The effect of coronary artery plaque composition, morphology and burden on Absorb bioresorbable vascular scaffold expansion and eccentricity — A detailed analysis with optical coherence tomography

https://doi.org/10.1016/j.ijcard.2015.01.033Get rights and content

Highlights

  • This study assesses the impact of coronary plaque composition, morphology and burden on Absorb BVS expansion visualized with Optical Coherence Tomography.

  • Lower SEC was significantly associated with greater fibrous plaque (FP) area, thickness and arc angle.

  • Lower SEC was significantly associated with greater CP area, CP thickness, CP angle and lower CP depth.

  • Lower Scaffold Expansion Index (SEI) was associated with greater calcific plaque (CP) area, thickness and lower CP depth.

  • Greater FP area was associated with greater SEI, even after adjustment for target vessel size.

  • Greater FP angle and quadrants occupied were also associated with greater SEI.

  • BVS expansion and eccentricity are significantly impacted by plaque composition, morphology and burden.

Abstract

Aims

Suboptimal stent expansion correlates with adverse cardiac events. There is limited information regarding Absorb bioresorbable vascular scaffold (BVS) expansion characteristics. Optical coherence tomography (OCT) allows for high-resolution assessment of plaque morphology, composition and assessment of BVS expansion. This study evaluates coronary plaque composition, morphology and burden and their effect on Absorb BVS expansion using OCT.

Methods and results

Two thousand three hundred and thirty four frames totalling 462.6 mm of BVS from twenty OCT-guided BVS implantations were examined. 200 μm longitudinal cross-sections of each BVS were analysed for lumen contours and plaque characteristics. The relationship between each plaque characteristic and scaffold expansion index (SEI) or scaffold eccentricity index (SEC) was analysed by repeated measures ANOVA.

Forty-four fibrous and 265 calcific plaques were identified. Lower SEI was significantly (p < 0.001) associated with greater calcific plaque (CP) area (mean SEI 78.9% vs. 80.0%), thickness (78.5% vs. 80.4%) and lower CP depth (78.3% vs. 80.2%). Lower SEC was significantly (p < 0.001) associated with greater fibrous plaque (FP) area (0.84 vs. 0.85), thickness (0.83 vs. 0.86), arc angle (0.84 vs. 0.85), greater CP area (0.83 vs. 0.86), CP thickness (0.83 vs. 0.86), CP angle (0.84 vs. 0.85) and lower CP depth (0.84 vs. 0.85). Greater FP area was associated with greater SEI (81.0% vs. 80.0%, p < 0.001), even after adjustment for target vessel size. Greater FP angle (80.7% vs 78.3%, p < 0.001) and quadrants occupied were also associated (80.0% vs 78.5%, p < 0.002) with greater SEI.

Conclusion

BVS expansion and eccentricity are significantly impacted by plaque composition, morphology and burden.

Introduction

Percutaneous coronary intervention (PCI) has evolved in recent decades with the use of bare metal stents (BMS) to drug eluting stents (DES) [1] and most recently bioresorbable scaffolds (BVS). The Absorb BVS (Abbott Vascular, Santa Clara, USA) consists of a semi-crystalline poly-l-lactide backbone coated with the anti-proliferative agent, everolimus [2]. The poly-l-lactide backbone is progressively degraded by hydrolysis from 6 to 12 months and is fully resorbed after 2 years [3].

Metallic stent expansion parameters such as eccentricity and symmetry have a known association with adverse clinical outcomes [4], [5]. In the MUSIC trial, the use of intravascular ultrasound (IVUS) demonstrated that the set criteria (stent apposition, stent minimal lumen area ≥ 90% of average reference lumen area, eccentricity index ≥ 0.7) were correlated with favourable clinical and angiographic outcomes [6].

