New absorbable stent era begins

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The world’s first drug-eluting bioresorbable stent, developed by Abbott Vascular, received the CE mark on 10 January 2011. The Absorb device has been designed to completely dissolve and restore natural vessel, avoid long-term problems seen with the current drug-eluting stents. Experts tell Cardiovascular News why it is too early to conclude what the role of absorbable devices will be and explain what still needs to be investigated.

 

Juhani Airaksinen, head of Cardiology, Department of Medicine, Turku University Hospital, Finland, said that, in theory, the absorbable stent could avoid most of the current long-term problems of stenting. “So far, the research experience has been very promising. There were no cases of late (or acute) stent thrombosis and very low rate of major adverse cardiac events. Most of the struts are gone within two years according to the optical coherence tomography studies and coronary vasomotion seems to be restored,” Airaksinen said.

 

“On the other hand, we have to acknowledge the shortcomings of the present studies. The number of patients is very limited and all the treated lesions were simple. We do not know how the stent works in everyday practice with more complicated lesions. In these cases we often need good radial force together with properties enabling safe and quick stent delivery. We are eagerly waiting for the results from the ongoing larger studies, including the European trial that will enrol approximately 500 patients,” he added.

 

The bioresorbable vascular scaffold has shown to dissolve within approximately two years, leaving patients with a treated vessel free of a permanent metallic implant. The Absorb device is made of polylactide, a proven biocompatible material that is commonly used in medical implants such as resorbable sutures. Since a permanent metallic implant is not left behind, a patient’s vessel may ultimately have the ability to move, flex and pulsate like an untreated vessel. In addition, continuing research indicates that the need to administer long-term dual anti-platelet therapy to patients may be reduced because the temporary scaffold is completely resorbed.

Andreas Baumbach, consultant cardiologist, Division of Specialised Services, University Hospitals Bristol, UK, said it would be wrong to assume that the absorbable technology can replace workhorse stents for all clinical scenarios.

 

“The current stent platforms are highly sophisticated metal scaffoldings that can be implanted into difficult lesions, through extreme tortuosity and within heavily calcified vessels of a wide range of sizes,” he commented.

 

Imaging assessment

 

Intracoronary diagnostic techniques (intravascular ultrasound and optical coherence tomography) in patients undergoing procedures with the absorbable stent subsequently confirmed the ability of these devices to provide an early scaffold of the vessel and to maintain lumen gain at long-term follow-up, Fernando Alfonso, University Hospital, Clinico San Carlos, Madrid, Spain, said.

 

“Furthermore, these imaging techniques provided persuasive (seeing is believing!) evidence confirming the ‘disappearance’ of the device struts at long-term follow-up. Initial concerns (from the small Cohort A) suggested that partial recoil of the scaffolding structure may implicate in poorer mid-term lumen results as compared with those obtained with last generation drug-eluting stent. These concerns appear to be fully dissipated with recent data from the last generation of the Absorb device,” Alfonso said.

The future

 

So, what is the future for practical use of the bioresorbable stent? Renu Virmani, medical director, CVPath Institute, Gaithersburg, USA, said she could see the device being used in young individuals with proximal, discrete (one or two) lesions in the presence of aggressive medical therapy which will result in the vessel being returned to its pre-symptomatic state i.e., minimal atherosclerosis with a functional endothelium.

 

“I am not convinced that the current device can be used in heavily calcified or very complex long lesions, which require overlap. This is just the beginning where much improvement (thin struts and greater radial strength) and better understanding are needed. Currently it can only be used in very select patients and by interventionalists, with specialised training in the use of this device,” she added.

 

“The bioabsorbable stents are only just emerging as a relevant clinical tool and will almost certainly initially be used in less complex scenarios. The use of a completely absorbable scaffold in various clinical presentations from stable angina to acute coronary syndromes and ST elevation myocardial infarction needs to be assessed in clinical trials. I am, however, convinced that the benefit of a completely disappearing stent that leaves behind a healed and functioning vessel with normal endothelial function must be the ultimate goal. We will see a series of clinical trials that will define their ultimate benefit for patients,” Baumbach said.