6-Month Evaluation of a Transcatheter Aortic Valve (Myval) in a Novel Ovine, Supra-Aortic Banding Model.

The aim of the study was to evaluate a balloon expandable transcatheter heart valve (THV) system (Myval) at 6-month follow-up in ovine banding model. Eleven THV systems were implanted via carotid approach. There were 2 procedure-related deaths and 2 premature deaths. At 6 months all valves that completed follow-up (n = 7) were functional, with no significant regurgitation, calcification, thrombi, or vegetation. Mean pressure gradient was 21.9 ± 11 mm Hg, maximum velocity = 3.3 ± 1 m/s, and ejection fraction was 53.3 ± 6%. Myval THV showed optimal hemodynamic performance and biocompatibility.

Scientific and Regulatory Policy Committee Points to Consider for Medical Device Implant Site Evaluation in Nonclinical Studies.

Nonclinical implantation studies are a common and often critical step for medical device safety assessment in the bench-to-market pathway. Nonclinical implanted medical devices or drug-device combination products require complex macroscopic and microscopic pathology evaluations due to the physical presence of the device itself and unique tissue responses to device materials. The Medical Device Implant Site Evaluation working group of the Society of Toxicologic Pathology's (STP) Scientific and Regulatory Policy Committee (SRPC) was tasked with reviewing scientific, technical, and regulatory considerations for these studies. Implant site evaluations require highly specialized methods and analytical schemes that should be designed on a case-by-case basis to address specific study objectives. Existing STP best practice recommendations can serve as a framework when performing nonclinical studies under Good Laboratory Practices and help mitigate limitations in standards and guidances for implant evaluations (e.g., those from the International Organization for Standardization [ISO], ASTM International). This article integrates standards referenced by sponsors and regulatory bodies with practical pathology evaluation methods for implantable medical devices and combination products. The goal is to ensure the maximum accuracy and scientific relevance of pathology data acquired during a medical device or combination drug-device implantation study.

Chronic myocardial and coronary arterial effects of intracoronary supersaturated oxygen therapy in swine with normal and ischemic-reperfused myocardium.

The study assessed chronic myocardial, coronary and systemic effects of intracoronary supersaturated oxygen (SSO2) therapy. Left anterior descending coronary arteries of 40 swine were stented and randomized to 90-min selective intracoronary infusion of SSO2 (pO2 760-1000 mmHg) or normoxemic saline. In 20 out of 40 animals, SSO2 delivery followed a 60-min balloon occlusion to induce myocardial infarction (MI). In both normal and MI models, intracoronary treatment with hyperoxemic SSO2 therapy showed no evidence of coronary thrombosis. There were no biologically relevant differences between treatments at either time point in regard to coronary intervention site healing and neointimal growth. No signs of any myocardial or systemic toxicity were observed after 7 or 30 days. A trend was observed toward reduced incidence of microscopic MI scars and reduced infarct size in histopathology, as well as toward better recovery of echocardiographically evaluated global and regional contractility at 30 days. No treatment related infarcts or thromboemboli were observed in the downstream organs.

In vivo safety study using radiation at wavelengths and dosages relevant to intravascular imaging.

SIGNIFICANCE: Intravascular photoacoustic (IVPA) imaging can identify native lipid in atherosclerotic plaques in vivo. However, the large number of laser pulses required to produce 3D images is a safety concern that has not been fully addressed. AIM: We aim to evaluate if irradiation at wavelengths and dosages relevant to IVPA imaging causes target vessel damage. APPROACH: We irradiate the carotid artery of swine at one of several energy dosages using radiation at 1064 or 1720 nm and use histological evaluation by a pathologist to identify dose-dependent damage. RESULTS: Media necrosis was the only dose-dependent form of injury. Damage was present at a cumulative fluence of 50 J / cm2 when using 1720 nm light. Damage was more equivocally identified at 700 J / cm2 using 1064 nm. CONCLUSIONS: In prior work, IVPA imaging of native lipid in swine has been successfully conducted below the damage thresholds identified. This indicates that it will be possible to use IVPA imaging in a clinical setting without damaging vessel tissue. Future work should determine if irradiation causes an increase in blood thrombogenicity and confirm whether damaged tissue will heal over longer time points.

