Stephan Langer

Ultrastructural Analysis of Vascular Calcifications in Uremia

Accelerated intimal and medial calcification and sclerosis accompany the increased cardiovascular mortality of dialysis patients, but the pathomechanisms initiating microcalcifications of the media are largely unknown. In this study, we systematically investigated the ultrastructural properties of medial calcifications from patients with uremia. We collected iliac artery segments from 30 dialysis patients before kidney transplantation and studied them by radiography, microcomputed tomography, light microscopy, and transmission electron microscopy including electron energy loss spectrometry, energy dispersive spectroscopy, and electron diffraction. In addition, we performed synchrotron x-ray analyses and immunogold labeling to detect inhibitors of calcification. Von Kossa staining revealed calcification of 53% of the arteries. The diameter of these microcalcifications ranged from 20 to 500 nm, with a core-shell structure consisting of up to three layers (subshells). Many of the calcifications consisted of 2- to 10-nm nanocrystals and showed a hydroxyapatite and whitlockite crystalline structure and mineral phase. Immunogold labeling of calcification foci revealed the calcification inhibitors fetuin-A, osteopontin, and matrix gla protein. These observations suggest that uremic microcalcifications originate from nanocrystals, are chemically diverse, and intimately associate with proteinaceous inhibitors of calcification. Furthermore, considering the core-shell structure of the calcifications, apoptotic bodies or matrix vesicles may serve as a calcification nidus.

Surgical correction of failed thoracic endovascular aortic repair

OBJECTIVE The number of thoracic aortic endovascular procedures is increasing rapidly, and the clinical outcome largely depends on the underlying aortic pathology. When primary stent grafting is unsuccessful, secondary endovascular solutions are most often feasible. However, in recurrent endovascular failure without further minimally invasive options, conservative treatments or conversion to open surgery are the only remaining therapeutic strategies. METHODS In our experience, 106 patients received thoracic aortic endovascular treatment. Five of these patients and three from other centers underwent conversion to open repair because of 4 type Ia endoleaks (3 thoracic aortic aneurysms, 1 traumatic rupture), 2 retrograde type A dissections, 1 type Ib endoleak with contained rupture, and 1 secondary false aneurysm rupture due to stent graft migration. The latter four were surgical emergencies; the other four were urgent or elective procedures. Three patients underwent supracoronary arch replacement through sternotomy. One patient had arch and proximal descending aortic replacement, three had hemiarch and descending aortic replacement, and one had descending aortic replacement through left thoracotomy. Five stent grafts were totally removed, and three endografts were left in situ. All conversions were performed according to a protocol including total extracorporeal circulation (n = 7) or left heart bypass (n = 1), cerebrospinal fluid drainage and monitoring motor-evoked potentials, transcranial Doppler, and electroencephalography. RESULTS All patients survived the surgical procedure. Six patients had an uneventful postoperative course, whereas necrotic cholecystitis developed in one patient who required cholecystectomy and prolonged intensive care stay. One polytrauma patient died from secondary rupture due to prosthesis infection 24 days after stent graft explantation. No stroke, paraplegia, renal failure, or other major complication occurred. With a mean follow-up of 14 months (range, 4-71 months), seven patients are alive without any sign of recurrent aortic problems. CONCLUSION Failure of thoracic endovascular aortic repair comprises a new aortic pathology. Secondary endovascular treatment is feasible in most patients; however, some patients will require open surgery to repair failures of thoracic endovascular aortic treatment. These procedures constitute a large surgical trauma and require an extensive protocol, including extracorporeal circulation, neuromonitoring, and adjunctive modalities to provide organ protection. We recommend that these procedures be performed in centers with experience and the infrastructure to offer these protective measures.

Chronic kidney disease aggravates arteriovenous fistula damage in rats.

Neointimal hyperplasia (NIH) and impaired dilatation are important contributors to arteriovenous fistula (AVF) failure. It is unclear whether chronic kidney disease (CKD) itself causes adverse remodeling in arterialized veins. Here we determined if CKD specifically triggers adverse effects on vascular remodeling and assessed whether these changes affect the function of AVFs. For this purpose, we used rats on a normal diet or on an adenine-rich diet to induce CKD and created a fistula between the right femoral artery and vein. Fistula maturation was followed noninvasively by high-resolution ultrasound (US), and groups of rats were killed on 42 and 84 days after surgery for histological and immunohistochemical analyses of the AVFs and contralateral femoral vessels. In vivo US and ex vivo morphometric analyses confirmed a significant increase in NIH in the AVFs of both groups with CKD compared to those receiving a normal diet. Furthermore, we found using histological evaluation of the fistula veins in the rats with CKD that the media shrank and their calcification increased significantly. Afferent artery dilatation was significantly impaired in CKD and the downstream fistula vein had delayed dilation after surgery. These changes were accompanied by significantly increased peak systolic velocity at the site of the anastomosis, implying stenosis. Thus, CKD triggers adverse effects on vascular remodeling in AVFs, all of which contribute to anatomical and/or functional stenosis.

