Author + information
- Received November 30, 2010
- Revision received March 18, 2011
- Accepted March 28, 2011
- Published online September 1, 2011.
- Josep Gomez-Lara, MD⁎,
- Maria Radu, MD⁎,
- Salvatore Brugaletta, MD⁎,
- Vasim Farooq, MBChB⁎,
- Roberto Diletti, MD⁎,
- Yoshinobu Onuma, MD⁎,
- Stephan Windecker, MD†,
- Leif Thuesen, MD‡,
- Dougal McClean, MD§,
- Jacques Koolen, MD, PhD∥,
- Robert Whitbourn, MD¶,
- Dariusz Dudek, MD#,
- Pieter C. Smits, MD, PhD⁎⁎,
- Evelyn Regar, MD, PhD⁎,
- Susan Veldhof, RN††,
- Richard Rapoza, PhD‡‡,
- John A. Ormiston, MBChB, PhD§§,
- Hector M. Garcia-Garcia, MD, PhD⁎ and
- Patrick W. Serruys, MD, PhD⁎,⁎ ()
- ↵⁎Reprint requests and correspondence
: Dr. Patrick W. Serruys, Thoraxcenter, Erasmus University Medical Center, ‘s-Gravendijkwal 230, Ba-583, 3015 CE Rotterdam, the Netherlands
Objectives The aim of this study is to assess the serial changes in strut apposition and coverage of the bioresorbable vascular scaffolds (BVS) and to relate this with the presence of intraluminal masses at 6 months with optical coherence tomography (OCT).
Background Incomplete strut/scaffold apposition (ISA) and uncovered struts are related to a higher risk of scaffold thrombosis. Bioresorbable vascular scaffolds can potentially avoid the risk of scaffold thrombosis because of its complete resorption. However, during the resorption period, the risk of scaffold thrombosis is unknown.
Methods OCT was performed in 25 patients at baseline and 6 months. Struts were classified according to apposition, coverage, and presence of intraluminal masses. Persistent ISA was defined as malapposed struts present at baseline and follow-up, and late acquired ISA as ISA developing at follow-up, and scaffold pattern irregularities when the strut distribution suggested scaffold fracture.
Results At baseline, 3,686 struts were analyzed: 128 (4%) were ISA, and 53 (1%) were located over side-branches (SB). At 6 months, 3,905 struts were analyzed: 32 (1%) ISA, and 35 (1%) at the SB. Persistent ISA was observed more frequently than late acquired-ISA (81% vs. 16%, respectively; 3% were unmatchable). Late acquired ISA was associated with scaffold pattern irregularities, which were related to overstretching of the scaffold. Uncovered struts (63 struts, 2%) were more frequently observed in ISA and SB struts, compared with apposed struts (29% vs. 1%; p < 0.01). Intraluminal masses (14 cross-sections, 3%; in 6 patients, 24%) were more frequently located at the site of ISA and/or uncovered struts (39% vs. 2% and 13% vs. 2%, respectively; p < 0.01).
Conclusions The lack of strut apposition at baseline is related to the presence of uncovered struts and intraluminal masses at 6 month. An appropriate balloon/artery ratio respecting the actual vessel size and avoiding the overstretching of the scaffold can potentially decrease the risk of scaffold thrombosis. (ABSORB Clinical Investigation, Cohort B [ABSORB B]; NCT00856856)
- bioresorbable scaffolds
- incomplete stent
- late acquired incomplete stent
- optical coherence tomography
- strut apposition
- uncovered struts
Serial intravascular ultrasound (IVUS) imaging of metallic drug-eluting stents (DES) has shown that incomplete stent/strut apposition (ISA) at follow-up can be caused by the persistence of ISA observed at baseline or by the new appearance of late acquired incomplete scaffold/strut apposition (LAISA) (1,2). Recent reports suggest that strut apposition is important for the development of strut coverage, because malapposed struts are more frequently uncovered at follow-up, as compared with apposed struts (3,4). Furthermore, the absence of neointimal coverage as well as the presence of malapposed struts have been related to late stent thrombosis, even in patients treated with dual antiplatelet therapy (5,6).
