Transarterial aortic valve replacement with a self expanding stent in pigs

Addressing Cardiovascular Toxicity Risk of Electronic Nicotine Delivery Systems in the Twenty-First Century: "What Are the Tools Needed for the Job?" and "Do We Have Them?"

Cigarette smoking is positively and robustly associated with cardiovascular disease (CVD), including hypertension, atherosclerosis, cardiac arrhythmias, stroke, thromboembolism, myocardial infarctions, and heart failure. However, after more than a decade of ENDS presence in the U.S. marketplace, uncertainty persists regarding the long-term health consequences of ENDS use for CVD. New approach methods (NAMs) in the field of toxicology are being developed to enhance rapid prediction of human health hazards. Recent technical advances can now consider impact of biological factors such as sex and race/ethnicity, permitting application of NAMs findings to health equity and environmental justice issues. This has been the case for hazard assessments of drugs and environmental chemicals in areas such as cardiovascular, respiratory, and developmental toxicity. Despite these advances, a shortage of widely accepted methodologies to predict the impact of ENDS use on human health slows the application of regulatory oversight and the protection of public health. Minimizing the time between the emergence of risk (e.g., ENDS use) and the administration of well-founded regulatory policy requires thoughtful consideration of the currently available sources of data, their applicability to the prediction of health outcomes, and whether these available data streams are enough to support an actionable decision. This challenge forms the basis of this white paper on how best to reveal potential toxicities of ENDS use in the human cardiovascular system-a primary target of conventional tobacco smoking. We identify current approaches used to evaluate the impacts of tobacco on cardiovascular health, in particular emerging techniques that replace, reduce, and refine slower and more costly animal models with NAMs platforms that can be applied to tobacco regulatory science. The limitations of these emerging platforms are addressed, and systems biology approaches to close the knowledge gap between traditional models and NAMs are proposed. It is hoped that these suggestions and their adoption within the greater scientific community will result in fresh data streams that will support and enhance the scientific evaluation and subsequent decision-making of tobacco regulatory agencies worldwide.

Dos and don'ts in large animal models of aortic insufficiency

Aortic insufficiency caused by paravalvular leakage (PVL) is one of the most feared complications following transcatheter aortic valve replacement (TAVI) in patients. Domestic pigs (Sus scrofa domestica) are a popular large animal model to study such conditions and develop novel diagnostic and therapeutic techniques. However, the models based on prosthetic valve implantation are time intensive, costly, and often hamper further hemodynamic measurements such as PV loop and 4D MRI flow by causing implantation-related wall motion abnormalities and degradation of MR image quality. This study describes in detail, the establishment of a minimally invasive porcine model suitable to study the effects of mild-to-moderate “paravalvular“ aortic regurgitation on left ventricular (LV) performance and blood flow patterns, particularly under the influence of altered afterload, preload, inotropic state, and heart rate. Six domestic pigs (Swiss large white, female, 60–70 kg of body weight) were used to establish this model. The defects on the hinge point of aortic leaflets and annulus were created percutaneously by the pierce-and-dilate technique either in the right coronary cusp (RCC) or in the non-coronary cusp (NCC). The hemodynamic changes as well as LV performance were recorded by PV loop measurements, while blood flow patterns were assessed by 4D MRI. LV performance was additionally challenged by pharmaceutically altering cardiac inotropy, chronotropy, and afterload. The presented work aims to elaborate the dos and don'ts in porcine models of aortic insufficiency and intends to steepen the learning curve for researchers planning to use this or similar models by giving valuable insights ranging from animal selection to vascular access choices, placement of PV Loop catheter, improvement of PV loop data acquisition and post-processing and finally the induction of paravalvular regurgitation of the aortic valve by a standardized and reproducible balloon induced defect in a precisely targeted region of the aortic valve.

