Long-term integrity of 53 iliac vein stents after catheter-directed thrombolysis.

BACKGROUND: Long-term surveillance data on venous stent integrity is sparse. There is limited knowledge on whether duplex ultrasound (DUS) can detect potential stent deformities such as kinking, straightening, and fracture, which may impact long-term patency of the stented veins. PURPOSE: To assess venous stent integrity after at least five years of follow-up and to establish the efficacy of DUS as surveillance in patients with venous stent. MATERIAL AND METHODS: A total of 45 patients with acute iliac-femoral deep vein thrombosis (DVT) treated with catheter directed thrombolysis (CDT) and stenting >5 years before follow-up. Stents were evaluated with 3D volume low dose non-contrast computed tomography (CT) and DUS for kinking, straightening, stent fracture, and patency. Results from CT scans and DUS were compared to assess the overall agreement between the methods. RESULTS: Median follow-up was 13.2 years (mean = 11.2 years; range = 5.2-15.8 years). 3D CT reconstructions showed normal stent configuration in 47 stents (89%). All intact stents were identified by DUS. In the remaining six stents, 3D CT reconstructions showed compression, tapering, kinking, and minor fracture. DUS recognized all stent complications except the minor fracture. Overall agreement between CT and DUS was 98% (kappa = 0.90). Two cases of stent occlusion were found. CONCLUSION: The long-term physical resilience of iliac vein stents evaluated with 3D CT in patients treated with CDT for iliofemoral DVT was high. Stent deformities were mostly compression, whereas fracture was rarely seen. DUS seems to be sufficient to evaluate venous stent integrity.

Evidence for Local Spots of Viscous Electron Flow in Graphene at Moderate Mobility.

Dominating electron-electron scattering enables viscous electron flow exhibiting hydrodynamic current density patterns, such as Poiseuille profiles or vortices. The viscous regime has recently been observed in graphene by nonlocal transport experiments and mapping of the Poiseuille profile. Herein, we probe the current-induced surface potential maps of graphene field-effect transistors with moderate mobility using scanning probe microscopy at room temperature. We discover micrometer-sized large areas appearing close to charge neutrality that show current-induced electric fields opposing the externally applied field. By estimating the local scattering lengths from the gate dependence of local in-plane electric fields, we find that electron-electron scattering dominates in these areas as expected for viscous flow. Moreover, we suppress the inverted fields by artificially decreasing the electron-disorder scattering length via mild ion bombardment. These results imply that viscous electron flow is omnipresent in graphene devices, even at moderate mobility.

Invited Review Article: Multi-tip scanning tunneling microscopy: Experimental techniques and data analysis.

In scanning tunneling microscopy, we witness in recent years a paradigm shift from "just imaging" to detailed spectroscopic measurements at the nanoscale and multi-tip scanning tunneling microscope (STM) is a technique following this trend. It is capable of performing nanoscale charge transport measurements like a "multimeter at the nanoscale." Distance-dependent four-point measurements, the acquisition of nanoscale potential maps at current carrying nanostructures and surfaces, as well as the acquisition of I - V curves of nanoelectronic devices are examples of the capabilities of the multi-tip STM technique. In this review, we focus on two aspects: How to perform the multi-tip STM measurements and how to analyze the acquired data in order to gain insight into nanoscale charge transport processes for a variety of samples. We further discuss specifics of the electronics for multi-tip STM and the properties of tips for multi-tip STM, and present methods for a tip approach to nanostructures on insulating substrates. We introduce methods on how to extract the conductivity/resistivity for mixed 2D/3D systems from four-point measurements, how to measure the conductivity of 2D sheets, and how to introduce scanning tunneling potentiometry measurements with a multi-tip setup. For the example of multi-tip measurements at freestanding vapor liquid solid grown nanowires, we discuss contact resistances as well as the influence of the presence of the probing tips on the four point measurements.

Excellent long-term results with iliac stenting in local anesthesia for post-thrombotic syndrome.

