (HR, 1.894; 95% CI, 1.019 to 3.519; p = 0.043) independently predicted VA failure.

CONCLUSION

A high MPV was associated with an increased risk of VA failure, whereas aspirin resistance showed only a weak association. The MPV may predict VA survival in HD patients.

Creation of Arteriovenous Fistulas and Grafts Concomitantly with Endovascular Correction of Outflow Veins: A Hybrid Procedure

BACKGROUND

Achieving well-functioning dialysis fistulas is a common problem in dialyzed patients, and it is mainly caused by the pathologies of vessels used for fistula creation. Hybrid therapies, combining surgical and endovascular procedures, potentially enable the creation of functional dialysis fistulas in patients with vessels that are otherwise unsuitable for vascular access.

METHODS

Between January 1, 2014 and June 30, 2018, we created dialysis fistulas simultaneously with endovascular correction of outflow pathologies in 15 patients. The included patients had a long history of dialysis (median 10.5 years, range 3-22) and many previous dialysis access procedures (mean 5.3 procedures, range 2-9). In 13 patients (86.7%), the fistula was created on the upper arm; in 5 patients (33.3%), it was arteriovenous graft done with polytetrafluoroethylene (PTFE) prosthesis (in an additional 3 patients, a PTFE prosthesis was used to extend the vein), and 7 patients had native vessel fistulas (46.7%). Endovascular procedures, in some cases performed on more than 1 vein, were applied for correction of the subclavian vein (8 patients, 53.3%); brachiocephalic vein (6 patients, 40.0%); cephalic, basilic, and axillary veins (2 patients each, 13.3%); and superior cava vein (1 patient, 6.7%). Access for the endovascular procedure was achieved through a dissected vein used for arteriovenous anastomosis. The fistula function was monitored, and all complications of dialysis access were noted. The median follow-up in the observed group was 18 months. We compared the patency of dialysis fistula creation combined with endovascular correction of outflow vein pathology to our results of standard dialysis fistula operations: radiocephalic dialysis fistula creation (RCAVF group, 65 patients) and dialysis fistula stenosis angioplasty (PTA group, 30 patients).

RESULTS

The 12- and 24-month primary patency rates of dialysis fistulas created in hybrid procedures with simultaneous outflow vein pathology correction were 72.7% and 63.6%, respectively. No early complications related to endovascular or open procedures were observed.

CONCLUSIONS

A hybrid procedure for the creation of a dialysis fistula with the simultaneous correction of outflow pathologies enables a properly functioning dialysis fistula to be obtained. This procedure can be performed in patients with complicated vascular situations, enabling the creation of dialysis fistulas. Our results of hybrid procedures, involving simultaneous endovascular correction of the outflow vein with dialysis fistula creation, showed the efficiency and good results.

A Comparative Study Regarding Deep and Superficial Veins for Venous Outflow in Forearm Loop Arteriovenous Grafts

BACKGROUND

The purpose of the study was to compare the access patency rates of forearm loop arteriovenous grafts (AVGs) using deep veins and superficial veins for venous outflow.

METHODS

The medical records of patients on dialysis were retrospectively reviewed to identify the individual risk factors and the outcomes of forearm loop AVGs according to their outflow types.

RESULTS

Overall, 170 cases were enrolled in this study. Of these, 103 cases (60.6%) used deep veins for outflow. Most patients using deep vein outflow had their venous anastomosis above the elbow (P = 0.000). Patients with venous anastomosis above the elbow were more likely to be female (P = 0.049) and have a lower albumin level (P = 0.025). The primary patency rates for superficial vein outflow and deep view outflow were 35.5% and 29.4% at 12 months and 18.9% and 4.9% at 24 months, respectively. There was a statistically significant difference between the two groups (P = 0.013). The assisted primary patency rates for superficial venous outflow and deep vein outflow were 85.5% and 79.5% at 12 months and 73.2% and 59.6% at 24 months, respectively (P = 0.139). Primary and assisted primary patency rates did not differ according to the crossing of the elbow.

CONCLUSIONS

The primary patency rate of AVGs using deep veins for outflow was inferior to AVGs using superficial veins. But the assisted primary patency rate showed no difference. The use of a deep vein for outflow in the forearm loop AVG is a safe strategy for patients with exhausted superficial veins.

Ten Year Experience of Using Cryopreserved Arterial Allografts for Distal Bypass in Critical Limb Ischaemia

OBJECTIVE/BACKGROUND

In critical limb ischaemia (CLI), current guidelines recommend revascularisation whenever possible, preferentially through endovascular means. However, in the case of long occlusions or failed endovascular attempts, distal bypasses still have a place. Single segment great saphenous vein (GSV), which provides the best conduit, is often not available and currently there is no consensus about the best alternative graft.

METHODS

From January 2006 to December 2015, 42 cryopreserved arterial allografts were used for a distal bypass. Autologous GSVs or alternative autologous conduits were unavailable for all patients. The patients were observed for survival, limb salvage, and allograft patency. The results were analysed with Kaplan-Meier graphs.