Safety and Performance Evaluation of Su2ura Approximation, a New Suturing Device, in Pigs.

One of the challenging aspects of minimal invasive surgery (MIS) is intracorporal suturing, which can be significantly time-consuming. Therefore, there is a rising need for devices that can facilitate the suturing procedure in MIS. Su2ura Approximation Device (Su2ura Approximation) is a novel device developed to utilize the insertion of anchors threaded with stitches to allow a single action placement of a suture. The objective of this study was to evaluate the long-term safety and tissue approximation of Su2ura Approximation in comparison to Endo Stitch + Surgidac sutures in female domestic pigs. All incision sites were successfully closed by both methods. Firm consolidation within and around the incision site was noted in several animals in both treatment groups, which corresponded histopathologically to islands of ectopic cartilage or bone spicules within the fibrotic scar. These changes reflect heterotopic ossification that is commonly seen in the healing of abdominal operation sites in pigs. No other abnormal findings were observed throughout the study period. In conclusion, the use of Su2ura Approximation under the present experimental conditions revealed no safety concerns.

Digital 3D Topographic Microscopy: Bridging the Gaps Between Macroscopy, Microscopy and Scanning Electron Microscopy.

Re-endothelialization of vascular lumen after endovascular procedures is a critical healing milestone and is subjected to routine pathological evaluation during preclinical safety assessment of new cardiovascular devices. Gross evaluation, microscopic evaluation, and scanning electron microscopy (SEM) are the methods of choice for evaluation of vascular surfaces. In this article, we present a new digital imaging approach of surface topography herein referred to as topographical digital microscopy (TDM) that is able to meet the objectives of endovascular healing assessment in a single instrumental platform combined with the same sample preparation techniques as for histology or SEM. This platform is taking advantage of digitally managed illumination, X-Y stitching, and Z-stacking to enable direct optical imaging of tissue surfaces at levels of details ranging from the macroscopic to the cellular level. This technique is enabled by advances in digital optical microscopy and provides images in color and 3 dimensions that can help in the analysis, especially in distinguishing biologically meaningful observations from technical preparation artifacts and in visualizing surface topography.

Nanospheres encapsulated everolimus delivery into arterial wall-the tissue pharmacokinetics and vascular response experimental study.

OBJECTIVE: This study aimed to evaluate the pharmacokinetic profile and tissue effects of everolimus delivered into arterial wall using biodegradable nanospheres. BACKGROUND: Delivery of everolimus into the arterial wall is challenging due to its low-lipophilic profile. METHODS: A pharmacokinetic study included 28 porcine coronary arterial segments initially injured with balloon angioplasty followed by the local delivery of everolimus encapsulated in nanospheres (EEN) via injection through a microporous delivery catheter. The animals were sacrificed at 1 hour, 1,7,28, and 90-day follow-up. In the tissue effects study 16 coronary bare metal stent (BMS) were implanted following EEN delivery, 15 BMS following nanospheres delivery without the drug (reference group) and 16 implanted BMS served as a control. Angiographic and histology follow-up was scheduled at 28 and 90-day. RESULTS: The study showed high-everolimus concentrations in arterial tissue early after nanoparticles delivery followed by its gradual decrease to 1.15 ± 0.40 ng/mg at 90 days. Histology analysis showed favorable biocompatibility and healing profile with comparable area stenosis between groups at both time-points. CONCLUSIONS: The present study demonstrates for the first time the safety, biocompatibility, and long-term retention of everolimus in arterial tissue after single local delivery of biodegradable nanospheres.

The Application, Challenges, and Advancement Toward Regulatory Acceptance of Digital Toxicologic Pathology: Results of the 7th ESTP International Expert Workshop (September 20-21, 2019).

