In vitro and in vivo corrosion properties of new iron-manganese alloys designed for cardiovascular applications.

The principle of biodegradation for the production of temporary implant materials (e.g. stents) plays an important role in the treatment of congenital heart defects. In the last decade several attempts have been made with different alloy materials-mainly based on iron and magnesium. None of the currently available materials in this field have demonstrated satisfying results and have therefore not found entry into broad clinical practice. While magnesium or magnesium alloy systems corrode too fast, the corrosion rate of pure iron-stents is too slow for cardiovascular applications. In the last years FeMn alloy systems were developed with the idea that galvanic effects, caused by different electrochemical properties of Fe and Mn, would increase the corrosion rate. In vitro tests with alloys containing up to 30% Mn showed promising results in terms of biocompatibility. This study deals with the development of new FeMn alloy systems with lower Mn concentrations (FeMn 0.5 wt %, FeMn 2.7 wt %, FeMn 6.9 wt %) to avoid Mn toxicity. Our results show, that these alloys exhibit good mechanical features as well as suitable in vitro biocompatibility and corrosion properties. In contrast, the evaluation of these alloys in a mouse model led to unexpected results-even after 9 months no significant corrosion was detectable. Preliminary SEM investigations showed that passivation layers (FeMn phosphates) might be the reason for corrosion resistance. If this can be proved in further experiments, strategies to prevent or dissolve those layers need to be developed to expedite the in vivo corrosion of FeMn alloys.

Biocompatibility of fluoride-coated magnesium-calcium alloys with optimized degradation kinetics in a subcutaneous mouse model.

The principle of biodegradation has been considered for many years in the development of cardiovascular stents, especially for patients with congenital heart defects. A variety of materials have been examined with regard to their suitability for cardiovascular devices. Iron- and magnesium-based stents were investigated intensively during the last years. It has been shown, that iron, or iron based alloys have slow degradation kinetics whereas magnesium-based systems exhibit rapid degradation rates. Recently we have developed fluoride coated binary magnesium-calcium alloys with reduced degradation kinetics. These alloys exhibit good biocompatibility and no major adverse effects toward smooth muscle and endothelial cells in in vitro experiments. In this study, these alloys were investigated in a subcutaneous mouse model. Fluoride coated (fc) magnesium, as well as MgCa0.4%, MgCa0.6%, MgCa0.8%, MgCa1.0%, and a commercially available WE43 alloy were implanted in form of (fc) cylindrical plates into the subcutaneous tissue of NMRI mice. After a 3 and 6 months follow-up, the (fc) alloy plates were examined by histomorphometric techniques to assess their degradation rate in vivo. Our data indicate that all (fc) alloys showed a significant corrosion. For both time points the (fc) MgCa alloys showed a higher corrosion rate in comparison to the (fc) WE43 reference alloy. Significant adverse effects were not observed. Fluoride coating of magnesium-based alloys can be a suitable way to reduce degradation rates. However, the (fc) MgCa alloys did not exhibit decreased degradation kinetics in comparison to the (fc) WE43 alloy in a subcutaneous mouse model.

Histological and molecular evaluation of iron as degradable medical implant material in a murine animal model.

A small animal model was established to evaluate the potential of iron as a degradable implant material. After insertion into the tail of mice, the implants gradually degraded over a clinically relevant time period of several months. Histological analysis and gene expression data from whole-genome microarray analyses indicated a limited inflammatory reaction. No evidence of cellular responses to excess iron ions was detected, suggesting that the iron degradation products were metabolically inactive. Iron-rich compounds could be detected in the vicinity of the implant and in individual cells distant from the implantation site. These results demonstrate that the mouse model could be useful for the primary in vivo evaluation of novel implant materials and that iron degradation products can accumulate in diverse organs of the body.

One plug may not be enough: a novel technique for the occlusion of high-flow vascular connections: combined AGA vascular plug II and coil occlusion of a sequester artery in a patient with Scimitar Syndrome.