RESULTS

Estimates of secondary patency at one, two and five years were 81%, 73%, and 57%, respectively. Estimates of primary patency rates at one, two and five years were 60%, 56%, and 26%, respectively. Estimates of limb salvage rates at one, two and five years were 89%, 89%, and 82%, respectively. Estimates of survival rates at one, two and five years were 92%, 76% and 34%, respectively. At 30 days, major amputations and major adverse cardiac events were one and zero, respectively. Six major amputations occurred during the long-term follow up.

CONCLUSION

Despite a low primary patency rate at two years, the secondary patency of arterial allografts is acceptable for distal bypasses. This suggests that cryopreserved arterial allografts are a suitable alternative for limb saving distal bypasses in the absence of venous conduits, improving limb salvage rates and, possibly, quality of life.

Small Saphenous Vein and Arm Vein as Bypass Grafts for Upper Extremity Ischemia

BACKGROUND

Bypass in the upper extremity is a rare procedure mainly performed for chronic ischemia, trauma, or hemodialysis access complications. Feasibility and success of use of the arm vein and small saphenous vein (SSV) for autologous vein bypass have been reported in peripheral artery bypass procedures. There are very few reports on the use of alternative veins in upper extremity bypass. We report our experience with arm vein and SSV as a graft source in upper extremity arterial disease.

METHODS

Retrospective analysis of a consecutively collected case series in an academic tertiary referral center from January 2010 to February 2018. Study end points were primary patency, secondary patency, limb salvage, and survival.

RESULTS

In total, 47 patients were treated with upper extremity bypass either using the SSV (n = 17) or arm veins (n = 30). Indications were either acute (n = 12) or chronic ischemia (n = 35) caused by acute (n = 8) and chronic (n = 9) trauma, sequela of iatrogenic interventions (n = 4), peripheral artery disease (n = 14), thrombangiitis obliterans (n = 3), and dialysis-access-related complications (n = 9). An arm vein was used in 30 and the SSV in 17 patients. Primary patency after 12 months was 87% with the SSV and 75% with an arm vein (P = 0.8) and 63% and 75% after 36 months (P = 0.9). Secondary patency were 100% with an arm vein and 100% with the SSV after 36 months (P = 0.4). One patient had to undergo major amputation and 2 minor amputations.

CONCLUSIONS

Arm vein revascularization using the primarily arm vein or SSV as a bypass conduit can be performed with reasonable mortality and morbidity rates and provide good results comparable with the greater saphenous vein.

Arteriovenous conduits for hemodialysis: how to better modulate the pathophysiological vascular response to optimize vascular access durability

Vascular access is the lifeline for patients on hemodialysis. Arteriovenous fistulas (AVFs) are the preferred vascular access, but AVF maturation failure remains a significant clinical problem. Currently, there are no effective therapies available to prevent or treat AVF maturation failure. AVF maturation failure frequently results from venous stenosis at the AVF anastomosis, which is secondary to poor outward vascular remodeling and excessive venous intimal hyperplasia that narrows the AVF lumen. Arteriovenous grafts (AVGs) are the next preferred vascular access when an AVF creation is not possible. AVG failure is primarily the result of venous stenosis at the vein-graft anastomosis, which originates from intimal hyperplasia development. Although there has been advancement in our knowledge of the pathophysiology of AVF maturation and AVG failure, this has not translated into effective therapies for these two important clinical problems. Further work will be required to dissect out the mechanisms of AVF maturation failure and AVG failure to develop more specific therapies. This review highlights the major recent advancements in AVF and AVG biology, reviews major clinical trials, and discusses new areas for future research.

Endovascular intervention in the maintenance and rescue of paediatric arteriovenous fistulae for hemodialysis

BACKGROUND

Arteriovenous fistulae (AVF) provide superior primary vascular access for children on chronic dialysis compared to central venous catheters (CVC). However, AVFs inevitably develop complications and will require some intervention to maintain long-term functional patency.

METHODS

We report an 'endovascular-first' approach to the maintenance and rescue of paediatric AVFs. Thirty interventions targeting 46 lesions in 18 children (median age 11 years [range 5-17]) were performed. Sixty-eight percent of the AVFs were brachio-cephalic fistulae, 26% brachio-basilic fistulae and 5% radio-cephalic fistulae. Immediate functional success was 86% with good dialysis adequacy (mean urea reduction ratio > 70%) at 3 months post procedure.

RESULTS

There was one significant complication, consisting of an AVF rupture which was managed with a covered stent.

CONCLUSIONS

Repeated interventions may be necessary to maintain AVF patency and avoid central venous catheters. This is the largest series reported to date.

Drug-eluting stents are associated with improved outcomes for the treatment of infrainguinal bypass graft stenoses

BACKGROUND

Existing endovascular therapies for failing infrainguinal bypass grafts are associated with modest patency rates. The use of everolimus drug-eluting stents (eDESs) for endovascular bypass graft revision has not yet been reported. The objective of this study was to describe and to compare clinical outcomes of eDESs vs percutaneous cutting balloons (PCBs) vs percutaneous transluminal angioplasty (PTA) for the treatment of infrainguinal bypass graft stenoses.