BACKGROUND: Only 20% of iliac veins will recanalize on anticoagulation (AC) treatment alone and may, therefore, develop venous obstruction after iliofemoral deep venous thrombosis (DVT). A considerable number of these patients will suffer from post-thrombotic syndrome (PTS) leading to impaired quality of life in more than 50%. Endovascular treatment for iliac vein obstruction using stents is known to alleviate PTS symptoms in selected patients. PURPOSE: To report the Danish long-term results of endovascular treatment with iliac stenting. MATERIAL AND METHODS: From 2000 to 2013 consecutive patients were evaluated and 19 patients with severe venous claudication were identified and subsequently underwent angioplasty and stenting. AC treatment was prescribed for 6 months, and knee-high class II compression stocking recommended for 1 year. Scheduled follow-up was done in the outpatient clinic at 6 weeks, 3 months, and annually thereafter. RESULTS: Nineteen patients, all women, all with left-sided iliac vein obstruction, and all with severe PTS symptoms were included. The median follow-up time was 81 months (range, 1-146 months; mean, 69 months). Primary patency rate of the inserted iliac stent was 89% (17/19) and 16 patients (84 %) had almost or total symptom relief at follow-up. CONCLUSION: Endovascular stenting of iliac obstruction in local anesthesia is minimally invasive and shows excellent long-term outcomes for patients suffering from PTS.

Surface and Step Conductivities on Si(111) Surfaces.

Four-point measurements using a multitip scanning tunneling microscope are carried out in order to determine surface and step conductivities on Si(111) surfaces. In a first step, distance-dependent four-point measurements in the linear configuration are used in combination with an analytical three-layer model for charge transport to disentangle the 2D surface conductivity from nonsurface contributions. A termination of the Si(111) surface with either Bi or H results in the two limiting cases of a pure 2D or 3D conductance, respectively. In order to further disentangle the surface conductivity of the step-free surface from the contribution due to atomic steps, a square four-probe configuration is applied as a function of the rotation angle. In total, this combined approach leads to an atomic step conductivity of σ(step)=(29±9) Ω(-1) m(-1) and to a step-free surface conductivity of σ(surf)=(9±2)×10(-6) Ω(-1)/□ for the Si(111)-(7×7) surface.

[Acute iliofemoral deep venous thrombosis should be treated with catheter-directed thrombolysis]. / Akut iliofemoral venøs trombose bør behandles med kateterbaseret trombolyse.

Treatment of acute iliofemoral deep venous thrombosis (DVT) with catheter-directed thrombolysis (CDT) has been performed in Denmark since 1999. The purpose of CDT is to dissolve thrombus and to restore the venous lumen as fast as possible and thereby save venous valve function and prevent postthrombotic syndrome. Danish studies have shown that treatment of acute iliofemoral DVT using CDT results in good patency, preserves venous valve function, reduces the frequency of PTS, and is associated with a higher quality of life.

Postthrombotic syndrome and quality of life in patients with iliofemoral venous thrombosis treated with catheter-directed thrombolysis.