With advancements in whole slide imaging technology and improved understanding of the features of pathologist workstations required for digital slide evaluation, many institutions are investigating broad digital pathology adoption. The benefits of digital pathology evaluation include remote access to study or diagnostic case materials and integration of analysis and reporting tools. Diagnosis based on whole slide images is established in human medical pathology, and the use of digital pathology in toxicologic pathology is increasing. However, there has not been broad adoption in toxicologic pathology, particularly in the context of regulatory studies, due to lack of precedence. To address this topic, as well as practical aspects, the European Society of Toxicologic Pathology coordinated an expert international workshop to assess current applications and challenges and outline a set of minimal requirements needed to gain future regulatory acceptance for the use of digital toxicologic pathology workflows in research and development, so that toxicologic pathologists can benefit from digital slide technology.

Local Tolerance and Biodegradability of a Novel Artificial Dura Mater Graft Following Implantation Onto a Dural Defect in Rabbits.

Dura mater defects are a common problem following neurosurgery. Dural grafts are used to repair these defects; among them are biodegradable polymeric synthetic grafts. ArtiFascia is a novel synthetic and fibrous Dural graft, composed of poly(l-lactic-co-caprolactone acid) (PLCL) and poly(d-lactic-co-caprolactone acid). In this study, the biodegradability and local tolerance of ArtiFascia was evaluated in rabbits and compared with a bovine collagen matrix as a reference control. ArtiFascia implantation resulted in the formation of neo-dura at the site of implantation and recovery of the dural damage and the calvaria bone above. The implanted graft was completely absorbed after 12 months and the remaining macrophages were morphologically consistent with the anti-inflammatory M2-like phenotype, which contributes to tissue healing and are not pro-inflammatory. The site of the drilled skull bone had a continuous smooth surface, without exuberant tissue or inflammation and a newly formed trabecular bone formation indicated the healing process of the bone. These results support the local tolerability and biodegradability of ArtiFascia when used as a dural graft in rabbits. This study suggests that PLCL-based grafts including ArtiFascia are safe and effective to repair Rabbit Dura.

A neurovascular high-frequency optical coherence tomography system enables in situ cerebrovascular volumetric microscopy.

Intravascular imaging has emerged as a valuable tool for the treatment of coronary and peripheral artery disease; however, no solution is available for safe and reliable use in the tortuous vascular anatomy of the brain. Endovascular treatment of stroke is delivered under image guidance with insufficient resolution to adequately assess underlying arterial pathology and therapeutic devices. High-resolution imaging, enabling surgeons to visualize cerebral arteries' microstructure and micron-level features of neurovascular devices, would have a profound impact in the research, diagnosis, and treatment of cerebrovascular diseases. Here, we present a neurovascular high-frequency optical coherence tomography (HF-OCT) system, including an imaging console and an endoscopic probe designed to rapidly acquire volumetric microscopy data at a resolution approaching 10 microns in tortuous cerebrovascular anatomies. Using a combination of in vitro, ex vivo, and in vivo models, the feasibility of HF-OCT for cerebrovascular imaging was demonstrated.

D-PLEX100 in an Abdominal Surgery Incision Model in Miniature Swine: Safety Study.

Surgical site infections (SSIs) are a common surgical-related complication. To avoid these complications, a new biodegradable polymer-lipid encapsulation matrix that provides controlled release of doxycycline (doxycycline/polymer-lipid encapsulation matrix [D-PLEX]) has been developed. The aim of this comprehensive study was to evaluate the potential safety of D-PLEX100 in abdominal surgical site. D-PLEX100 was administered into incisions of abdominal surgical site in Yucatan miniature swine, which were followed for up to 6 months and compared to sham-control swine. The D-PLEX100 mass did not migrate from the incisional site, and there was no evidence for systemic toxicity or other safety concerns. Surgical incision sites, including the peritoneal surface, were fully healed at 6 months in all animals. Most of the D-PLEX100 mass was absorbed during the first 3 months, and by 6 months, D-PLEX100 was fully absorbed. Toxicokinetic evaluation revealed that doxycycline concentrations were evident at 30 minutes and persisted to 8 days (71 mg/kg) or at least 15 days (284 mg/kg) and were no longer present in plasma by day 29. This study supports the safety of D-PLEX100 and its favorable degradability profile. A clinical study is being performed to assess the safety and the efficacy of D-PLEX100 to prevent human abdominal SSIs.

