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Implantation of bioresorbable scaffolds (BRS) results in more periprocedural MIs than use of first-generation sirolimus-eluting stents (SES) despite the devices’ similar strut thicknesses, according a small observational study published online May 20, 2015, ahead of print in JACC: Cardiovascular Interventions. The greater strut width of BRS likely explains the finding, the authors say.

While new BRS iterations with narrower struts are expected to be available in 2016, say Antonio Colombo, MD, of San Raffaele Hospital (Milan, Italy), and colleagues, operators should be aware of the current design’s drawback and consider protecting side branches by using guidewires until the end of the procedure to minimize occlusion risk.

For the study, the investigators examined data on 157 consecutive patients who underwent PCI with a BRS (Absorb; Abbott Vascular) from May 2012 through April 2014 and 895 patients who received an SES (Cypher Bx Velocity or Cypher Select; both Cordis) from January 2004 through October 2009 at 2 high-volume Italian centers. The final analysis comprised 147 BRS patients propensity-matched with 352 SES patients.

Baseline and lesion characteristics were comparable between the groups, except for greater use of predilation and IVUS (both P < .001) and a lower rate of treatment of the RCA (P = .01) in the BRS group. In addition, the BRS group had a lower percentage diameter stenosis and acute gain (both P < .001).

Thirty-Day, 1-Year Clinical Outcomes Similar Between Devices

There were no differences between the study groups in MACE (all-cause mortality, follow-up MI, and TVR) or its individual components at either 30 days or 1 year. However, the incidence of periprocedural MI trended higher with BRS (table 1).

In addition, Academic Research Consortium–defined definite stent thrombosis occurred in 1 patient treated with BRS and 3 patients treated with SES, with no difference between the groups (P = .89).

On multivariate analysis, the independent predictors of periprocedural MI were LAD PCI (OR 2.60; 95% CI 1.16-5.81) and abluminal strut surface area as an index of strut width (OR [per 10-mm² increase] 1.07; 95% CI 1.03-1.12).

Thickness as Important as Width

The fact that the abluminal strut surface area of the BRS is about twice as large as that of the SES for devices of the same diameter suggests that this difference could have an impact on periprocedural MI, the authors say. In addition, the more asymmetric expansion of BRS “may lead to nonuniform strut distribution and result in a more frequent incidence of side-branch occlusions,” they note.

Moreover, the link between LAD PCI and periprocedural MI may be explained by the vessel’s supplying a large myocardial territory and harboring multiple small branches, which may be adversely affected during stent implantation, according to the authors.

The higher incidence of periprocedural MI with BRS in the current analysis compared with the rates reported in the ABSORB EXTEND and ABSORB II studies (2.1% and 5%, respectively) is likely due to “the [greater] severity of lesions treated and the more complex patient characteristics,” the authors say. However, they acknowledge, the absence of cardiac enzyme measurements in the SES group precluded use of a more up-to-date definition of periprocedural MI, and therefore these data should be interpreted with caution.

In addition to potential confounding, the study is limited by changes in PCI technique and medical therapy between the earlier SES and current BRS eras, the investigators observe, adding that before the impact of strut width on periprocedural MI can be generalized, “larger studies including different types of stents are required.”

Wider Struts a Trade-off for Greater Radial Force

Recoil problems with the original Absorb device were resolved by creation of more uniform strut distribution resulting in more even support of the arterial wall, Alexandre Abizaid, MD, PhD, and José de Ribamar Costa Jr, MD, PhD, both of the Instituto Dante Pazzanese de Cardiologia (São Paulo, Brazil), told TCTMD in an email. The trade-off was an abluminal strut surface area much larger than that of metallic stents and greater vessel surface coverage. 

However, they say, the side branches that are occluded after Absorb implantation tend to be tiny (< 1.5 mm) and blocking them usually does not translate into clinical events. Even so, Drs. Abizaid and Costa add, “precautionary measures, including placement of a wire in the side branches, are justified when the side branch is deemed relevant and should perhaps be performed more readily with BRS [than DES]—not forgetting that side-branch crossing after BRS deployment might be more difficult.”

All device companies, including Abbott, are currently “developing a new generation of their [polymer] BRS with thinner and also narrower struts,” Drs. Abizaid and Costa note. “However, it is uncertain whether these devices will maintain the radial force achieved by their predecessors.”

Meanwhile, new bioresorbable materials, including metals such as magnesium and iron, are being tested that may be able to mimic the physical properties of the current alloys used in durable metallic stents, they say. If this testing is successful, “this might represent an important step toward decreasing abluminal strut surface area and overcoming the limitation of side-branch occlusion,” Drs. Abizaid and Costa conclude.

Note: Dr. Colombo is a faculty member of the Cardiovascular Research Foundation, which owns and operates TCTMD.

 

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