BACKGROUND: Postthrombotic syndrome (PTS) is a common complication after iliofemoral venous thrombosis, often resulting in poor quality of life (QOL) among the affected patients. This study assessed development of PTS and its effect on QOL among patients treated for iliofemoral venous thrombosis by catheter-directed thrombolysis. METHODS: Patients admitted with an iliofemoral venous thrombosis and treated with catheter-directed thrombolysis at Gentofte University Hospital from 1999 to 2008 were invited to participate. Duplex ultrasound imaging was used to assess venous patency and valve function. Each patient completed the generic Short-Form 36-item (SF-36) health survey assessment, producing physical component (PCS) and mental component summary (MCS) scores, and the disease-specific Venous Insufficiency Epidemiological and Economic Study (VEINES)-Quality of Life (QOL)/Symptoms (Sym), questionnaires to assess QOL. PTS was assessed using the Villalta scale. RESULTS: The study included 109 patients. Median follow-up was 71 months. PTS developed in 18 patients (16.5%) and of those, initial thrombolysis was successful in 13. Patients with PTS had significantly worse mean ± standard deviation scores than patients without PTS on VEINES-QOL (34.2 ± 9.6 vs 53.1 ± 6.6; P < .0001), VEINES-Sym (34.0 ± 8.8 vs 53.2 ± 6.6; P < .0001), SF-36 MCS (44.2 ± 15.5 vs 52.3 ± 11.0; P = .005), and SF-36 PCS (42.3 ± 9.1 vs 53.5 ± 7.8; P < .0001) subscales. Patients with reflux or chronic occlusions, or both, had significantly lower mean ± SD scores than patients with patent veins without reflux on VEINES-QOL (43.5 ± 14.3 vs 51.0 ± 8.8; P = .044) and SF-36 PCS (47.2 ± 10.9 vs 52.4 ± 8.5; P = .049) scales. CONCLUSION: PTS was associated with worse QOL, although only a few patients developed PTS after catheter-directed thrombolysis of iliofemoral venous thrombosis. Patients with patent veins and sufficient valves have higher QOL scores than patients with reflux and occluded veins.

Acute iliofemoral venous thrombosis in patients with atresia of the inferior vena cava can be treated successfully with catheter-directed thrombolysis.

PURPOSE: To assess the effectiveness and clinical outcomes of catheter-directed thrombolysis in patients with atresia of the inferior vena cava (IVC) and acute iliofemoral deep vein thrombosis (DVT). MATERIALS AND METHODS: From 2001 to 2009, 11 patients (median age, 32 y) with atresia of the IVC and acute iliofemoral DVT in 13 limbs were admitted for catheter-directed thrombolysis. Through a multiple-side hole catheter inserted in the popliteal vein, continuous pulse-spray infusion of tissue plasminogen activator and heparin was performed. Thrombolysis was terminated when all thrombus was resolved and venous outflow through the paravertebral collateral vessels was achieved. After thrombolysis, all patients received lifelong anticoagulation and compression stockings and were followed up at regular intervals. RESULTS: Ultrasound or computed tomography revealed absence of the suprarenal segment of the IVC in two patients, and nine were diagnosed with absence of the infrarenal segment of the IVC. Median treatment time was 58 hours (range, 42-95 h). No deaths or serious complications occurred. Overall, complications were observed in four patients, one of whom required blood transfusion. Three patients were diagnosed with thrombophilia. Median follow-up was 37 months (range, 51 d to 96 mo). All patients had patent deep veins and one developed reflux in the popliteal fossa after 4 years. No thromboembolic recurrences were observed during follow-up. CONCLUSIONS: Catheter-directed thrombolysis of patients with acute iliofemoral DVT and atresia of the IVC is a viable treatment option, as reasonable clinical outcomes can be obtained.

Flash pulmonary edema in patients with renal artery stenosis--the Pickering Syndrome.

AIM: We report the prevalence of flash pulmonary edema in patients consecutively referred for balloon angioplasty of uni- or bilateral renal artery stenosis (PTRA), and describe the characteristics of this special fraction of the patients. We further report two unusual cases. METHODS AND MATERIAL: Review of medical records from 60 patients consecutively referred for uni- or bilateral PTRA from 2004-2005 in Copenhagen County. RESULTS: Eight out of 60 patients had one or more episodes of flash pulmonary edema before PTRA. Compared with the remaining patients, they had a higher prevalence of bilateral stenosis (50% vs 27%) and coronary artery disease (75% vs 28%). However, only one of eight had severe systolic dysfunction of the left ventricle. After PTRA, two recurrences of flash pulmonary edema were observed. One was caused by severe restenosis and did not recur after aorto-renal bypass surgery. The other one was caused by rapid atrial fibrillation and did not recur after pacemaker and medical treatment. CONCLUSION: Flash pulmonary edema can be observed in patients with unilateral as well as bilateral stenosis. The prognosis is usually excellent upon treatment of the stenoses. Recurrences are rare unless restenosis occurs, and therefore, regular control, e.g. by Doppler-ultrasound examination is recommended.

