The effect of high-flow arteriovenous fistulas on systemic haemodynamics and brain oxygenation.

AIMS: High-flow arteriovenous fistula (AVF) for haemodialysis leads to profound haemodynamic changes and sometimes to heart failure (HF). Cardiac output (CO) is divided between the AVF and body tissues. The term effective CO (COef) represents the difference between CO and AVF flow volume (Qa) and better characterizes the altered haemodynamics that may result in organ hypoxia. We investigated the effects of Qa reduction on systemic haemodynamics and on brain oxygenation. METHODS AND RESULTS: This is a single-centre interventional study. Twenty-six patients on chronic haemodialysis with high Qa (>1500 mL/min) were indicated for surgical Qa reduction for HF symptoms and/or signs of structural heart disease on echocardiography. The included patients underwent three sets of examinations: at 4 months and then 2 days prior and 6 weeks post-surgical procedure. Clinical status, echocardiographical haemodynamic assessment, Qa, and brain oximetry were recorded. All parameters remained stable from selection to inclusion. After the procedure, Qa decreased from 3.0 ± 1.4 to 1.3 ± 0.5 L/min, P < 0.00001, CO from 7.8 ± 1.9 to 6.6 ± 1.5 L/min, P = 0.0002, but COef increased from 4.6 ± 1.4 to 5.3 ± 1.4 L/min, P = 0.036. Brain tissue oxygen saturation increased from 56 ± 11% to 60 ± 9%, P = 0.001. CONCLUSIONS: Qa reduction led to increased COef. This was explained by a decreased proportion of CO running through the AVF in patients with Qa > 2.0 L/min. These observations were mirrored by higher brain oxygenation and might explain HF symptoms and improved haemodynamics even in asymptomatic high Qa patients.

Treatment of failing arterio-venous dialysis graft by angioplasty, stent, and stent graft: Two-years analysis of patency rates and cost-effectiveness.

The objective of this prospective randomized single-center study was to compare primary and secondary patency rates, number of percutaneous transluminal angioplasty (PTA) interventions and cost-effectiveness among PTA, deployment of a stent, or a stent graft in the treatment of failing arteriovenous dialysis grafts (AVG) due to restenosis in the venous anastomosis or the outflow vein. Altogether 60 patients with failing AVG and restenosis in the venous anastomosis or the outflow vein were randomly assigned to either PTA, placement of a stent (E-Luminexx®) or stent graft (Fluency Plus®). After the procedure, patients with stent or stent graft received dual antiplatelet therapy for the next three months. Follow-up angiography was scheduled at 3, 6, and 12 months unless requested earlier due to suspected stenosis or malfunction of the access. Subsequently, angiography was performed only if requested by the clinician. During a median follow-up of 22.4 (IQR=5.7) months patients with PTA, stent, or stent graft required 3.1±1.7, 2.5±1.7, or 1.7±2.1 (P=0.031) secondary PTA interventions. The primary patency rates were 0, 18 and 65% at 12 months and 0, 18 and 37% at 24 months in the PTA, stent, and stent graft group respectively (P<0.0001). The cost of the procedures in the first two years was €7,900±€3,300 in the PTA group, €8,500±€4,500 in the stent group, and €7,500±€6,200 in the stent graft group (P=0.45). We conclude that the treatment of failing dialysis vascular access by the deployment of a stent graft significantly improves its primary patency rates and decreases the number of secondary PTA interventions; however, the reduction in costs for maintaining AVG patency is not significant.

Basilic Vein Transposition Used as a Tertiary Vascular Access for Hemodialysis: 15 Years of Experience.

