First Implanted Biodegradable Stent Shows Positive Safety at 10 Years

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The first fully biodegradable stent implanted in human patients shows major adverse event rates similar to those of bare-metal stents (BMS) and overall acceptable long-term safety out to 10 years, according to research published online April 16, 2012, ahead of print in Circulation. The findings should aid in the development of the drug-eluting version of the technology, the authors say.

The Igaki-Tamai stent (Kyoto Medical Planning, Kyoto, Japan) is made of biodegradable poly-L-lactic acid (PLLA) that ultimately metabolizes to carbon dioxide and water. The stent is CE mark approved in Europe.

Kunihiko Kosuga, MD, PhD, of Shiga Medical Center (Shiga, Japan), and colleagues electively treated 50 Japanese patients (63 lesions) with 84 Igaki-Tamai stents between September 1998 and April 2000, following them for over 10 years (mean 121 months). All patients had stable ischemic coronary disease.

At 10 years, freedom from all-cause death was 87%, with 98% of patients free from cardiac death and 50% free from MACE (table 1).

Table 1. Long-term MACE at 10 Years

^a Academic Research Consortium-defined.

The 5-year TLR rate (18%) is comparable to that of conventional BMS, the authors note.

Duration of dual antiplatelet therapy (aspirin and ticlopidine) was determined by the attending physicians. Of 48 patients with follow-up regarding dual therapy, duration was less than 3 months in two-thirds of patients (66%), 4 to 12 months in 20%, and 13 to 36 months in 10%. Within 3 years after Igaki-Tamai implantation, the drugs were restarted in 4 patients due to implantation of additional stents or cerebral infarction.

The single case of acute scaffold thrombosis was the first reported PLLA thrombosis in humans. It occurred after dual therapy cessation following an acute hemorrhagic gastric ulcer, indicating that “even though the stent material is not metallic, antiplatelet therapy is mandatory,” according to Dr. Kosuga and colleagues.

On QCA, minimum lumen diameter (MLD) decreased from 2.68 ± 0.43 mm at postprocedure to 1.76 ± 0.74 mm at 6 months, but improved to 2.22 ± 0.56 mm at 3 years. Likewise, on IVUS analysis, minimum lumen area (MLA) decreased from 5.44 ± 1.89 mm² at postprocedure to 3.64 ± 1.68 mm² at 6 months, but improved to 5.18 ± 2.09 mm² at 3 years.

The decrease in MLA and MLD at 6 months with subsequent improvement by 3 years is similar to that seen with metallic stents, the authors note.

Now You See It . . .

Serial IVUS data of 13 lesions treated with a single Igaki-Tamai stent and without TLR showed a significant increase in hyperechogenicity of the scaffolded segment after stent implantation (P = 0.018). This was followed by a significant reduction in hyperechogenicity that was detected after 12 months, with a value at 36 months comparable to that seen prior to implantation—meaning the stents had completely disappeared from coronary arteries by 3 years, as opposed to the expected time frame of 6 months.

The authors conclude that “acceptable MACE rates similar to those of BMS and scaffold thrombosis rates without stent recoil [or] vessel remodeling sugges[t] the long-term safety of the Igaki-Tamai stent,” adding that the results are “essential in paving the way for a bioabsorbable drug-eluting PLLA stent, especially from the standpoint of long-term safety.”

There is currently 1 fully bioabsorbable DES at an advanced stage of development, the everolimus-eluting PLLA-based BVS stent (Abbott Vascular, Santa Clara, CA), implanted in human patients after the Igaki-Tamai stent.

Solving the Problems of Metallic Stents

According to the authors, bioabsorbable stents can ameliorate many of the known drawbacks with current BMS and DES, such as the potential for thrombosis and malapposition. “All these problems with metallic stents can be solved by using fully biodegradable stents, because there are no foreign materials after PLLA degradation,” they note.

In an e-mail communication with TCTMD, John A. Ormiston, MB, ChB, of Mercy Hospital (Auckland, New Zealand), indicated that the major implication of the 10-year results is the overall safety of PLLA stents in coronary arteries, with low reintervention rates over the course of the study. He also noted that when Dr. Kosuga retrieved tissue percutaneously by directional atherectomy in a patient 42 months after implantation, there was almost no inflammation.

And the longer length of time for scaffold bioresorption should not be concerning, Dr. Ormiston said. “In fact if the struts were completely absorbed by [6] months they probably would not provide sufficient duration of radial support to prevent negative remodeling (vessel shrinkage), which is the major cause of restenosis after balloon angioplasty,” he noted.

Antiproliferative Agent Likely Necessary

Importantly, a resorbable scaffold may help reduce the late complications of stenting, Dr. Ormiston theorized, adding that to be effective, such stents will likely need to elute an antiproliferative agent to limit the intimal hyperplasia that is the main cause of post stenting restenosis.

“To be fully healthy an artery needs to be exposed to normal pulsatile and sheer forces rather than being caged by a rigid stent,” Dr. Ormiston said. “An artery is capable of vasomotion and [can potentially respond] to physiological need after resorbable scaffold implantation in contrast to after metallic stent implantation.”

Another benefit of biodegradable stents is that “imaging with MRI and CTA is not impeded after polymeric scaffold implantation,” Dr. Ormiston added. “Many patients and cardiologists would prefer a resorbable scaffold rather than a permanent metallic implant if all else is equal.”

 

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Source:
Nishio S, Kosuga K, Igaki K, et al. Long-term (>10 years) clinical outcomes of first-in-man biodegradable poly-l-lactic acid coronary stents: Igaki-Tamai stents. Circulation. 2012;Epub ahead of print.

 

 

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