Patient acceptance of whole-body magnetic resonance angiography: A prospective questionnaire study.

BACKGROUND: Whole-body magnetic resonance angiography (WB-MRA) is a noninvasive method for diagnosing the systemic distribution of atherosclerosis. Numerous studies have demonstrated the feasibility and diagnostic performance of WB-MRA, but no studies have investigated patient acceptance of this imaging method. PURPOSE: To measure patient acceptance of WB-MRA compared to the gold standard, digital subtraction angiography (DSA), in patients with peripheral arterial disease (PAD). MATERIAL AND METHODS: In a prospective design, 79 consecutive patients (51 male, mean age 67 years) with symptomatic PAD, scheduled to undergo both WB-MRA and DSA, were included. Patient acceptance of each imaging procedure was assessed with a postal questionnaire (13 questions). A five-point rank scale (1, no discomfort; 5, severe discomfort) was used to grade patient discomfort. RESULTS: One patient was excluded from data analysis (did not undergo DSA). Of the remaining 78 patients, 69 completed the questionnaire (response rate 88%). Overall discomfort scores were higher in DSA compared to WB-MRA (mean 2.1 and 1.7, respectively; P = 0.06). In WB-MRA, overall discomfort was strongly correlated to feeling confined in the MRI system (R = 0.77, P< 0.001). In DSA, discomfort was strongly correlated to arterial puncture (R = 0.66, P< 0.001) and contrast injection (R= 0.65, P< 0.001). Injection of iodinated contrast agent at DSA was graded more uncomfortable than injection of gadolinium-based contrast agent at WB-MRA (mean 2.1 vs. 1.5, respectively; P<0.001). Sixty-two patients (90%) were willing to repeat WB-MRA, and 64 patients (93%) would repeat DSA if they needed another vascular examination. Forty-one patients preferred WB-MRA (60%), 12 patients preferred DSA (17%), and 16 patients had no preference (23%). Patient preference of WB-MRA over DSA was statistically significant (P< 0.001). CONCLUSION: Patient acceptance of WB-MRA is superior to that of DSA in patients with PAD, with the majority of patients preferring WB-MRA.

Whole-body magnetic resonance angiography with additional steady-state acquisition of the infragenicular arteries in patients with peripheral arterial disease.

The purpose of this investigation was to determine if addition of infragenicular steady-state (SS) magnetic resonance angiography (MRA) to first-pass imaging improves diagnostic performance compared with first-pass imaging alone in patients with peripheral arterial disease (PAD) undergoing whole-body (WB) MRA. Twenty consecutive patients with PAD referred to digital-subtraction angiography (DSA) underwent WB-MRA. Using a bolus-chase technique, first-pass WB-MRA was performed from the supra-aortic vessels to the ankles. The blood-pool contrast agent gadofosveset trisodium was used at a dose of 0.03 mmol/kg body weight. Ten minutes after injection of the contrast agent, high-resolution (0.7-mm isotropic voxels) SS-MRA of the infragenicular arteries was performed. Using DSA as the "gold standard," sensitivities and specificities for detecting significant arterial stenoses (>/=50% luminal narrowing) with first-pass WB-MRA, SS-MRA, and combined first-pass and SS-MRA were calculated. Kappa statistics were used to determine intermodality agreement between MRA and DSA. Overall sensitivity and specificity for detecting significant arterial stenoses with first-pass WB-MRA was 0.70 (95% confidence interval 0.61 to 0.78) and 0.97 (0.94 to 0.99), respectively. In first-pass WB-MRA, the lowest sensitivity was in the infragenicular region, with a value of 0.42 (0.23 to 0.63). Combined analysis of first-pass WB-MRA and SS-MRA increased sensitivity to 0.81 (0.60 to 0.93) in the infragenicular region, with specificity of 0.94 (0.88 to 0.97). Sensitivity and specificity for detecting significant arterial stenoses with isolated infragenicular SS-MRA was 0.47 (0.27 to 0.69) and 0.86 (0.78 to 0.91), respectively. Intermodality agreement between MRA and DSA in the infragenicular region was moderate for first-pass WB-MRA (kappa = 0.49), fair for SS-MRA (kappa = 0.31), and good for combined first-pass/SS-MRA (kappa = 0.71). Addition of infragenicular SS-MRA to first-pass WB MRA improves diagnostic performance.