The History of Transcatheter Aortic Valve Implantation (TAVI)-A Personal View Over 25 Years of development

In the early 1990s, the idea of Transcatheter Aortic Valve Implantation (TAVI) emerged from clinicians by the insight that the long-term hemodynamic and clinical results of aortic balloon valvuloplasty to treat aortic stenonosis were not satisfying. Thus, Anderson and Cribier developed the balloon-expandable and Figulla and Laborde the self-expendable TAVI systems. Sceptical views by the surgical colleagues and the industry delayed the rapid development of this disruptive new therapy until 2002, when Alain Cribier demonstrated for the first time the proof of his concept. Bulky devices and paravalvular leakages in patients treated in terms of compassionate care resulted in high mortality rates. From 2005 onwards, the treatment of patients not at highest risk using smoother devices in clinical trials could demonstrate that the technology was equivalent to surgical aortic valve replacement. The transapical access route initiated the heart team approach with the surgical colleagues, however, this access route is presently expiring due to its greater trauma. The need to treat also aortic regurgitation is addressed by the "clipping technology" of JenaValve™. Ongoing clinical trials investigate an extended indication for TAVI at an earlier stage of aortic stenosis, or in reduced ejection fraction, and just demonstrated the safety and efficiency even in low surgical risk patients.

The transcatheter valve technology pipeline for treatment of adult valvular heart disease

The transcatheter valve technology pipeline has started as simple balloon valvuloplasty for the treatment of stenotic heart valves and evolved since the year 2000 to either repair or replace heart valves percutaneously with multiple devices. In this review, the present technology and its application are illuminated and a glimpse into the near future is dared from a physician's perspective.

Two- and three-dimensional transoesophageal echocardiography in large swine used as model for transcatheter heart valve therapies: standard planes and values

OBJECTIVES

Swine models are widely used to develop new techniques and materials for the treatment of heart valve disease like aortic valve and mitral valve transcatheter interventions and to train physicians in these techniques. Transoesophageal echocardiography (TOE) is crucial in these models. We defined standard planes of 2D and 3D TOE in healthy pigs undergoing transcatheter heart valve interventions.

METHODS

Twenty healthy pigs (weight 56-106 kg) underwent different mitral and aortic valve interventions (transcatheter aortic valve implantations, implantations of a mitral band, bicuspidization of the aortic valve, trans-septal punctures). For image guidance of the procedures, an adult TOE probe was introduced under direct vision in the oesophagus. Before the procedure itself was performed, a standardized protocol was used to determine normal values for anatomical and functional echocardiographic parameters.

RESULTS

Positioning of the probe was possible in all animals and ideal when achieving a distance from the front teeth (incisors) of 40-60 cm. Anteflexion and lateroflexion of the probe was necessary to achieve optimal imaging quality. 2D visualization of all relevant cardiac structures was possible. The aortic annulus diameter was 24.1 ± 2.5 mm, the sinus of valsalva diameter was 30.6 ± 4 mm and the sinotubular junction diameter was 25.2 ± 4 mm. The ascending aorta had a diameter of 24 ± 4 mm and the descending aorta a diameter of 16 ± 5 mm. The mitral valve anterior-posterior diameter was 31.8 ± 4 mm and the commissure to commissure diameter was 40.5 ± 5 mm resulting in a mitral valve area of 10.7 ± 1.5 cm(2). 3D visualization was possible for the aortic and the mitral valve. None of the animals showed any pathology except one that had a dilated left ventricle and moderate mitral valve insufficiency. Left and right ventricular dimensions and the anatomy of the aortic-, mitral-, tricuspid and pulmonary valve as well as of the aorta were comparable with those of the human anatomy.

CONCLUSIONS

2D and 3D TOE can be routinely applied as image guidance in pigs used as a model for the development and training of new techniques to treat heart valve disease.