Long-term performance and biocompatibility of a novel bioresorbable scaffold for peripheral arteries: A three-year pilot study in Yucatan miniswine.

AIMS: Peripheral arteries are constantly exposed to deformation (elongation, twisting, shortening, compression) making bioresorbable scaffolds (BRS) a potentially attractive therapeutic alternative to metallic stents. We conducted a long-term pilot preclinical study of a novel sirolimus-eluting BRS in peripheral arteries. METHODS AND RESULTS: Fourteen BRS were deployed in iliofemoral arteries of seven healthy Yucatan miniswine and examined with imaging, pharmacokinetic, histopathologic, and polymer degradation techniques at 0, 30, 90, 180 days, 1, 2, and 3.3 years. Angiographic late luminal loss remained unchanged at 30 and 180 days but significantly decreased from 1 to 3.3 years. optical coherence tomography (OCT) showed late increase in lumen area (1 year: 14.70 ± 3.58 mm2 , 2 years 22.04 ± 3.81 mm2 , and 3.3 years 23.45 ± 7.07 mm2 ; p < .05) primarily due to scaffold area enlargement between 1 and 3.3 years, while there was no difference in the percent area stenosis at all time points. Histologic evidence of scaffold degradation was observed starting at 2 years, with minimal inflammatory reaction. At 3.3 years, BRS struts were rarely discernible by OCT, confirmed by a nearly complete polymer degradation by molecular weight analysis. CONCLUSIONS: In this pilot study, novel sirolimus-eluting BRS showed promising acute and chronic performance in the iliofemoral arteries of Yucatan miniswine.

Evaluation of a Novel Spun Polytetrafluoroethylene Stent Graft in an Ovine External Iliac Artery Model.

PURPOSE: To evaluate the patency, cellular response, and thrombogenicity of a novel vascular stent graft. MATERIALS AND METHODS: Test stent grafts, incorporating luminal spun polytetrafluoroethylene and a nonpermeable fluoropolymer layer, and control stent grafts, constructed of permeable expanded polytetrafluoroethylene, were implanted in the external iliac arteries of 14 adult sheep with a median weight of 73.4 kg ranging from 60.6-86.8 kg for 30 (n = 4), 90 (n = 4), and 180 (n = 6) days. Angiographic patency and percent diameter stenosis (%DS) were assessed at termination. Excised stent grafts were fixed and stained for histopathologic analysis, including neointimal coverage (NC) assessment. RESULTS: Test and control device migration occurred in 1 animal, resulting in test device thrombosis. Both devices were excluded from analysis. Mean %DS in test and control implants was 4.6% and 8.2% (P = .563), 2.0% and 10.9% (P = .363), and 2.1% and 10.3% (P = .009) at 30, 90, and 180 days, respectively. Median NC scores at 30, 90, and 180 days were significantly lower in middle test device sections (P < .05). Proximal and distal test and control sections exhibited similar median NC scores at all time periods (P > .05). When present, test and control devices exhibited no neointimal detachment from the graft surface. Except for the migrated test device, no thrombus was observed. Transgraft cellular migration was absent in test devices but present in control devices with tissue accumulation around the stent struts. CONCLUSIONS: Test and control devices demonstrated excellent patency in an ovine model. Compared to the control, test devices exhibited significantly lower %DS values at 180 days and significantly lower mid-device NC scores at 30, 90, and 180 days.

Randomized Controlled Study of an Absorbable Vena Cava Filter in a Porcine Model.