Dilatation of aortic grafts over time: what to expect and when to be concerned.

Dilatation of aortic prosthetic grafts is commonly reported, but most reports are anecdotal, with little objective data in the literature. We performed a prospective trial of 303 patients who underwent prosthetic graft repair for aortic aneurysm or occlusive disease, randomizing patients between insertion of a woven polyester or expanded polytetrafluoroethylene (ePTFE) graft. Patients were followed with computed tomography and ultrasonography for up to 5 years in order to assess the frequency and magnitude of postoperative dilatation. Graft dilatation was documented in patients with polyester grafts at 12 months. Thereafter and up to 60 months, polyester grafts did not dilate further. After 5 years, polyester prostheses had dilated by 25% and ePTFE by 12.5%, as determined by computed tomography imaging. These observations suggest that dilatation of prosthetic grafts is more frequent with knitted polyester grafts compared with ePTFE. Dilatation occurs within the first year after implantation and can be, in part, explained by a discrepancy between the initial nominal graft diameter and its diameter after clamp release, probably due to an in vivo adaptation of the textile structure. Interestingly, graft dilatation did not appear to be associated with an increased frequency of graft-related complications.

Whole-body magnetic resonance angiography at 3 tesla using a hybrid protocol in patients with peripheral arterial disease.

The purpose of this study was to determine the diagnostic performance of 3T whole-body magnetic resonance angiography (WB-MRA) using a hybrid protocol in comparison with a standard protocol in patients with peripheral arterial disease (PAD). In 26 consecutive patients with PAD two different protocols were used for WB-MRA: a standard sequential protocol (n = 13) and a hybrid protocol (n = 13). WB-MRA was performed using a gradient echo sequence, body coil for signal reception, and gadoterate meglumine as contrast agent (0.3 mmol/kg body weight). Two blinded observers evaluated all WB-MRA examinations with regard to presence of stenoses, as well as diagnostic quality and degree of venous contamination in each of the four stations used in WB-MRA. Digital subtraction angiography served as the method of reference. Sensitivity for detecting significant arterial disease (luminal narrowing > or = 50%) using standard-protocol WB-MRA for the two observers was 0.63 (95%CI: 0.51-0.73) and 0.66 (0.58-0.78). Specificities were 0.94 (0.91-0.97) and 0.96 (0.92-0.98), respectively. In the hybrid protocol WB-MRA sensitivities were 0.75 (0.64-0.84) and 0.70 (0.58-0.8), respectively. Specificities were 0.93 (0.88-0.96) and 0.95 (0.91-0.97). Interobserver agreement was good using both the standard and the hybrid protocol, with kappa = 0.62 (0.44-0.67) and kappa = 0.70 (0.59-0.79), respectively. WB-MRA quality scores were significantly higher in the lower leg using the hybrid protocol compared to standard protocol (p = 0.003 and p = 0.03, observers 1 and 2). Distal venous contamination scores were significantly lower with the hybrid protocol (p = 0.02 and p = 0.01, observers 1 and 2). In conclusion, hybrid-protocol WB-MRA shows a better diagnostic performance than standard protocol WB-MRA at 3 T in patients with PAD.

[A hybrid approach to surgery for thoracic aortic aneurysm]. / Hybridoperation af torakalt aortaaneurisme.

A 57-year-old male, previously treated surgically with insertion of grafts for type A and B aortic dissection, presented with a pulsatile mass in the jugular fossa. Further examination verified a pseudoaneurysm the inlet of which was located at the proximal anastomotic site of the descending aortic graft and a newly developed aneurysm of the aortic arch. Using a left lateral thoracotomy to avoid manipulation of the pseudoaneurysm, we adopted a hybrid approach by first debranching the subclavian and carotid arteries from the descending aorta followed by endoluminal grafting of the aortic arch. The pseudoaneurysm was successfully excluded.

