Atsushi Sakaoka

Vascular responses to a biodegradable polymer (polylactic acid) based Biolimus A9-eluting stent in porcine models

AIMS The time-dependent changes in endothelial and healing properties of coronary arteries implanted with a biodegradable polymer-based biolimus A9-eluting stent (BioPol-BES) have not been investigated. We evaluated the short-term and the long-term in vivo response of BioPol-BES, as compared to a permanent polymer-based sirolimus-eluting stent (PermPol-SES), and a bare metal stent (BMS). METHODS AND RESULTS Overlapping stents were placed in 33 swine (n=11 for BES, SES, and BMS, respectively) for two and four weeks and single stents in 30 miniature pigs (n=18 for BES, n=9 for SES, n=3 for BMS) for three, nine and 15-month evaluations. The vessel patency, arterial healing and endothelialisation were assessed by angiography, histopathology and scanning electron microscopy. At four weeks, the endothelialisation at overlapping stent regions was greater with BioPol-BES (87.8±3.7%) and BMSs (98.0±0.4%) than with PermPol-SES (66.4±3.2%). The inflammation score in vessels implanted with single BioPol-BES increased slightly from three to 15 months (0.00±0.00 to 0.28±0.14), while this increase was more pronounced with PermPol-SES (0.11±0.07 to 1.56±0.68). Compared to BMS moderate lymphocyte infiltration was seen with BioPol-BES, and marked granulomatous formation with PermPol-SES. CONCLUSIONS The level of endothelial coverage in BioPol-BES was comparable to BMS at four weeks, with no significant increase of inflammatory reaction up to 15 months.

Neuromatous Regeneration as a Nerve Response After Catheter-Based Renal Denervation Therapy in a Large Animal Model Immunohistochemical Study

Background—Renal denervation (RDN) emerged as a therapeutic option for resistant hypertension. Nerve regrowth after RDN has been questioned. We aimed to characterize the nerve response after RDN. Methods and Results—Swine underwent bilateral RDN and were followed up for 7, 30, and 90 days and evaluated with S100 (Schwann cell), tyrosine hydroxylase (TH; efferent nerves), and growth-associated protein 43 (neurite regeneration) markers. At 7 days, nerve changes consisted of necrosis associated with perineurial fibrosis and distal atrophy with inflammation. At 30 days changes were substituted by healing changes (ie, fibrosis). This response progressed through 90 days resulting in prominent neuroma formation. Immunohistochemistry at 7 days: TH staining was strongly decreased in treated nerves. Early regenerative attempts were observed with strongly TH and growth-associated protein 43 positive and weak S100 disorganized nerve sprouts within the thickened perineurium. Distal atrophic nerves show weak staining for all 3 markers. At 30 days, affected nerves show a weak TH and S100 staining. Evident growth-associated protein 43+ disorganized neuromatous tangles in the thickened perineurium of severed nerves were observed. At 90 days, some TH expression was observed together with prominent S100+ and growth-associated protein 43+ neuromatous tangles with disorganized architecture. The potential for regenerative activity is unlikely based on the disrupted architecture of these neuromatous tangles at the radiofrequency lesion sites. Conclusions—This study is the first documentation that a progressive regenerative response occurs as early as 7 days after RDN, resulting in a poorly organized neuromatous regeneration. This finding is of paramount importance to further establish the potential functional significance of a regeneration after RDN.

Different Vascular Responses to a Bare Nitinol Stent in Porcine Femoral and Femoropopliteal Arteries

Nitinol stents are widely used for the treatment of peripheral arterial diseases in lower extremity arteries and have shown different clinical outcomes depending on implanted arterial segments. We aimed to compare histopathological responses to nitinol stents in femoral artery (FA) with those in femoropopliteal artery (FPA), which is markedly bended during knee flexion. A single nitinol stent was implanted in FA and FPA of 21 domestic swine. The stented vessels were angiographically assessed and then harvested for histopathology at 1 and 3 months after implantation. Angiographic late lumen loss was significantly greater in FPA than in FA at 3 months. Neointimal area decreased in FA and increased in FPA from 1 to 3 months. Compared with FA, peri-strut area of FPA showed more pronounced hemorrhage and fibrin deposition at 1 month and angiogenesis and inflammation at 1 and 3 months. Injury to internal elastic lamina or media was minimal in both FA and FPA at both time points. In conclusion, vascular responses to nitinol stents were different between FA and FPA with respect to time course of neointimal formation and progress of healing, suggesting that repetitive interaction between stent and vessel wall during dynamic vessel motion affected vascular responses.