A 5-year-old male presented at birth with tachypnea and abnormal chest x-ray. He was diagnosed with Scimitar Syndrome in the neonatal period by ultrasound, which revealed partial anomalous pulmonary venous return (PAPVR) of the right pulmonary vein to the inferior vena cava, as well as dextroversion of the heart, hypoplastic right pulmonary artery, and right lung hypoplasia. Due to the large shunt volume, the patient exhibited signs of congestive heart failure with dilatation of the left atrium and left ventricle. The patient underwent cardiac catheterization, which confirmed the presence of PAPVR as well as a large aorto-pulmonary collateral connecting the sequester to the descending aorta. Due to the high flow within the sequester artery a combined "sandwich" technique was used with two AGA vascular plugs (II) and MWCE Tornado coils. Complete closure of the collateral was achieved.

Influence of Fe(II) and Fe(III) on the expression of genes related to cholesterol- and fatty acid metabolism in human vascular smooth muscle cells.

Iron is the major alloy component for a large variety of cardiovascular devices such as stents. In recent studies it has been shown that biodegradable iron or iron based stents exhibit good mechanical features with no pronounced neointimal proliferation. Whole genome gene profiling using DNA chip technology revealed that genes involved in cholesterol and fatty acid metabolism (low-density lipoprotein receptor, LDL-R; 3-hydroxy-3-methylglutaryl-Coenzyme A synthase 1 (HMGCS1) and fatty acid desaturase 1 (FADS1) are up-regulated after exposure of vascular smooth muscle cells with soluble ferrous iron. To analyze the effects of iron on these genes in detail we co-incubated human vascular smooth muscle cells for 12 and 24 h with different concentrations of ferrous (soluble iron(II)-gluconate) and ferric iron (soluble iron(III)-chloride), Ferrlecit, a commercially available drug (ferric iron-gluconate complex) and solid iron coils. The expression of LDL-R, HMGCS1 and FADS1 was analyzed using TaqMan Real-time PCR. After 24 h, all forms of iron led to a significant up-regulation of the examined genes. At high concentrations the expression rates declined, probably as a result of reduced metabolic activity. The most prominent effects were observed after co-incubation with Ferrlecit, probably caused by an increased bioavailability of the iron gluconate complex. We postulate that both, bi- and trivalent forms of iron induce the expression of LDL-R, HMGCS1 and FADS1 by generation of highly reactive oxygen species. Further animal experiments using tissues from iron-stented vessels may lead to a more profound insight into iron induced expression of cholesterol- and fatty acid metabolism related genes.

Coil occlusion of a subclavian mycotic aneurysm.

We report the first successful application of nonferromagnetic embolization coils for endovascular exclusion of a mycotic right subclavian artery aneurysm. A 58-year-old woman presented with acute cervical pain and a pulsatile mass in the right supraclavicular fossa under antibiotic medication for subacute infectious endocarditis. Diagnostic work-up including duplex sonography, digital subtraction angiography, and magnetic resonance imaging demonstrated a saccular aneurysm of the extrathoracic right subclavian artery. As an alternative to open surgery or stent-graft repair, this pathology was electively treated by transcatheter coil embolization. No neurological deficit or ischemic symptoms were noted during 9 months clinical follow-up. Multislice computed tomography scan revealed complete occlusion of the mycotic aneurysm 6 months after the interventional procedure. Transcatheter closure with Inconel embolization coils is a cost-effective and safe therapeutic option in patients with mycotic aneurysm originating from the subclavian artery.

Apoptosis-regulated survival of primarily extravascular cells in proliferative active poststent neointima.