The novel everolimus-eluting bioresorbable vascular scaffolds (BVS) are promising intravascular devices that can potentially circumvent the risk of malapposed and uncovered struts at follow-up. Notably, at 2 years after implantation, the polymeric material has been shown to be resorbed with the disappearance of struts that were initially malapposed or at side branches (SBs) (7). The first-generation BVS (version 1.0) demonstrated a high rate of malapposed struts before complete resorption, with a rate of malapposed struts at 6 months higher than at baseline (6% vs. 5%, respectively; p < 0.01). This uncommon phenomenon was caused by a low rate of resolved malapposed struts and by the occurrence of LAISA at 6-month follow-up (8). The late scaffold area reduction (shrinkage) observed at 6 months was the most plausible explanation for the higher rate of ISA observed at follow-up compared with baseline. Despite this, only 1% of struts remained uncovered at 6-month follow-up (8).
The new-generation BVS (version 1.1) uses a new platform design and a different processing of the polymer, as compared with the previous generation of BVS (version 1.0), resulting in an increased radial force and longer retention of mechanical integrity (9). Consequently, there is now no detectable loss in scaffold area at 6 months (10,11). Nevertheless, ISA and uncovered struts can still be detected with the new generation of BVS, but the fate of these struts is unknown.
The aim of our study is to describe the serial changes of ISA and uncovered struts at baseline and at 6-month follow-up of the new generation of BVS (version 1.1), as assessed by optical coherence tomography (OCT).
The ABSORB Cohort B (A Clinical Evaluation of the Bioabsorbable Everolimus Eluting Coronary Stent System [BVS EECSS] in the Treatment of Patients With de Novo Native Coronary Artery Lesions) trial is a nonrandomized, multicenter, single-arm, efficacy-safety study (12). The study included 101 patients that were allocated to 6-month angiographic and intravascular imaging control (cohort B1) or 12-month angiographic and intravascular imaging control (cohort B2). All lesions were treated with a single-size device (3 × 18 mm) of the new generation of BVS (version 1.1). The OCT imaging was an optional investigation performed in selected participating centers. In brief, the common inclusion criteria were patients 18 years of age or older, with a diagnosis of stable, unstable, or silent ischemia that presented with a de novo lesion in a native coronary artery between 50% and 99% of the luminal diameter and a Thrombolysis In Myocardial Infarction flow grade of 1 or more. Exclusion criteria included patients with an evolving myocardial infarction, stenosis of the left main or ostial right coronary artery, presence of intracoronary thrombus, or heavy calcification.
The present study is a post hoc analysis of those patients included in the ABSORB cohort B1 that were serially imaged with OCT at baseline and at 6-month follow-up.
The BVS version 1.1 revision is a balloon-expandable device, consisting of a polymer backbone of poly-l-lactide coated with a thin layer of a 1:1 mixture of an amorphous matrix of poly-d,l-lactide polymer containing 100 μg/cm2 of the antiproliferative drug everolimus. The implant is radiolucent but has 2 platinum markers at each edge, which allows visualization on angiography and other imaging modalities. Physically, the scaffold has struts with an approximate thickness of 150 μm arranged as in-phase zigzag hoops linked together by 3 longitudinal bridges.
Lesions were treated with routine interventional techniques. As per protocol, pre-dilation with conventional balloons was mandatory. Pre-dilation balloons should be shorter than the length of the scaffold and 0.5-mm smaller in diameter than the reference vessel. The BVS implantation should not exceed the burst pressure as indicated by the product chart (16 atm). Post-dilation with a balloon shorter than the implanted device was allowed at the discretion of the operator but, when performed, should only be done with balloons sized to fit within the boundaries of the scaffold. Intravascular imaging techniques were performed when optimal BVS placement was obtained according to the judgment of the physician on the basis of angiographic results. In case of suboptimal deployment as assessed by intravascular imaging techniques, post-dilations were allowed at discretion of the operator until optimal stent placement was achieved (on the basis of angiography). After the last post-dilation, a new intravascular imaging acquisition was performed and was used for the study analysis.
The OCT imaging was performed with 2 different OCT systems (M3 Time-Domain System and C7XR Fourier-Domain System; LightLab Imaging, Westford, Massachusetts). The M3 OCT system used a standard intracoronary guidewire to cross the target lesion, and then a single-lumen (e.g., Transit, Cordis, Johnson and Johnson, Miami, Florida, or ProGreat, Terumo, Tokyo, Japan) or double-lumen catheter (0.023-inch TwinPass, Vascular Solutions, Inc., Minneapolis, Minnesota) was required to exchange the conventional wire with the LightLab Imaging ImageWire. Pullback was performed during continuous injection of contrast medium (1 to 3 ml/s, iodixanol 370; Visipaque, GE Healthcare, Cork, Ireland) through the guide catheter with an injection pump. The automated pullback was performed at 3 mm/s with a frame rate of 20 images/s.