Time-Resolved 3D MR Angiography of the Foot at 3 T in Patients with Peripheral Arterial Disease

OBJECTIVE The objective of our study was to prove the feasibility and clinical relevance of fast contrast-enhanced time-resolved 3D MR angiography (MRA) with submillimeter spatial resolution at a high magnetic field strength. SUBJECTS AND METHODS Twenty-one patients (five women, 16 men; mean age +/- SD, 65 +/- 14 years) were examined on a 3-T whole-body MR system with an 8-element phasedarray coil for preoperative evaluation of the pedal arterial system and assessment of the visualized vessels to serve as a graft touch-down site in pedal bypass surgery. Time-resolved 3D MRA of the foot was performed after automatic injection of 0.2 mmol/kg of gadobenate dimeglumine using a sagittal gradient-echo T1-weighted sequence (TR/TE, 4.2/1.6; flip angle, 30 degrees ; field of view, 290 mm; matrix, 352; 120 slices; slice thickness, 0.8 mm) with a spatial resolution of 0.8 x 0.8 x 1.6 mm reconstructed to 0.6 x 0.6 x 0.8 mm and a temporal resolution of 3.9 seconds using keyhole and sensitivity-encoding (SENSE) technology (SENSE factors: 4 in anteroposterior direction and 2 in right-left direction). Dynamic subtractions and rotating maximum intensity projections were calculated. The original image data sets were transferred to a dedicated workstation for objective signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) analysis of the arteries. Subjective image analysis regarding image quality and diagnostic findings was performed by two radiologists in consensus. RESULTS In all patients, images of diagnostic quality were obtained. Despite the known limitations regarding signal intensity measurements in images acquired with the use of parallel imaging technique, SNR and CNR proved to be excellent, with mean +/- SD values of 294 +/- 158 and 248 +/- 144, respectively. Although most of the patients had diabetic foot syndrome with arteriovenous shunting, the arteries and the potential vessel for bypassing could be clearly separated from the veins in each case due to the temporal information given by our study. The ability to reliably discriminate arteries from veins is of high clinical relevance in planning pedal bypass surgery. CONCLUSION Fast contrast-enhanced time-resolved 3D MRA of the foot at 3 T is feasible and of high clinical value for the preoperative evaluation of the arterial supply of the foot.

Brain and spinal cord protection during simultaneous aortic arch and thoracoabdominal aneurysm repair

OBJECTIVE We assessed the surgical and neurological outcome of patients undergoing simultaneous repair of aortic arch and descending thoracic aortic aneurysms (DTAA) or thoracoabdominal aortic aneurysms (TAAA) via left thoracotomy or thoracolaparotomy. METHODS During a 6-year period, we performed 32 procedures in 23 male and 9 female patients with DTAA or TAAA with concomitant aortic arch aneurysms. The mean age of the patients was 50.9 years (range, 18-75 years). Twenty-two patients suffered from DTAA, 4 had type-I TAAA, and 6 had type-II TAAA. The entire aortic arch was involved in 12 patients and the distal hemi-arch in 20 patients. The mean diameter of the aneurysms was 6 cm (range, 4.9-7.6 cm). All patients were operated on according to the protocol with cerebrospinal fluid drainage, distal aortic and selective organ perfusion, as well as antegrade brain perfusion. Neuromonitoring was performed by means of motor evoked potentials (MEPs), transcranial Doppler (TCD), and electroencephalography (EEG). RESULTS All patients survived the surgical procedure and 30-day mortality did not occur. At the end of the procedure, all patients had adequate MEPs, TCD, and EEG. One patient died 47 days after operation due to gastrointestinal bleeding and therapy-resistant coagulopathy. Major postoperative complications like paraplegia or paraparesis, renal failure, and myocardial infarction were not encountered. One patient had a stroke but neurological deficits were irrelevant. Mean preoperative creatinine level was 125 mmol/L, which peaked to a mean maximal level of 130 and returned to 92 mmol/L at discharge. Other complications included bleeding requiring surgical intervention (n = 4), arrhythmia (n = 1), pneumonia (n = 5), and respiratory distress syndrome (n = 2). At a median follow-up of 38 months, all but 1 patient was alive and free of re-intervention. CONCLUSION Single-stage repair of aortic arch and concomitant thoracic and thoracoabdominal aortic aneurysms via left-sided thoracotomy or thoraco-laparotomy yields excellent short- and midterm outcomes. Monitoring of cerebral and spinal cord function contributes to improved neurologic outcome.