BACKGROUND: Increased proliferation, mitigated apoptosis, and recruitment of primarily extravascular cells to injured vessels are important processes during neointima formation. Therefore, the goal of this study was to assess the spatiotemporal balance between proliferation and apoptosis and the influence of apoptosis on the survival of primarily extravascular cells in in-stent neointima. METHODS: Minipigs underwent stent implantation to abdominal aortic segments. At Days 1, 7, 14, 30, 60, and 90 after injury, arterial cross sections were analyzed by TUNEL assay to detect apoptotic cells. For immunohistochemical detection of Ki67+/proliferating cell nuclear antigen (PCNA)+ proliferative, caspase3+ apoptotic, S100+/fascin+ dendritic, GFAP+ neural crest-derived cells and CD14+ monocytes/macrophages, the alkaline phosphatase-anti-alkaline phosphatase (APAAP) method was used. RESULTS: In the incipient cell-rich neointima, both frequency of proliferation and apoptosis was maximal (Ki67, 28.5±2.2%; PCNA, 25.4±3.8%; TUNEL, 8.6±0.4%; caspase3, 7.9±4.3%). With time, parallel to the decline in the neointima cellularity, signaling for proliferation and apoptosis decreased. Throughout the time course of neointima development, the apoptotic activity was detected in primarily extravascular cells. CONCLUSIONS: Imbalance between proliferation and apoptosis and recruitment of dendritic cells, monocytes/macrophages, and neural crest-derived cells to the injured vessels may partly explain the formation of the hypercellular in-stent neointima. Herein, apoptosis is an important factor that regulates survival of primarily extravascular neointimal cells.

Development and biocompatibility of a novel corrodible fluoride-coated magnesium-calcium alloy with improved degradation kinetics and adequate mechanical properties for cardiovascular applications.

Recently, corrodible magnesium-based alloys have been introduced for use as cardiovascular stents and orthopedic implants. However, rapid corrosion rates have raised questions about their biocompatibility. Therefore, we developed a binary fluoride-coated magnesium-calcium alloy with improved degradation kinetics. Biocompatibility of the alloys was evaluated with metabolic assays (colorimetric WST-1 test). Furthermore, five different probes of magnesium-calcium alloys (MgCa 0.4, 0.6, 0.8, 1.2, and 2.0 wt %) were cocultivated with human smooth muscle cells and endothelial cells. To investigate the decomposition kinetics in a physiological environment the alloys were used untreated and fluoride coated (MgF(2)). Mg and Ca decreased the metabolic activity in vascular cells dose-dependently, with cytotoxic effects only at unphysiological concentrations. Uncoated magnesium alloys showed signs of decomposition after a short incubation time of 24 h in contrast to MgF(2) coated alloys. After 10 days smooth muscle and endothelial cells around the alloys were still alive, whereas colonization of the surfaces was only observed for smooth muscle cells. The fluoride-coated MgCa alloys exhibited good results concerning mechanical properties, degradation kinetics, and biocompatibility in vitro. We conclude that a binary fluoride magnesium-calcium alloy is a promising candidate for the production of cardiovascular stents.

First experience with the BioSTAR-device for various applications in pediatric patients with congenital heart disease.

BACKGROUND: Interventional closure of atrial septal defects (ASD) and surgical tunnel fenestrations in Fontan patients has become the procedure of choice for many years. Recently, the BioSTAR Occluder, a modification of the Starflex device with a resorbable matrix has become available. PATIENTS: Ten Biostar devices were implanted in nine children with interatrial septal defects, one within a fontan baffle, eight with secundum atrial septal defects. The age of the patients ranged from 11 months to 17 years, the body weight ranged from 12.9-78 kg. RESULTS: 10 BioSTAR devices were implanted in nine patients. In one patient, two BioSTAR devices were used to occlude multiple defects within the oval fossa. All defects were successfully and uneventfully occluded. Mean procedure time was 56 (range 28-125). Mean fluoroscopy time was 4.8 (range 1.1 to 13.0) min. None of the nine patients showed residual shunts after device implantation. After 30 days no shunt was seen in the control transthoracic echocardiography. No adverse effects like allergic reactions, tachyarrhythmia or thrombembolic events occurred in any of the patients. CONCLUSION: The BioSTAR closure device is a safe and effective device for the closure of a variety of interatrial shunts in children including multifenestrated interatrial defects and fontan fenestrations, however, possible long term consequences (e.g., fractures, recurrent shunts after scaffold degradation) remain to be studied.

Common signatures for gene expression in postnatal patients with patent arterial ducts and stented arteries.

