Summary
Background
Optical coherence tomography is a high-resolution imaging technology that allows in vivo assessment of neointimal hyperplasia and strut coverage after coronary stenting.
Aim
Assessment of spatial distribution of healing, 6 months after zotarolimus-eluting stent implantation.
Methods
Forty-two zotarolimus-eluting stents were monitored by optical coherence tomography 6 months after implantation. Mean neointimal strut coverage thickness and percentage of neointimal hyperplasia were measured every millimetre. Non-covered strut ratios were assessed on each slice. In addition, the spatial distribution of neointimal hyperplasia and strut coverage were analysed longitudinally on five stent segments and axially on each slice.
Results
There were no clinical events at 6 months under dual antiplatelet therapy. The optical coherence tomography analysis showed a mean neointimal hyperplasia thickness of 333 ± 147 μm and neointimal hyperplasia obstruction of 36.1 ± 12.3%. The percentage of covered struts at 6 months was very high (98.9%). Only 6/745 slices analysed (0.8%) had non-covered strut ratios exceeding 30%. There was no significant heterogeneity in either longitudinal or axial neointimal hyperplasia distribution. No thrombi were observed.
Conclusion
This optical coherence tomography study found relatively constant neointimal hyperplasia thickness, regardless of the zotarolimus-eluting stent length or diameter. This spatially homogeneous neointimal hyperplasia was associated with near-total coverage of all struts, 6 months after implantation.
Résumé
Contexte
L’imagerie par cohérence optique (OCT) est une imagerie de haute résolution permettant l’analyse in vivo de l’hyperplasie néo-intimale et de la couverture des mailles des stents.
Objectif
Analyse quantitative de la couverture néo-intimale de stents au zotarolimus à six mois et de sa distribution spatiale.
Méthode
Quarante-deux stents au zotarolimus ont été contrôlé par OCT six mois après leur implantation. L’épaisseur moyenne de la couverture néo-intimale des mailles et le pourcentage d’hyperplasie néo-intimale ont été mesurés tous les millimètres. Sur chaque coupe, le ratio de mailles non couvertes est mesuré. La distribution spatiale de l’hyperplasie néo-intimale et de la couverture du stent est analysée longitudinalement sur cinq segments du stent et axialement sur chaque coupe.
Résultats
Il n’y a pas eu d’évènements cliniques à six mois sous double anti-agrégation plaquettaire. L’analyse OCT retrouve une épaisseur moyenne d’hyperplasie néo-intimale de 333 ± 147 μm et une obstruction néo-intimale de 36,1 ± 12,3 %. Le pourcentage de mailles couvertes à six mois est élevé de 98,9 %. Seulement six coupes sur les 745 analysées (0,8 %) ont un ratio de mailles non couvertes/couvertes de plus de 30 %. La distribution de l’hyperplasie néo-intimale est homogène en axial et en longitudinal. Aucun thrombus n’a été visualisé.
Conclusion
Cette analyse OCT retrouve une épaisseur d’hyperplasie néo-intimale relativement homogène dans le stent, quelle que soit sa longueur ou son diamètre. Cette homogénéité d’hyperplasie néo-intimale est associée à une couverture quasi totale des mailles six mois après l’implantation des stents.
Background
Randomised studies have shown that DESs significantly reduce clinical restenosis rates compared with bare-metal stents . This benefit is due to inhibition of intimal neoproliferation . Animal and autopsy studies, however, have shown this effect to be associated with delayed or deficient arterial healing. It is therefore advisable to continue dual antiplatelet therapy beyond the first month post stenting, in order to avoid late intrastent thrombosis . In a series of 8000 DESs, Wenaweser et al. reported a consistent 0.6% annual late thrombosis rate over the first 4 years post stenting .
Intrastent thrombosis is a multifactorial phenomenon , but one significant factor is failure of stent–strut re-endothelialization . Post-mortem studies of stented subjects have reported deficient re-endothelialization to be more frequently associated with late intrastent thrombosis than with other causes of death .
OCT is a high-resolution (around 10 microns) imaging technology that is particularly well adapted for the study of the most superficial layers of the vessel wall and for strut-by-strut stent analysis. Several recent studies have focused on OCT analysis of neointimal coverage in bare-metal and first-generation DESs .
The present study used OCT to quantify and analyse the spatial distribution of NIH and strut coverage, 6 months after ZES implantation.
Methods
Study population and methods
Between October 2006 and September 2007, 25 patients (21 men, four women) gave consent and were included in this prospective, observational study. These 25 patients were selected from the 220 patients who underwent ZES implantation in our centre during the study period, using the following inclusion criteria: consent and feasibility of OCT. Exclusion criteria were left main coronary artery stenosis, bypass lesion, ostial stenosis, renal insufficiency, acute coronary syndrome, stent overlapping, contraindication for DES and OCT limitations. OCT limitations were tortuous and calcified vessels, proximal lesion or large coronary diameter (> 3.5 mm) preventing the good saline flush downstream of an occlusion balloon that is necessary for image quality. The 25 patients underwent native coronary stenting, using a total of 42 ZESs. Angiographic analyses were done at baseline and after angioplasty. The angiograms were evaluated by a QCA system (QuantCor, CASS II, Siemens, Erlangen, Germany). An angiographic control with OCT was scheduled at 6 months post stenting. Restenosis was defined as > 50% lumen narrowing on QCA.