Assessment of lumen geometry, plaque composition, morphology and burden has markedly advanced in recent times with the advent of intravascular optical coherence tomography (OCT). OCT is a light-based imaging modality that provides high-resolution cross-sectional images of the coronary vasculature. It has high axial (10 μm) and lateral resolutions (20–40 μm) [7], allowing for unprecedented diagnostic imaging detail of the coronary vasculature during PCI [8]. OCT differentiates tissue characteristics based on polarisation properties of light and permits precise measurements of plaque morphology, composition and burden within the coronary arteries [8], [9], [10], [11].

Due to its unique design, BVS has different expansion characteristics compared with metallic stents and thus knowledge from metallic stents cannot be transferred directly to BVS. It has previously been demonstrated that appropriate BVS deployment is related to angiographic assessment of maximal lumen diameter prior to the implantation [12]. However, there is currently limited information regarding BVS expansion characteristics with respect to coronary plaque burden. Therefore we sought to evaluate the effect of coronary plaque composition, morphology and burden on Absorb BVS expansion using OCT.

Section snippets

Study design and patient population

Seventeen consecutive patients undergoing OCT-guided BVS implantation from August 2012 to March 2013, at the Royal North Shore Hospital were reviewed. All BVS case data were entered prospectively into a local database, based on a predetermined data set. This included information on patient demographics, risk factors, and outcome measures. All information was entered by the operator at the time of the index procedure and cross-checked and updated by an independent audit officer at the end of the

Statistics

The relationship between each plaque characteristic and scaffold expansion and scaffold eccentricity index was analysed by a repeated measures ANOVA to take into account repeated measures on each scaffold analysed. Statistical significance was accepted as p < 0.05. SAS version 9.3 (SAS Institute Inc., Cary, NC, USA) was used for all statistical analyses.

Patient demographics and procedural data

Two thousand three hundred and thirty four OCT cross-section frames totalling 462.6 mm of BVS were analysed in 17 patients with unstable angina pectoris who underwent OCT-guided BVS implantation. Patient demographics and procedural data can be seen in Table 1. A total of 20 BVS were implanted. The mean subject age was 50.2 years with a SD of 11.7 years. Fourteen (82%) were males, 13 (76%) patients were dyslipidemic, 9 (53%) were hypertensive, 4 (24%) were current smokers and 3 (18%) were diabetic.

Results

Greater calcific plaque burden as represented by greater CP area (mean SEI 78.9% vs. average SEI 80.0%, p < 0.05), thicker CP (78.5% vs. 80.4%) and CP closer to the lumen (78.3% vs. 80.2%, p < 0.001) significantly correlated with a reduced BVS expansion for each cross section analysed within the coronary vasculature (Fig. 2). The correlation was maintained even after CP thickness was adjusted for using the underlying target vessel size (78.5% vs. 80.4%, p < 0.001). However, the correlation was no

Discussion

A number of different forces may affect coronary BVS deployment. These include transmitted forces from non-diseased sections of the coronary artery, the elastic recoil of the diseased segment, as well as atheromatous lesion characteristics.

Thus, in order to obtain optimal BVS implantation it is crucial to understand these aspects, in particular how individual lesion characteristics may play a role. Underlying coronary atheromatous lesions have a number of different characteristics and our study

Limitations

Although OCT has many benefits for in-vivo assessment of the coronary vasculature, it also has some limitations. In-order to have adequate OCT pullbacks for analysis, blood within the vessel lumen needs to be purged prior to imaging. This makes assessment of long vessel segments with a single pullback difficult as residual blood attenuates the light penetration and may create suboptimal imaging for lumen border and coronary vasculature delineation [22]. Eccentric wire position in the lumen can

Conclusion

The current study is one of the first to study plaque burden and its effect on BVS expansion characteristics. BVS expansion and eccentricity are significantly impacted by plaque composition, morphology and burden. Although significant associations between plaque burden and BVS expansion characteristics were demonstrated, the clinical significance of these findings is unknown. Further research into this area to examine the clinical significance on cardiovascular outcomes is needed.

Disclosures

Associate Professor Ravinay Bhindi was supported by Heart Research Australia, Sydney, Australia. Associate Professor Gemma Figtree was supported by Sydney Medical Foundation, Sydney Australia. All other authors have reported that they have no relationships to disclose.

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