Magnesium Stents Research Articles

Absorbierbare Stents

Coronary stent implantation started in Germany 20 years ago. In the beginning, the progress was very slow and accelerated 10 years later. Meanwhile, coronary stent implantation is a standard procedure in interventional cardiology. From the beginning of permanent stent implantation, research started to provide temporary stenting of coronary arteries, first with catheter-based systems, later with stent-alone technology. Stents were produced from polymers or metal. The first polymer stent implantation failed except the Igaki-Tamai stent in Japan. Newly developed absorbable polymer stents seem to be very promising, as intravascular ultrasound (IVUS) and optical coherence tomography have demonstrated. Temporary metal stents were developed based on iron and magnesium. Currently, the iron stent is tested in peripheral arteries. The absorbable magnesium stent (Biotronik, Berlin, Germany) was tested in peripheral arteries below the knee and meanwhile in the multicenter international PROGRESS-AMS (Clinical Performance and Angiographic Results of Coronary Stenting with Absorbable Metal Stents) study. The first magnesium stent implantation was performed on July 30, 2004 after extended experimental testing in Essen. The magnesium stent behaved like a bare-metal stent with low recoil of 5-7%. The stent struts were absorbed when tested with IVUS. Stent struts were not visible by fluoroscopy or computed tomography (CT) as well as magnetic resonance imaging (MRI). That means, that the magnesium stent is invisible and therefore CT and MRI can be used for imaging of interventions. Only using micro-CT the stent struts were visible. The absorption process could be demonstrated in a patient 18 days after implantation due to suspected acute coronary syndrome, which was excluded. IVUS showed a nice open lumen. Stent struts were no longer visible, but replaced by tissue indicating the previous stent location. Coronary angiography after 4 months showed an ischemia-driven target lesion revascularization rate of 23.8% which was below the 30% cut point of the study protocol. No myocardial Q wave infarction or death were reported. The primary endpoint was reached. During the follow-up period, vasomotion was tested in some of the patients. The proof of principle was confirmed: restoration of vasomotion during acetylcholine testing. The development of the absorbable magnesium stent, which was pushed forward by B. Heublein, Hanover, Germany, has been successful and opens new possibilities for treatment of coronary arteries. Permanent foreign-body implantation is avoided allowing further revascularization procedures in the future, bypass grafting, and restoration of vasomotion. Even prophylactic stenting in nonsignificant stenosis, like vulnerable lesions, may become a regular procedure. Noninvasive coronary imaging by CT and MRI is now possible. Stenting of children and in peripheral arteries may become a standard procedure. Currently, the degradation process of the magnesium stent has to be prolonged, and the neointima proliferation rate has to be reduced so that the DREAM (Drug-Eluting Absorbable Magnesium Stent) concept of Ron Waksman, Washington, DC, USA, can be realized.

Temporary scaffolding of coronary arteries with bioabsorbable magnesium stents: a prospective, non-randomised multicentre trial

Coronary stents improve immediate and late results of balloon angioplasty by tacking up dissections and preventing wall recoil. These goals are achieved within weeks after angioplasty, but with current technology stents permanently remain in the artery, with many limitations including the need for long-term antiplatelet treatment to avoid thrombosis. We report a prospective multicentre clinical trial of coronary implantations of absorbable magnesium stents. We enrolled 63 patients (44 men; mean age 61.3 [SD 9.5 years]) in eight centres with single de novo lesions in a native coronary artery in a multicentre, non-randomised prospective study. Follow-up included coronary angiography and intravascular ultrasound at 4 months and clinical assessment at 6 months and 12 months. The primary endpoint was cardiac death, non-fatal myocardial infarction, or clinically driven target lesion revascularisation at 4 months 71 stents, 10-15 mm in length and 3.0-3.5 mm in diameter, were successfully implanted after pre-dilatation in 63 patients. Diameter stenosis was reduced from 61.5 (SD 13.1%) to 12.6 (5.6%) with an acute gain of 1.41 mm (0.46 mm) and in-stent late loss of 1.08 mm (0.49 mm). The ischaemia-driven target lesion revascularisation rate was 23.8% after 4 months, and the overall target lesion revascularisation rate was 45% after 1 year. No myocardial infarction, subacute or late thrombosis, or death occurred. Angiography at 4 months showed an increased diameter stenosis of 48.4 (17.0%). After serial intravascular ultrasound examinations, only small remnants of the original struts were visible, well embedded into the intima. Neointimal growth and negative remodelling were the main operating mechanisms of restenosis. This study shows that biodegradable magnesium stents can achieve an immediate angiographic result similar to the result of other metal stents and can be safely degraded after 4 months. Modifications of stent characteristics with prolonged degradation and drug elution are currently in development.