The detailed molecular processes associated with postnatal remodelling of blood vessels are presently not understood. To characterize the response of the patients undergoing stenting of the patent arterial duct, we harvested samples of vascular tissue during surgical repair. Histological analysis of explanted ducts confirmed the patency of the ducts immediately after birth. As expected, a previously unstented duct that was examined 7 months after birth had become closed and ligamentous. Whole genome expression profiling of these samples showed that a large fraction, over 10%, of the gene sequences examined were expressed differentially between the samples taken from patients with open as opposed to the ligamentous duct. Interestingly, in 2 patients in whom closure was prevented by insertion of stents, one showed an expression profile that was similar to that of the patient initially having an unstented open duct, whereas the other was more closely related to the profile of the patient with a duct that had become ligamentous. Moreover, in 2 specimens obtained from patients with stented pulmonary arteries, a large fraction of the genes that were differentially expressed were identical to the pattern seen in the samples from the patients with open ducts. The gene regulation appeared to be independent of the nature of the respective malformations, and the site of implantation of the stents. These findings suggest that a set of differentially expressed genes are indicative for a transcriptional programme in neonatal remodelling of the arterial duct, which may also take place in patients in whom ductal closure is prevented by stents, or in those with stented pulmonary arteries. The differentially expressed genes included a significant number of extracellular matrix synthetic genes, and could therefore be predictive for vascular remodelling and neointimal formation.

Rare earth metals used in biodegradable magnesium-based stents do not interfere with proliferation of smooth muscle cells but do induce the upregulation of inflammatory genes.

Rare earth metals are added to corrodible magnesium-based alloys in low amounts (up to 10%) to improve their mechanical properties and to decrease the degradation rate. Cerium (Ce), neodymium (Nd), yttrium (Y), and ytterbium (Yb) are already used for degradable cardiovascular stents. Little is known about the biocompatibility of rare earth metals released during the degradation process of the implant. Therefore the biocompatibility of rare earth metals was assessed with regard to metabolic activity of human vascular smooth muscle cells (SMCs). After coincubation with the trivalent chlorides (0.5-100 microg/mL) of rare earth metals for 24, 72, 144, and 240 h metabolic activity was determined at each time point using the colometric WST-1 test. The tested rare earth metals did not lead to significant changes in metabolic activity over a wide concentration range. However, at high concentrations a decrease was observed. Apoptotic or necrotic effects were not observed. Furthermore, we analyzed the effects of Ce, Nd, Y, and Yb on the expression of genes involved in inflammatory processes. The expression of IL-6, IL-8, and ICAM-1 in SMCs after exposure to Ce, Nd, Y, and Yb (5 and 50 microg/mL) was measured using quantitative real-time PCR. Significant up-regulation of IL-6, IL-8, and ICAM-1 genes were only found after 24 h, mainly for a concentration of 50 microg/mL. Our cell culture data indicate that rare earth metals influence cellular processes of vascular cells. Whether adverse effects occur also in in vivo is the topic of further investigations.

Open heart surgery for a very-low-weight (660 g) premature infant.

An intracardiac calcified thrombus in a premature infant weighing only 660 was successfully removed using normothermic caval inflow occlusion. This technique avoids the use of a heart-lung machine with its deleterious effects for this specific group of patients. In addition, closure of the persistent ductus arteriosus by ligation was accomplished. Because the authors see increasing numbers of preterm neonates who need intensive care management, their experience may be helpful for those dealing with this group of patients.

Cells of primarily extravascular origin in neointima formation following stent implantation: coordinated expression of endothelial progenitor, dendritic and neural crest-derived cells.