METHODS

A multicenter, single-institution retrospective analysis of patients with infrainguinal bypass graft stenoses treated by endovascular intervention (August 2010-December 2017) was conducted. The primary study outcome was primary patency of the treated lesion. The secondary outcome was limb salvage. Outcomes are described overall and stratified by endovascular treatment modality using Kaplan-Meier curves and log-rank tests.

RESULTS

During the 7-year study period, 43 patients with 78 infrainguinal bypass stenoses were treated by endovascular intervention (eDES, 15; PCB, 23; PTA, 40). Mean age was 63.3 ± 1.7 years, 53.5% were male, and 55.8% were black. The majority of patients were diabetic (60.5%) with a history of smoking (74.4%), and nearly all (83.7%) had two or more comorbidities. Half (48.7%) of bypasses treated were femoral-popliteal bypasses, followed by popliteal-distal (25.6%) and femoral-tibial (25.6%) configurations. The location of revision was the proximal anastomosis in 37.2%, midbypass in 25.6%, and distal anastomosis in 37.2%. There were no significant differences in baseline characteristics, bypass configuration, or revision location between treatment groups (P ≥ .19). Technical success for endovascular bypass intervention was 100%. At 2 years after intervention, primary patency was significantly better for patients treated with eDES (81.8%) compared with PCB (54.7%) or PTA (33.2%; log-rank, P = .03). Limb salvage was achieved in 93.6% of patients, including 86.7%, 91.3%, and 97.5% for eDES, PCB, and PTA, respectively (P = .30).

CONCLUSIONS

This is the first study reporting the results of eDESs for the treatment of infrainguinal bypass graft stenoses. Use of eDESs for endovascular bypass graft revision not only is feasible but may have better primary patency than other endovascular therapies. These data suggest that eDESs may be considered a safe and efficacious endovascular technique in the armamentarium for treatment of infrainguinal bypass graft stenoses.

Prediction of vascular access stenosis: Blood temperature monitoring with the Twister versus static intra-access pressure ratio

Background

The Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines recommend intra-access flow (Qa) measurement as the preferred vascular access surveillance method over static intra-access pressure ratio (SIAPR). Recently, it has become possible to perform Qa measurement during hemodialysis using thermodilution method called blood temperature monitoring (BTM) with the Twister device. The aim of this study was to investigate the correlation between Qa by BTM and SIAPR and to compare the performance of two tests in prediction of vascular access stenosis.

Methods

The study was performed from January 2016 to November 2017 and included 97 patients with arteriovenous fistulas (AVF). Qa by BTM and SIAPR were simultaneously measured every 1~3 months with a total of 449 measurements during study period.

Results

In our study population, mean age was 59.9±10.0 years and 61.9% were diabetes. The mean Qa obtained by BTM was 1186±588 mL/min. There was no correlation between Qa by BTM and venous SIAPR (r = 0.061, P = 0.196). Angiography identified 36 stenotic AVFs (37.1%) among the study subjects. They included 13 cases with only inflow stenosis, 6 with only outflow stenosis, and 17 with stenosis on both sides. Receiver-operating characteristic (ROC) curve analysis showed that Qa by BTM had higher discriminative ability to diagnose vascular access stenosis compared to SIAPR (P <0.001). The Qa less than 583 mL/min showed the highest diagnostic accuracy in vascular stenosis prediction.

Conclusion

Intradialytic measurement of Qa by BTM showed better diagnostic power over venous SIAPR in prediction of vascular access stenosis.

Early cannulation of bovine carotid artery grafts (Artegraft) after primary vascular access and fistula revision procedures

OBJECTIVE

Tunneled dialysis catheter (TDC) use has been associated with increased infectious complications and mortality in hemodialysis-dependent patients. Unfortunately, patients who undergo fistula revisions or creation of a new arteriovenous fistula frequently require a TDC during the postoperative period. Bovine carotid artery grafts (BCAGs) can be used as an early-access dialysis conduit to reduce TDC dependence. This study describes the performance of BCAGs that were cannulated early (<3 days) after implantation and associated clinical outcomes.

METHODS

BCAGs were implanted in 63 consecutive dialysis-dependent patients. Patients and dialysis centers were directly provided early cannulation instructions; 31 (49%) patients were cannulated early, and of the 31 patients cannulated early, 21 (68%) were cannulated during the first postoperative day. Early complications, primary patency, secondary patency, and TDC incidence were monitored through clinic visits, hospital records, and phone calls to dialysis centers.

RESULTS

The primary patency of BCAGs at 1 year in the early and late cannulation cohorts was 28% and 39%, respectively. The secondary patency of BCAGs at 1 year in the early and late cannulation cohorts was 74% and 77%, respectively. Early complications occurred in 11 (19%) patients who received a BCAG. There were no significant differences in complication rates between early and late cannulation patients. Of the 24 patients who underwent the operation without a pre-existing TDC, only three (13%) required TDC placement during the 30-day postoperative period.

CONCLUSIONS

BCAGs can be cannulated early without increased complication rates or a negative impact on midterm patency. Early cannulation of BCAGs obviates the need for a TDC postoperatively in dialysis-dependent patients undergoing primary vascular access or fistula revision procedures.

