Imaging assessment of bioresorbable vascular scaffolds.

Vascular reparative therapy has become a reality with bioresorbable scaffolds (BRSs). To assess acute and long-term performance of the device, multimodality imaging would be essential. Radiopacity of metal hinders the imaging assessment, whereas radiolucent polymeric scaffolds allow for a precise imaging assessment with either invasive or non-invasive modality at baseline and at follow-up, which is one of the advantages of polymeric BRSs. Recent large trials evaluating clinical results of the first-generation BRS technology raised concerns about the safety and efficacy of these devices, namely, scaffold thrombosis. Intensive research with multimodality imaging in the field is being conducted to have in-depth understanding of the issues, which will facilitate the improvement of implantation techniques and the development of the next-generation BRSs. The current review focuses on the clinical application of the imaging modalities to assess the short- and long-term performance of the Absorb BVS.

Serial Assessment of Tissue Precursors and Progression of Coronary Calcification Analyzed by Fusion of IVUS and OCT: 5-Year Follow-Up of Scaffolded and Nonscaffolded Arteries.

OBJECTIVES: The aim of this study was to assess calcium growth with fused grayscale intravascular ultrasound (IVUS), IVUS-virtual histology, and optical coherence tomography (OCT) from baseline to 5-year follow-up in patients treated with bioresorbable vascular scaffolds. BACKGROUND: IVUS and OCT have individual strengths in assessing plaque composition and volume. Fusion of images obtained using these methods could potentially aid in coronary plaque assessment. METHODS: Anatomic landmarks and endoluminal radiopaque markers were used to fuse OCT and IVUS images and match baseline and follow-up. RESULTS: Seventy-two IVUS-virtual histology and OCT paired matched cross-sectional in- and out-scaffold segments were fused at baseline and follow-up. In total, 46 calcified plaques at follow-up were detected using the fusion method (33 in-scaffold, 13 out-scaffold), showing either calcium progression (52.2%) or de novo calcifications (47.8%). On OCT, calcification volume increased from baseline to follow-up by 2.3 ± 2.4 mm3 (p = 0.001). The baseline virtual histologic tissue precursors of dense calcium at follow-up were necrotic core in 73.9% and fibrous or fibrofatty plaque in 10.9%. In 15.2%, calcium was already present at baseline. Precursors on OCT were lipid pool in 71.2%, fibrous plaque in 4.3%, and fibrocalcific plaque in 23.9%. CONCLUSIONS: The use of OCT and IVUS fusion imaging shows similar calcium growth in- and out-scaffold segments. Necrotic core is the most frequent precursor of calcification. The scaffold resorption process creates a tissue layer that re-caps the calcified plaques. (Absorb Clinical Investigation, Cohort B [ABSORB B]; NCT00856856).

Comparative assessment of "plaque/media" change on three modalities of IVUS immediately after implantation of either everolimus-eluting bioresorbable vascular scaffold or everolimus-eluting metallic stent in Absorb II study.

The purpose of the study to assess the comparability of immediate changes in plaque/media volume (PV) on three modalities of intravascular ultrasound (IVUS) after implantation of either bioresorbable vascular scaffold (BVS) or everolimus-eluting metallic stent (EES) in Absorb II Study. The two devices have different device volume and ultrasound backscattering that may interfere with the "plaque/media" assessed by three modalities on IVUS: grayscale, backscattering of radiofrequency and brightness function. In a multicenter randomized controlled trial, 501 patients with stable or unstable angina underwent documentary IVUS pre- and post- implantation. The change in plaque/media volume (PV) was categorized into three groups according to the relative PV change in device segment: PV "increased" >+5% (PVI), PV unchanged ±5% (PVU), and PV decreased <-5% (PVD). The change in PV was re-evaluated three times: after subtraction of theoretical device volume, after analysis of echogenicity based on brightness function. In 449 patients, 483 lesions were analyzed pre- and post-implantation. "PVI" was more frequently observed in BVS (53.8%) than EES group (39.4%), p = 0.006. After subtraction of the theoretical device volume, the frequency of "PVI" decreased in both BVS (36.2%) and EES (32.1%) groups and became comparable (p = 0.581). In addition, the percentage of "PVI" was further reduced in both device groups after correction for either radiofrequency backscattering (BVS 34.4% vs. EES 22.6%) or echogenicity (BVS 25.2% vs. EES 9.7%). PV change in device segment was differently affected by BVS and EES devices implantation due to their differences in device volume and ultrasound backscattering. It implies that the lumen volume was also artifactually affected by the type of device implanted. Comparative IVUS assessment of lumen and plaque/media volume changes following implantation of BVS and EES requires specific methodological adjustment.