The C7XR system used a conventional wire to cross the segment of interest. The OCT imaging catheter (Dragonfly, LightLab Imaging) was then advanced distally to the treated region. Pullback was performed during continuous injection of contrast medium (3 ml/s, iodixanol 370; Visipaque) through the guide catheter with an injection pump. The automated pullback rate was 20 mm/s, and the frame rate was 100 images/s.
Offline OCT qualitative data analysis was carried out by 2 expert analysts with the proprietary software for offline analysis (LightLab Imaging). Both investigators were blinded to the patient, procedural, and clinical characteristics as well as to the clinical outcomes. Adjusting for the pullback speed, the analysis of contiguous cross-sections was performed at 1-mm longitudinal intervals within the treated segment (7 cross-sections/mm in case of M3 OCT system and 5 cross-sections/mm in case of C7 OCT system).
At baseline, embedded struts were defined as present when more than one-half thickness of the strut was impacted into the vessel wall; protruding struts were defined as struts being in contact with the vessel wall but with less than one-half strut thickness impacted into the vessel wall. Both embedded and protruding struts presented with different degrees of apposed struts at follow-up, but we made no distinction. At baseline and follow-up, malapposed struts were defined as struts where the abluminal surfaces were separated from the vessel wall by flush; and SB struts were defined as struts overlying the ostium of an SB (Fig. 1). It is noteworthy that, in contrast with metallic stents, the BVS allows the assessment of the structures located behind the struts without the usual shadowing of metallic struts. Therefore, strut malapposition can be easily assessed when the polymeric strut is separated from the vessel wall. At follow-up, the absence of strut coverage was defined when 1 of the strut corners preserved the right angle shape without signs of neointimal tissue (Fig. 1). Although strut apposition and coverage was measured as a consensus between 2 analysts, a total of 100 random images of 10 different patients were analyzed separately by 2 analysts to ensure the agreement of the qualitative assessments. Scaffold pattern irregularities were defined when struts were found in locations incongruent with the scaffold pattern. They were classified into 2 categories: 1) 2 struts overhanging each other in the same angular sector of the lumen perimeter, with or without malapposition; and/or 2) isolated struts located more or less at the center of the vessel without obvious connection to the expected adjacent strut pattern. At follow-up, protruding masses attached to the vessel wall or floating masses without contact with the vessel wall have been suggested to be thrombi (3). However, the distinction between thrombi and neointimal protrusions into the lumen is not always possible. Therefore, any irregular mass attached to the polymeric struts or floating into the lumen has been classified as intraluminal mass without distinction between thrombus and neointima.
With clear landmarks in the longitudinal OCT images, all cross-sections with at least 1 ISA or SB strut at baseline were matched with the corresponding image of all the possible cross-sections of the entire recording at follow-up (every 7 cross-sections/mm in case of M3 OCT system and every 5 cross-sections/mm in case of C7 OCT system). Every single ISA or SB strut at baseline was investigated at follow-up, to assess its apposition and the state of neointimal coverage. Similarly, those images with at least 1 ISA and/or uncovered struts at follow-up were matched to the corresponding image at baseline of all possible cross-sections of the entire recording at baseline and investigated to assess the original state of strut apposition.
Statistical analysis was performed with the SPSS software (version 15.0, SPSS, Inc., Chicago, Illinois). Discrete variables are presented as counts and percentages and continuous variables as mean ± SD. Comparisons of continuous variables between baseline and follow-up have been estimated with the nonparametric Wilcoxon signed-rank test. Comparison of percentages of uncovered struts between apposed and nonapposed struts has been performed with the Mann-Whitney U test at strut level analysis. Adjustments for clustering data at the patient and frame level analysis have not been performed. A 2-sided p value ≤0.05 was considered statistically significant.
The interobserver agreement for qualitative measurements was quantified by the Cohen's kappa test for concordance (13). In accordance with previous publications, a value <0 indicates poor agreement, 0 to 0.20 indicates slight agreement, 0.21 to 0.40 indicates fair agreement, 0.41 to 0.60 indicates moderate agreement, 0.61 to 0.80 indicates good agreement, and 0.81 to 1.0 indicates excellent agreement (14).