Drug-Eluting Stent Shows Similar Patency Results as Prosthetic Bypass in Patients with Femoropopliteal Occlusion in a Randomized Trial

BACKGROUND

Claudication and critical limb threatening ischemia are significant causes of mortality in the elderly. The gold standard of superficial femoral artery (SFA) revascularization is thus far considered to be the femoropopliteal bypass. The aim of this study was to compare mid-term patency between drug-eluting stents (DESs) and prosthetic bypass grafts (BSX). Studies have reported comparable results for both the methods.

METHODS

Forty-six patients with claudication or rest pain due to a 5-25 cm SFA occlusion were randomized between DES and BSX groups. The follow-up period was 24 months, and the primary outcome measure was overall patency. Secondary outcome measures were primary and primary assisted patency, change in ankle-brachial index (ABI), and amputation-free survival.

RESULTS

Forty-one patients were eventually analyzed. Six-month secondary patency was 91% (DES) versus 83% (BSX) (P = 0.450). The corresponding numbers at 12 months in the DES and BSX groups were 74% and 80% (P = 0.750), respectively. At 24 months, the respective numbers were 56% and 71% (P = 0.830). There were no statistically significant differences in primary or assisted primary patency at 1, 6, or 12 months.

CONCLUSION

There were no demonstrable differences in patency rates or clinical outcomes such as ABI or major amputations between DES and BSX. Although underpowered, the results suggest noninferiority of the DES compared with prosthetic bypass surgery.

TRIAL REGISTRATION

The trial was preregistered at ClinicalTrials.org (NCT01450722).

Physical examination of the hemodialysis arteriovenous fistula to detect early dysfunction

The maintenance of vascular access patency for end-stage renal disease patients on hemodialysis is necessary for survival. Many nephrologists, nurse practitioners, and nurses have limited experience with the physical examination of the arteriovenous fistula. In this review, we define key terms used in the assessment of an arteriovenous fistula. We discuss the arteriovenous fistula physical exam, including details of inspection, palpation, and auscultation. Using these concepts, we review the abnormal findings that can assist practitioners in determining the location of a stenosis. We review the existing literature that validates physical exam findings with gold standard tests such as ultrasound and angiography. Finally, we review data supporting the value of training physicians and nurses in arteriovenous fistula physical examination.

Stenting of an endograft limb in its acute occlusion after endovascular intervention for an abdominal aortic aneurysm

Endovascular abdominal aortic aneurysm repair (EVAR) has recently become an operation of choice in the presence of clinical, anatomic and organizational conditions for implantation of a stent graft. However, like any other operation, EVAR bears the risk of various complications. Due to low frequency of EVAR, the problem concerning appropriate policy of managing patients presenting with such types of complications may be difficult. Thrombosis of a stent graft's components is encountered more often compared with "open" prosthetic repair of the abdominal aorta. This complication more frequently requires interventions in the scope of femoro-femoral bypass grafting. Attempts of thrombextraction may lead to disconnection of a stent graft's modules and to embolic complications. Presented herein is a clinical case report wherein proceeding from objective examination and laboratory instrumental studies, namely angiography, we chose a policy of endovascular intervention (stenting) for thrombosis of a stent graft's limb. At 2 years of follow up the patient is currently in a satisfactory condition, as confirmed by the findings of MSCT angiography two years after the intervention.

Influence of Iliac Stenotic Lesions on Blood Flow Patterns Near a Covered Endovascular Reconstruction of the Aortic Bifurcation (CERAB) Stent Configuration

PURPOSE

To investigate the effect of distal stenotic lesions on flow patterns near a covered endovascular reconstruction of the aortic bifurcation (CERAB) configuration used in the treatment of aortoiliac occlusive disease.

METHOD

Laser particle image velocimetry measurements were performed using in vitro models of the aortic bifurcation with and without a CERAB configuration in place. A hemodynamically nonsignificant stenosis (ΔP: 9 mm Hg), a hemodynamically significant (ΔP: 26 mm Hg) stenosis, and a total occlusion were simulated in the left iliac arteries. Velocity fields and time-averaged wall shear stress (TAWSS) were calculated.

RESULTS

Hemodynamically significant distal lesions did not influence the inflow patterns or TAWSS (0.5-0.6 Pa) in either model. However, hemodynamically significant distal stenotic lesions caused a 2-fold decrease in peak outflow velocities (control: 106 vs 56 cm/s, CERAB: 96 vs 54 cm/s) and a 3-fold decrease in TAWSS (control: 1.34 vs 0.44 Pa, CERAB: 0.75 vs 0.21 Pa). There was a 2-fold decrease in wall shear stress in the CERAB outflow compared with the control, independent of lesion severity.

CONCLUSION

In the CERAB technique, adequate distal runoff is identified as an important parameter to ensure patency. This in vitro study showed that distal stenotic lesions influence aortic bifurcation outflow patterns and TAWSS more extensively in the CERAB configuration. Distal stenotic lesions could therefore increase the risk of disease progression and loss of stent patency. In vivo studies are necessary to confirm these observations.

