Absorbable Metal Stents
An update on the clinical data resulting from study of this innovative technology.
Percutaneous coronary and peripheral vascular intervention procedures frequently include implantation of permanent metal stents to minimize the risk of vessel recoil after balloon dilatation. Despite the positive initial impact of stent placement on the success rate of percutaneous interventions, permanent metallic implants pose the risk of a continuous interaction between nonabsorbable stents and surrounding tissue, leading to physical irritation, long-term endothelial dysfunction, or chronic inflammatory reactions.1
Absorbable stents are currently discussed as a means to combine a midterm mechanical vessel support with the advantage of having no long-term presence of the implant,2-6 which removes a potential trigger for late restenosis (Figure 1).7 The chance of having a tool that supports the vessel wall after percutaneous intervention procedures, while retaining a quasi-native vessel in the long-term perspective, seems to be attractive. With respect to the possible necessity of a bypass graft in the following years, the discontinued use of implanted stents is advisable.
The first clinical experience with the Absorbable Metal Stent (AMS; Biotronik GmbH & Co., Berlin, Germany) was performed in the treatment of below-the-knee lesions.8-12 Twenty patients (10 male, 10 female; mean age, 76 years) with cronic limb ischemia (CLI) and short, localized infrapopliteal disease underwent AMS placement between December 2003 and January 2004. The mean lesion length was 11 mm (range, 2 mm to 20 mm), and the mean vessel diameter was 2.7 mm (range, 2.5 mm to 3 mm), with a mean stenosis of 84% (range, 75% to 95%). One patient presented with an ulcerated lesion, three patients presented with associated thrombi, and 14 calcified stenoses were diagnosed. Prior to the infrapopliteal procedure, all inflow-limiting lesions above the knee were treated. All lesions were first dilated, and AMS implantation was only performed in cases of suboptimal angiographic result after PTA (>30% residual stenosis, flow-limiting dissection, or intimal flap). In two cases, postdilatation was performed. Procedural success was achieved in all 20 patients. A total of 23 AMS stents were implanted; in three patients, two stents were implanted for longer or tandem lesions.
The follow-up included blood analysis, clinical examination, and duplex at discharge, 1, 3, 6, 12, and 24 months. Duplex and occasional MR angiography controls were able to demonstrate the gradual absorption process. The 24-month follow-up (Kaplan-Meier calculation) showed a primary patency rate of 73.3% and a limb salvage rate of 94.7%. This experience showed that in the first-in-man below-the-knee use AMS implantation resulted in safe procedures, with a good 2-year patency and limb salvage rate. Moreover, the AMS provided sufficient support and was absorbed producing almost no artifact on MR imaging.
AMS Insight Study
The next step in the clinical evaluation of AMS in below-the-knee indications is the prospective, randomized, international, and multicenter AMS Insight I study, which is being conducted in Europe and is currently finalizing patient inclusion. In the AMS Insight I study, the effect of AMS implantation is compared to PTA in the treatment of infrapopliteal lesions in CLI patients. One hundred seventeen patients (Rutherford class 4 and 5) will be enrolled in 15 international centers. The study primary endpoints are the safety (1-month MACE rate) and efficacy (6-month patency rate) of the AMS compared to optimal PTA. The study is currently ongoing. Clinical and duplex follow-up will be performed at 1 day, 1, 6, and 12 months, with a control angiography planned at 6 months. Based on the same protocol, the US counterpart of this trial, AMS Insight II, will start enrolling patients in fall 2007. In total, 200 patients will be enrolled in 20 clinical centers.
In addition to the investigations performed in the peripheral indication, the AMS has also been evaluated for the coronaries. Progress-AMS was a prospective, multicenter, consecutive, nonrandomized first-in-man (coronary) study to evaluate the clinical feasibility of the AMS in the treatment of a single de novo lesion in a native coronary artery. The study included 63 patients at eight international clinical sites. The first-in-man coronary study showed that the application of the stents is feasible (high technical and procedural success); we have seen no death, no myocardial infarction, and no stent thrombosis in the 63 patients. The study met the primary endpoint (MACE <30%). Further improvement in stent design, coating, and combination with drug are the focus of the present research and development efforts to further improve efficacy for coronary use.
The AMS technology platform is proven and MRI/CT compatible, with absorption confirmed by IVUS during follow-up. Future AMS projects are the development of a large balloon-expandable AMS for the treatment of peripheral stenosis in large vessels. Even more appealing is the perspective to combine the advantages of AMS with local drug-eluting technology: this double approach can better address the overall patient clinical outcome because local drug therapy may optimize the results obtained with mechanical treatment (ie, minimizing inflammation, reducing cells' proliferation, etc.).
Marc Bosiers, MD, is from the Department of Vascular Surgery, AZ St-Blasius, Dendermonde, Belgium. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Bosiers may be reached at + 32 5225 28 22; email@example.com.
Koen Deloose, MD, is from the Department of Vascular Surgery, AZ St-Blasius, Dendermonde, Belgium. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Deloose may be reached at +32 5225 25 17; firstname.lastname@example.org.
Jürgen Verbist, MD, is from the Department of Cardiovascular and Thoracic Surgery, Imelda Hospital, Bonheiden, Belgium. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Verbist may be reached at +32 1550 61 97; email@example.com.
Patrick Peeters, MD, is from the Department of Cardiovascular and Thoracic Surgery, Imelda Hospital, Bonheiden, Belgium. He has disclosed that he holds no financial interest in any product or manufacturer mentioned herein. Dr. Peeters may be reached at +32 1550 61 97; firstname.lastname@example.org.