The ABSORB Cohort B1 study included 45 patients, 28 of whom were imaged with OCT at baseline. Two patients were excluded due to suboptimal quality of the OCT recording (lack of imaging of the full length and/or perimeter of the implant); and 1 asymptomatic patient withdrew consent to invasive control at 6-month follow-up. The remaining 25 patients, all of whom were serially imaged with OCT at baseline and 6-month follow-up, were included in the present study. A total of 11 and 9 patients were imaged with the M3 OCT system at baseline and follow-up, respectively; whereas 14 and 16 patients were imaged with the C7 OCT system at baseline and follow-up, respectively. Only 2 patients were imaged with different OCT systems at baseline and follow-up.
Baseline clinical and angiographic characteristics are shown in Table 1. Mean age was 62.4 years; 80% were men, and 8% were diabetic. The clinical indication of the index procedure was stable angina in 84% of patients. A total of 85% of patients had single-vessel disease.
Qualitative OCT findings at baseline
Qualitative OCT findings at baseline are shown in Table 2. At baseline, 3,686 struts in 424 frames were analyzed: 2,554 were classified as protruding (69.3%), 951 as embedded (25.8%), 128 as ISA (3.5%), and 53 struts were overlying an SB (1.4%). Figure 2 shows the distribution of malapposed and SB struts throughout the length of the BVS.
A total of 80 of 90 baseline images with ISA and/or SB struts were properly matched with the corresponding frame at 6-month follow-up. Therefore, 95.3% of malapposed and 84.9% of SB struts were properly matched between time points. At follow-up, the fate of the malapposed struts observed at baseline was: 80.5% resolved into apposed struts, and 14.8% persisted as ISA (4.7% were unmatchable).
Qualitative OCT findings at 6-month follow-up
At 6 months, all polymeric struts were visible, remaining with the preserved box appearance. Qualitative OCT findings are shown in Table 3. At follow-up, 3,905 struts in 433 frames were analyzed: 3,838 were apposed (98.3%), 32 were malapposed (0.8%), and 35 were located over an SB (0.9%). Lack of tissue coverage was detected in 63 struts (1.6%). Distribution of ISA, SB, and uncovered struts throughout the length of the BVS is shown in Figure 2.
A total of 43 of 3,838 apposed struts (1.1%) were uncovered, whereas 10 of 32 ISA struts (31.3%) and 10 of 35 SB struts (28.6%) were uncovered. The comparison of the rate of uncovered plus apposed struts (1.1%) with the rate of uncovered plus ISA or SB struts (29.0%) was statistically significant (p < 0.01) (Fig. 3).
At 6 months, intraluminal masses were observed in 14 cross-sections (2.9%) in 6 patients (24.0%). Notably, intraluminal masses were more often associated with malapposed and/or uncovered struts rather than apposed and covered struts. Of struts with attached intraluminal masses, 40.0% of struts were malapposed and uncovered, 18.2% were malapposed and covered, 9.3% were apposed and uncovered, and 0.9% were apposed and covered (p < 0.01).
A total of 51 of 53 cross-sections with ISA or uncovered struts were properly matched with the corresponding image at baseline. Likewise, 97.1% of malapposed and 95.2% of uncovered struts were properly matched. The ISA was more frequently caused by persistent ISA (81.3%) rather than LAISA (15.6%); 3.1% of the struts were unmatchable. Late acquired ISA was only found in 2 patients (8.0%). Serial analysis of uncovered struts showed that, at baseline, 36 matched struts were classified as protruding (57.1%), 4 as embedded (6.3%), and 10 as ISA (15.9%), and 10 struts were overlying an SB (15.9%); 4.8% were unmatchable.
At 6-month follow-up, no death, spontaneous acute myocardial infarction, scaffold thrombosis, or target lesion revascularization of the 25 patients included in the present study were documented. One patient experienced a periprocedural acute myocardial infarction at the time of the index procedure without any further complications. Another patient with suboptimal OCT imaging at baseline (and excluded from our study) presented with nonclinically driven target lesion revascularization at day 33. At that time, OCT imaging showed scaffold pattern irregularities demonstrating substantial structural distortion, with intraluminal masses attached to the malapposed struts. At the time of the index procedure, this patient was also treated with a post-dilation balloon that achieved a larger predicted diameter than the maximum limit recommended for the BVS.