Sustained Thromboresistant Bioactivity with Reduced Intimal Hyperplasia of Heparin-Bonded Polytetrafluoroethylene Propaten Graft in a Chronic Canine Femoral Artery Bypass Model

BACKGROUND

Bypass graft thrombosis remains a significant mode of failure in prosthetic graft revascularization. The purpose of this investigation was to evaluate the long-term thromboresistant effect of heparin-bonded expanded polytetrafluoroethylene (ePTFE) graft using Carmeda BioActive Surface technology in a canine model.

METHODS

Bilateral femorofemoral artery bypass grafts with ePTFE grafts were performed in 25 adult grayhound dogs. In each animal, a heparin-bonded ePTFE graft (Propaten, WL Gore) was placed on one side, whereas a control nonheparin graft was placed on the contralateral side. The graft patency was assessed at 1, 6, 12, 18, and 24 months (n = 5 per group) following the bypass. Heparin bioactivity of the graft material was analyzed. The effect of intimal hyperplasia was also assessed.

RESULTS

All bypass grafts were patent at 1 month. Significantly greater patency rates were noted in the Propaten group compared to the control group at 12, 18, and 24 months, which were 84%, 80%, and 80% vs. 55%, 35%, and 20%, respectively (P < 0.02). There was a significant reduction in the anastomotic neointimal area and neointimal cell proliferation in Propaten grafts compared with control grafts at all groups between 6 and 24 months (P < 0.05). Heparin bioactivity as measured by antithrombin binding assay was demonstrated in the Propaten graft between 1 and 24 months. Mean heparin activities on Propaten grafts ranged from 26.3 ± 6.4 pmol/cm² to 18.4 ± 8.7 pmol/cm² between 1 and 24 months, which were significantly greater than the control group (P < 0.001). Differences between mean heparin activities of explanted Propaten graft samples at the various time points were nonsignificant (P > 0.05).

CONCLUSIONS

Heparin-bonded ePTFE graft provides a thromboresistant surface and reduced anastomotic intimal hyperplasia at 2 years. The stable heparin bioactivity of the Propaten graft confers an advantage in long-term graft patency.

Hyperspectral imaging for monitoring of perfusion failure upon microvascular anastomosis in the rat hind limb

BACKGROUND/PURPOSE

Objective, reliable and easy monitoring of microvascular tissue perfusion is a goal that was achieved for many years with limited success. Therefore, a new non-invasive hyperspectral camera system (TIVITA™) was tested for this purpose in an in vivo animal model.

METHODS

Evaluation of tissue oxygenation during ischemia and upon reperfusion was performed in left hind limb in a rat model (n=20). Ischemia was induced by clamping and dissection of the superficial femoral artery. Reperfusion of the limb was achieved by microsurgical anastomosis of the dissected artery. Oxygenation parameters of the hind limb were assessed via TIVITA™ before and immediately after clamping and dissection of the artery, 3 and 30min after reperfusion as well as on postoperative days 1 and 2. Thereby, the non-operated hind limb served as control. As clinical parameters, the refill of the anastomosis as well as the progress of the affected leg were assessed.

RESULTS

In 12 from 20 cases, TIVITA™ recorded a sufficient reperfusion with oxygenation parameters comparable to baseline or control condition. However, in 8 from 20 cases oxygenation was found impaired after reperfusion causing a re-assessment of the microvascular anastomosis. Thereby, technical problems like stenosis or local thrombosis were found in all cases and were surgically treated leading to an increased tissue oxygenation.

CONCLUSIONS

The TIVITA™ camera system is a valid non-invasive tool to assess tissue perfusion after microvascular anastomosis. As it safely shows problems in oxygenation, it allows the clinician a determined revision of the site in time in order to prevent prolonged ischemia.

Imaging and Physiology to Guide Venous Graft Interventions Without Contrast Administration in Advanced Renal Failure

We describe step-by-step "zero-contrast" saphenous vein bypass graft intervention using a modified technique.

Surgeon, not institution, case volume is associated with limb outcomes after lower extremity bypass for critical limb ischemia in the Vascular Quality Initiative

OBJECTIVE

Studies from large administrative databases have demonstrated associations between institutional case volume and outcomes after lower extremity bypass (LEB). We hypothesized that increased institutional and surgeon volume would be associated with improved outcomes after LEB. Using a national, prospectively collected clinical database, the objective of this study was to determine the effects of both surgeon and institutional volume on outcomes after LEB.

METHODS

The Vascular Quality Initiative (VQI) was queried to identify all LEBs for critical limb ischemia or claudication between 2004 and 2014. Average annual case volume was calculated by dividing an institution's or surgeon's total LEB volume by the number of years they reported to the VQI. Institutional and surgeon volumes were analyzed as continuous variables to determine the impact of volume on major adverse cardiac events (MACEs), major adverse limb events (MALEs), graft patency, and amputation-free survival. Hierarchical regression models were used with cases clustered by surgeon and center. Time-dependent outcomes were evaluated with multivariable shared frailty Cox proportional hazards models.

