The first bioresorbable vascular scaffold (BVS) stent to enter the market was Abbott’s ABSORB, a drug-eluting polymer stent that received CE Mark approval in 2011 and FDA approval in 2016. However, this was a short-lived stent, and Abbott ended U.S. sales in September 2017. According to an AHA/ASA Journals report, “Three-Year Outcomes With the Absorb Bioresorbable Scaffold”, a meta-analysis of the four randomized ABSORB trials indicated that the ABSORB stent was associated with increased target lesion failure and device thrombosis rates when compared to cobalt-chromium everolimus-eluting stents.
Magnesium: advantages and challenges
A stent that remains in the body only long enough to allow for vascular healing is still considered a best-case scenario. With the shortcomings of polymer stents, device manufacturers turned to magnesium. A metal stent allows for increased radial support and could allow for early endothelialization, potentially reducing late thrombosis. However, Mg alloys are not free from challenges. According to a National Center for Biotechnology Information article, “A promising biodegradable magnesium alloy suitable for clinical vascular stent application”, early MG alloys had resorption/corrosion rates that were too short, causing stent failure before the vessel was healed. These alloys were also known to have extensive pitting during the corrosion process.
However, a newer alloy, namely JDBM-2, extends structural integrity for up to six months. Additional processes and techniques have been studied to further extend structural integrity and allow for uniform corrosion throughout the corrosion process. A World Journal of Engineering and Technology article, “Reduction in the Corrosion Rate of Magnesium and Magnesium Alloy Specimens and Implications for Plain Fully Bioresorbable Coronary Artery Stents: A Review”, outlines some of the different approaches to increase resorption times.
Mg alloy brings benefits
The first company to overcome these challenges and bring a magnesium alloy bioresorbable scaffold stent to market was Biotronik, which received CE Mark approval for its Magmaris stent in 2016. Biotronik achieved this with its proprietary Mg alloy, which the vendor claims has approximately a 95% resorption at 12 months. According to Biotronik’s website, the Magmaris stent also facilitates rapid endothelial growth, less recoil, and better delivery when compared to polymeric scaffold stents.
Studies proving the safety and efficacy of the Magmaris stent include the BIOSOLVE-I and BIOSOLVE-II trials and the ongoing BIOSOLVE-IV registry. The Cardiovascular News article, “CRT 2019: Early resorption and low complications demonstrated for Magmaris”, states that initial data from the BIOSOLVE-IV registry strengthens the clinical evidence in favor of the Magmaris stent.
Quicker resorption could help many patients
A stent that resorbs in only 12 months opens the door for a much larger patient population than that allowed using polymer scaffold stents. The resorption rates of polymer scaffold stents are 3+ years, which requires patients to remain on dual antiplatelet medication for at least that amount of time. Since antiplatelet medication cannot be stopped during the resorption period due to a high risk of stent thrombosis, patients at high risk for major surgery within the resorption period, or patients who are not medication-compliant, often due to medication cost, are not candidates for these stents.
Needing to remain on antiplatelet medication for a shorter period of time is a huge cost savings to patients and can potentially allow patients who need or may need major surgery to be Magmaris stent candidates as long as their surgical needs can be postponed for the 12 month resorption period. With the promising data from Biotronik’s trials and registry, FDA approval for the Magmaris stent is being eagerly anticipated in the U.S.