OBJECTIVES: In-stent restenosis due to neointima formation is a major limitation following stent implantation. Recently, several studies reported mobilization of primarily extravascular cells to the arterial sites after balloon angioplasty. Therefore, the goal of the present study was to assess the coordinated neointimal expression of endothelial progenitor, dendritic and neural crest-derived cells after stent implantation. METHODS: Male minipigs underwent stent implantation in abdominal aortic segments. Animals were sacrificed at 1, 7, 14, 30, 60 or 90 days. Cross sections of the injured vessels were obtained for immunohistochemistry using specific antibodies for the detection of endothelial progenitor (CD133), dendritic (S100) and neural crest-derived cells (GFAP), as well as monocytes/macrophages (CD14) and T lymphocytes (CD3). RESULTS: As a key finding, frequency of CD133, S100, GFAP, CD14 and CD3 (18.5 +/- 3.6, 14.9 +/- 1.8, 10.6 +/- 1.1, 40.2 +/- 8.3 and 5.0 +/- 0.6%, respectively) in neointima was maximal at day 7. With ongoing neointima enlargement, expression of these cells decreased. In advanced neointima, labeled cells were predominantly localized at luminal and stented sites. Media showed almost no immunoreactivity of the markers studied, whereas adventitial zones of neovascularization revealed some signals. CONCLUSIONS: Endothelial progenitor, dendritic, neural crest-derived and inflammatory cells are consistently recruited into arterial neointima, mostly at early time points after stent implantation.

Anterograde stent implantation for treatment of recurrent coarctation after Norwood operation.

Although balloon angioplasty (BA) has become the standard therapy for recurrent aortic arch obstruction, pressure gradient relief is often not complete, with a high incidence of restenosis after BA. We report our experience with anterograde stent implantation for treatment of recurrent arch obstruction in patients with hypoplastic left heart syndrome after Norwood operation. Between March 2003 and January 2006, seven patients with the Norwood procedure required BA. The average weight was 6.3 kg (range, 4.4-9.8 kg). Four patients had undergone prior BA. For the purpose of relieving aortic arch obstruction, we used five Palmaz Genesis (PG) XD stents, and for palliative purposes we used one PG 124P stent and one Jostent, 6-12 mm. The average time after Norwood stage I was 177 days (range, 56-365 days). In six of seven patients the procedure was performed antegradely from the femoral vein. In all patients the procedure was effective. The peak systolic gradient fell from 29 mm Hg (range, 5-70 mm Hg) to 3 mm Hg (range, 0-10 mm Hg). There were no complications. No aneurysm, stent dislocation, or severe bleeding was observed. In two of seven patients three growth-related redilatations were performed. We conclude that implantation of stents at the site of recurrent coarctation after Norwood operation shows excellent gradient relief. To reduce the risk of vascular complications due to arterial access in this small group of patients, the procedure can be done safely anterogradely.

Implantation of stents for treatment of recurrent and native coarctation in children weighing less than 20 kilograms.

We report our experience with implantation of stents for treatment of recurrent and native aortic coarctation in children weighing less than 20 kilograms. We treated 9 such patients between March, 2003, and January, 2006. In 2 patients, the coarctation had not previously been treated, while in 7 it had recurred after surgery. The patients had a median weight of 14 kilograms, with a range from 5.5 to 19 kilograms. Balloon dilation was needed in 1 patient before the stent was implanted. We used Palmaz Genesis XD stents in 7 patients, these having lengths from 19 to 29 millimetres, 1 Palmaz Genesis 124P stent, and 1 peripheral JoStent with a diameter of 6 to 12 millimetres. Implantation was effective in all patients. Immediately after implantation, the mean peak systolic gradient decreased from 30 millimetres of mercury, the range having been 15 to 50 mm, to 3 millimetres of mercury, with the final range from zero to 10 mm. There were no complications, with no observations of aneurysms, dissections, or dislocated stents. In 1 patient, the peripheral pulse was weak secondary to arterial access, but treatment with Heparin led to complete resolution. It was necessary to re-dilate the stent in another patient, while 2 others are scheduled for redilation because of growth-related restenosis. Our findings suggest that implantation of stents can produce excellent relief of the gradient produced by recurrent or native coarctation. The process is safe and effective in patients weighing less than 20 kilograms.

Ultrafast time-resolved contrast-enhanced 3D pulmonary venous cardiovascular magnetic resonance angiography using SENSE combined with CENTRA-keyhole.