Optical coherence tomography procedure
Optical coherence tomography at 6 months post stenting immediately followed the control angiography. A 6F catheter was used to inject 30 UI/kg of unfractionated heparin intra-arterially. A 0.014-inch guide was introduced into the vessel and positioned distally to the stent. A Helios™ coaxial occlusion balloon catheter (LightLab Imaging, Westford, MA, USA) was then introduced along the guide across the vessel until the balloon marker was at the distal extremity of the stent. The guide was then withdrawn and replaced by a 1.4F optic fibre, connected up to the OCT system (M2 version, LightLab Imaging, Westford, MA, USA) and inserted through the balloon until distal to the stent. The occlusion balloon was then withdrawn until proximal to the DES and inflated to between 0.4 and 0.7 atm. Physiological saline was then injected downstream of the occlusion balloon via its coaxial catheter; 30 mL were injected during each pullback. OCT gives a clear image once the lumen is sufficiently transparent. Automatic light-source pullback then began (1 mm/s, with 15 image/s acquisitions). A 30-mm DICOM-format video recording of the artery was made, including the stented segment. The balloon was then deflated and the saline injection stopped. Several pullbacks were sometimes needed for analysis of the longest stents. Pullback was repeated until perfect visualization of the whole length of all stents was obtained.
Optical coherence tomography analysis
Optical coherence tomography images were selected from the DICOM pullback recordings every millimetre (every 15 images) over the entire stented segment and were analysed by two independent operators ( Fig. 1 ).
Each strut was classified into one of four categories:
- •
well apposed to vessel wall with apparent neointimal coverage (A);
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well apposed to vessel wall but without neointimal coverage (non-coverage being defined as absence of any visible structure between lumen and vessel on OCT, with strut reflection) (B);
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malapposed to vessel wall without neointimal coverage (malapposition being defined as > 110 μm distance between strut reflection and vessel wall, corresponding to OCT axial resolution + ZES strut thickness) (C);
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located at a bifurcation (D).
Struts in class A were assigned their measured coverage thickness in micrometer; otherwise, the assigned value was 0.
Strut information was used to produce cross-sectional criteria:
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overall NIH quantification, in terms of mean strut coverage thickness;
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cross-sectional heterogeneity of NIH, in terms of the coefficient of variation (i.e. standard deviation divided by mean) of strut coverage thickness;
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global coverage deficiency, in terms of the non-covered strut ratio, defined as the proportion of struts in categories B, C and D.
NIH quantification was also assessed in each slice from both lumen area (in millimetre square) and stent area (in millimetre square), computing percentage NIH area, defined as NIH obstruction (%) = (stent area–lumen area)/SA*100.
Longitudinal NIH distribution was assessed using the mean values for each of the aforementioned criteria on each of five predefined longitudinal stent segments of equal length (proximal, proximal-medial, medial, distal-medial and distal).
Statistical analysis
Categorical variables are described as frequencies and percentages. Continuous variables are displayed as means ± standard deviations. Longitudinal NIH distribution used a mixed linear model to account for segment nesting within a given stent. Longitudinal effect (i.e. possible longitudinal NIH distribution heterogeneity) was assessed through a global F statistic, completed, as appropriate, by post-hoc multiple comparison of the five predefined stent segments.
The analyses were performed using SAS 9.2 software (SAS Institute, Inc., Cary, NC, USA).
Results
Population characteristics
Population characteristics are given in Table 1 . The 25 included patients (mean age, 59.7 ± 10.1 years) were stented at severe coronary stenosis sites (77.5 ± 8.9% diameter stenosis on QCA). Minimum lesion diameter and length were 0.67 ± 0.29 mm and 14.45 ± 5.68 mm, respectively, with a reference diameter of 2.99 ± 0.33 mm.
| Characteristic | |
|---|---|
| Patients | 25 (100) |
| Age (years) | 59.7 ± 10.1 |
| Men | 21 (84) |
| Cardiovascular risk factors | |
| Tobacco smoke | 14 (56) |
| Diabetes mellitus | 7 (28) |
| High blood pressure | 12 (48) |
| High blood cholesterol | 15 (60) |
| Obesity | 7 (28) |
| Heredity | 9 (36) |
| History of coronary artery disease | 2 (8) |
| Context of stable angina | 25 (100) |
| Number of stents per patient | 1.68 ± 0.56 |
| Lesions | 42 (100) |
| Target vessel | |
| LAD | 19 (45) |
| LCX | 7 (17) |
| RCA | 16 (38) |
| Lesion type (ACC/AHA) | |
| A | 6 (14) |
| B1 | 24 (57) |
| B2 | 12 (29) |
| C | 0 (0) |
| Reference lumen diameter (mm) | 2.96 ± 0.33 |
| Minimum lumen diameter (mm) | 0.67 ± 0.29 |
| Diameter stenosis (%) | 77.5 ± 8.9 |
| Lesion length (mm) | 14.45 ± 5.68 |
| Zotarolimus stents used | 42 (100) |
| Stent diameter (mm) | 3.01 ± 0.34 |
| Stent length (mm) | 18.40 ± 6.30 |
| Maximum inflation pressure (atm) | 14.0 ± 2.4 |
| Direct stenting | 34 (81) |
| Post dilatation | 7 (17) |
| Final success | 42 (100) |
| Post angioplasty QCA data | |
| Reference vessel diameter (mm) | 2.99 ± 0.33 |
| Minimum lumen diameter (mm) | 2.92 ± 0.35 |
| Diameter stenosis (%) | 2.3 ± 3.4 |
| Acute gain (mm) | 2.25 ± 0.34 |
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