ABSORB: First-in-Man Evaluation of a Fully Bioabsorbable Everolimus-Eluting Coronary Stent -- 6-Month Angiographic and IVUS Results

Luis Gruberg, MD, FACC

Disclosures

May 01, 2007

Although only preliminary, the ABSORB results serve us to understand and improve the design of bioabsorbable stents.

The development of a nonmetal, bioabsorbable, drug-eluting stent has been an attractive concept for some time. Such a stent would have the potential to minimize the chronic inflammatory effects of coatings and may reduce the length of time of required dual antiplatelet therapy. Reintervention with either bypass surgery or stents would be easier, and magnetic resonance imaging and computed tomographic compatibilities would permit for noninvasive follow-up.

One such stent, the BVS (Abbott, Abbott Park, Illinois), is a polylactic acid polymer, everolimus-eluting stent. Polylactic acid polymer is degraded in the body via the Krebs cycle into CO2 and water and leaves no drug or polymer behind after its elution period, which is estimated to be between 12 and 18 months.

The ABSORB trial was a prospective, multicenter, open-label, first-in-man study that assessed the BVS stent in patients with single, de novo lesions in 3.0-mm vessels. Clinical follow-up was at 30, 180, and 270 days and every 12 months up to 5 years. Quantitative coronary angiography (QCA), intravascular ultrasound (IVUS), virtual histology, and palpography were performed at baseline and at 2 years. Optical coherence tomography was done at baseline, 180 days, and 2 years in up to 10 patients in each cohort. The 6-month results were presented at the American College of Cardiology (ACC) meeting.

A total of 30 patients were enrolled in the study; 4 patients were excluded, 3 because of need for bailout stenting and 1 due to device failure. The majority of patients were men (58%) and only 4% of patients had diabetes ( Table 1 ). At 6-month angiographic follow-up, QCA was available in 26 patients and IVUS was available in 24 patients.

At 6-month angiographic follow-up, the acute gain was 1.24 ± 0.42 mm; in-stent late loss was 0.44 ± 0.35 mm with a minimal lumen diameter of 1.88 ± 0.29 mm. In addition, the binary restenosis rate was 11.5% without the need for target lesion revascularization. The percentage of acute stent recoil was 6.85 ± 6.96%. By IVUS, acute incomplete apposition was seen in 6 of 26 patients, and at 6-month follow-up, it persisted in 4 patients. Late-acquired incomplete apposition was seen in 7 patients. The IVUS results are shown in Table 2 .

The rate of clinical events was extremely low. There was only 1 non-Q-wave myocardial infarction, which required intervention -- yielding an overall target lesion revascularization rate of 3.3%.

  1. The bioabsorbable everolimus-eluting stent is safe and effective with an acceptable rate of late loss (0.44 mm), possibly driven by bioactive remodeling or mechanical late recoil, which can be addressed by modifying the stent design.

  2. Intrastent neointimal hyperplasia was reduced.

  3. The rate of major adverse cardiac events was low.

  4. There was no occurrence of late stent thrombosis.

Although only preliminary, the ABSORB results serve us to understand and improve the design of bioabsorbable stents. The lack of radial strength, the development of early- and late-acquired stent malapposition, and the incidence of late stent recoil seem to be major issues associated with the design of the BVS stent.

The currently available metallic stents have certainly evolved significantly since the introduction of the first bare-metal stent. New thin-strut, alloy stents have yielded surprisingly good results, especially in simple lesions and in low-risk patients. However, the need to treat more complex lesions and higher-risk patients has surged the need for drug-eluting stents. The first generation of these drug-eluting stents has shown amazingly good results with regard to late loss and neointimal formation. Unfortunately, the need for prolonged dual antiplatelet therapy to prevent the incidence of late stent thrombosis has prompted us to reexamine the use of these promising stents.

The concept behind the use of bioabsorbable stents, particularly with respect to the need for shorter regimens of dual antiplatelet therapy, is attractive; however, from the present results we can see that there is still plenty of work ahead and many hurdles to pass.

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