[Modern treatment of type B dissections]. / Moderne behandling af type B-aortadissektion.

Rapid classification is essential in the management of aortic dissections, as Type A dissections require surgery, while the optimal treatment of Type B dissections is controversial. Medical treatment with antihypertensive medication and analgesics has so far been the main treatment of uncomplicated Type B dissections, while surgery has been reserved for complications and persistent pain in spite of medical treatment. Endovascular techniques are less invasive than open repair and show promising early results.

[Bilateral deep venous thrombosis and vena cava aplasia treated with local thrombolysis]. / Bilateral dyb venøs trombose og vena cava-aplasi behandlet med lokal trombolyse.

In this case report the treatment of a young man with bilateral iliaco-femoral DVT and vena cava aplasia is presented. The patient was treated with catheter-directed thrombolysis; the catheters were introduced in the thrombus of both legs via v. popliteae. The treatment led to almost complete thrombus resolution and no valvular incompetence at three months follow-up. In our opinion this treatment should be offered even in complex cases of acute proximal deep venous thrombosis.

[Endovascular treatment of chronic iliac vein obstruction in patients with venous claudication]. / Endovaskulaer behandling af kronisk vena iliaca-okklusion hos patienter med venøs claudicatio.

INTRODUCTION: Proximal deep venous thrombosis (DVT) often leads to venous outflow obstruction in chronic venous insufficiency (CVI). This paper presents our clinical experience with iliac vein stent placement. MATERIALS AND METHODS: Between January 2001 and November 2004 balloon dilation and stent placement for the relief of iliac vein obstruction was intended in ten patients suffering from venous claudication. Median age was 35 years (range 21-42). Eight patients had earlier been treated for proximal DVT on the left side and two patients had May-Thurner syndrome. Ultrasound scanning was performed on all patients for the detection of iliac vein obstruction. It was a requirement that all patients had an open deep venous system without reflux distally to the occlusion. The procedure was carried out under local anaesthesia and all patients were anticoagulated postoperatively. RESULTS: There was one technical failure and nine patients were treated successfully. In one of these patients the stent rethrombosed after two days but the thrombus was lysed and the patient was restented more distally. All patients were discharged with an open venous system. At follow-up, eight of the nine stents were patent. Five patients had normal walking distance and three had improved. The median follow-up time was 32.5 months (range 6-53 months). CONCLUSION: The correction of iliac vein obstruction with the placement of stents in patients with venous claudication seems to be an effective, safe method which is minimally invasive. Short term patency is satisfactory but the long term results of stents in the venous system are not known and longer follow-up is required.

[Subintimal angioplasty of long femoropopliteal artery occlusions]. / Subintimal angioplastik af lange femoropopliteale arterieokklusioner.

INTRODUCTION: Subintimal angioplasty is a newer method in the treatment of lower extremity atherosclersosis. This paper reports the results of our first experiences with long (>10 cm) femoropopliteal artery occlusions. MATERIALS AND METHODS: In the period from July 1999 to July 2003, 28 patients were treated with subintimal angioplasty. The indication was intermittent claudication or critical ischaemia. The patients were followed clinically to evaluate the patency. The results are reported retrospectively. RESULTS: The technical success rate was 25/28 (89%). Patients with intermittent claudication experienced relief of symptoms after the intervention, and their median ankle-brachial index increased significantly. The primary patency rate for patients with intermittent claudication treated successfully was 53% after one year. Critical ischaemia was associated with a lower patency rate. CONCLUSION: Subintimal angioplasty can be used in the treatment of long (>10 cm) femoropopliteal artery occlusions with a high technical success rate. Our patency rates are comparable with those recorded in the literature but are still lower than those after distal bypass surgery. Thus, subintimal angioplasty may be used in treatment of patients for whom open vascular surgery is impossible or as a bridge to open vascular surgery in young patients with severe intermittent claudication.