Unmasking pedal arteries in patients with critical ischemia using time-resolved contrast-enhanced 3D MRA

OBJECTIVE To test the diagnostic relevance of fast Gadobenate dimeglumine (Gd-BOPTA) enhanced, time-resolved, three-dimensional magnetic resonance angiography (t3D MRA) of distal calf and pedal vasculature in critical limb ischemia in a prospective comparison with conventional selective digital subtraction angiography (DSA) and high-resolution duplex ultrasound (US) scan. METHODS From April 2007 to June 2008, 34 feet of 29 consecutive patients suffering from limb-threatening ischemia underwent diagnostic US scan, DSA, and t3D MRA before treatment. The investigations took place within 3 days. A t3D MRA was performed using a 3 Tesla whole-body magnetic resonance (MR) system with an eight-element phased-array coil. Image quality and diagnostic findings were subjectively analyzed by two radiologists and one vascular surgeon. Each distal calf and foot was divided into six arterial segments for DSA and t3D MRA, and four segments were investigated by US scan. Patency or occlusion was studied with all the techniques, whereby DSA and t3D MRA were additionally evaluated in patients having greater or less than 50% stenosis. Finally, images were visually assessed by the three observers by applying a six-point grading scale. The acquired data was statistically analyzed using McNemars test and Wilcoxons matched-pairs signed-rank sum test. The P values of less than an alpha level of .05 were considered to be statistically significant. RESULTS We achieved MRA images of diagnostic quality in all patients. Significantly more patent pedal arteries were identified by applying t3D MRA than DSA (P < .001) and US scan (P < .02). For estimating the degree of stenosis, no technique proved to be superior (P > .28). Overall image quality was rated best for t3D MRA. Additionally, potential bypass target vessels could be clearly discriminated from pedal veins due to the temporal resolution. CONCLUSION In our prospective study, t3D MRA has been proven to be superior to DSA and US scan in pedal vasculature imaging in critical limb ischemia. This is a valuable, noninvasive method for detecting potential pedal bypass target arteries.

Functional and structural response of arterialized femoral veins in a rodent AV fistula model

BACKGROUND Neointimal hyperplasia is considered to be the major cause of arteriovenous fistula (AVF) failure, resulting in vein wall thickening, stenosis and, ultimately, occlusion. Ultrasound (US) has been shown to be effective for detecting these morphological changes in patients. The aim of this study was to develop an experimental AVF model in the rat that shows typical features of fistula maturation and allows longitudinal monitoring of fistula veins by high-resolution ultrasound. METHODS AVFs were created by a handsewn end-to-side anastomosis between the femoral vein and the femoral artery in 15 rats. A group of sham-operated animals (n = 3) served as controls. Time-related functional and morphological AVF characteristics were assessed up to 12 weeks using ultrasound (15-MHz transducer) and were correlated to histopathological changes. RESULTS All rats survived surgery, and the patency rate was 93%. US showed a 2-fold increase in the fistula vein diameter and mean flow velocity as well as a 4-fold increase in the intima-media thickness without significant luminal loss. The afferent femoral artery exhibited no change in intima-media thickness and only minimal adaptive increases in diameter and flow velocity. Histological evaluation confirmed these observations. CONCLUSIONS Our AVF model in the rat demonstrates maturation effects in fistula veins similar to typical clinical findings in haemodialysis patients. Noninvasive ultrasound proved to be a valuable tool for longitudinal in vivo monitoring of the fistulas in this rodent model.

Non- invasive in vivo analysis of a murine aortic graft using high resolution ultrasound microimaging