Qualitative coverage agreement between the 2 analysts
Two analysts investigated, in separate analyses, 100 selected cross-sections of 10 different patients with 767 struts. Both analysts agreed in 710 and 35 covered and uncovered struts, respectively. The Kappa index was 0.75 (good agreement).
The main findings of our study are: 1) with the BVS version 1.1, the number of malapposed struts decreased from baseline to 6-month follow-up; 2) 80% of the malapposed struts observed at baseline resolved into apposed struts at follow-up, with a relatively low rate of LAISA at 6 months; 3) as at baseline and follow-up, ISA and SB struts were associated with a lack of strut coverage at 6 months; and 4) intraluminal masses were rarely observed but were more frequently associated with ISA and uncovered struts.
With metallic-DES, acute ISA ranged from 3.7% to 11.6% of the total amount of struts in patients without ST-segment elevation myocardial infarction (15,16). Patients with at least 1 malapposed strut ranged from 32% to 88% in the same clinical setting (17,18). Our study observed a rate of acute ISA of 3.5%; and 17 patients (68%) presented with at least 1 malapposed strut. These findings suggest that the BVS might have a similar rate of acute ISA, as compared with metallic-DES.
Figure 2 shows the distribution of the malapposed struts throughout the BVS length. According to this figure, malapposed struts were distributed with a particular pattern and were more frequently located at the 2 edges (especially at the proximal edge), with few malapposed struts being located in the central segments of the BVS. This is probably caused by the placement of the central segment of the BVS at the site of the minimal lumen area and by the use of post-dilation balloons (in 56% of patients), shorter than the length of the scaffold, applied at the central segment of the BVS. At baseline, 2 of 25 patients presented with scaffold pattern irregularities resulting in acute strut malapposition. Both patients were treated with post-dilation balloons immediately after the BVS implantation. In both cases, post-dilation balloons were inflated at pressures that resulted in predicted device diameters (according to the manufacturer's chart) larger than the recommended limits for the BVS implantation (3.3 mm for a 3.0-mm nominal diameter BVS). Scaffold pattern irregularities were located at the proximal edges and extended over 2 to 4 mm of the scaffold length. In these images, the number of ISAs were 2 and 5 struts, respectively. Additionally, no intraluminal mass was observed in these frames.
ISA at 6 months
Malapposed struts of different metallic-DES ranged from 0% to 15% of the total amount of struts at 6 months in non–ST-segment elevation myocardial infarction patients (19–21). In a single study comparing different metallic-DES, zotarolimus DES presented with lower rates of malapposed struts (0.0%), as compared with paclitaxel (0.7%) or sirolimus DES (1.9%) (19). All serial OCT imaging studies performed with metallic-DES have found a progressively decreasing amount of malapposed struts over time (21,22). Unfortunately, at the time of the present study, no OCT data were available for the everolimus DES at 6-month follow-up.
The healing process of the different metallic-DES is extremely heterogeneous, with little data being available with regard to the healing process of malapposed struts. Serial OCT imaging of sirolimus DES at baseline and 10-month follow-up showed a high rate of persistent malapposed struts, with 65% of ISA struts observed at baseline remaining malapposed at follow-up. Late acquired ISA was observed in 7.3% of malapposed struts at follow-up (3). Although there are many IVUS studies with serial strut analysis at baseline and at follow-up, the low sensitivity of IVUS to assess ISA—when compared with OCT—challenges the comparability of the results (23). Nevertheless, IVUS was able to identify some of the mechanisms involved in the appearance of LAISA with metallic-DES. Some patients experienced positive remodeling due to vessel and lumen enlargement without increasing the plaque area. In these cases, the vessel wall separated from the apposed strut causing LAISA. This mechanism was more frequently related to sirolimus DES (24,25) rather than paclitaxel DES (1,25), everolimus DES (26), or zotarolimus DES (27).
The first generation of the everolimus-eluting BVS (version 1.0) presented with more malapposed struts at 6 months than at baseline. A total of 78% of malapposed struts observed at baseline persisted at 6 months. Late acquired ISA was observed in 1.0% of the total amount of struts and represented 16% of the total amount of ISA at follow-up (8). The most plausible explanation for this phenomenon was the loss in scaffold area observed during the first 6 months, when the BVS version 1.0 had a premature loss of its radial force and structural continuity (10). This phenomenon caused the displacement of the scaffold into the lumen and probably delayed the healing of previously (baseline) malapposed struts. Likewise, this probably caused the appearance of new malapposed struts at follow-up that were apposed at baseline (LAISA). As assessed by IVUS (8), positive remodeling was not observed with the BVS (version 1.0), unlike what was previously reported in DES.