PURPOSE: To compare the safety and efficacy of an absorbable inferior vena cava (IVC) filter and a benchmark IVC filter in a porcine model. MATERIALS AND METHODS: A randomized controlled Good Laboratory Practice study was performed in Domestic Yorkshire cross swine. Sixteen swine were implanted with an absorbable IVC filter (test device; Adient Medical, Pearland, Texas); 8 were implanted with a benchmark metal IVC filter (control device; Cook Medical, Bloomington, Indiana). All animals underwent rotational digital subtraction pulmonary angiography and cavography (anteroposterior and lateral) before filter deployment and 5 and 32 weeks after deployment. Terminal procedures and necropsy were performed at 32 weeks. The IVC, heart, lungs, liver, and kidneys were harvested at necropsy. The reported randomized controlled GLP animal study was conducted at Synchrony Labs, Durham, North Carolina. RESULTS: One animal died early in the test cohort of a recurring hemorrhage at the femoral access site resulting from a filter placement complication. All other animals remained clinically healthy throughout the study. No pulmonary embolism was detected at the 5- and 32-week follow-up visits. The absorbable filter subjects experienced less caval wall perforation (0% vs 100%) and thrombosis (0% vs 75%). The control device routinely perforated the IVC and occasionally produced collateral trauma to adjacent tissues (psoas muscle and aorta). The veins implanted with the absorbable filter were macroscopically indistinguishable from normal adjacent veins at 32 weeks except for the presence of radiopaque markers. Nontarget tissues showed no device-related changes. CONCLUSIONS: Implantation of the absorbable IVC filter in swine proved safe with no pulmonary emboli detected. There was complete to near-complete resorption of the filter polymer by 32 weeks with restoration of the normal appearance and structure of the IVC.

Functional remodeling of an electrospun polydimethylsiloxane-based polyether urethane external vein graft support device in an ovine model.

Saphenous vein graft (SVG) failure rates are unacceptably high, and external mechanical support may improve patency. We studied the histologic remodeling of a conformal, electrospun, polydimethylsiloxane-based polyether urethane external support device for SVGs and evaluated graft structural evolution in adult sheep to 2 years. All sheep (N = 19) survived to their intended timepoints, and angiography showed device-treated SVG geometric stability over time (30, 90, 180, 365, or 730 days), with an aggregated graft patency rate of 92%. There was minimal inflammation associated with the device material at all timepoints. By 180 days, treated SVG remodeling was characterized by minimal/nonprogressive intimal hyperplasia; polymer fragmentation and integration; as well as the development of a neointima, and a confluent endothelium. By 1-year, the graft developed a media-like layer by remodeling the neointima, and elastic fibers formed well-defined structures that subtended the neo-medial layer of the remodeled SVG. Immunohistochemistry showed that this neo-media was populated with smooth muscle cells, and the intima was lined with endothelial cells. These data suggest that treated SVGs were structurally remodeled by 180 days, and developed arterial-like features by 1 year, which continued to mature to 2 years. Device-treated SVGs remodeled into arterial-like conduits with stable long-term performance as arterial grafts in adult sheep.

Histology Strategies for Medical Implants and Interventional Device Studies.

Histology of medical devices poses a variety of unique challenges. Comprehensive histologic assessment of medical devices often requires spatial context and high-quality retention of the device-tissue interface. However, the composition of many medical devices is often not amenable to traditional paraffin embedding and thus alternative specialized methodologies such as hard resin embedding must be used. Hard resin embedding requires specialized laboratory technical expertise and equipment, and the fixation techniques and resin composition used markedly impact the feasibility of immunohistochemistry. For the continuity of spatial context during histologic evaluation, additional imaging methods such as macrophotography, radiography, micro-Computerized Tomography (microCT), or magnetic resonance imaging (MRI) can be used to guide sectioning and to complement histologic findings. Although standardized approaches are scarce for medical devices, important considerations specific to medical device histology are discussed, including general specimen preparation, special considerations for devices by organ system, and the challenges of immunohistochemistry. Histologic preparation of medical devices must be thoughtful, thorough, and tailored to achieve optimal histologic outcomes for complex, valuable, and often limited implant specimens.