RESULTS

From 2004 to 2014, there were 14,678 LEB operations performed at 114 institutions by 587 surgeons. Average annual institutional volume ranged from 1.0 to 137.5 LEBs per year, with a median of 26.9 (interquartile range, 14-45.3). Average annual surgeon volume ranged from 1 to 52 LEBs per year with a median of 5.7 (interquartile range, 2.5-9.3). Institutional LEB volume was not associated with MACEs or MALEs or with loss of patency. However, average annual surgeon volume was independently associated with reduced MALEs and improved primary patency. Institutional and surgeon volume did not predict MACEs.

CONCLUSIONS

In contradistinction to previous studies, there was no relationship in this study between institutional LEB volume and outcomes after LEB. However, greater average annual surgeon volume was associated with improved primary patency and decreased risk of MALEs. Open LEB remains a safe and effective procedure for limb salvage. Limb-related outcomes in critical limb ischemia and claudication will be optimized if surgeons maintain adequate volume of LEB.

Pre-existing arterial pathologic changes affecting arteriovenous fistula patency and cardiovascular mortality in hemodialysis patients

The radiocephalic arteriovenous fistula (AVF) provides optimal vascular access for hemodialysis; it has a higher long-term patency rate and fewer complications than other vascular access methods. However, the AVF has a high primary failure rate. The presence of small-diameter vessels at anastomosis sites is an important risk factor for AVF failure. However, in a recent study, despite selecting an adequate artery and vein for creating an AVF by routine preoperative vascular mapping, AVF maturation and primary failure occurred. Thus, pre-existing arteriosclerosis at AVF anastomosis sites likely contributes to AVF failure. In this review, we discuss the relationship between pathologic changes and AVF patency in hemodialysis patients. Because arteriosclerosis of the major arteries such as the coronary and carotid arteries is associated with cardiovascular mortality, we also review the impact of arteriosclerosis of upper arm arteries at AVF anastomosis sites on cardiovascular mortality in hemodialysis patients.

Tissue-engineered vascular grafts for congenital cardiac disease: Clinical experience and current status

Congenital heart disease is a leading cause of death in the newborn period, and man-made grafts currently used for reconstruction are associated with multiple complications. Tissue engineering can provide an alternative source of vascular tissue in congenital cardiac surgery. Clinical trials have been successful overall, but the most frequent complication is graft stenosis. Recent studies in animal models have indicated the important role of the recipient׳s immune response in neotissue formation, and that modulating the immune response can reduce the incidence of stenosis.

Cardiovascular Risk Reduction is Important for Improving Patient and Graft Survival After Ligation and Bypass Surgery for Popliteal Artery Aneurysm

OBJECTIVES

To report outcomes following ligation and bypass (LGB) surgery for popliteal artery aneurysm (PAA) and study factors influencing patient and graft survival.

MATERIALS AND METHODS

A retrospective review of patients undergoing LGB surgery for PAA between September 1999 and August 2012 at a tertiary referral vascular unit was performed. Primary graft patency (PGP), primary-assisted graft patency (PAGP), and secondary graft patency (SGP) rates were calculated using survival analyses. Patient, graft aneurysm-free survival (GAFS), aneurysm reperfusion-free survival (ARFS), and amputation-free survival (AFS) rates were also calculated. Log-rank testing and Cox proportional hazards modeling were used to perform univariate and multivariate analysis of influencing factors, respectively.

RESULTS

Eighty-four LGB repairs in 69 patients (mean age 71.3 years, 68 males) were available for study. The 5-year PGP, PAGP, SGP, and patient survival rates were 58.1%, 84.4%, 85.2%, and 81.1%, respectively. On multivariate analysis, the principal determinants of PGP were urgency of operation ( P = .009) and smoking status ( P = .019). The principal determinants of PAGP were hyperlipidemia status ( P = .048) and of SGP were hyperlipidemia ( P = .042) and cerebrovascular disease (CVD) status ( P = .045). The principal determinants of patient survival were previous myocardial infarction ( P = .004) and CVD ( P = .001). The 5-year GAFS, ARFS, and AFS rates were 87.9%, 91.6%, and 96.1%, respectively.

CONCLUSION

This study has shown that traditional cardiovascular risk factors, such as a smoking and ischemic heart disease, are the most important predictors of early graft failure and patient death following LGB surgery for PAA.

A bifrequent passive sensor system for measurement of the pulse wave velocity in a stent

In-stent restenosis (ISR) is a frequent complication after stent implantation. Recently, a passive sensor system for integration into a stent has been presented, which is designed to detect an ISR early by measuring the local pulse wave velocity (PWV). This system is based on two pressure sensitive transponders, the resonance frequency of which hits the frequency of a magnetic field generated by an externally applied transceiver coil during a pulse cycle. This method is limited in applicability by the largest PWV it can measure. In this contribution a modified sensor system is investigated, which operates at two separate frequencies for each transponder. It has been shown that this modification solves the problem of limited PWV measurement range. Additionally, the previously developed model was shown to be valid for bifrequent operation. Furthermore, the influence of the system parameters on measurement precision have been investigated and verified in simulations.