Optimal implantation site of transponders for identification of experimental swine

Use of transponders, small electronic identification devices, in experimental swine is expected to be more reliable than the current common use of ear tags. However, it is necessary to determine the optimal implantation site for transponders with high readability, retentionability (i.e., long-term retention in tissues without detachment or loss), and biocompatibility, as this has not yet been investigated. Thus, we aimed to determine the optimal implantation site. Two types of transponders were subcutaneously implanted into four different sites (ear base, ear auricle, ventral neck, and back) in 3 domestic swine each. The transponders were scanned at 1, 2, 3, and 84 days after implantation. The location of the transponders was examined by X-ray and echography at 84 days. Histopathological examinations were performed at 84 days. The transponders in the back were successfully scanned in a shorter time than those in other implantation sites, without any re-scanning procedures. X-ray examination revealed one transponder in the ventral neck was lost, whereas those in the other sites were retained in their original location for 84 days. Echography indicated that the transponders in the back were retained more deeply than those in other implantation sites, suggesting better retentionability. Acceptable biocompatibility was confirmed in all implantation sites, as evidenced by the finding that all transponders were covered by a connective tissue capsule without severe inflammation. In conclusion, the present results demonstrated that the back is the optimal implantation site for transponders in experimental swine.

Quantitative angiographic anatomy of the renal arteries and adjacent aorta in the swine for preclinical studies of intravascular catheterization devices

Swine are the most common animal model in preclinical studies of cardiovascular devices. Because of the recent trend for development of new devices for percutaneous catheterization, especially for the renal arteries (RAs), we examined the quantitative anatomical dimensions of the RAs and adjacent aorta in swine. Angiographic images were analyzed in 66 female Yorkshire/Landrace crossbred swine. The diameter of both the right and left main RA was 5.4 ± 0.6 mm. The length of the right main RA was significantly longer than that of the left (29.8 ± 7.5 mm vs. 20.6 ± 5.4 mm, respectively; P<0.001). The diameter of both the right and left branch RA with diameters ≥3 mm (the target vessel diameter of recently developed devices) was 3.8 ± 0.5 mm. The right branch RA was significantly longer than that of the left (18.9 ± 7.8 mm vs. 16.4 ± 7.4 mm, respectively; P<0.05). The branching angle of the right RA from the aorta was significantly smaller than that of the left (91 ± 12° vs. 103 ± 15°, respectively; P<0.001). The diameters of the suprarenal and infrarenal aorta were 10.6 ± 1.1 mm and 9.7 ± 0.9 mm, respectively. In conclusion, because of their similar dimensions to human, swine are an appropriate animal model for assessing the safety of, and determining optimal design of, catheter devices for RAs in simulated clinical use. However, there were species differences in the branching angle and adjacent aorta diameter, suggesting that swine models alone are inadequate to assess the delivery performance of catheter devices for RAs.

Accurate Depth of Radiofrequency-Induced Lesions in Renal Sympathetic Denervation Based on a Fine Histological Sectioning Approach in a Porcine Model

Background— Ablation lesion depth caused by radiofrequency-based renal denervation (RDN) was limited to <4 mm in previous animal studies, suggesting that radiofrequency-RDN cannot ablate a substantial percentage of renal sympathetic nerves. We aimed to define the true lesion depth achieved with radiofrequency-RDN using a fine sectioning method and to investigate biophysical parameters that could predict lesion depth. Methods and Results— Radiofrequency was delivered to 87 sites in 14 renal arteries from 9 farm pigs at various ablation settings: 2, 4, 6, and 9 W for 60 seconds and 6 W for 120 seconds. Electric impedance and electrode temperature were recorded during ablation. At 7 days, 2470 histological sections were obtained from the treated arteries. Maximum lesion depth increased at 2 to 6 W, peaking at 6.53 (95% confidence interval, 4.27–8.78) mm under the 6 W/60 s condition. It was not augmented by greater power (9 W) or longer duration (120 seconds). There were statistically significant tendencies at 6 and 9 W, with higher injury scores in the media, nerves, arterioles, and fat. Maximum lesion depth was positively correlated with impedance reduction and peak electrode temperature (Pearson correlation coefficients were 0.59 and 0.53, respectively). Conclusions— Lesion depth was 6.5 mm for radiofrequency-RDN at 6 W/60 s. The impedance reduction and peak electrode temperature during ablation were closely associated with lesion depth. Hence, these biophysical parameters could provide prompt feedback during radiofrequency-RDN procedures in the clinical setting.

Acute changes in histopathology and intravascular imaging after catheter-based renal denervation in a porcine model

We first aimed to identify the histopathological changes occurring immediately after renal denervation (RDN) with radiofrequency energy, and then to assess the feasibility of determining procedural success using currently available clinical intravascular imaging techniques.

TCT-838 Effects of Oversizing on Neointimal Formation after Self-Expanding Bare Metal Stents in Porcine Femoral Arteries

Stent oversizing has been suggested as a cause of restenosis in superficial femoral artery (SFA) in previous animal studies with stents lacking reported clinical performance. In this study, we investigated whether oversizing of a clinically available stent also promotes restenosis in a porcine model