INTRODUCTION As yet, murine aortic grafts have merely been monitored histopathologically. The aim of our study was to examine how these grafts can be monitored in vivo and non-invasively by using high-resolution ultrasound microimaging to evaluate function and morphology. A further aim was to prove if this in vivo monitoring can be correlated to immunohistological data that indicates graft integrity. METHODS Murine infrarenal aortic isografts were orthotopically transplanted into 14 female mice (C57BL/6-Background) whereas a group of sham-operated animals (n = 10) served as controls. To assess the graft morphology and hemodynamics, we examined the mice over a post-operative period of 8 weeks with a sophisticated ultrasound system (Vevo 770, Visual Sonics). RESULTS The non-invasive graft monitoring was feasible in all transplanted mice. We could demonstrate a regular post-transplant graft function and morphology, such as anterior/posterior wall displacement and wall thickness. Mild alterations of anterior wall motion dynamics could only be observed at the site of distal graft anastomosis (8 weeks after grafting (transplant vs. sham mice: 0.02 mm ± 0.01 vs. 0.03 mm ± 0.01, p<0.05). However, the integrity of the entire graft wall could be confirmed by histopathological evaluation of the grafts. CONCLUSIONS With regard to graft patency, function and morphology, high resolution ultrasound microimaging has proven to be a valuable tool for longitudinal, non-invasive, in vivo graft monitoring in this murine aortic transplantation model. Consequently, this experimental animal model provides an excellent basis for molecular and pharmacological studies using genetically engineered mice.

Carbon Dioxide Contrast Agent for CT Arteriography: Results in a Porcine Model

PURPOSE To test the feasibility of carbon dioxide (CO(2))-enhanced computed tomographic (CT)-arteriography in an animal model. MATERIALS AND METHODS Five domestic swine underwent digital subtraction angiography (DSA), conventional CT angiography with iodinated contrast material, and CO(2)-enhanced CT arteriography. For each CO(2)-enhanced DSA image series, 100 mL of pressurized CO(2) was injected at 1.3 bar. CT imaging was performed according to a standardized scan protocol (2 x 32 x 0.6 mm; 120 kV, 210 mAs(eff), 330 msec gantry rotation time). Iodinated contrast material was administered intravenously according to a biphasic injection protocol. For CO(2)-enhanced CT arteriography, CO(2) was administered intraarterially via a catheter placed in the juxtarenal aorta. An injection pressure of 0.65 bar (volume flow rate, 7.5 mL/sec) was applied. Images were assessed visually by two observers on a four-point grading scale. Absolute intraarterial attenuation values were measured. RESULTS Image quality was rated to be the best for standard DSA. CO(2)-enhanced DSA was rated slightly superior to CO(2)-enhanced CT arteriography. No examination was considered to be nondiagnostic. The average multislice spiral CT (MSCT) scan duration was 7.9 sec +/- 0.6. The average amount of gas required for CO(2)-enhanced CT arteriography was 104 mL +/- 4, compared with 400 mL for CO(2)-enhanced DSA. Absolute attenuation values were significantly higher with CO(2)-enhanced CT arteriography (aorta, -928 HU +/- 39) than with standard CT angiography (490 HU +/- 40; P < .0001). CONCLUSIONS CO(2)-enhanced CT arteriography is feasible. In a porcine model, this technique is capable of depicting the aortoperipheral vessels down to the lower limb. These results warrant further studies of the diagnostic value of CO(2)-enhanced MSCT arteriography for the detection of arterial pathologic processes.

Cardiovascular remodeling during arteriovenous fistula maturation in a rodent uremia model

Purpose The aim of this study was to evaluate cardiovascular remodeling after arteriovenous fistula (AVF) surgery and to characterize the effect of chronic kidney disease (CKD) in a rodent femoral AVF model. Methods Sixteen rats (8 healthy; 8 CKD) underwent femoral AVF surgery; 4 animals served as controls. AVF and cardiac morphology as well as function were assessed during the fistula maturation process (until day 84 after surgery) using magnetic resonance imaging and histopathological analyses. Results Histopathological analysis revealed that a glomerular and interstitial nephropathy caused CKD. In healthy and CKD animals, AVF surgery resulted in progressive downstream vein dilation and a subsequent cardiac adaptation. This vein dilation during maturation was less in CKD rats during the early postoperative course (day 21: p=0.0475) and similar thereafter until day 84. The dilation was accompanied by an aggravation of neointimal hyperplasia (NIH) and calcification in AVFs of CKD rats. The chronic volume overload resulted in both groups in a significantly increased end-diastolic volume (healthy rats: p=0.0087; CKD rats: p=0.0333). Simultaneously, cardiac output increased 195% in healthy and 244% in uremic rats, which was caused by both a significantly increased stroke volume and heart rate. The left ventricular mass rose in AVF animals and was increased at the end of the study period, indicating a distinct cardiac hypertrophy. Conclusion Our rat model showed typical cardiovascular features of the AVF maturation process, which strongly resemble clinical findings in patients. Uremia caused inferior dilation in the early phase after surgery and an exacerbation of NIH. This model should help to identify the cellular and molecular mechanisms that contribute to AVF failure.