Patency of Saphenous Vein Grafts Using the PAS-Port System During Coronary Artery Bypass Surgery

BACKGROUND

Several proximal anastomosis devices have been developed to shorten the time required for a proximal anastomosis and to avoid aortic cross-/side-clamping during coronary artery bypass grafting. This study retrospectively examined the patency of saphenous vein grafts (SVGs) using the PAS-Port System (Cardia Inc, Redwood City, CA).

METHODS

From 2004 to 2014, 451 patients underwent coronary artery bypass graft operations requiring at least 1 proximal anastomosis using a PAS-Port device. A total of 802 PAS-Port devices were used, and 95.0% (762 of 802) were implanted successfully. Among the successfully implanted anastomoses, 76.8% (585 of 762) were evaluated using coronary angiography or multidimensional computed tomography, or both. The evaluations were performed between postoperative days 4 and 3,182 (mean, 319 ± 624 days). The early (1 to 365 days) and the midterm to long-term (more than 366 days) occlusion rates were examined. A complete postoperative clinical course was recorded for 70.7% of the patients.

RESULTS

Overall, 93.8% (549 of 585) of the device-dependent SVGs were patent. The patency rates of device-dependent SVGs that were 1, 2, 3, 4, 5, 6, 7, and 8 years old were 90.1% ± 1.8%, 87.1% ± 2.3%, 86.1% ± 2.5%, 82.9% ± 3.3%, 80.6% ± 3.9%, 77.2% ± 5.0%, 77.2% ± 5.0%, and 70.2% ± 8.1%, respectively. The longest follow-up period was 3,182 days (8.7 years). The occlusion rate for device-dependent SVGs tended to decrease as the number of patients accumulated.

CONCLUSIONS

The PAS-Port system provided acceptable SVG patency and clinical outcome for the early and midterm to long-term. There may be a learning curve for the use of PAS-Port device that affects the device-dependent SVG patency.

[Repeat prosthetic repair of the internal carotid artery]

Described herein is a clinical case report regarding reoperation on carotid arteries for thrombosis of a synthetic graft of the internal carotid artery in a patient presenting with a multifocal atherosclerotic lesion. Despite medicamentous treatment carried out after the primary operation, the presence of major risk factors had unfavourably contributed to progression of the disseminated atherosclerotic process. During eight years, the patient had endured reconstructive interventions on the brachiocephalic and coronary arteries, as well as on the vessels of the iliac-femoral-popliteal segment. Taking into consideration the peculiarities of the vascular anatomy, the degree of stenosis of the internal carotid artery with the presence of thrombotic masses in the lumen, and thrombosis inside the graft, a decision was made to perform repeat "open" reconstruction consisting in successful common carotid-internal carotid prosthetic repair using a synthetic graft with resection of the external carotid artery.

Assessing the effect of endoprosthetic repair of the thoracic portion on aortic remodelling after surgical correction for DeBakey type I dissection

OBJECTIVE

The purpose of the study was to evaluate the influence of endoprosthetic repair of the aortic thoracic portion on remodelling of the descending aorta in patients after the surgical stage of correction for DeBakey type I aortic dissection.

PATIENTS AND METHODS

The authors retrospectively analysed a group of 12 patients (9 men and 3 women) subjected to endoprosthetic repair of the aortic thoracic portion after previously performed surgical correction of the ascending aorta and its braches. The average age of the patients amounted to 48 (43-56.7) years. All patients underwent multispiral computed tomography (MSCT) first performed at admission, then immediately after implantation of the stent graft and at 6, 12 and 24 months after discharge. The Control Group consisted of nine patients with a previous history of DeBakey type I aortic dissection, who had endured only surgical correction of the ascending aorta and arch.

RESULTS

The success rate of the intervention amounted to 100%. There were no signs of ischaemia of the spinal cord, visceral organs or lower limbs. The diameter of the implanted stent grafts varied from 28 to 40 mm and the length ranged from 140 to 204 mm. Seven (58%) patients of the Study Group as early as during a year were found to have no blood flow along the false channel. The false channel remained patent in 100% of the Control Group patients. Over a two-year period of follow up, in patients after endoprosthetic repair, the diameter of the false channel did not increase. In the Control Group patients during the same period of follow up, there was a tendency towards an increase in the aortic diameter at the expense of dilatation of the false channel, with an enlargement of the false channel of the descending aorta at the level of the diaphragm from 1.8 (1.57-2.1) to 2.05 (1.7-2.31) cm (p=0.4) and at the level of the renal arteries from 1.5 (1.32-1.8) to 1.8 (1.58-1.97) cm (p=0.4). There were no lethal outcomes during follow up.

CONCLUSION

Endoprosthetic repair of the thoracic portion after surgical correction was in the remote period accompanied and followed by stabilization of the diameter of the descending aorta, as well as contributed to closure of the false channel.

Arteriovenous fistula patency in the 3 years following vonapanitase and placebo treatment

OBJECTIVE

This study explored the long-term outcomes of arteriovenous fistulas treated with vonapanitase (recombinant human elastase) at the time of surgical creation.

