生物可吸收支架：回缩、逐渐消失

Bioabsorbable Everolimus Stent Shrinks, Then Fades Away

要点：
.BVS生物可吸收支架显示出比金属DES更高的晚期回缩率
.多聚物骨架可能是支架降解的原因
.钙化斑块回缩得更少

根据发表在2008年11月11日JACC上的一项研究：经过6个月血管内超声测量，BVS生物可吸收依维莫司洗脱支架显示出比金属DES更高的回缩力，后者可能依赖于支架所在管腔形态。

由鹿特丹Erasmus医疗中心Nico Bruining博士领导的研究小组，观察了首次临床应用ABSORB试验的16例患者，这些患者置入BVS（生物可吸收依维莫司洗脱冠状支架，加利福尼亚. 圣克拉拉. 雅培血管仪器部门），治疗单支、原发冠脉病变。该支架以多聚左旋乳酸骨架作为载体，右旋多聚物为涂层，左旋乳酸包含依维莫司并控制其释放。除了2个不透射线的标记物外，BVS所有的组分有望在2、3年内被人体完全吸收。

可是，研究人员对早期BVS吸收的力学特征知之甚少。Bruining博士和他的同事们通过血管内超声在6个月时发现了可吸收支架的绝对回缩为（0.65 ± 1.71 ）mm2，同时相对回缩为（7.60 ± 23.3）%。

通过比较，作者指明，金属支架绝对回缩和相对回缩都更低。例如Xience V（雅培公司）药物洗脱支架和早先的Palmaz-Schatz支架：Xience V 6个月时绝对回缩为0.02 mm2、相对回缩 0.3%；Palmaz-Schatz 4个月时绝对回缩为0.1 mm2、相对回缩为0.6%。

钙化病变有更高的回缩率

有趣的是，绝对回缩率和相对回缩率随着置入支架节段形态变化而变化，钙化斑块晚期回缩率明显低于纤维细胞或纤维坏死斑块的晚期回缩率。（表1）

研究人员承认：“很明显，与金属支架相比，BVS血管支架的特性不会维持很长时间”，并给出了可能的解释。第一，多聚物支架比金属支架更易被人体接受，并且可能更适应富有弹性的动脉壁。另外，因为BVS被设计成能被逐渐吸收，聚合物骨架能够变弱并消失径向强度。在与TCTMD的e-mail交流中，哥伦比亚大学医学中心（纽约）的Gregg W. Stone博士同意，与金属支架比较，研究中的回缩可能会因为随着BVS的部分降解而强度降低。Stone博士指出：“金属DES回缩为0”，但回缩会导致晚期丢失和再狭窄，理论上甚至会诱发支架血栓，“但是在置入BVS的前30例患者中没有发现支架血栓”。

通过血管内超声的随访，研究发现：与Taxus紫杉醇（波士顿科学公司，迈尔密）洗脱支架相似，BVS晚期管腔丢失为（0.45 ± 0.39）mm。

病变形态可能会指导临床决策

在TCTMD的e-mail交流中，Bruining博士同意，6个月时 BVS支架的回缩量需要降低，并且关注病变形态可能会有助于决定在哪里或者是否应该置入可吸收支架，但是需要更多的研究支持。

Bruining博士说：“对于所研究的BVS型生物可吸收支架，在支架特征和病变形态（组分）之间似乎存在一定的联系，”并且目前的研究因IVUS使用的增加也证实了这一点。一个更具方法学的结论是IVUS数据（图象数据）比直观的数量结果更能提供详细的信息。

在TCT 2008上，ABSORB研究2年数据报告，发生一例缺血驱动的主要不良心脏事件、无心源性死亡、无支架血栓及无缺血驱动的靶血管血运重建。

参考资料：
Tanimoto S, Bruining N, van Domburg RT, et al. Late stent recoil of the bioabsorbable everolimus-eluting coronary stent and its relationship with plaque morphology. J Am Coll Cardiol 2008;52:1616-1620.
Serruys PW, Ormiston JA. ABSORB trial: Two-year IVUS, IVUS-VH, and OCT results of the clinical evaluation of the bioabsorbable everolimus-eluting coronary stent system in the treatment of patients with de novo native coronary artery lesions [TCT 2008 abstract TCT-64]. Am J Cardiol 2008;102:32i.

（source：www.tctmd.com）

（《医心评论》 陆卫 翻译 刘瑞琦 校对）

From JACC: Bioabsorbable Everolimus Stent Shrinks, Then Fades Away

Key Points:
BVS bioabsorbable stent shows higher late recoil than metallic-based DES
Stent degradation, polymer backbone may be reason
Less shrinkage in segments with calcified plaque

By Jason Kahn
Six-month intravascular ultrasound (IVUS) measurements of the BVS bioabsorbable, everolimus-eluting stent show a higher degree of recoil compared to metallic-based drug-eluting stents (DES) that may be dependent on lesion morphology in the stented segment, according to a study in the November 11, 2008, issue of the Journal of the American College of Cardiology.

Researchers led by Nico Bruining, PhD, of Thoraxcenter/Erasmus Medical Center (Rotterdam, the Netherlands), looked at 16 patients in the first-in-man ABSORB trial who received the BVS (Bioabsorbable eVerolimus-eluting coronary Stent, Abbott Vascular, Santa Clara, CA) for single, de novo native coronary artery lesions. The stent has a backbone of poly-L-lactic acid that provides support and a coating of poly-D, L-lactic acid that contains and controls the release of everolimus. All components of the BVS except for 2 radio-opaque markers are expected to be fully absorbed in the human body within 2 to 3 years.

Researchers, though, had little knowledge about the mechanical behavior of BVS prior to its absorption. Using IVUS, Dr. Bruining and colleagues found an absolute stent recoil of 0.65 ± 1.71 mm2 with the bioabsorbable stent at 6 months, and a percent stent recoil of 7.60 ± 23.3% at the same time point.

By comparison, the authors note, absolute recoil and percent recoil are lower for metallic based stents such as Xience V (Abbott Vascular), which also elutes everolimus, and the original Palmaz-Schatz stent: 0.02 mm2 and 0.3% for Xience V at 6 months; 0.1 mm2 and 0.6% for Palmaz-Schatz at 4 months.

More Shrinkage with Calcified Lesions
Interestingly, both absolute recoil and percent recoil differed by lesion morphology in the stented segment, with calcified plaques resulting in significantly less late recoil than fibrocellular or fibronecrotic plaque types (table 1).

The researchers acknowledge that “it is obvious that the vessel scaffolding properties of the BVS have not been maintained for a long period compared with metallic stents,” and give some possible explanations. For one, polymer-based stents are more flexible than metallic stents, and may be more affected by the elastic properties of the arterial wall. In addition, since the BVS is designed to be gradually absorbed, the polymer backbone could weaken and lose its radial strength.