Absorbable coronary stents

The concept of percutaneous coronary intervention with bioabsorbable stents has created interest because the need for stenting is temporary, and beyond the first few months there are disadvantages of a permanent implant. Conventional stents limit restenosis by holding back intimal flaps that have separated from deeper layers, and by preventing vessel recoil. The excessive healing response to stenting that contributes to restenosis could be abolished by coating stents with antiproliferative drugs. However, late-stent thrombosis sometimes occurs, probably because such drugs hinder the healing process that covers stent struts with endothelial cells. 1 Kotani J-I Awata M Nato S et al. Incomplete neointimal coverage of sirolimus-eluting stents: angioscopic findings. J Am Coll Cardiol. 2006; 47: 2108-2111 Crossref PubMed Scopus (436) Google Scholar , 2 Finn AV Joner M Nakazawa G et al. Pathological correlates of late drug-eluting stent thrombosis: strut coverage as a marker of endothelialization. Circulation. 2007; 115: 2435-2441 Crossref PubMed Scopus (1148) Google Scholar Temporary scaffolding of coronary arteries with bioabsorbable magnesium stents: a prospective, non-randomised multicentre trialThis study shows that biodegradable magnesium stents can achieve an immediate angiographic result similar to the result of other metal stents and can be safely degraded after 4 months. Modifications of stent characteristics with prolonged degradation and drug elution are currently in development. Full-Text PDF

Early restenosis following biodegradable stent implantation in an aortopulmonary collateral of a patient with pulmonary atresia and hypoplastic pulmonary arteries

Traditionally, the implantation of stents in young children with small blood vessels has been avoided as the presence of a metallic or fixed stent structure limits the ability to further dilate the stent with vessel growth. Pulmonary atresia with ventricular septal defect and hypoplastic pulmonary arteries represents one such cohort where the placement of fixed nondegradable stents has been difficult. We report a 2-month-old girl with pulmonary atresia, VSD, and multiple aorto-pulmonary collaterals with severely hypoplastic pulmonary arteries who underwent placement of a biodegradable magnesium stent within a stenotic aorto-pulmonary collateral. Although there was an initial significant increase in vessel diameter, significant restenosis occurred 4 months after stent placement. This to our knowledge represents the first case of the use of biodegradable stents in a child with severely hypoplastic pulmonary arteries. Although further refinements in stent technology are required, this development will hopefully usher in a new era of potential intervention in children previously deemed unsuitable for stent placement.

First biodegradable metal stent in a child with congenital heart disease: Evaluation of macro and histopathology

New developments in stent technology led to the first biodegradable magnesium stents. To overcome the fundamental restrictions of conventional stent implantation, these new stents may improve interventional therapy, also in small children. What remains after complete degradation of a magnesium stent is of particular interest and concern. At the autopsy, 2 months after the projected complete degradation time of the 3.0 x 10 mm(2) stent, no solid compounds were detected, and the vessel diameter had increased slightly to 3.7 mm. Histological preparation revealed an amorphous to jelly-like substitute of the magnesium struts mainly consisting of calcium phosphate covered by fibrotic tissue. Immunological staining revealed no relevant inflammatory reaction to the stent material. Neointima proliferation was detected around the struts with some cellular infiltration of the calcium-phosphate material. These pathological and histological findings show minimal alteration of the vessel wall and an increase of the arterial diameter after stent degradation. This is an important precondition for further use of biodegradable stents in small infants. Further observations have to prove whether these findings do reproduce in other settings also.

Congenital pulmonary sling, aorto–pulmonary window and pulmonary vein obstruction as a diagnostic and therapeutic challenge in an infant with VACTERL association

In a newborn with anal atresia and urethral valves an incomplete VACTERL association, was diagnosed and a colon anus praeter was placed. Sweating and heart murmur led to cardiac diagnostics. By 2D colour Doppler echocardiography a huge atrial septal defect and pulmonary venous stenoses were diagnosed. Additionally, a pulmonary sling combined with an aortopulmonary window (AoPAw) was suspected and later confirmed by angiography. Heart failure developed and closure of the AoPAw, transplantation of the left pulmonary artery and closure of the atrial septal defect was performed at the age of 4 weeks. But the patient did not improve. Pulmonary hypertension with suprasystemic pressure in the right ventricle originating from a stenosis of the new orifice of the left pulmonary artery and obstruction of the right pulmonary veins was diagnosed by echocardiography and confirmed by angiography. At the age of 8 months the orifice of the left pulmonary artery was enlarged by a patch, the obstruction of left sided pulmonary veins was opened, and the rightsided pulmonary veins were newly implanted into the left atrium. Finally the inter-atrial communication was closed by a patch plastic. Again, postoperatively the patient improved only slightly. At the age of 10 months trans-septal catheterisation was performed. Angiography revealed a successful balloon dilatation of the long obstruction of the right pulmonary veins. Later on, an absorbable magnesium stent was implanted into the right upper pulmonary vein and medication with an endothelin antagonist was started. Temporarily the patient improved significantly. Within 6 weeks, right ventricular systolic pressure was again suprasystemic due to extreme inflow obstruction of the right pulmonary vein diagnosed by echocardiography. Severe heart failure developed and at the age of 1 year the patient died.

