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Noninvasive coronary computed tomographic angiography (CTA) can be used to evaluate the effectiveness of a metal-free bioabsorbable scaffold, according to a subanalysis of the ABSORB trial published online August 7, 2013, ahead of print in the Journal of the American College of Cardiology. Meanwhile, 2- and 3-year data from ABSORB show small declines in minimal lumen area with the innovative device but signs of restoration of vasoreactivity in the scaffolded area as well as lumen enlargement.

For cohort B of the ABSORB trial, 101 patients with 102 de novo lesions were treated at 12 centers with the second-generation Absorb bioresorbable vascular scaffold (BVS; Abbott Vascular, Santa Clara, CA). Predilation was mandatory.

The balloon-expandable BVS has a polylactide backbone coated with a thin polylactide polymer containing everolimus. The bioabsorbable polymer releases everolimus over about 30 days, while the scaffolding degrades to lactic acid over about 2 years, according to preclinical research.

CT Angiography Valuable, FFR_CT Not So Much

For the current analysis, investigators led by Koen Nieman, MD, PhD, of Erasmus Medical Center (Rotterdam, The Netherlands) gathered data from a subset of 71 patients at 9 centers who underwent coronary CTA with at least 64-slice technology. Median radiation dose was 6.8 mSv. Vessel cross sections were reconstructed at approximately 1-mm increments, extending 5 mm beyond the scaffold.

At 18 months, the 61 evaluable scans showed the following metrics:

• Mean In-Scaffold Lumen Area: 5.1 ± 1.4 mm²
• Minimal Lumen Area: 3.5 ± 1.0 mm²
• Maximum Lumen Area: 7.0 ± 2.1 mm²
• Average Area Stenosis: 22.7 ± 22.4%

 In addition, 38 patients from the CTA subset (57%) were assessed with CT-based FFR, showing a mean gradient of -0.03 ± 0.04. Using a cutoff of < 0.80, there was no correlation between area stenosis and minimal lumen area or FFR_CT gradient. The largest FFR_CT gradient was associated with only 9.4% area stenosis, a minimal lumen area of 3.2 mm², and low FFR_CT values in all distal branches, suggesting systematic underestimation of stenosis. The FFR_CT gradient ranged from -0.02 to -0.09 in patients with an area stenosis of ≥ 50%.

Paralleling the angiographic metrics, at 18 months, there were 3 non-Q-wave MIs, 5 ischemia-driven TLRs, and no cardiac deaths, for an overall MACE rate of 7.9%.

The authors observe that “[f]or decades, new percutaneous coronary therapies have required invasive angiography to assess late lumen loss. Considering the good diagnostic accuracy of [coronary CTA] in the absence of metal stents, and advantages in safety, [this technology] offers a noninvasive alternative to catheterization both for clinical care as well as research.”

In a telephone interview with TCTMD, David E. Kandzari, MD, of the Piedmont Heart Institute (Atlanta, GA), agreed that noninvasive imaging is a plus for the BVS, though the current algorithm used to derive FFR measurements clearly has limitations. In addition, the radiation exposure from CT was comparable to that from catheterization, he noted.

In fact, the radiation exposure was “way too high,” Robert S. Schwartz, MD, of the Minneapolis Heart Institute Foundation (Minneapolis, MN), told TCTMD in a telephone interview, adding that current-generation scanners expose patients to a fraction of that dose. Moreover, the failure to employ the latest CT technology may have contributed to the poor performance of FFR_CT, he added.

Longer-term Follow-up

Results of QCA, IVUS, and OCT assessments as well as longer-term clinical data of Cohort B1 (n = 45) as well as the full Cohort B were reported by Patrick W. Serruys, MD, also of the Erasmus Medical Center, at the American College of Cardiology Scientific Session/i2 Summit in March 2013.

From 6 months to 2 years, late loss increased from 0.17 mm to 0.27 mm on QCA, with an increase in neointima of 0.68 mm² on OCT and 0.17 mm² on IVUS. Vasomotion was demonstrated on QCA both before and after nitrate administration, suggesting recovery of endothelial function and vasoreactivity.

Struts still recognizable on OCT at 2 years showed 99% neointimal coverage, with signs of bioresorption accompanied by an increase in mean scaffold area compared with baseline (0.54 mm² on IVUS; P = 0.003 and 0.77 mm² on OCT; P = 0.016). On OCT there were clear signs of late enlargement of the scaffold area.

At 2 years, the rate of MACE for the full cohort was 9.0%, while at 3 years it was 6.8% for the B1 subset, with no instances of scaffolding thrombosis.

Clinical Relevance Remains Uncertain

“I don’t think there’s any remarkable theme with these [imaging] metrics,” Dr. Kandzari said. “The big issue is that at a patient level, hard outcomes as well as TLR seem to be similar to those of existing metallic-based DES.” A device that would dissolve and return the vessel to its normal physiological state is intuitively very appealing, he observed, but the challenge is showing that those features reduce the likelihood of future events and thus set the BVS apart from DES.

For example, a distinctive BVS finding is a return of vasomotion in the scaffolded segment as the device dissolves. But Dr. Schwartz called this more of a marketing point, noting that the clinical importance of vasomotion remains to be determined.

In addition, the researchers pointed to “a new phenomenon:” late enlargement of the scaffold area. This likely represents positive remodeling in which the vessel expands outward, Dr. Schwartz said. This well-known process in atherosclerotic vessels may be enhanced by the gradual dissolution of the scaffold, he commented.

Drs. Kandzari and Schwartz both stressed that the BVS needs to be tested in more and higher-risk patients with complex lesions. In addition, issues of progressive neoplasia and late stent thrombosis should be evaluated over longer time periods, well beyond the resorption of the scaffold, Dr. Kandzari said. He also advocated exploration of endpoints that address clinical dilemmas, such as possible reduction of the duration of dual antiplatelet therapy.

Meanwhile, a large pivotal US trial is under way. ABSORB III, which is comparing the BVS with Xience stents, has 1-year target lesion failure as its primary endpoint, although a subset of patients will be evaluated on vasomotion.

Sources:

1. Nieman K, Serruys PW, Onuma Y, et al. Multislice computed tomography angiography for non-invasive assessment of the 18-months performance of a novel radiolucent bioresorbable vascular scaffolding device (ABSORB trial). J Am Coll Cardiol. 2013;Epub ahead of print.
2. Serruys PW. First report of the three year clinical and multi-modality imaging results of the ABSORB trial evaluating the Absorb everolimus-eluting bioresorbable vascular scaffold in the treatment of patients with de novo native coronary artery lesions. Presented at: American College of Cardiology Scientific Session; March 10, 2013; San Francisco, CA.

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