Pathology Approaches to Determine Safety and Efficacy of Cardiac Ablation Catheters.

Cardiac electrophysiology utilizes nonimplantable, catheter-based devices for diagnosis and treatment of arrhythmias as well as electroanatomical mapping of cardiac chambers. Gross pathology and histopathological assessments in preclinical studies play critical roles in determining the safety and efficacy of cardiac ablation systems used to treat tachyarrhythmias. The pathologist must assess ablation sites, adjacent structures and organs, and downstream organs to characterize the effects of the ablation treatment and determine whether adverse local reactions, collateral injury, or downstream thromboembolism are present. Histopathological assessment serves as an adjunct to electroanatomical data in determining efficacy in preclinical studies. Histopathology is the standard in definitively demonstrating transmurality of ablation lesions, which is necessary for complete conduction block, as well as showing the linear or circumferential distribution of a contiguous, transmural ablation lesion necessary for electroanatomical isolation of entire target structures such as pulmonary veins and the cavotricuspid isthmus, which are involved in propagating certain arrhythmias. This article will detail gross and histological methods for the pathology assessment of preclinical studies evaluating the safety and/or efficacy of cardiac ablation catheter systems as well as discuss correlation of pathology data with other supporting evidence for safety and efficacy such as acute, electroanatomical data.

Pathology of Bioabsorbable Implants in Preclinical Studies.

Bioabsorbable implants can be advantageous for certain surgical tissue bioengineering applications and implant-assisted tissue repair. They offer the obvious benefits of nonpermanence and eventual restoration of the native tissue's biomechanical and immunological properties, while providing a structural scaffold for healing and a route for additional therapies (i.e., drug elution). They present unique developmental, imaging, and histopathological challenges in the conduct of preclinical animal studies and in interpretation of pathology data. The bioabsorption process is typically associated with a gradual decline (over months to years) in structural strength and integrity and may also be associated with cellular responses such as phagocytosis that may confound interpretation of efficacy and safety end points. Additionally, as these implants bioabsorb, they become increasingly difficult to isolate histologically and thus imaging modalities such as microCT become very valuable to determine the original location of the implants and to assess the remodeling response in tandem with histopathology. In this article, we will review different types of bioabsorbable implants and commonly used bioabsorbable materials; additionally, we will address some of the most common challenges and pitfalls confronting histologists and pathologists in collecting, handling, imaging, preparing tissues through histology, evaluating, and interpreting study data associated with bioabsorbable implants.

Safety of catheter-based radiofrequency renal denervation on branch renal arteries in a porcine model.

OBJECTIVES: We aimed to investigate the safety of radiofrequency (RF)-renal denervation (RDN) on branch renal arteries (RAs) in a porcine model. BACKGROUND: The efficacy of RF-RDN was enhanced by treatment of the branch RA, in addition to the main RA. However, there are concerns regarding the safety of RF-RDN on branch RA because of their smaller diameter and proximity to the kidney. METHODS: RF was delivered to 24 RA from 12 swine. A total of 8 RA from 4 swine were untreated. Treated RA were examined by angiography and histopathology at 7, 30, and 90 days. Serum creatinine concentration, biophysical parameters during RF delivery, and renal norepinephrine concentration were also assessed. RESULTS: Angiography revealed minimal late lumen loss and diameter stenosis in the main and branch RA at any time point. There was no change in serum creatinine after RF-RDN. Histopathologically, no augmentation of medial damage or neointimal formation was found in branch RA compared with main RA. No or minimal damage to surrounding tissues including the kidneys, ureters, lymph nodes, and muscles was observed at any time point in both the main and branch RA. Equivalent electrode temperature in the main and branch RA was achieved by automatic adjustment of output power by the generator. The renal norepinephrine concentration was significantly lower in the treated group compared with the untreated group. CONCLUSIONS: RF-RDN on branch RA was safe in a porcine model, with stenosis-free healing of treated arteries and negligible kidney damage at 7, 30, and 90 days.

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.