Cath Lab Digest

Introduction
Peripheral stents aim to support revascularization procedures of intravascular stenoses by mechanically preventing vessel recoil and counteracting pathophysiologic processes of luminal re-narrowing triggered by procedural injury of the vessel wall. Despite improvements in stenting techniques and concomitant medication, repeated intervention due to target lesion restenosis is necessary on a significant percentage of patients. The permanent presence of an artificial implant plays a prominent role in the discussion of mechanisms causing in-stent restenosis. Permanent metallic implants pose the risk of a continuous interaction between non-absorbable stent and surrounding tissue, leading to physical irritation, long-term endothelial dysfunction, or chronic inflammatory reactions.¹ In addition, there is a risk of stent fracture due to external mechanical forces. To overcome these shortcomings, the technology of stenting has moved towards the development of temporary implants composed of biocompatible materials that mechanically support the vessel during the high-risk period for recoil and then completely degrade in the long-term perspective.^2-6 This removes a potential trigger for late restenosis.⁷

The intended performance of an AMS is to mechanically prevent early vascular recoil (short-term effect), to lose mechanical stiffness after acute risk of recoil is eliminated and thereby enable positive remodelling of the vessel wall (mid-term effect), to be absorbed completely (long-term effect) and, at any point in time, to minimize pathophysiologic mechanisms of restenosis through its material properties. During the development of the AMS, several technical requirements were fulfilled. Mechanical properties should be very similar to those of stainless steel and maintain its mechanical integrity for the initial period of time after implantation.

In order to avoid inflammatory and foreign body reactions, the metallic material should mainly consist of elements present in the human body. Moreover, the unwanted side-effects, such as toxicity and thrombogenicity, should be avoided. Magnesium was found to be an ideal basis for developing an absorbable metal stent meeting all technological and clinical requirements.⁷ A specific magnesium alloy containing magnesium (more than 90%) and other rare earth elements was selected for stent construction. The tubular-slotted, balloon-expandable stent is sculpted by laser from a single tube of a bioabsorbable magnesium alloy (Figure 1). The stent, sized 3.0 mm in diameter and 10 or 15 mm in length, is pre-mounted on a 6F rapid-exchange delivery system with 0.014" inner distal lumen. Animal investigations demonstrated superior in vivo performance of the AMS,7 in particular, higher in-stent minimal lumen diameter (MLD) compared to conventional metal stents, paving the way to their clinical application.

After having documented 3-month results of this first worldwide clinical application of the recently developed Absorbable Metal Stent (Magic, BIOTRONIK, Germany) in 20 CLI patients,¹³ we present final clinical results of the patients treated with AMS after 12 months in this communication.

Methods

Between December 2003 and January 2004, 20 patients were treated with AMS in 2 clinical centers. Nine patients have been classified as Rutherford class 4 (ischemic rest pain) and 11 as class 5 (minor tissue loss). Patients had a mean age of 76 ± 8 years (range 59-96); 10 were male and 10 were female. Risk factors included previous peripheral vascular intervention (16 patients), hypertension (14), coronary disease (11), obesity (10), diabetes (10), nicotine abuse (10), hypercholesterolemia (8), renal insufficiency (4) and cerebrovascular disease (3). Patients had diagnosed atherosclerotic lesions of 84% (70-95%) stenosis in the proximal two thirds of one or more of the infrapopliteal arteries. Lesion length was 11 mm (2-20 mm), i.e. the lesions could be covered with one or two stents of 15 mm in length. Target vessel diameter was 3.0 mm.

Written patient consent was required prior to patient enrollment. Local ethics committee approval was received prior to study initiation. This study was conducted in accordance with the Declaration of Helsinki.

During the procedure, inflow-limiting stenoses of vessels above the knee was treated before the lesion below the knee was addressed. After successful passage of the lesion below the knee using a guide wire, diagnostic angiography of the lesion area and distal run-off were performed. The lesion was then dilated with a coronary Percutaneous Transluminal Angioplasty (PTA) balloon under angiographic control. In case of insufficient restoration of blood flow by PTA alone, the stenosed area was treated by maximally 2 AMS implants. Immediate procedural success, defined as less than 30% residual stenosis, as well as post-procedural vessel run-off were confirmed by angiography. To assess good stent positioning of the radiolucent stents, IVUS control (Volcano Therapeutics Inc., Rancho Cordova, CA) was performed at the end. The aim of treatment was to restore one straight line of flow to the foot. Antiplatelet therapy was administered for at least one month after the procedure.