INTRODUCTION: The quality of the life in patients requiring long term hemodialysis is directly proportional to the long-term patency of their vascular access. Basilic vein transposition for vascular access (BAVA) represents a suitable option for creating a tertiary native vascular access for hemodialysis on the upper extremities for patients requiring long term hemodialysis. The purpose of the study is to compare BAVAs with arteriovenous grafts (AVG). METHOD: Data collection was based on selecting all of the patients with BAVA created in the time period in between January 1996 and August 2011. A questionnaire was created and sent to the selected hemodialysis centers. The resulting set of data was statistically analyzed and evaluated. RESULTS: In the time period between 1 January 1996 and August 2011, arteriovenous access for hemodialysis was created in 6754 patients (7203 procedures in total). Out of these patients, 175 BAVAs were created. Our patient database of those undergoing the BAVA procedure consisted of 98 females (56%) and 77 males (44%) with an average age of 64.5 years. The prevalence of diabetes mellitus was 60% (105 patients). Primary patency after 12 months was 68.8%, 24 months 59.7%, 36 months 53.8, 48 months 53.8%, and 60 months 50%. Primary assisted patency after 12 months was 89.9%, 24 months 84.6%, 36 months 77.8%, 48 months 77.9%, 60 months 70.8%. Secondary patency after 12 months was 89.4%, 24 months 86.9%, 36 months 81%, 48 months 78.9%, 60 months 75.7%. Twenty-nine BAVAs (16.5%) were obliterated. CONCLUSION: Patients benefit from this type of procedure due to the longer patency of a native arteriovenous access, as well as a lower incidence of infectious complications.

Arteriovenous grafts: early ultrasonography tells their fortune.

BACKGROUND: The patency of arteriovenous grafts (AVG) for hemodialysis is mostly limited by growing stenoses that lead to decreasing of blood flow, thromboses and finally to access failure. The aim of this study was to find out if detection of any pathology by duplex Doppler ultrasonography (DDU) early after creation of AVG could identify those with lower survival. METHODS: We retrospectively enrolled AVG examined by DDU in our center within 40 days after their creation during the last 10 years. The findings were divided into 4 subgroups: (1a) normal finding, (1b) DDU risk factor (low flow volume, medial calcinosis of the feeding artery, presence of intimal hyperplasia in the venous anastomosis), (2a) non-significant or (2b) significant stenosis. The primary outcome measure was the cumulative survival of people with AVGs, and the secondary was the primary (unassisted) survival. All patients underwent DDU surveillance every 3 months with pre-emptive treatment of significant stenoses. RESULTS: Overall, 340 cases were found; the median follow-up was 565 days. Normal DDU finding had 60% cases, DDU risk factor 18% cases, non-significant stenosis 13% cases and significant stenosis 9% cases. Occurrence of early significant stenosis was associated with high risk of access loss (hazards ratio (HR) 14.73; 95% CI 5.10-42.58; p < 0.0001). Similarly, the presence of a DDU risk factor and of a non-significant stenosis were related to significantly shorter access lifespan (HR 2.86; 95% CI 1.10-7.40; p = 0.03 and HR 2.83; 95% CI 1.12-7.17; p = 0.03, respectively). CONCLUSION: DDU examination of AVG early after their creation can identify those at higher risk and may contribute to individualize the surveillance strategy.

Long-term arterial adaptation to high blood flow in the feeding artery of vascular access for hemodialysis.

PURPOSE: Arteries continuously respond to changing tissue demands and to hemodynamic conditions by altering their diameter and wall structure. The relatively slow dilatation of the feeding artery of vascular accesses continues at least two years after access creation with a continuous decrease in wall shear rate (WSR), which however, remains highly supra-physiological. The aim of this study was to test the hypothesis that after a longer time period the WSR returns to its baseline value. METHODS: In a cross-sectional study patients with arteriovenous fistulae were classified into four groups according to the access vintage (from new access to accesses older than six years). The WSR, cross-sectional area, and mean circumferential wall stress were measured and compared between groups. RESULTS: WSR decreased from group 1 (fistula < ninety days old) to group 4 (fistulae > six years old) with a concomitant increase in internal diameter. Patients with the oldest access had normal WSR values (compared to the contralateral brachial artery) and the largest internal diameter of the feeding artery. In diabetic patients the absolute values of WSR were higher and internal diameter was lower compared to nondiabetic patients. CONCLUSIONS: Brachial artery WSR is normal in accesses older than six years with an increased internal diameter and wall cross-sectional area as compared to "younger" accesses. This suggests a process of vascular remodeling with an increase in vascular wall mass and normalization of WSR to physiologic values at the price of increased mean cross-sectional wall stress.

Low-flow polytetrafluoroethylene accesses: ultrasound surveillance and preemptive interventions ensure long-term patency.

