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The objective of the study is to validate intravascular quantitative echogenicity as a surrogate for molecular weight assessment of poly-l-lactide-acid (PLLA) bioresorbable scaffold (Absorb BVS, Abbott Vascular, Santa Clara, California). We analyzed at 9 time points (from 1- to 42-month follow-up) a population of 40 pigs that received 97 Absorb scaffolds. The treated regions were analyzed by echogenicity using adventitia as reference, and were categorized as more (hyperechogenic or upperechogenic) or less bright (hypoechogenic) than the reference. The volumes of echogenicity categories were correlated with the measurements of molecular weight (Mw) by gel permeation chromatography. Scaffold struts appeared as high echogenic structures. The quantification of grey level intensity in the scaffold-vessel compartment had strong correlation with the scaffold Mw: hyperechogenicity (correlation coefficient = 0.75; P < 0.01), upperechogenicity (correlation coefficient = 0.63; P < 0.01) and hyper + upperechogenicity (correlation coefficient = 0.78; P < 0.01). In the linear regression, the R2 for high echogenicity and Mw was 0.57 for the combination of hyper and upper echogenicity. IVUS high intensity grey level quantification is correlated to Absorb BVS residual molecular weight and can be used as a surrogate for the monitoring of the degradation of semi-crystalline polymers scaffolds.

Background: Scattering centers (SC) are often observed with optical coherence tomography (OCT) in some struts of bioresorbable vascular scaffolds (BVS). These SC might be caused by crazes in the polymer during crimpdeployment (more frequent at inflection points) or by other processes, such as physiological loading or hydrolysis (eventually increasing with time). The spatial distribution and temporal evolution of SC in BVS might help to understand their meaning. Methods and Results: Three patients were randomly selected from 12 imaged with Fourier-domain OCT at both baseline and 6 months in the ABSORB cohort B study (NCT00856856). Frame-by-frame analysis of the SC distribution was performed using spread-out vessel charts, and the results from baseline and 6 months were compared. A total of 4,328 struts were analyzed. At baseline and follow-up all SC appeared at inflection points. No significant difference was observed between baseline and 6 months in the number of SC struts (14.9 vs. 14.5%, P=0.754) or in the distribution of SC. The proportion and distribution of SC did not vary substantially among the patients analyzed. Conclusions: The SC observed in OCT imaging of the BVS are located exclusively at inflection points and do not increase with time. These findings strongly suggest that SC are caused by crazes in the polymer during crimp-deployment, ruling out any major role of hydrolysis or other time-dependent processes.