In our study, with the new generation of BVS (version 1.1), the percentage of malapposed struts at 6-month follow-up was inferior to that at baseline (0.8% vs. 3.5%, respectively; p < 0.01). Only 15% of the malapposed struts at baseline persisted at follow-up. Late acquired ISA was observed in 5 struts (1.0%) in 2 patients and represented 16% of malapposed struts at follow-up. The mechanism owing to LAISA in these 2 patients was the emergence of scaffold pattern irregularities not observed at baseline. Scaffold pattern irregularities were extended over 4 mm throughout the length of the BVS and were mainly located at the proximal edge. The IVUS analysis showed the absence of positive remodeling at the site of the external elastic membrane in those patients (data not shown). Figures 4 and 5⇓⇓ show matched OCT images from baseline to 6-month follow-up of the 2 patients with LAISA caused by the emergence of scaffold pattern irregularities. Although scaffold pattern irregularities were not observed in any of those patients at baseline, it is remarkable that the respective patients had been treated with post-dilation with balloons that over-stretched the BVS to larger diameters than the recommended maximum device diameter of 3.3 mm.
The matched images of the 7 struts with acute ISA due to acute scaffold pattern irregularities (at baseline) evolved to ISA + covered (3 struts) and to ISA + uncovered (4 struts) at 6 months. None of the cases were related to LAISA.
Strut coverage at 6-month follow-up
Strut coverage of different metallic-DES is extremely heterogeneous. At 6 months, sirolimus DES presented with a rate of uncovered struts from 8.7% to 15.0% (19–22). Uncovered struts with paclitaxel DES ranged from 2.7% to 5.0% (19,20), and zotarolimus DES presented with 0% of uncovered struts in a single report (19).
In our study, with the new generation of BVS (version 1.1), a total of 1.6% of struts were uncovered at 6-month follow-up. The distribution of uncovered struts throughout the BVS length did not show any particular pattern (Fig. 2). However, uncovered struts at follow-up were relatively more frequently found in struts that at baseline were ISA and SB struts rather than apposed struts. Similar results have been obtained with serial OCT imaging of sirolimus DES. Ozaki et al. (3) found a higher percentage of uncovered struts, at 10-month follow-up, in struts that were malapposed at baseline (65.4%) as compared with struts that were apposed (8.6%). The first generation of everolimus-eluting BVS (version 1.0) presented with 1.0% of uncovered struts at 6-month follow-up (8). Although the rate of ISA at 6 months was relatively high, uncovered struts were not commonly found. Moreover, the mean neointimal hyperplasia area was statistically higher with the BVS version 1.0 than with the BVS version 1.1 (10). There is no clear explanation for these findings. One hypothesis is that the advanced resorption state and the strut appearance changes observed with the BVS version 1.0 at 6 months as compared with the BVS 1.1 could trigger a higher neointimal response and strut coverage.
Intraluminal masses at 6-month follow-up
Lack of neointimal coverage of different DES was proposed as the best predictor of late stent thrombosis in pathological studies (6). However, although sirolimus DES presented with a higher percentage of uncovered struts compared with paclitaxel DES, thrombi were more frequently found with paclitaxel DES (20). This observation supports the concept of a multicausal pathogenesis of late stent thrombosis, including malapposition, expansive vessel remodeling, and other factors that can initiate thrombus formation (28,29). Due to its high resolution, OCT is able to visualize, with great detail, many of the proposed predictors of late stent thrombosis in vivo (3,30). With sirolimus DES, Ozaki et al. (3) found 4.1% of frames with thrombi at 10-month follow-up; thrombi were more frequently observed in frames with ISA than in those without this feature (21% vs. 2%, respectively, p < 0.01). Our study found 14 cross-sections (2.9%) in 6 patients (24%) containing intraluminal masses at 6-month follow-up. Intraluminal masses were more frequently observed in cross-sections with ISA than without (39% vs. 2%; p < 0.01) and in cross-sections with uncovered struts than without (13% vs. 2%; p < 0.01), supporting that malapposition and absence of coverage can initiate thrombosis. However, whether this is of clinical importance needs to be further investigated. Figure 5 shows intraluminal masses attached to malapposed and uncovered struts in 1 patient with acquired scaffold pattern irregularities and LAISA at 6 months.
