FEATURE CARDIOLOGY 017
The new kid on The block bioabsorbable coronary sTenTs:
By: Dr. Zubin Nalladaru MBBS MS MCh, Department of Cardiac Surgery, The City Hospital, Dubai Healthcare City, UAE
INTRODUCTION AND HISTORY Coronary heart disease is one of the leading causes of death in the world. One of the most common medical interventions performed today is the percutaneous coronary intervention (PCI), which opens clogged or damaged coronary arteries. The first PCI was performed in 1977 using a balloon to open the blocked artery (balloon angioplasty). Since then, PCI has undergone many developments including the use of bare metal stents and now the widely used drug eluting stents (DES). The bioabsorbable drug eluting stents heralds the fourth generation
in PCI. Bioabsorbable stents were first implanted in animals in 1980. The Igaki-Tamai stent was the first bioabsorbable stent to be implanted in humans. This stent is made of Poly-L-Lactic Acid (PLLA), has a thickness of 0.17 mm, has a zigzag helical coil pattern, and is balloon-expandable. The study proved PLLA to be safe in human coronary arteries. According to the initial 6-month results, 15 patients electively underwent the stent implantation; 25 stents were successfully implanted in 19 sites in the 15 patients. In the study, no stent thrombosis and no major adverse cardiac event occurred within the first six months, meaning that there were no deaths, heart attacks, or coronary artery bypass surgeries. Full degradation took 18-24 months. Furthermore, at about 36 months, lumen size
Finally, metallic stents pose artefacts with modern imaging technologies such as magnetic resonance imaging (MRI) and multi-slice computerized tomography (MSCT), which eventually will become the default non-invasive imaging modality for the coronary anatomy.
ARE BIOABSORBABLE STENTS THE ANSWER? Bioabsorbable stents, once they are absorbed, leave behind only the healed natural vessel, allowing restoration of vasoreactivity with the potential of vessel remodelling. The use of bioabsorbable stents may prevent permanent obstruction of side branches and eliminate the consequences of a ‘full-metal jacket’. Late stent thrombosis is unlikely since the stent is gone, and prolonged antiplatelet therapy is not necessary in this instance. Bioabsorbable stents can be used as a delivery device for agents such as drugs and genes, and will perhaps play a role in the treatment of vulnerable plaque. Transferring genes that code key regulatory pathways of cell proliferation inside the cells of the arterial wall using polymer stents as vehicles is feasible. Regardless of which agent (drug or gene) will finally conquer re-stenosis, a polymer stent remains an optional vehicle for such delivery. Finally, bioabsorbable stents are compatible with MRI and MSCT imaging.
“bioabsorbable stents, once they are absorbed, leave behind only the healed natural vessel,
allowing restoration of vasoreactivity with the potential of vessel remodelling”
increased. While they had limited patients, the team viewed their initial 6-month results as promising. However, the Igaki-Tamai stent lacked a drug coating, and since focus turned to bioabsorbable stents coated with drugs, the development of the Igaki-Tamai stent halted.
PROBLEMS WITH METALLIC STENTS Despite the development and progression of metallic stents, they continue to have limitations such as stent thrombosis, which requires prolonged anti- platelet therapy, and mismatch of the stent to the vessel size, which often results in a smaller lumen after stent implantation. Further, metallic stents prevent the lumen expansion associated with late favorable remodelling. Permanent metallic stents impair the vessel geometry and often obstruct side branches. Drug-eluting stents are a breakthrough in the development of stents, with their ability to significantly reduce restenosis rates and the need for repeat revascularization. Nevertheless, they are still associated with subacute and late thrombosis, and necessitate prolonged antiplatelet therapy for at least 12 months. Further, the polymer used as a vehicle for drug delivery may induce vessel irritation, endothelial dysfunction, vessel hypersensitivity and chronic inflammation at the stent site. Excessive use of stents in the coronary vasculature (full metal jacket) may interfere with traditional re-interventional techniques such as bypass graft surgery.
CURRENTLY AVAILABLE DRUG ELUTING BIOABSORBABLE STENT The ABSORB stent (Abbott Vascular, figure 1) has received the CE mark and is authorized for sale in Europe for the treatment of coronary artery disease. ABSORB currently is under development and is not available for sale in the United States. It is made of polylactide, a proven biocompatible material that is commonly used in medical implants such as dissolvable sutures. The stent delivers everolimus, an anti-proliferative drug. Everolimus has been shown to inhibit treated-site neointimal growth in the coronary vessels following vascular device implantations, due to its anti-proliferative properties. Since a permanent metallic implant is not left behind, naturally occurring vessel functions may be restored, which is one of the features that make this device a significant advancement. A full-scale European commercial launch of ABSORB with a broad size matrix is planned by the end of 2012.
CLINICAL TRIALS The ABSORB trial is the first clinical trial evaluating a drug eluting bioabsorbable vascular scaffold (BVS) for the treatment of coronary artery disease. Abbott is the only company with five-year clinical data on a complete patient set evaluating the safety and performance of this technology. The ABSORB trial is a prospective, non-randomized, two-stage
www.lifesciencesmagazines.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84