Resorbable Magnesium Scaffold Use in STEMI

Abstract

Implantation of drug-eluting stents remains the standard of care in the setting of revascularization for patients with ST-segment elevation myocardial infarction; however, accurate assessment of the true vascular anatomy is often limited by vasoconstriction and thrombotic occlusion, which may lead to undersizing of stents deployed. The new generation of resorbable magnesium scaffold offers the attractive properties of maintaining vessel patency in the acute phase and avoiding the permanent caging of a potentially undersized stent, and our case series demonstrates the feasibility of its use in patients with ST-segment elevation myocardial infarction.

Visual Summary

Visual Summary.

Resorption of RMS After 4 Months

Case 1

A 62-year-old man with hypertension, diabetes mellitus, and a history of percutaneous coronary intervention (PCI) to the left anterior descending artery (LAD) 14 years ago presented to our unit for inferior ST-segment elevation myocardial infarction (STEMI). A bedside echocardiogram showed impaired left ventricular contractility, with inferior and inferoseptal akinesia. He was loaded with oral ticagrelor and intravenous heparin and proceeded to primary PCI.

Take-Home Messages

• •Freesolve RMS appears to be a safe option for use in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention, as demonstrated in our case series with interval imaging analysis.
• •Adequate lesion preparation and postdilatation are crucial to successful RMS implantation.

A 6-F JR 4 guiding catheter was engaged to the right coronary artery (RCA). A coronary angiogram revealed critical stenosis over the proximal RCA (Figure 1A). Intravascular ultrasound (IVUS) showed plaque rupture as well as mild calcification at the proximal RCA (Figure 1B). The proximal RCA lesion was predilated with a 3.0-mm noncompliant coronary balloon. A 3.5 × 30 mm Freesolve resorbable magnesium scaffold (RMS) (Biotronik) was inserted into the proximal RCA and deployed at nominal pressure by slow inflation. The scaffold was further postdilated up to high pressure (20 atm) with 3.0-mm and 3.5-mm noncompliant balloons at distal and proximal stent segments, respectively, under IVUS guidance (Figure 1C).

Figure 1.

PCI of Case 1

(A) Pre-PCI angiogram of RCA. (B) IVUS assessment showing plaque rupture over the proximal RCA. (C) Freesolve RMS deployed over the proximal RCA. (D) Final angiogram of the index PCI. (E) OCT assessment at index PCI. (F) OCT 3D reconstruction of the scaffold at index PCI. (G) Restudy angiogram at 4 months. (H) OCT assessment at 4 months. (I) OCT 3D reconstruction at 4 months, with only remnants of the scaffold being visible. IVUS = intravascular ultrasound; OCT = optical coherence tomography; PCI = percutaneous coronary intervention; RCA = right coronary artery; RMS = resorbable magnesium scaffold.

Poststenting angiographic results were excellent, complemented with IVUS and optical coherence tomography (OCT) imaging demonstrating excellent stent expansion and apposition (Figures 1D to 1F, Video 1). The patient was uneventful after the procedure and discharged on day 5 of hospitalization. Dual antiplatelet therapy was continued and planned for 1 year. Stage PCI to the left coronary artery was scheduled.

The patient was uneventful after discharge. Restudy angiography and intravascular imaging with OCT of the RCA were performed at 4 months after the index procedure during the scheduled stage PCI of the left circumflex artery (Video 2). Endothelization and resorption of the implanted RMS were well demonstrated on OCT. Analysis of the OCT images suggested that the majority of the optical reflection signal from the metallic scaffold was absent. 3D stent reconstruction rendering only showed the contour of the former RMS, which is strikingly different from the metallic signal observed during scaffold deployment (Figures 1G to 1I).

Case 2

A 41-year-old man with unremarkable past health presented with acute onset chest pain radiating to the left shoulder. An electrocardiogram showed ST-segment elevation over leads II, III, and aVF. He was started on dual antiplatelet therapy and heparin. An angiogram showed critical lesions over the mid and distal RCA, respectively (Figure 2A). OCT assessment showed plaque erosion at the distal RCA with the presence of white thrombi (Figure 2B).

