New stents for the future
Drug-eluting stents to treat narrowed coronary vessels met with sensational success, and then things became rather quiet. Now, two new developments from Cordis and Biotronik are being tested at Essen University Hospital, Germany. We asked Professor Holger Eggebrecht, head of the hospital’s cardiac catheter lab, why these new models look important.
Apart from technical aspects, the clinical success of a stent is reflected by a low MACE rate (major adverse cardiac events), Professor Eggebrecht explained. ‘The restenosis rate of coronary arteries after stent implantation is an important criterion for choosing a good stent. With a restenosis rate of only around 5% drug eluting stents have achieved very good results compared to non-coated stents, which have restenosis rates of up to 30%. However, one problem with drug eluting stents is that -- because of the polymer coating -- they don’t heal as quickly.’ Hence the First-in-Man study of the completely new type of depot-stent from Cordis, which has a biologically degradable polymer.
‘But technical aspects, such as a thin stent profile, must also be considered when choosing a stent. For example, for very calcified lesions cardiologists use a stent with a particularly thin profile so that they can actually reach the narrowed coronary artery in the first place.
‘Conventional drug eluting stents work with a polymer coating that remains forever and can hinder stent healing into the body, so the patient has to take Aspirin and Clopidogrel for at least six months after surgery to lower the risk of stent thrombosis, which can occur about a year or one and a half years later. It’s important that surgery is avoided within the first year after a stent implantation.
‘The new Cordis stent has small reservoirs on its surface, which contain the drug. The drug is bound to a biodegradable polymer, which releases the drug contained in the reservoirs of the new Cordis stent within just 90 days and is then completely absorbed. Afterwards, the stent is basically no longer coated and can therefore heal better. This correspondingly reduces the period of time required for oral medication to be administered, as well as the risk of complications. The reservoir design also makes it possible to work with different types of drugs for the outside and inside so that, for example, the outside of the stent, which is close to artery wall, can be coated with a drug to prevent scar tissue forming, whilst the side facing the inside of the artery is coated with a thrombocyte inhibitor for anticoagulation. A further advantage over the old generation of stents is that the new model has a much thinner design, so the stent fits well into all types of constrictions.
‘Biotronik’s innovative stent is a temporary implant; it doesn’t remain in the body. Based on a magnesium alloy, it stabilises constriction in the artery only for as long as required. The stent system itself serves to prevent renewed constriction of a coronary vessel following balloon dilation. This happens during the acute phase, in the first days and up to four weeks after an intervention, when the vessels threaten to recoil. The Biotronik stent is drug coated (Paclitaxel) to prevent scar tissue forming on the inside of arteries. In research, the most difficult issue was to understand how long the life of the stent needs to be to do its job. The new stent now lasts for half a year.’
Although there are certainly some promising approaches to improving uncoated stents, Dr Eggebrecht explained that industry mostly backs further development in drug eluting implants. It’s problematic because uncoated stents are still the most widely used, but there are very few current studies on their use. ‘This is why we’ve initiated an EU-wide study that examines the use of bare metal by Biotronik (Prokinetic Energy) in 1,000 patients at 50 heart centres. As yet, hardly any reliable data are available on the success rate of bare metal stents compared to drug coated implants.
‘The superiority of drug coated stents compared to non-coated implants has been proved in numerous studies worldwide and now we use them in 80% of cases. There are clear indications why coated stents are used: Small vessel diameter and the existence of diabetes. The risk of stent thrombosis can also be reduced by increasing the dilation pressure during stent implantation, so the stent can evenly achieve its nominal diameter and offers a smaller contact surface for clot formation. The use of non-coated stents is only advisable in the case of older patients with a higher risk of bleeding. The higher costs of drug coated stents are not that relevant; patient safety is definitely the priority. Clinical monitoring in the cardiac catheter lab is and will remain important so that the success of respective interventions can be assessed.’
30.08.2010