PURPOSE: To evaluate the diagnostic benefit of time-resolved CENTRA-keyhole contrast-enhanced cardiovascular magnetic resonance angiography (CE-CMRA) for improving arterial-venous separation of pulmonary vessels. METHODS: Twenty-three patients (18 males; age = 58 +/- 11y) after radiofrequency pulmonary vein isolation to treat atrial fibrillation were examined using CENTRA-keyhole based multi-phase 3D CE-CMRA yielding 6 near-isotropic 3D datasets every 1.6 s (50-60 coronal partitions, 1.4 x 1.4 x 1.3 mm, SENSE-factor 3). Results were compared with conventional non-keyhole CE-CMRA (identical parameters, SENSE-factor 2). RESULTS: Data acquisition was accelerated by a speedup factor of approximately 9 compared with the reference CE-CMRA (SENSE 1.5*, keyhole 6*). No pulmonary venous stenoses were detected by either method, overall pulmonary venous diameters were 17.1 +/- 3.6 mm. Applying Bland-Altman analysis, vessel diameters differed by a mean of 0.1 mm + 2.1 mm/-2.0 mm (mean +/- 2 SD), indicating close agreement between both techniques. Interobserver variability was higher for CENTRA-keyhole (mean = 0.1 mm; mean +/- 2 SD: +2.5 mm/-2.3 mm) compared to conventional technique (0.0 mm; +1.6 mm/-1.5 mm), corresponding to a percentual deviation (mean +/- 2 SD) of the mean diameter of approximately +/- 15% (keyhole CE-CMRA) and +/- 10% (conventional CE-CMRA), respectively. Using keyhole-based time-resolved CE-CMRA, the contrast between pulmonary veins versus aorta/pulmonary artery was significantly increased (p < 0.05), which improved vessel depiction. In 12 cases, the contrast bolus arrival was delayed in one of the pulmonary veins by 1 dynamic frame (= 1.6 seconds); in 7 cases by 2 frames (= 3.2 seconds) and in 1 subject by 3 frames (= 4.8 seconds). The bolus usually appeared first in the upper right pulmonary vein whereas a delay occurred most often in the lower left pulmonary vein. CONCLUSIONS: Conventional CE-CMRA may be advantageous for accurate vessel size measures as evidenced by superior interobserver reproducibility in this study. Multi-dynamic CE-CMRA using CENTRA-keyhole with SENSE, however, allows for improved arterio-venous separation of pulmonary vessels and additional dynamical information on pulmonary venous perfusion, while maintaining high spatial resolution. Exact bolus timing is no longer needed.

Resolution of protein-losing enteropathy after radiofrequency perforation and subsequent stent implantation for relief of complete occlusion of a redirected left superior vena cava.

The application of radiofrequency (RF) technologies in the treatment of congenital heart defects has provided a safe and effective alternative to conventional therapies in the restoration of vascular patency for a variety of arterial and venous occlusions. This report concerns an 8-year old girl that developed protein-losing enteropathy and elevated central venous pressure after occlusion of a surgically redirected anomalous draining left superior vena cava (SVC). Cardiac catheterization revealed complete obstruction of the anastomosis of the SVC into the coronary sinus. Transcatheter recanalization by RF perforation and subsequent stent implantation led to the restoration of upper venous blood flow and the resolution of her symptoms.

Long-term biocompatibility of a corrodible peripheral iron stent in the porcine descending aorta.

Currently there are no biodegradable stents available for treatment of vascular obstructions in patients with congenital heart defects. This study was performed to evaluate the safety of a corrodible stent produced from pure iron in a peripheral stent design (6-12mm diameter) in a slotted tube design similar to a commercially available 316-L stent which served as control. Both stents were implanted into the descending aorta of 29 minipigs with an overstretch injury without technical problems. Two animals died after the implantation not related to the iron stent. The remaining 27 minipigs were followed for 1-360 days. Histomorphometry and quantitative angiography showed no difference with regard to the amount of neointimal proliferation between 316-L and iron stents. Histopathological examination of heart, lung, spleen, liver, kidney and para-aortic lymphatic nodes demonstrated no signs of iron overload or iron-related organ toxicity. Adjacent to the iron stent struts, there was no evidence for local toxicity due to corrosion products. We conclude that iron is a suitable metal for the production of a large-size degradable stent with no local or systemic toxicity. A faster degradation rate, however, is desirable and further studies have to focus on the modification of the composition and design of the stent to expedite the degradation process.