Self-Expanding Stent and Delivery System for Aortic Valve Replacement

Currently, aortic valve replacement procedures require a sternotomy and use of cardiopulmonary bypass (CPB) to arrest the heart and provide a bloodless field in which to operate. A less invasive alternative to open heart surgery is transapical or transcatheter aortic valve replacement (TAVR), already emerging as a feasible treatment for patients with high surgical risk. The bioprosthetic valves are delivered via catheters using transarterial or transapical approaches and are implanted within diseased aortic valves. This paper reports the development of a new self-expanding stent for minimally invasive aortic valve replacement and its delivery device for the transapical approach under real-time magnetic resonance imaging (MRI) guidance. Made of nitinol, the new stent is designed to implant and embed a commercially available bioprosthetic aortic valve in aortic root. An MRI passive marker was affixed onto the stent and an MRI active marker to the delivery device. These capabilities were tested in ex vivo and in vivo experiments. Radial resistive force, chronic outward force, and the integrity of bioprosthesis on stent were measured through custom design dedicated test equipment. In vivo experimental evaluation was done using a porcine large animal model. Both ex vivo and in vivo experiment results indicate that the self-expanding stent provides adequate reinforcement of the bioprosthetic aortic valve and it is easier to implant the valve in the correct position. The orientation and positioning of the implanted valve is more precise and predictable with the help of the passive marker on stent and the active marker on delivery device. The new self-expanding nitinol stent was designed to exert a constant radial force and, therefore, a better fixation of the prosthesis in the aorta, which would result in better preservation of long-term heart function. The passive marker affixed on the stent and active marker embedded in the delivery devices helps to achieve precise orientation and positioning of the stent under MRI guidance. The design allows the stent to be retracted in the delivery device with a snaring catheter if necessary. Histopathology reports reveal that the stent is biocompatible and fully functional. All the stented bioprosthesis appeared to be properly seated in the aortic root.

Percutaneous aortic valve replacement. Part 3: Balloon counterpulsation of a novel temporary aortic valve

A previously published two-part study described an engineering design of a percutaneous aortic valve (PAV) replacement system, which utilizes a novel temporary aortic valve (TAV) support to improve procedural outcomes and safety. Conceptually, this investigational approach can promote accurate PAV placement, procedural hemodynamic stability, smaller catheter delivery system, reduction in PAV regurgitation, reduction in conduction and vascular complications. The balloon TAV can potentially facilitate the PAV replacement procedure by serving as the patient's surrogate aortic valve while the native valve is pretreated and replaced. The original TAV is designed to function with an effective aortic stenosis and insufficiency in moderate ranges, which lessens from the patient's more critical valve condition, should be well tolerated when the native valve becomes nonfunctional during the replacement process. Further optimization of the TAV's hemodynamic profile could further improve the system's overall performance and enhance the realization of a truly minimally invasive, cath lab-based PAV replacement procedure comparable to that of percutaneous coronary intervention. This study explores design permutations from the original published TAV, including varying the number of balloons and adding balloon counterpulsations, to improve upon its hemodynamic profile to better serve as the patient's surrogate valve and the overall PAV replacement procedure.

Percutaneous aortic valve replacement (part 2): Miniaturization of the delivery system based on the novel temporary valve technology

Percutaneous aortic valve replacement remains an investigational procedure challenged by multiple key issues. In part 1 of this 2 part series, the issue of precise placement of the percutaneous aortic valve was addressed by a novel design of a delivery and deployment system. The design and use of a hemodynamics supporting temporary aortic valve was highlighted, which can stabilize the hemodynamic and local flow conditions for a more controlled and precise placement of the percutaneous aortic valve. In this part 2 study, the issue of vascular access complications is addressed. The current large French size catheter systems can cause significant vascular injuries; the catheter diameter must be reduced for this procedure to be safe and routine. The hemodynamic support of the temporary aortic valve system allows for the formulation of a novel approach to reduce the catheter-delivery system. The miniaturization strategies consist of pretreatment of the aortic annulus and assembly of the percutaneous aortic valve apparatus in a piecemeal fashion of smaller components. Each component would, therefore, require a smaller diameter delivery catheter. The combined strategies as described in this 2 part series aim at realizing the percutaneous aortic valve replacement as a routine, fully percutaneous and cath lab-based.

[Transcatheter-based aortic valve implantation. Present and future technologies]

The calcified aortic stenosis is the dominating valve disease. Patients affected are most common elderly people in the 8th or 9th decade of their life who often show associated comorbidities like reduced left ventricular function, impaired renal function, pulmonary hypertension, and further diseases (diabetes mellitus, stroke, chronic obstructive pulmonary disease). In many cases perioperative morbidity and mortality are too high for surgical valve replacement and patients are rejected. Nevertheless, prognosis of aortic stenosis is worse, if the typical symptoms like dyspnea on exertion, syncope, and angina occur. The transcatheter aortic valve implantation is an alternative treatment for this particular group of patients. The aortic valve bioprosthesis consists of a balloon-expandable stent or a self-expandable frame, in which a valve of bovine or porcine pericardium is incorporated. The implantation is performed by retrograde access via the femoral artery; the balloon-expandable prosthesis can also be implanted by transapical approach. Alternatively, the subclavian artery is chosen for access. More frequently, the implantation is performed in analgosedation with the patient awake that favors the transfemoral approach. A further reduction of the available prosthesis and new types of valves which are under current experimental tests and clinical evaluation contribute to this development.

