A histopathological comparison of different definitions for quantifying in-stent neointimal tissue: implications for the validity of intracoronary ultrasound and optical coherence tomography measurements

Preliminary outcomes of single antiplatelet therapy for surface-modified flow diverters in an animal model: analysis of neointimal development and thrombus formation using OCT

Objective

To evaluate the rate of neointimal development and thrombus formation of surface-modified flow diverters in single antiplatelet therapy (SAPT) using optical coherence tomography (OCT) in a porcine model.

Methods

We divided 10 experimental pigs into two groups. One group (n=6) received dual antiplatelet therapy (DAPT) and the other group (n=4) received SAPT. Four stents (two per carotid artery) were implanted in both groups. The stents used were the Pipeline Flex embolization device (PED Flex), Pipeline Flex with Shield technology (PED Shield), and the Solitaire AB stent. All animals underwent weekly angiography and OCT. The OCT data were analyzed using the following measurements: neointimal ratio ((stent – lumen area)/stent area), stent-coverage ratio (number of stent struts covered by neointima/total stent struts), and the presence or absence of thrombus formation per 1 mm cross-section.

Results

PED Flex and Shield in the SAPT group had higher neointimal ratios than in the DAPT group (P<0.001, respectively). In the DAPT group, the speed of endothelial growth on day 7 in the PED Shield group was higher than that in the PED Flex group (P<0.001). In the SAPT group, PED Flex demonstrated significantly more thrombus formation on day 7 than PED Shield (P<0.001).

Conclusions

The PED Shield stent showed faster endothelial growth than the other devices and comparable neointimal volume. There was significantly less thrombus formation on PED Shield than PED Flex when using SAPT in a porcine model.

Analysis of neointima development in flow diverters using optical coherence tomography imaging

BACKGROUND

Flow diverters are used for the treatment of intracranial aneurysms. Surface modification may decrease the thrombogenicity of flow diverters but the details are unknown. Optical coherence tomography (OCT) is an intravascular imaging test with high resolution which identifies neointimal growth over stents. We compared the development of neointima in a flow diverter and stents with and without surface modification in a swine model.

METHODS

In this study we implanted four devices (two in each carotid artery) in four pigs. The devices used were the Pipeline Flex embolization device (PED Flex, n=6), PED with Shield technology (PED Shield, n=6), and Solitaire AB (n=4). Serial carotid angiographic and OCT images were obtained on days 0, 7, 14, and 21. The data analyzed included: neointimal area (lumen area - stent area), neointimal ratio ([lumen area - stent area]/stent area), and the neointimal thickness ratio (minimum neointimal thickness/maximum neointimal thickness).

RESULTS

There was no significant difference in where neointima formation was initiated in relation to the implanted device (distal vs middle vs proximal). The PED Shield had a trend towards earlier endothelial formation at day 7. By day 21 the neointimal ratio was significantly higher for the PED Flex and PED Shield devices than for Solitaire (p<0.05 and p<0.01, respectively). The neointimal thickness ratio was significantly higher with PED Shield than with PED Flex and Solitaire (p<0.05 and p<0.01, respectively).

CONCLUSIONS

OCT enabled us to follow and compare in vivo the development of neointima over implants. PED Shield showed a similar neointimal volume to PED Flex and more concentric neointima.

Histological validation of frequency domain optical coherence tomography for the evaluation of neointimal formation after a novel polymer-free sirolimus-eluting stent implantation

Novel polymer-free drug-eluting stents have been developed to reduce polymer-related adverse events. However, neointimal coverage after polymer-free DES implantation is unclear and validation between optical coherence tomography (OCT) and histology is required. Sixteen polymer-free sirolimus-eluting stents were randomly implanted into coronary arteries of 8 normal swine. OCT and histological measurement were conducted at 3 or 6 months after stent placement. For quantitative measures, lumen area, stent area, neointimal area and neointimal thickness were validated in every single OCT and histology matched cross-section. Moreover, for qualitative analysis, OCT signal patterns of neointimal tissue were classified as homogeneous, layered and heterogeneous patterns based on optical intensity and backscatter pattern and peri-strut inflammation was also determined by histology. In total, 70 OCT and histology matched cross-sections were analyzed. At quantitative analysis, good correlations and agreements were found in the measurement of lumen area (ICC = 0.67, P<0.001), neointimal area (ICC = 0.89, P<0.001) and neointimal thickness (ICC = 0.94, P<0.001) except for stent area (ICC 0.19, P = 0.13) between OCT and histology. At qualitative analysis, lymphocyte infiltrations of peri-strut were more frequently seen in heterogeneous sections than in homogeneous sections (10/14 sections, 71.4% vs. 12/50 sections, 24%; P = 0.003). In conclusion, OCT has proper correlation and agreement with histology in assessment of neointimal formation and heterogeneous neointima assessed by OCT may also be associated with peri-strut inflammation detected in histology after polymer-free sirolimus-eluting stents implantation, supporting the use of OCT to evaluate neointimal coverage after polymer-free stent implantation in clinical practice.