Thrombosis and myocardial infarction: the role of bioresorbable scaffolds

Abstract

Coronary stents have dramatically improved the treatment of coronary artery stenosis. In-stent-restenosis (ISR) and stent thrombosis (ST) pose major obstacles to the success of coronary stenting. Drug-eluting stents (DES) emerged as a major breakthrough in stenting and significantly reduced ISR. Despite taking dual antiplatelet therapy (DAPT), very late ST has remained a major obstacle in the success of DES. This occurs regardless of the type of polymer or antiproliferative agent in the contemporary stents. Such adverse events occur at a rate of approximately 2% to 3% per year after first year, which have been attributed to the strut fractures, loss of vessel compliance and vasomotion, and neoatherosclerosis. Fully bioresorbable scaffolds (BRS) have emerged in an effort to overcome these limitations leading to a "leave nothing behind" approach. While appealing, the initial experience with BRS technology was hampered by increased rates of BRS thrombosis compared with DES. In this review, we summarized underlying mechanisms leading to BRS failure and provided insights into optimizing BRS deployment with intravascular imaging. In addition, we outlined the perspectives of new generations BRS with thinner struts and new designs as well as alternative materials to improve outcome.

Figure 1.

Lumen area changes by OCT after BMS (top) vs. BRS (bottom) deployment in swine model during 4-year period. A significant increase in lumen area of BRS vs. BMS occurred between 2 and 4 years, as a result of positive vessel remodeling and plaque regression. OCT: Optical coherence tomography; BMS: Bare-metal stents; BRS: Bioresorbable scaffolds.

Figure 2.

Early scaffold thrombosis after 6 days of BRS deployment. OCT shows the evidence for BRS malapposition (as shown by the white arrows and platelet thrombus in the lumen as shown by the red arrows. BRS: Bioresorbable scaffolds; OCT: optical coherence tomography.

Figure 3.

OCT imaging of the BRS vs. Drug-eluting stents. (A) OCT image of BRS. The struts are translucent, which leads to excellent imaging of the artery; (B) OCT images of metallic stent. The metallic struts are not translucent to the OCT and that led to the typical shadow into the vessel wall with “sunflower artifact”. OCT: Optical coherence tomography; BRS: bioresorbable scaffold.

Figure 4.

Schematic representative image of BRS deployment in the coronary artery. (A) BRS across the lesion; (B) After BRS deployment and post-dilation; and (C) final results showing struts are apposed against the vessel wall. BRS: Bioresorbable scaffold.

Figure 5.

Schematic representative image of suboptimal BRS deployment in the coronary artery. (A) BRS across the stenosis; (B) After BRS deployment and post-dilation, struts are malapposed, as shown by the arrow. BRS: Bioresorbable scaffold.

Figure 6.

OCT analysis of BRS deployment. (A) After BRS deployment, there is incomplete strut apposition (ISA). (A1) There are 4 malapposed struts between 10 and 12 o’clock position in (A1); (A2) showing the area of malapposed struts (highlighted in green); (B1) Tissue prolapse, defined as tissue protruding between the struts. The prolapse area was measured as the difference between the struts and lumen area (highlighted in green in (B2); (C) An example of edge dissection (arrow) distal to the BRS. Because of the large lumen size and small circumferential extension of dissection, no additional BRS was deployed; (D) BRS strut fracture shown by the arrow. OCT: Optical coherence tomography; BRS: bioresorbable scaffold.

Figure 7.

Very late BRS thrombosis. (A) Coronary angiography shows successful 3 BRSs deployment in the left circumflex coronary artery. (B) Patient was admitted with acute myocardial infarction one year after BRS deployment showing complete occlusion of the BRS. (C) OCT shows strut fracture (shown by the arrowhead) and platelet thrombus (shown by the arrow). OCT: Optical coherence tomography; BRS: bioresorbable scaffold.

Figure 8.

The use of a standard approach shown schematically by IVUS. (A) Following stent deployment and post-dilation, IVUS was performed using the automatic pullback recordings from distal part of the vessel to proximal; (B and D) Plaque burden (PB) was measured in a segment at the 5 mm proximal or distal to the stent edges. If the PB was > 50% or in the event of edge dissection, a stent was deployed; (C) at the lesion site, if minimum stent area (MSA) was < 5.4 mm² or < 90% of distal reference lumen area (DRLA), further post-dilation of the stent was performed using high-pressure balloon inflation sized to the distal EEM diameter. Repeat IVUS pullback was performed to investigate whether the optimal stent results, defined as MSA ≥ 5.4 mm² or ≥ 90% of DRLA at the lesion site and plaque burden < 50% at the stent edges with no edge dissection, were achieved.