BACKGROUND: Vascular accesses (especially polytetrafluoroethylene grafts) with a permanently low flow (Qa <600 ml/min) are prone to thrombosis and thus have short patency. The reason for a permanently low flow is usually medial calcinosis of the inflow artery in diabetics. We retrospectively studied the long-term patency of low-flow grafts with careful ultrasound surveillance and preemptive interventions. METHODS: Twenty subjects with Qa permanently <600 ml/min were included. Ultrasound surveillance was performed every 3 months in addition to classical monitoring techniques. Significant stenosis was strictly defined as the combination of B-mode narrowing >50% + >2-fold peak systolic velocity increase + 1 additional criterion (residual diameter <2.0 mm or flow volume decrease by >20%). Such stenoses were treated by preemptive percutaneous intervention. Primary and secondary patencies were calculated. RESULTS: The primary patency was 357 ± 316 days and the secondary (cumulative) patency was 996 ± 702 days. The number of interventions was 2.09/patient year, but >10 in 6 (33%) subjects. 93 and 80% of grafts were patent 1 and 2 years after access creation, respectively. CONCLUSION: Low-flow accesses undergoing ultrasound surveillance with strict diagnostic criteria and preemptive interventions had patencies similar to accesses with normal Qa in our study. This was enabled by a relatively high rate of interventions.

Short-term outcomes of borderline stenoses in vascular accesses with PTFE grafts.

BACKGROUND: There are controversial data about vascular access stenosis surveillance by ultrasonography. The definition of stenosis significance varies among centres. We performed a retrospective study to describe short-term outcomes of borderline asymptomatic stenoses defined by precise criteria and to determine possible risk factors of stenosis progression. METHODS: We studied the outcome of borderline stenoses in accesses with PTFE grafts. Stenosis was considered significant if there was a combination of >50% lumen reduction and peak systolic ratio >2, together with at least one of the following additional criteria: (1) residual diameter <2.0 mm and (2) flow reduction of >25% or actual flow volume <600 ml/min. Stenosis was considered borderline in the absence of the additional criteria. RESULTS: Of the 102 borderline stenoses, after 11 +/- 6 weeks, 55 remained non-progressive, in 38 the degree of the stenosis progressed, in 8 a percutaneous transluminal angioplasty (PTA) was performed due to clinical indication and only 1 thrombosed. A significant relative risk of developing significant stenosis was found in grafts with prior PTA [RR = 1.91 (95% CI: 1.27, 2.88), P = 0.002] and in female gender [RR = 2.29, (95% CI: 1.29, 4.06), P = 0.025]. CONCLUSIONS: Delaying PTA of borderline stenoses is safe using this watch-and-wait strategy and stenoses remain stable over at least short time, but with higher risk of progression especially after prior PTA. We believe that the definition of precise criteria of stenosis significance is necessary for the benefit of ultrasound surveillance.

Creation of dialysis vascular access with normal flow increases brain natriuretic peptide levels.

BACKGROUND: Chronic heart failure is very common in hemodialyzed patients due to several factors such as intermittent volume overload, anemia, and hypertension. Dialysis access flow is usually considered to have a minor effect. We hypothesized that creation of dialysis access with "normal" flow would lead to elevation of B-type natriuretic peptide (BNP), which is a sensitive marker of heart failure. METHODS: We included subjects with a newly created, well-functioning vascular access and normal left ventricular ejection fraction. They were examined before access creation (baseline), then again 6 weeks and 6 months after the surgery. Only subjects with access flow (Qa) < 1500 ml/min were included. Changes of BNP levels and their relation to access flow were studied. RESULTS: We examined 35 subjects aged 60.6 +/- 13.5 years. Qa was 789 +/- 361 and 823 +/- 313 ml/min at 6 weeks and 6 months after the surgery, respectively. Within 6 weeks after access creation, BNP rose from 217 (294) to 267 (550) ng/l (median (quartile range)) with P = 0.003. Qa was significantly related to BNP levels 6 weeks after access creation (r = 0.37, P = 0.036). Six months after access creation, there was only a trend of BNP decrease (235 (308) ng/l, P = 0.44). Creatinine, blood urea nitrogen and hemoglobin levels as well as patients' weight did not change significantly. CONCLUSIONS: Creation of dialysis access with "normal" flow volume leads to significant increase of BNP, which is related to the value of access flow. The increase of BNP probably mirrors worsening of clinically silent heart failure.

Factors associated with impaired arterial adaptation to chronically high wall shear rate in the feeding artery of PTFE grafts.