Catheter-based modification of heart valve diseases: from experimental to clinical application

Efforts to modify cardiac valve defects using catheter-based techniques are increasing at the present time. We present observations on cardiac valve morphology and disease and review the progress being made to address valve defects with these innovative methods. Some new procedures developed through animal experimentation have already been put to use in clinical practice, but the newness of these techniques and the small number of cases in which they have been applied to date precludes an evaluation of their long-term durability. Although at the present time cardiac surgery remains the standard for treating most cases of valve disease, in certain situations a catheter-based treatment might provide a reasonable alternative, even if only temporary, especially for individuals with serious disease who are not suitable candidates for surgery.

Percutaneous heart valve replacement: histology and calcification characteristics of biological valved stents in juvenile sheep

INTRODUCTION

Percutaneous techniques to replace the pulmonary valve are emerging as an alternative to congenital cardiac surgical procedures. Promising experimental and early clinical results have been reported so far, focusing on technical feasibility and valved stent function. The present study aimed to describe the micropathology after experimental percutaneous valve replacement.

METHODS

Self-expanding nitinol stents carrying a valved bovine jugular vein were transfemorally implanted into the pulmonary position of nine sheep. After 3 months of survival, macro- and micropathological examinations were carried out using standard staining techniques and immunohistochemistry. Additionally, calcification characteristics were determined by X-ray examinations and von Kossa stainings.

RESULTS

Six of nine animals survived the 3-month study time with good angiographic and echocardiographic function. All valves were grossly functional at the time of explantation. Slight fibrous overgrowth was seen at the inflow portions of two valved stents. No cuspal perforations or intracuspal hematomas were observed. Light microscopy proved the absence of cellular inflammatory infiltrates in any tissue samples. The myocardium directly proximal to the stent appeared structurally normal without calcification. The overall structure of the native pulmonary artery was well preserved with few mineral deposits spread diffusely throughout the wall distal to the stent. Massive calcification appeared in the bovine jugular-vein wall together with increased numbers of T lymphocytes. Neither calcific deposits in the cusps nor extrinsic mineralization was noted.

CONCLUSION

For the first time, micropathologic evaluation of percutaneously implanted heart valves is described. The results demonstrate that calcification of valved stents occurs in the wall portions without affecting the cusps. The cardiac structures in the vicinity had normal histology without inflammation.

Percutaneous Implantation of the CoreValve Self-Expanding Valve Prosthesis in High-Risk Patients With Aortic Valve Disease

BACKGROUND

The morbidity and mortality of surgical aortic valve replacement are increased in elderly patients with multiple high-risk comorbid conditions. Therefore, a prospective, single-center, nonrandomized study was performed in high-risk patients with aortic valve disease to evaluate the feasibility and safety of percutaneous implantation of a novel self-expanding aortic valve bioprosthesis (CoreValve).

METHODS AND RESULTS

Symptomatic high-risk patients with an aortic valve area <1 cm2 were considered for enrollment. CoreValve implantation was performed under general anesthesia with extracorporeal support using the retrograde approach. Clinical follow-up and transthoracic echocardiography were performed after the procedure and at days 15 and 30 after device implantation to evaluate short-term patient and device outcomes. A total of 25 patients with symptomatic aortic valve stenosis (mean gradient before implantation, 44.2+/-10.8 mm Hg) and multiple comorbidities (median logistic EuroScore, 11.0%) were enrolled. Device success and procedural success were achieved in 22 (88%) and 21 (84%) patients, respectively. Successful device implantation resulted in a marked reduction in the aortic valve gradients (mean gradient after implantation, 12.4+/-3.0 mm Hg; P<0.0001). The mean aortic regurgitation grade was unchanged. Major in-hospital cardiovascular and cerebral events occurred in 8 patients (32%), including mortality in 5 patients (20%). Among 18 patients with device success surviving to discharge, no adverse events occurred within 30 days after leaving the hospital.