Acute Gain in Minimal Lumen Area Following Implantation of Everolimus-Eluting ABSORB Biodegradable Vascular Scaffolds or Xience Metallic Stents: Intravascular Ultrasound Assessment From the ABSORB II Trial.

OBJECTIVES: The study compared, by intravascular ultrasound (IVUS), acute gain (AG) at the site of the pre-procedural minimal lumen area (MLA) achieved by either the Absorb (Abbott Vascular, Santa Clara, California) scaffold or the Xience stent and identified the factors contributing to the acute performance of these devices. BACKGROUND: It is warranted that the acute performance of Absorb matches that of metallic stents; however, concern exists about acute expansion and lumen gain with the use of Absorb. METHODS: Of a total of 501 patients (546 lesions) in the ABSORB II (ABSORB II Randomized Controlled Trial) randomized trial, 445 patients with 480 lesions were investigated by IVUS pre- and post-procedure. Comparison of MLA pre- and post-procedure was performed at the MLA site by matching pre- and post-procedural IVUS pullbacks. RESULTS: Lower AG on IVUS (lowest tertile) occurred more frequently in the Absorb arm than in the Xience arm (3.46 mm(2) vs. 4.27 mm(2), respectively; p < 0.001; risk ratio: 3.04; 95% confidence interval: 1.94 to 4.76). The plaque morphology at the MLA cross-section was not independently associated with IVUS acute gain. The main difference in AG in MLD by angiography was observed at the time of device implantation (Xience vs. Absorb, Δ+1.50 mm vs. Δ+1.23 mm, respectively), whereas the gain from post-dilation was similar between the 2 arms (Δ+0.16 mm vs. Δ+0.16 mm) when patients underwent post-dilation, although expected balloon diameter was smaller in the Absorb arm than in the Xience arm (p = 0.003) during post-dilation. CONCLUSIONS: At the site of the pre-procedural MLA, the increase of the lumen post-procedure was smaller in the Absorb-arm than in the Xience arm. To achieve equivalent AG to Xience, the implantation of Absorb may require more aggressive strategies at implantation, pre- and post-dilation than the technique used in the ABSORB II trial. (ABSORB II Randomized Controlled Trial [ABSORB II]; NCT01425281).

Quantitative assessment of the stent/scaffold strut embedment analysis by optical coherence tomography.

The degree of stent/scaffold embedment could be a surrogate parameter of the vessel wall-stent/scaffold interaction and could have biological implications in the vascular response. We have developed a new specific software for the quantitative evaluation of embedment of struts by optical coherence tomography (OCT). In the present study, we described the algorithm of the embedment analysis and its reproducibility. The degree of embedment was evaluated as the ratio of the embedded part versus the whole strut height and subdivided into quartiles. The agreement and the inter- and intra-observer reproducibility were evaluated using the kappa and the interclass correlation coefficient (ICC). A total of 4 pullbacks of OCT images in 4 randomly selected coronary lesions with 3.0 × 18 mm devices [2 lesions with Absorb BVS and 2 lesions with XIENCE (both from Abbott Vascular, Santa Clara, CA, USA)] from Absorb Japan trial were evaluated by two investigators with QCU-CMS software version 4.69 (Leiden University Medical Center, Leiden, The Netherlands). Finally, 1481 polymeric struts in 174 cross-sections and 1415 metallic struts in 161 cross-sections were analyzed. Inter- and intra-observer reproducibility of quantitative measurements of embedment ratio and categorical assessment of embedment in Absorb BVS and XIENCE had excellent agreement with ICC ranging from 0.958 to 0.999 and kappa ranging from 0.850 to 0.980. The newly developed embedment software showed excellent reproducibility. Computer-assisted embedment analysis could be a feasible tool to assess the strut penetration into the vessel wall that could be a surrogate of acute injury caused by implantation of devices.