Bioabsorbable metal stents for percutaneous treatment of critical recoarctation of the aorta in a newborn

In neonates and infants with critical aortic coarctation, balloon angioplasty is considered for rescue therapy of heart failure. The use of conventional stents is limited because of further vessel growth, the need of redilation, and later surgical removal. However, a novel bioabsorbable magnesium stent (AMS) might overcome such restrictions of vessel stenting in newborns. Presented is the first use of an AMS for acute treatment of a newborn with severely impaired heart function due to a long segment recoarctation after a complex surgical repair. We hypothesize that bioabsorbable stents will dramatically change the treatment of coarctation and recoarctation in newborns.

Safety and efficacy of bioabsorbable magnesium alloy stents in porcine coronary arteries

We aimed to determine the safety and efficacy of biobasorbable magnesium alloy stents in porcine coronary arteries. Bioabsorbable magnesium stents carry the potential to overcome the limitations posed by permanent metallic stents such as chronic inflammation, late stent thrombosis, prolonged antiplatelet therapy, and artifacts when imaged by multislice-computed tomography or magnetic resonance imaging. Magnesium alloy stents or stainless steel stents were randomly deployed in coronary arteries of domestic or minipigs. Domestic pigs were sacrificed at 3 days (n = 2) or 28 days, and minipigs at 3 months. At 3 days, magnesium alloy stents were intact, but started to show signs of degradation by 28 days. There was no evidence of stent particle embolization, thrombosis, excess inflammation, or fibrin deposition. At 28 days and 3 months, neointimal area was significantly less in magnesium alloy stent segments (2.44 +/- 0.88 mm(2) and 1.16 +/- 0.19 mm(2)) as compared with the stainless steel stent segments (5.03 +/- 1.5 mm(2) and 1.72 +/- 0.68 mm(2), P < 0.001 and 0.02). Quantitative coronary analysis indicates that percentage area stenosis and percentage diameter stenosis in magnesium alloy stent segments improved significantly at 3 months as compared to 28 days. Despite decreased neointimal hyperplasia, lumen area of the magnesium alloy stented vessels did not improve significantly. Magnesium alloy stents are safe and are associated with less neointima formation; however, reduced neointima did not result in larger lumen.

The Road to Bioabsorbable Stents: Reaching Clinical Reality?

This article provides an overview of the evolution of revascularization devices since Grüntzig's initial introduction of balloon angioplasty in 1977. In-stent restenosis (ISR) is the major shortcoming of conventional (permanent-implant) stent therapy; even with the innovation and promising benefits of drug-eluting stents, management of ISR is very difficult. ISR is mainly caused by the interaction between the blood and the stent surface and a permanent mechanical irritation of the vascular tissue. Thus stenting technology has moved toward the development of temporary implants composed of biocompatible materials which mechanically support the vessel during the period of high risk for recoil and then completely biodegrade in the long term. Preclinical and first clinical experiences with bioabsorbable magnesium stents are discussed.

First successful implantation of a biodegradable metal stent into the left pulmonary artery of a preterm baby

Stent implantation in the youngest patients with a congenital heart disease implicates limitations concerning further vessel growth, the need of staged redilation, and later surgical removal. The search to overcome these restrictions led to open stent designs, with a wide adaptability to the vessel growth and recently to the development of bioabsorbable stent materials. A preterm baby born at 26 weeks of gestation was referred to our clinic following inadvertent ligation of the left pulmonary artery. Despite efficient debanding, the left lung perfusion was absent. Implantation of a biodegradable 3 mm magnesium stent was performed in a hybrid procedure when the baby weighed 1.7 kg. Reperfusion of the left lung was established and persisted throughout the 4-month follow-up period during which the gradual degradation process of the stent completed. Additional interventions, should they become necessary, seem not to be limited. Despite the small size of the baby, the degradation process was clinically well tolerated. The mechanical and degradation characteristics of the magnesium stent proved to be adequate to secure reperfusion of the previously occluded left pulmonary artery. Bioabsorbable stents with different diameters may help develop new strategies in the therapy of vessel stenosis in pediatric patients.