CONCLUSIONS

Percutaneous implantation of the self-expanding CoreValve aortic valve prosthesis in high-risk patients with aortic stenosis with or without aortic regurgitation is feasible and, when successful, results in marked hemodynamic and clinical improvement.

Transapical Aortic Valve Implantation: An Animal Feasibility Study

BACKGROUND

Percutaneous aortic valve implantation has recently been performed in nonsurgical patients with severe aortic stenosis. Retrograde valve delivery has been problematic because of the size of the delivery system and concomitant peripheral vascular disease. We investigated a minimally invasive approach through the left ventricular apex for antegrade placement of a device-deliverable valve.

METHODS

Transapical aortic valve implantation was performed using a 23-mm equine valve mounted on a stainless steel stent in 24 swine (weight range, 35 to 45 kg). A limited or full sternotomy approach was used to access the apex of the heart. The crimped valve was introduced through a sheath in the left ventricular apex. Fluoroscopy and echocardiography were used for guidance. Deployments were performed on the beating heart either with ventricular unloading using femoral extracorporeal circulation or rapid ventricular pacing.

RESULTS

All valves were successfully delivered at the selected target site with acceptable visualization of the noncalcified aortic annulus. Valve migration occurred during eight deployments (two distal and six retrograde) secondary to persistent cardiac output, unfavorable annular anatomy, and dislodgement by the delivery catheter. Exact positioning of the nonmigrated valves at the aortic annulus was examined by necropsy of all animals at the end of the procedures. Paravalvular leak was noted in 14 of 18 (77.8%) valves remaining in situ.

CONCLUSIONS

The transapical approach was used for the successful antegrade placement of a stented valve, obviating the technical problems associated with a large delivery system transiting the peripheral vascular system. Stent design contributing to paravalvular leak remains problematic.

[Percutaneous cardiac valve replacement: a review]

Surgery is no longer the only technique to replace a cardiac valve. New percutaneous procedures allow aortic or pulmonary valve implantation. Even if the feasibility of these procedures has been proved, cases reported are very rare and selected. This emergent technology is still at an early stage of development and new prospective studies will be necessary to evaluate these procedures correctly before concluding their clinical benefit. At this time surgery remains the gold standard in terms of cardiac valve replacement.

Percutaneous transcatheter one-step mechanical aortic disc valve prosthesis implantation: a preliminary feasibility study in swine

PURPOSE

To evaluate the feasibility of one-step implantation of a new type of stent-based mechanical aortic disc valve prosthesis (MADVP) above and across the native aortic valve and its short-term function in swine with both functional and dysfunctional native valves.

METHODS

The MADVP consisted of a folding disc valve made of silicone elastomer attached to either a nitinol Z-stent (Z model) or a nitinol cross-braided stent (SX model). Implantation of 10 MADVPs (6 Z and 4 SX models) was attempted in 10 swine: 4 (2 Z and 2 SX models) with a functional native valve and 6 (4 Z and 2 SX models) with aortic regurgitation induced either by intentional valve injury or by MADVP placement across the native valve. MADVP function was observed for up to 3 hr after implantation.

RESULTS

MADVP implantation was successful in 9 swine. One animal died of induced massive regurgitation prior to implantation. Four MADVPs implanted above functioning native valves exhibited good function. In 5 swine with regurgitation, MADVP implantation corrected the induced native valve dysfunction and the device's continuous good function was observed in 4 animals. One MADVP (SX model) placed across native valve gradually migrated into the left ventricle.

CONCLUSION

The tested MADVP can be implanted above and across the native valve in a one-step procedure and can replace the function of the regurgitating native valve. Further technical development and testing are warranted, preferably with a manufactured MADVP.

Percutaneous therapies for valvular heart disease

Balloon valvuloplasty has been in clinical use for over 20 years, but the prospect of repairing and replacing cardiac valves via catheter-based techniques represents a truly recent development. This review introduces evolving technologies and their relevance to cardiovascular pathologists.

Percutaneous Valve Replacement: Significance of Different Delivery Systems In Vitro and In Vivo

BACKGROUND AND PURPOSE

Percutaneous heart valve replacement is an exciting growing field in cardiovascular medicine yet still with some major problems. Only sophisticated improvement of the instruments could make it a real alternative to conventional surgery. Therefore, the aim of this study was to evaluate different delivery devices for percutaneous heart valve replacement in vitro and in vivo.

