Bioresorbable scaffolds (BRS) were designed to combine the short-term advantages of permanent stents with the long-term benefit of complete reabsorption, facilitating the restoration of vasomotor and endothelial function. This technology helps prevent prolonged inflammation, maintains the integrity of distal bypass grafting sites, and allows unimpeded future vessel imaging. Despite the promising theoretical benefits of BRS, the initial generation of BRS devices exhibited higher rates of stent thrombosis in comparison to other stents
[8]. Newer generation devices appear to present a viable alternative to drug-eluting stents in the management of acute coronary syndromes (ACS) for several reasons: their different composition when compared to first-generation BRS, the optimized deployment technique, and the lesion selection. Notably, ACS lesions show specific characteristics based on the pathophysiology of the disease
[8]. Thus, various factors create favorable conditions for BRS implantation in ACS patients, including the vulnerable nature of the plaque, minimal calcification, the presence of a thrombus, and the relative youth of patients. BRS is radiolucent except for two metallic radio-opaque markers located at both extremities. This design feature aids in visualization during imaging procedures, ensuring accurate placement and monitoring of the scaffold. Thus, CCTA can delineate the contours of the scaffolded segment: markers easily enable the location of where BRS was implanted, and they can be distinguished from calcification because of the difference in attenuation
[9].
Figure 3 shows a CCTA analysis of scaffolded coronary segments: as highlighted by orange brackets, there is evidence of two little markers of the scaffold that appear completely reabsorbed: indeed, no struts are detectable, and the vessel lumen can be analyzed in depth also in the scaffolded part with no evidence of plaque proliferation. The diagnostic accuracy of coronary CT angiography in poli-LLA (poly-L-lactide) Everolimus scaffold was studied in the ABSORB II study (A Bioresorbable Everolimus-Eluting Scaffold Versus a Metallic Everolimus-Eluting Stent II)
[10]. The study provided the randomization of enrolled patients to receive treatment with BRS or drug-eluting stent. At the 3-year follow-up, patients treated with BRS underwent coronary angiography with intravascular ultrasound (IVUS) evaluation and CCTA. The study demonstrated that the CCTA diagnostic accuracy for detecting in-scaffold obstruction and luminal dimensions was similar to invasive coronary angiography (ICA) and IVUS. Analyzing scaffold segments, the sensitivity, specificity, and negative predictive values were 71%, 82%, and 97%, respectively, using IVUS as a reference. One limitation was its use of a 3-year follow-up period, which did not address the crucial question of assessing the occurrence of restenosis within the initial 12 months. It is during this period that most restenosis events occur, coinciding with the presence of BRS with thicker struts in place
[11]. Salinas P et al. performed the first case series of Magnesium bioresorbable scaffold investigated with CCTA at 1 year of follow-up
[12]. The CCTA in-scaffold percentage diameter stenosis and area stenosis were 22% and 39%, respectively, underlying plaque growth. Additionally, performing plaque characterization, the segments treated with RMS showed that the most common component of the plaque was the fibrous one (69% of the cases), suggesting that RMS allows for the stabilization of culprit lesions
[12]. Furthermore, anatomical findings can be combined with noninvasive fractional flow reserve derived from CCTA (FFR-CT) to distinguish the presence or absence of flow-limiting disease
[13]. A study by Tonet E et al. investigated the performance of CCTA and FFR-CT in 26 patients treated with Magnesium bioresorbable scaffold: all patients underwent CCTA 18 months after BRS implantation. The left anterior descending artery was the most commonly affected vessel. CCTA revealed patent scaffolded segments, with complete strut reabsorption observed in 93% of cases. FFR-CT demonstrated to be feasible in scaffolded segments with a median value of 0.88 [0.81–0.91].
Figure 4 shows a case from the above-reported study: BRS (orange bracket) appears to be characterized by plaque proliferation with a prevalent calcific component. FFR-CT analysis highlighted a significant stenosis related to the plaque. In conclusion, these results suggest that CCTA plus FFR-CT is a valuable noninvasive tool for the assessment of coronary arteries in subjects treated with BRS. Scaffolded segments can be easily distinguished, allowing for quantitative measurements and the calculation of noninvasive FFR. The analysis also indicates a tendency to observe plaque stabilization in the scaffolded segments with fibrosis and calcium
[14]. However, further evidence is needed in this setting of BRS patients.