BACKGROUND/AIMS: The feeding artery of dialysis vascular access is subjected to unusually high wall shear stress (WSS), a hemodynamic factor leading to vasodilatation, for at least several months after access creation. Physiologically, high WSS leads to compensatory endothelium-dependent vasodilatation. We supposed that the dilatation of the feeding artery continues to lower WSS during longer time period after access creation and that this process is limited by risk factors of endothelial dysfunction. METHODS: We examined the feeding artery of vascular accesses within 3 months, 1 and 2 years after access creation. By ultrasonography, we obtained internal diameter and blood velocity in the feeding arteries. We calculated wall shear rate (WSR). RESULTS: We examined 75 patients. Internal diameter rose from 3.9 +/- 0.1 mm (3 months) to 4.3 +/- 0.2 mm within the first year and to 4.6 +/- 0.2 mm within the second. Similarly, mean WSR decreased from 1,839 +/- 117 to 1,629 +/- 123 s(-1) and to 1,159 +/- 109 s(-1), respectively. The vasodilatation was limited by diabetes mellitus, hypercholesterolemia and hypertriglyceridemia. CONCLUSIONS: The feeding artery continues to dilate 2 years after access creation, with a simultaneous decrease in WSR. This process is dampened in patients with diabetes mellitus and dyslipidemia.

Diabetes and distal access location are associated with higher wall shear rate in feeding artery of PTFE grafts.

BACKGROUND: Surgical creation of permanent vascular access for haemodialysis leads to considerable haemodynamic changes. They could be implicated in the pathogenesis of access complications, which limit access survival, especially in diabetics. Physiologically, the relation between arterial diameter and blood velocity is maintained by wall shear stress (WSS), which is directly related to both blood viscosity and wall shear rate (WSR = blood velocity/internal diameter). Because of methodological difficulties, WSR is used as a measure of WSS. Extremely high values of WSS might induce hypercoagulable states, which might contribute to access thrombosis. We performed a study, which was aimed to (i) describe WSR values in feeding arteries of various polytetrafluoroethylene access types and (ii) prove that diabetic patients have higher WSR than non-diabetics. METHODS: A linear-array 11 MHz probe of SONOS 5500 (Phillips, USA) was used to obtain blood velocity and internal diameter in the feeding arteries of radial or brachial polytetrafluoroethylene grafts. WSR was calculated as 4 x blood velocity/internal diameter. We compared observed values of WSR according to feeding artery (radial vs brachial artery) and according to diabetic status using unpaired t-test. RESULTS: We included 106 patients (58 non-diabetic and 48 diabetic) in the study. WSR was significantly higher in radial arteries compared with brachial arteries independent of diabetes status. Diabetic subjects had significantly higher WSR in both radial and brachial arteries. CONCLUSIONS: Diabetes mellitus and distal vascular access creation are associated with higher WSR in the feeding artery. This could be of relevance in the pathogenesis of access complications, e.g. thrombosis, and thus lower patency rates in diabetic patients.

Regular ultrasonographic screening significantly prolongs patency of PTFE grafts.

BACKGROUND: Polytetrafluoroethylene (PTFE) dialysis grafts have considerably shorter patency than native arteriovenous fistulas, despite the use of a complex of screening monitoring methods (venous pressure, access flow). PTFE grafts are used often in subjects with depleted subcutaneous veins after previous abandoned accesses, so keeping the access patent is crucial. We hypothesized that regular duplex Doppler ultrasound screening for access stenoses, together with their sooner treatment, would prolong PTFE graft patency. METHODS: We performed a randomized, prospective study of PTFE grafts' cumulative patency in 192 subjects. In group 1, regular ultrasound examinations performed every 3 months was added to traditional screening (i.e., regular access examination at hemodialysis unit, monitoring of venous pressure and access flow). Group 2 was screened only traditionally (without ultrasound). Interventions of suspected stenoses were indicated by nephrologists, vascular surgeon, and, in group 1, also by ultrasonography. Classic ultrasound criteria for significant stenosis were used, even if the access flow had not been decreased. The mean follow-up lasted 392 +/- 430 days. RESULTS: Groups were similar with respect to age, gender, diabetes status, and number of previous abandoned accesses. Group 1 had significantly longer access patency (P < 0.001). Number of interventions per graft was 2.1 +/- 1.8 and 1.3 +/- 1.0 in group 1 and group 2. CONCLUSIONS: Regular screening duplex Doppler ultrasonography results in significantly longer PTFE graft patency due to early detection of access stenosis and, thus, more frequent elective interventions of access stenoses.

