Author + information
- Pannipa Suwannasom, MD,
- Yoshinobu Onuma, MD, PhD,
- Carlos M. Campos, MD,
- Shimpei Nakatani, MD,
- Yuki Ishibashi, MD, PhD,
- Hiroki Tateishi, MD, PhD,
- Maik J. Grundeken, MD,
- Bojan Stanetic, MD,
- Koen Nieman, MD, PhD,
- Hans Jonker, BSc,
- Hector M. Garcia-Garcia, MD, PhD,
- Patrick W. Serruys, MD, PhD∗ (, )
- investigators of ABSORB Cohort A, B and EXTEND trials
- ↵∗International Center for Circulatory Health, NHLI, Imperial College London, London, United Kingdom, P.O. box 2125, Rotterdam 3000CC, the Netherlands
The use of bioresorbable vascular scaffolds (BRS) is increasing in patients with coronary artery disease undergoing percutaneous coronary interventions. Because the devices are radiolucent on fluoroscopy, 2 adjacent cylindrical platinum markers are incorporated in the proximal and distal edges of the polymeric devices for precise scaffold deployment and post-dilation during the procedure. In addition, the metallic radio-opaque markers (MRMs) also provide anatomic landmarks for long-term follow-up when all the polymeric struts have been bioresorbed. There has been concern about the potential risk of MRM beads becoming dislodged from the device and embolized into the coronary bed after complete bioresorption of the polymeric struts. Beyond the biological hazard of MRMs embolization, the additional inconvenience is that the embolization may result in the incapacity to locate the coronary segment where the fully bioresorbed scaffold was implanted. Invasive assessment of BRS such as quantitative coronary angiography (QCA), intravascular ultrasound (IVUS), or optical coherence tomography (OCT) may be unable to detect the precise location of the MRMs either because of the resolution of the imaging technique (QCA) or as a result of wire artifact (IVUS, OCT) or mimicry by heavy calcium (IVUS). Multislice computed tomography coronary angiography (MSCT) has provided reliable assessment of the angiographic results up to 3 to 5 years (1,2) after scaffold implantation with accurate detection of the position of MRMs and their blooming effect without being dependent on the rate of image acquisition and wire artifact. In order to dispel the question of embolization of MRMs, we evaluated the persistent presence and location at 18 months of the MRMs following implantation of these fully bioresorbable scaffolds.
We retrospectively pooled data from the ABSORB trials (ABSORB Cohort A, ABSORB Cohort B, and ABSORB EXTEND) in which 943 patients with de novo native coronary artery lesions were treated with the fully resorbable everolimus-eluting Absorb scaffold (Abbott Vascular, Santa Clara, California); the details and primary outcome of each trial have been published (2–4). Of these 943 patients, 165 patients with 168 lesions underwent MSCT at 18 months. A list of the MSCT scanners, the acquisition protocol, and the MSCT analysis are described in the Online Appendix.
To establish the persistent presence of the MRMs in MSCT, both qualitative and quantitative evidence were required. The qualitative evidence was the ability to identify both proximal and distal MRMs position. Because calcified nodules (CN) could mimic MRMs, 4 criteria were used to identify the position of the radio-opaque markers: 1) typical location and orientation of the MRMs; 2) marker-to-marker length; 3) topographical relationship of the radio-opaque markers with anatomic landmarks visualized on MSCT and conventional coronary angiography; and 4) blooming artifact and its peak attenuation. The description of criteria and examples of MSCT images by using these 4 criteria are provided in Online Figure 1. The quantitative evidence is the MSCT scaffold length compared with its nominal length.
The statistical analysis is detailed in the Online Appendix.
A total of 168 lesions (12 lesions in ABSORB Cohort A, 61 lesions in ABSORB Cohort B, and 95 lesions in the ABSORB EXTEND study) were analyzed, and the study profile is shown in Online Figure 2. A total of 348 MRMs were evaluated by both quantitative and qualitative analyses; all MRMs were detected at the implantation site; and there was no evidence of marker embolization to distal vascular beds. The median MSCT scaffold length was 18.0 mm (ranging from 12 mm to 36 mm; interquartile range [IQR]: 17 to 19 mm) as well as the median nominal scaffold length was 18.0 mm (ranging from 12 mm to 28 mm) (Figure 1). The median difference in length between MSCT scaffold length and nominal scaffold length was 0.0 mm (IQR: −1.0 to 1.0 mm). There was a moderate correlation between MSCT mean lumen area (Mean LA) and QCA Mean LA (r = 0.54, p < 0.0001). A good correlation was observed between MSCT Mean LA and IVUS Mean LA, and between MSCT Mean LA and OCT Mean LA (r = 0.74 and r = 0.73, respectively; p < 0.0001) (Online Figure 3). The Mean LA measured by MSCT was comparable to QCA, but statistically lower than IVUS and OCT (Online Table 1). The reproducibility of the 4 criteria to identify MRMs from CN was good, r = 0.97; p < 0.0001 (Online Figure 4).
The attenuation of MRMs was approximately 30% higher than dense CN attenuation, but there was nevertheless a modest overlap of the attenuation values; MRM attenuation was sometimes lower than 1,000 HU as a result of the partial volume effect. The median peak density of MRMs was 1,368 HU (IQR: 1,158 to 1,715 HU) in contrast to the median peak density of CN that was 946 HU (IQR: 844 to 1,133 HU).
The main findings of this study are the following: 1) according to the criteria, all MRMs were identified and located at the site of the initial implantation; 2) the MSCT Mean LA was comparable to the Mean LA measured by QCA but lower than OCT and IVUS; and 3) the reproducibility in detecting of MRMs by using 4 criteria was high.
However, the distinction between calcified spots and metallic markers with computed tomography is also not easy to determine compared with OCT. The possible advantages of OCT are the ability to: 1) distinguish the MRMs from underlying calcium more clearly than MSCT; 2) measure the embedment of the struts; and 3) evaluate the thickness of neointima because of a higher axial resolution of around 10 to 15 μm as compared with MSCT.
The limitation in this study is that the study result was able to confirm the persistent presence of MRMs only at medium-term follow-up, and the long-term results still require investigation.
In conclusion, MRM recognition by MSCT is critical for precise noninvasive assessment of the coronary location of all MRMs. On the basis of our study criteria, there was no evidence of MRMs dislodgement and embolization 18 months after scaffold implantation.
Please note: The ABSORB trials were sponsored by Abbott Vascular. Dr. Nieman has received institutional research support from Siemens Medical Solutions, GE Healthcare, and Bayer HealthCare. Mr. Jonker is an employee of Cardialysis. Drs. Garcia-Garcia, Onuma, and Serruys are members of the Advisory Board of Abbott Vascular. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
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