In our study, the new generation of BVS presented with a lower rate of ISA, uncovered struts, and intraluminal masses as compared with sirolimus DES at 6-month follow-up. The polymeric nature of this new technology, however, could render it susceptible to iatrogenically induced scaffold pattern irregularities. These can lead to ISA and lack of strut coverage at 6-month follow-up. The 5 cases reported in our study were treated with aggressive post-dilations, probably resulting in overstretching of the scaffold at the time of the implantation. A third generation of the device is intended to raise the limit of deployment of the 3.0-mm nominal diameter device to 3.8 mm. Nevertheless, the previous generation of the BVS (version 1.0) showed a complete resorption of its components at 2-year follow-up without any malapposed or uncovered struts (7). Therefore, in this case, the treatment with dual antiplatelet therapy can become unnecessary. It is, however, currently uncertain whether the new generation of the BVS (version 1.1) will exhibit similar resorption characteristics at 2 years.
The first limitation of the present study is the limited number of patients. However, our report is 1 of the largest OCT studies with serial imaging of the same intracoronary device at baseline and at follow-up. The second limitation is the lack of statistical adjustment for clinical and anatomic covariables. The clustering essence of the OCT data (patient level, stent level, frame level, and strut level) needs a multilevel regression analysis not applied in our study. Moreover, the different OCT pullback speed, frame/rate, and quality of the image of the 2 OCT systems used in the present study hamper the matching of cross-sections between baseline and follow-up. A total of 12 cross-sections were unmatchable from baseline to follow-up or vice versa: 8 cross-sections were imaged with the M3 OCT system and 4 cross-sections were imaged with the C7 OCT system in both baseline and follow-up. Finally, the last limitation is the lack of results at very-long-term follow-up. The extrapolation of the 2-year follow-up results observed with the first generation of BVS (version 1.0) with the new generation of BVS (version 1.1) is purely speculative. However, all patients included in the ABSORB cohort B study will be reinvestigated at 2-year follow-up with invasive imaging techniques.
The new generation of BVS exhibited a low rate of acute, persistent, and late acquired incomplete strut/scaffold malapposition as well as uncovered struts. At baseline and follow-up, malapposed and SB struts were related to a lack of tissue coverage at 6 months. Scaffold pattern irregularities were the only cause observed in our study of late acquired malapposed struts and were also related to a lack of tissue coverage. Attached intraluminal masses occurred more frequently in malapposed and uncovered struts at 6 months. A more careful device implantation, with appropriate sizing of the vessel and respecting the deployment limits of inflation, will reduce the rates of acute ISA and scaffold pattern irregularities and, therefore, could circumvent most of the ISA, uncovered struts, and intraluminal masses observed at midterm follow-up.
The Absorb Cohort B study has been funded by Abbott Vascular (Santa Clara, California). Dr. Windecker has received research grants from Abbott, Cordis, Medtronic, Biosensors, and Boston Scientific. Dr. Dudek has received research grants or served as consultant/advisory board member for Abbott, Adamed, AstraZeneca, Biotronik, Balton, Bayer, BBraun, BioMatrix, Boston Scientific, Boehringer Ingelheim, Bristol-Myers Squibb, Cordis, Cook, Eli Lilly, EuroCor, Glaxo, Invatec, Medtronic, The Medicines Co., MSD, Nycomed, Orbus-Neich, Pfizer, Possis, Promed, Sanofi-Aventis, Siemens, Solvay, Terumo, and Tyco. Dr. Smits has received travel fees from Abbott Vascular. Ms. Susan Veldhof and Dr. Rapoza are employees of Abbott Vascular. Dr. Ormiston is on the advisory board of and has received minor honoraria from Abbott Vascular and Boston Scientific. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- bioresorbable vascular scaffolds
- drug-eluting stents
- incomplete scaffold/strut apposition
- intravascular ultrasound
- late acquired incomplete scaffold/strut apposition
- optical coherence tomography
- side branch
- Received November 30, 2010.
- Revision received March 18, 2011.
- Accepted March 28, 2011.
- American College of Cardiology Foundation
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