Figure 2.

PCI of Case 2

(A) Pre-PCI angiogram. (B) OCT preassessment showing plaque rupture with white thrombi. (C) Freesolve RMS deployment over the mid RCA. (D) Final angiogram of the index PCI. (E) OCT at a distal stent. (F) OCT at a proximal stent. (G) Restudy angiogram at 5 months. (H) OCT at 5 months, with only scanty scaffold fragments being visible. (I) IVUS at 5 months, with remnants of the scaffold seen as hyperechoic structures. IVUS = intravascular ultrasound; OCT = optical coherence tomography; PCI = percutaneous coronary intervention; RCA = right coronary artery; RMS = resorbable magnesium scaffold.

Thrombectomy was performed with 1 pass of CAT RX (Penumbra Inc) to the distal RCA. The mid to distal RCA was then predilated with a 3.5-mm noncompliant balloon, followed by the implantation of a 3.5 × 30 mm Freesolve RMS from the distal RCA to the posterior descending artery, across the right posterolateral branch, and another 4.0 × 30 mm Freesolve RMS over the mid RCA (Figure 2C). Further postdilatation with 3.0-mm, 3.5-mm, and 4.0-mm noncompliant balloons up to 24 atm was performed under OCT guidance to ensure adequate expansion of the scaffolds Video 3. Final angiographic results were found to be excellent with TIMI flow grade 3 to all branches (Figures 2D to 2F). Dual antiplatelet therapy was continued and planned for 1 year. The patient was uneventful and discharged 2 days after the PCI. Stage PCI to the left coronary artery was planned.

He was uneventful after discharge. Restudy of the RCA was performed at 5 months after the index PCI during the planned stage procedure of the left coronary artery. Angiogram showed patent scaffold with no significant restenosis (Figure 2G). OCT analysis showed that the majority of the optical reflection signal from the metallic scaffold was absent, with only scanty fragments still visible as reflective structures (Figure 2H). 3D stent rendering was able to visualize the contour of the former RMS (Video 4). However, the scaffold was still clearly discernible on IVUS as hyperechoic structures (Figure 2I, Video 5).

Case 3

A 41-year-old man with unremarkable past health had witnessed cardiac arrest at the emergency department, had an initial rhythm of ventricular fibrillation, achieved return of spontaneous circulation after prompt defibrillation, and was subsequently intubated for airway protection. An electrocardiogram showed ST-segment elevation and hyperacute T-wave over anterior leads. A coronary angiogram showed proximal LAD occlusion (Figure 3A).

Figure 3.

PCI of Case 3

(A) Pre-PCI angiogram showing the occluded proximal LAD. (B) Poststenting angiogram. (C) Restudy angiogram at 7 months. (D) OCT 3D rendering at 7 months, with only remnants of the scaffold being visible. LAD = left anterior descending artery; OCT = optical coherence tomography; PCI = percutaneous coronary intervention.

The proximal LAD was prepared with a 3.0-mm Wolverine cutting balloon (Boston Scientific) and further predilated with a 3.5-mm noncompliant balloon under IVUS guidance. A 3.5 × 18 mm Freesolve RMS was deployed over the proximal LAD and postdilated with a 3.5-mm noncompliant balloon up to 22 atm. Final angiographic and IVUS results were found to be excellent with good stent expansion and apposition (Figure 3B). The patient made good neurological recovery and was discharged 4 days after admission. Dual antiplatelet therapy was continued and planned for 1 year.

The patient remained asymptomatic. A restudy angiogram at 7 months showed well-maintained scaffold patency with no significant restenosis (Figure 3C and Video 6). OCT analysis showed near-complete resorption of the scaffold, with residual scaffold elements being well endothelized (Figure 3D, Video 7).