METHODS

A catheter prototype designed by our group, and two commercially available devices for the delivery of esophageal stents and aortic endoprostheses, were tested. After in vitro experiments, an ovine animal model of transfemoral pulmonary valve implantation was established using biological valved self-expanding stents. Only the delivery device for aortic endografts (Medtronic, Talent, Santa Rosa, CA, USA) allowed fast in vitro procedures without material fatigue. This device was chosen for the in vivo tests.

RESULTS

Technical success was achieved in 9 of 10 animals (90%). One animal died after perforation of the ventricular wall. Orthotopic pulmonary placement was performed in 6 animals and intentional supravalvular valved stent placement in 3 animals.

CONCLUSIONS

An adequate in vitro model for this evolving field of interventional heart valve replacement is presented. Furthermore, the present study pinpoints the key characteristics that are mandatory for a delivery system in percutaneous pulmonary valve implantation. With regard to the delivery device's ductility observed during this "venous" study, an approach to transfemoral aortic valve implantation seems feasible.

Advances in Experimental Percutaneous Pulmonary Valve Replacement

BACKGROUND

Percutaneous pulmonary valve implantation is emerging as an alternative and additional option for a successful surgical scheme. To date, these procedures are performed by the balloon-in-balloon technique. The use of self-expanding stents for percutaneous valve replacement is assumed to improve preservation of the valve in its folded condition in the application device and the valve's long-term functioning. Therefore, initial experience with the development of a completely percutaneous transfemoral technique for pulmonary valve implantation using a self-expanding valved stent is described.

METHODS

Bovine jugular xenografts were sutured into nitinol stents, and functional in vitro tests of valved stents were carried out. Transfemoral implantation in pulmonary position was acutely evaluated in 6 sheep weighing 22 to 29 kg. Radiologic evaluation was performed by angiography and multislice computed tomography (MSCT) scan. In addition, pathoanatomical studies were performed.

RESULTS

Exact implantation in pulmonary valve position was achieved in 5 of 6 sheep, with 1 early stent migration. Another sheep died before stent placement owing to perforation of the right ventricle by the delivery system. Orthotopic pulmonary valved stent position was depicted by MSCT in all other sheep (n = 4). The peak-to-peak transvalvular gradient was 8.2 +/- 3.9 mm Hg (n = 5). Postmortem examination revealed intact stent valves with no adherent clots. No macroscopic damage of the pulmonary artery was noted, whereas minor hematoma of the right atrium and the right ventricular outflow tract were observed in 2 hearts.

CONCLUSIONS

This acute study demonstrates that memory nitinol valved stents can be optimally deployed in the pulmonary position through the groin in sheep.

Percutaneous aortic valve replacement and mitral valve repair

For mitral regurgitation and aortic valve disease warranting replacement, the surgical approach has been the mainstay therapy since the 1960s. Technological advances have provided potentially less invasive alternatives to surgery. Novel catheter-based techniques include aortic valve replacement with a valved stent, and devices aimed at reconfiguring the annulus or approximating a portion of the leaflets for mitral regurgitation. The main considerations regarding aortic valved stents include device anchoring and orientation, potential restriction of coronary flow, optimal method of delivery, ideal leaflet material, stent characteristics, and valve durability. The catheter-based approaches to mitral regurgitation are undergoing further experimental and clinical evaluations, and its success will be partially dependent on a thorough understanding of the underlying valvular pathology. Patient selection will be a critical component in the long-term efficacy of these new therapies. Close collaboration among the cardiovascular specialists and biomedical engineers will enable the development of safe and effective devices.

Which strategy for a protein crystallization project?

The three-dimensional, atomic-resolution protein structures produced by X-ray crystallography over the past 50+ years have led to tremendous chemical understanding of fundamental biochemical processes. The pace of discovery in protein crystallography has increased greatly with advances in molecular biology, crystallization techniques, cryocrystallography, area detectors, synchrotrons and computing. While the methods used to produce single, well-ordered crystals have also evolved over the years in response to increased understanding and advancing technology, crystallization strategies continue to be rooted in trial-and-error approaches. This review summarizes the current approaches in protein crystallization and surveys the first results to emerge from the structural genomics efforts.