METHODS

This was a randomized, double-blind, placebo-controlled trial of 151 patients undergoing radiocephalic or brachiocephalic arteriovenous fistula creation who were randomized equally to placebo, vonapanitase 10 μg, or vonapanitase 30 μg. The results after 1 year of follow-up were previously reported. The current analysis occurred when the last patient treated was observed for 3 years. For the current analysis, the primary end point was primary patency; the secondary end points included secondary patency, use of the fistula for hemodialysis, and rate of procedures to restore or to maintain patency.

RESULTS

There was no significant difference in the risk of primary patency loss with vonapanitase 10 μg or 30 μg vs placebo. When seven initial patency loss events related to cephalic arch and central vein balloon angioplasty were excluded, the risk of patency loss was reduced with vonapanitase overall (hazard ratio [HR], 0.63; P = .049) and 30 μg (HR, 0.51; P = .03). In patients with radiocephalic fistulas (n = 67), the risks of primary and secondary patency loss were reduced with 30 μg (HR, 0.37 [P = .02] and 0.24 [P = .046], respectively). The rate of procedures to restore or to maintain fistula patency was reduced with 30 μg vs placebo (0.23 vs 0.72 procedure days/patient/year; P = .03) and also reduced in patients with radiocephalic fistulas with 30 μg vs placebo (0.17 vs 0.85 procedure days/patient/year; P = .048).

CONCLUSIONS

In this study, vonapanitase did not significantly improve primary patency in the primary analysis but did significantly improve primary patency in an analysis that excluded patency loss due to cephalic arch and central vein balloon angioplasty. In patients with radiocephalic fistulas, 30 μg significantly improved primary and secondary patency. Vonapanitase 30 μg decreased the rate of procedures to restore or to maintain patency in the analysis that included all patients and in the subset with radiocephalic fistulas.

Distinct impact of three different statins on arteriovenous fistula outcomes: a retrospective analysis

PURPOSE

Whether statins improve arteriovenous fistula (AVF) outcomes is still a matter of debate. Taking into consideration the existing physicochemical differences between individual drugs, this study evaluates the impact of three different statins (atorvastatin, rosuvastatin and simvastatin) on one-stage and two-stage AVF outcomes.

METHODS

Using a retrospective cohort of 535 patients, we analyzed the effects of each statin on primary failure and primary patency using multivariate logistic regressions and Cox proportional hazard models.

RESULTS

Out of the three statins analyzed, only atorvastatin improved the overall primary failure of AVF (odds ratio [OR] = 0.18, p = 0.005). Comparisons between the two AVF types demonstrated that this effect was due to a prominent reduction in primary failure of one-stage (OR = 0.03; p = 0.005), but not two-stage fistulas (OR = 0.43; p = 0.25). In contrast, primary patency of two-stage (hazards ratio [HR] = 0.51; p = 0.024), but not one-stage fistulas (HR = 0.98; p = 0.95), was improved by all statins as a group, but not by individual drugs.

CONCLUSIONS

Our results suggest that the potential benefit of statins on AVF outcomes is a drug-specific and not a class effect, and that such effect is also influenced by the type of fistula.

Endovascular Exclusion of Popliteal Artery Aneurysms With Expanded Polytetrafluoroethylene Stent-Grafts: Early Results

There is increasing interest in using endovascular methods instead of surgical reconstruction to treat popliteal artery aneurysms. Exclusive use of the Viabahn stentgraft, a nitinol stent covered with expanded polytetrafluoroethylene, was assessed in the treatment of patients who presented with popliteal artery aneurysms in the absence of acute limb ischemia. Technical success, endoleaks, graft patency, freedom from amputation, and aneurysm sac flow and size changes were assessed by duplex ultrasound. From June 2004 to March 2006, 16 men (mean age, 76 years; range, 65-83) underwent endovascular exclusion of 23 popliteal artery aneurysms (mean diameter, 2.5 cm; range, 1.3-6.7 cm). Nine lesions had partial thrombus on preprocedural duplex imaging. Nineteen of the 23 limbs treated had at least 2-vessel tibial artery runoff. Procedures were performed under local anesthesia using ipsilateral percutaneous antegrade arterial access. All patients received 75 mg/day of clopidogrel afterward. Follow-up assessments included direct clinical examinations and duplex ultrasonography performed 1, 3, 6, and 12 months after the procedure. Primary patency and amputation-free survival were calculated using Kaplan-Meier analysis. Complete aneurysm exclusion (technical success) was achieved in all cases. During the mean follow-up of 7 months (range, 1-21 months), 22 of 23 treated limbs remained asymptomatic. One stent-graft thrombosis occurred 6 months after the procedure and was successfully treated with percutaneous mechanical thrombectomy, balloon angioplasty of a stent-graft stenosis, and insertion of an uncovered nitinol stent. No popliteal artery aneurysm sac size enlargements or endoleaks were detected. At 12 months, the treated limb mean anklebrachial index was 1.0 (range, 0.82-1.31) and the primary and secondary patency rates were 93% and 100%, respectively. Early results with Viabahn endovascular stent-graft exclusion of asymptomatic popliteal artery aneurysms are promising. Patient selection for endovascular repair depends on suitable popliteal artery anatomy, extent of aneurysmal degeneration, and quality of tibial arterial runoff.

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.