Discussion

The first generation of bioresorbable vascular scaffold (BVS) had been shown to have more adverse ischemic events when compared with contemporary drug-eluting stents (DES) in previous trials, especially the rate of early stent thrombosis.¹ This was postulated to be due to suboptimal implementation of the 4P principle and thicker scaffold struts compared with metallic DES. The latest generation of drug-eluting resorbable coronary magnesium scaffold (Freesolve, Biotronik) has shown promising outcomes in the BIOMAG-I first-in-human study with a target lesion failure rate comparable with contemporary DES² and no recorded scaffold thrombosis event. It addresses the weakness of the Absorb BVS (Abbott Vascular) with faster absorption time, thinner struts, and higher radial strength. An ongoing BIOMAG-II randomized controlled trial will provide more data on the long-term safety and efficacy of RMS compared with DES; however, the population with STEMI, as in the cases presented here, is excluded from the study.

To the best of our knowledge, this is the first reported case series demonstrating successful use of the new-generation RMS in the setting of STEMI, with satisfactory angiographic and intravascular imaging results at 3 to 7 months. With experience from the era of BVS, the 4P principle, including proper patient and lesion selection, proper sizing, lesion preparation, and postdilatation with noncompliant balloons, was adhered to during the intervention to optimize the clinical and procedural outcomes. Such a systematic approach to scaffold implantation minimizes the risks of undersizing and underexpansion, which contributes to the incidence of adverse events. Imaging-guided PCI is important for the implantation of a newly introduced scaffold, allowing familiarization to the new device and avoiding unfavorable results, and is of particular significance in the case of RMS because it is not radio-opaque, and hence, the stent expansion cannot be assessed by fluoroscopy. We used IVUS or OCT in our cases for vessel sizing, followed by predilatation with a noncompliant balloon according to vessel size before scaffold deployment and subsequently postdilatation with a noncompliant balloon up to high pressure. Finally, postimplantation IVUS or OCT was performed to ensure optimal results with good stent expansion and no strut malapposition. We believe that our approach contributes to the good acute and intermediate results in both OCT- and IVUS-guided RMS implantation as shown in our cases.

The different imaging properties observed on OCT and IVUS at restudy are noteworthy for operators. In OCT, the optically reflective property of the RMS is already lost at restudy, evidencing the resorption of the scaffold. However, in IVUS, the remnants of the scaffold are still clearly discernible as hyperechoic structures resembling other contemporary DES. They likely represent the final degradation product amorphous calcium phosphate, as shown in the preclinical kinetic study of RMS,³ and should not be mistaken as a stent.

In the clinical setting of STEMI, determination of the true vascular anatomy and physiology, including vessel size and perfusion abnormality, is often unreliable as the vessel constriction and thrombotic occlusion due to the acute event hinder any accurate assessment. Compared with contemporary DES, RMS has the advantage of treating the culprit lesion in the acute setting while preserving the opportunity for accurate interval evaluation of the vessel parameters in a scaffold-free environment to guide further intervention. More evaluation will be needed to determine the performance of Freesolve RMS in STEMI and acute coronary syndrome settings.

Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Appendix

Video 1

Case 1 OCT After Index PCI

OCT = optical coherence tomography; PCI = percutaneous coronary intervention.

Video 2

Case 1 OCT at Restudy

OCT = optical coherence tomography.

Video 3

Case 2 OCT After Index PCI

OCT = optical coherence tomography; PCI = percutaneous coronary intervention.

Video 4

Case 2 OCT at Restudy

OCT = optical coherence tomography.

Video 5

Case 2 IVUS at Restudy

IVUS demonstrating remnants of the RMS as hyperechoic structures. IVUS = intravascular ultrasound; RMS = resorbable magnesium scaffold.

Video 6

Case 3 OCT at Restudy

OCT = optical coherence tomography.

Video 7

Case 3 OCT 3D Reconstruction at Restudy

OCT = optical coherence tomography.