Endovascular treatment of central vein stenoses and/or occlusions in hemodialysis patients.

PURPOSE: To report our experience and results with the endovascular treatment of central vein stenoses and occlusions in hemodialysis patients. METHODS: Between October 1999 and August 2001 (22 months) we performed 22 interventional procedures in 14 hemodialysis patients (8 women, 6 men) ranging in age from 38 to 87 years (mean 76 years). The indication for intervention was stenosis (n = 10) or occlusion (n = 4) of a central vein in the upper arm used for dialysis in patients with arm swelling and/or shunt malfunction. All patients had a previous history of subclavian vein cannulation. There were six percutaneous transluminal angioplasties (PTAs) and eight primary stent placements and eight repeat interventions. Seven were for restenoses and one for early occlusion, with two secondary stent placements and six PTA of in-stent stenoses. In two patients a second stent was implanted. The mean follow-up was 8.5 months (range 1-19 months). All stents were self-expandable with diameters ranging from 9 to 16 mm. RESULTS: All but one of the procedures was technically successful (95%, n = 21). The patient with an unsuccessful procedure died 1 month after the procedure, but the death was not procedure-related. During follow-up three patients died with a patent shunt and central vein, none of them in connection with the procedure. No complication occurred during the interventional procedures. One patient was lost to follow-up. The primary patency rate at 12 months was 43%, with a primary assisted patency rate of 83% and a secondary patency rate of 100% (n = 6). CONCLUSION: Central vein stenoses and occlusions are associated with previous subclavian vein cannulation. They are a serious problem in hemodialysis patients with a shunt on the same arm. Endovascular treatment is a suitable option for these patients.

Dialysis access-associated steal syndrome: the role of ultrasonography.

BACKGROUND: Ischemic steal syndrome is an infrequent, but potentially disabling complication of hemodialysis (HD) access creation. We analyzed the ability of duplex Doppler ultrasonography to reveal potential causes of ischemic steal syndrome in antebrachial accesses. METHODS: We performed 212 examinations on 121 patients. Ten patients suffered from ischemic steal syndrome. Complete length access evaluation was performed by a linear array 7.5 MHz ultrasound probe. RESULTS: Hand ischemia was explained by inflow artery stenosis in five cases. Excessive fistula flow due to large arteriovenous anastomosis was the suspected cause in two cases. The remaining two cases were characterized by high-resistant minimal flow in the ulnar artery with bi-directional flow in the distal part of the radial artery, suggesting stenoses located in the arcus palmaris. Duplex Doppler ultrasound had not revealed the etiology of clinically apparent hand ischemia in one case. Isolated inflow artery stenoses were treated successfully by percutaneous transluminal angioplasty. Patients with ischemic steal syndrome and high fistula flow were treated successfully by outflow vein banding. CONCLUSIONS: Duplex Doppler ultrasonography is a valuable tool for diagnosing the cause of ischemic steal syndrome and can probably replace angiography in some cases.

Many clinically silent access stenoses can be identified by ultrasonography.

BACKGROUND: Stenoses of vascular accesses are leading factors limiting access survival. Besides physical examination, screening of access stenoses is based mainly on the "dysfunction hypothesis", which states that progressive stenosis causes graft dysfunction, such as decreased flow. We tested whether Doppler ultrasonography could detect a number of clinically hidden access stenoses in otherwise well-managed patients. Indications from clinical evaluation regarding the presence of stenosis were compared with ultrasound findings. METHODS: We made 258 examinations in 193 patients. Whole-length morphological ultrasound examinations of vascular access were done with a 7.5 MHz linear array transducer. The combination of > 50% stenosis in B-mode and at least doubling of peak systolic velocity was the criterion for significant stenosis. We compared the specificity and sensitivity of clinical diagnosis or ultrasound. RESULTS: The sensitivity and specificity of the clinical diagnosis of stenosis were 35.8% and 92.8%, respectively. CONCLUSIONS: A considerable number of otherwise appropriately managed hemodialysis patients suffer from significant access stenosis. Wider use of Doppler ultrasonography would increase the proportion of clinically hidden stenoses diagnosed in time and thus might prolong access patency. Clinical suspicion of access stenosis is highly specific and such patients should be examined directly by angiography.