Development and initial experimental evaluation of a prosthetic aortic valve for transcatheter placement. Work in progress

How Transcatheter Aortic Valve Implantation (TAVI) Was Born: The Struggle for a New Invention

This story is about the invention of transcatheter aortic valve implantation (TAVI), and the people who transformed it from a concept and primitive device to a breakthrough lifesaving treatment for hundreds of thousands of patients with aortic valve stenosis. It is an inspirational example of a new disruptive technology that began with an idea most dismissed. The story describes the ups and downs from idea, design, construction, animal testing, proof-of-concept, scientific publication hurdles, a patent, license agreement, cooperation with several companies, fighting in patent courts in Europe and USA and finally how multinational companies financially bypassed the inventor. It is also a story about the struggles and battles the inventor experienced when injected into a world of lawyers and patent fights. I hope my personal story and journey can provide an inspiration and word of caution for new inventors.

Biomaterials in Valvular Heart Diseases

Valvular heart disease (VHD) occurs as the result of valvular malfunction, which can greatly reduce patient's quality of life and if left untreated may lead to death. Different treatment regiments are available for management of this defect, which can be helpful in reducing the symptoms. The global commitment to reduce VHD-related mortality rates has enhanced the need for new therapeutic approaches. During the past decade, development of innovative pharmacological and surgical approaches have dramatically improved the quality of life for VHD patients, yet the search for low cost, more effective, and less invasive approaches is ongoing. The gold standard approach for VHD management is to replace or repair the injured valvular tissue with natural or synthetic biomaterials. Application of these biomaterials for cardiac valve regeneration and repair holds a great promise for treatment of this type of heart disease. The focus of the present review is the current use of different types of biomaterials in treatment of valvular heart diseases.

Bioprinting of radiopaque constructs for tissue engineering and understanding degradation behavior by use of Micro-CT

Bioprinting has emerged as a potential technique to fabricate tissue engineering constructs and in vitro models directly using living cells as a raw material for fabrication, conforming to the heterogeneity and architectural complexity of the tissues. In several of tissue engineering and in vitro disease modelling or surgical planning applications, it is desirable to have radiopaque constructs for monitoring and evaluation. In the present work, enhanced radiopaque constructs are generated by substituting Calcium ions with Barium ions for crosslinking of alginate hydrogels. The constructs are characterized for their structural integrity and followed by cell culture studies to evaluate their biocompatibility. This was followed by the radiopacity evaluation. The radiological images obtained by micro-CT technique was further applied to investigate the degradation behavior of the scaffolds. In conclusion, it is observed that barium crosslinking can provide a convenient means to obtain radiopaque constructs with potential for multi-faceted applications.

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.

Development of an algorithm to plan and simulate a new interventional procedure

OBJECTIVES

The number of implanted biological valves for treatment of valvular heart disease is growing and a percentage of these patients will eventually undergo a transcatheter valve-in-valve (ViV) procedure. Some of these patients will represent challenging cases. The aim of this study was to develop a feasible algorithm to plan and in vitro simulate a new interventional procedure to improve patient outcome.

METHODS

In addition to standard diagnostic routine, our algorithm includes 3D printing of the annulus, hydrodynamic measurements and high-speed analysis of leaflet kinematics after simulation of the procedure in different prosthesis positions as well as X-ray imaging of the most suitable valve position to create a 'blueprint' for the patient procedure.

RESULTS

This algorithm was developed for a patient with a degenerated Perceval aortic sutureless prosthesis requiring a ViV procedure. Different ViV procedures were assessed in the algorithm and based on these results the best option for the patient was chosen. The actual procedure went exactly as planned with help of this algorithm.

CONCLUSIONS

Here we have developed a new technically feasible algorithm simulating important aspects of a novel interventional procedure prior to the actual procedure. This algorithm can be applied to virtually all patients requiring a novel interventional procedure to help identify risks and find optimal parameters for prosthesis selection and placement in order to maximize safety for the patient.

Transcatheter aortic valve replacement: historical perspectives, current evidence, and future directions

Severe aortic stenosis (AS) results in considerable morbidity and mortality without aortic valve replacement and is expected to increase in prevalence with the aging population. Because AS primarily affects the elderly, many patients with comorbidities are poor candidates for surgical aortic valve replacement (SAVR) and may not be referred. Transcatheter aortic valve replacement (TAVR) has emerged as transformative technology for the management of AS over the past decade. Randomized trials have established the safety and efficacy of TAVR with improved mortality and quality of life compared with medical therapy in inoperable patients, while demonstrating noninferiority and even superiority to SAVR among high-risk operative candidates. However, early studies demonstrated an early penalty of stroke and vascular complications with TAVR as well as increased paravalvular leak as compared with SAVR. Two device platforms have been evaluated and approved for use in the United States: the Edwards SAPIEN and the Medtronic CoreValve. Early studies also suggest cost-effectiveness for TAVR. Ongoing studies are evaluating new iterations of the aforementioned TAVR devices, novel device designs, and applications of TAVR in expanded populations of patients including those with lower risk profiles as well as those with comorbidities that were excluded from early clinical trials. Future improvements in TAVR technology will likely reduce periprocedural and long-term complications. Further studies are needed to confirm device durability over long-term follow-up and explore the applicability of TAVR to broader AS patient populations.

Percutaneous heart valves; past, present and future

Percutaneous heart valves provide a promising future for patients refused surgery on the grounds of significant technical challenges or high risk for complications. Since the first human intervention more than 10 years ago, over 50 different types of valves have been developed. The CoreValve and Edwards SAPIEN valves have both experienced clinical trials and the latter has gained FDA approval for implantation in patients considered inoperable. Current complications, such as major vascular bleeding and stroke, prevent these valves from being commonly deployed in patients considered operable in conventional surgery. This review focuses on the past and present achievements of these valves and highlights the design considerations required to progress development further. It is envisaged that, with continued improvement in valve design and with increased clinical and engineering experience, percutaneous heart valve replacement may one day be a viable option for lower-risk operable patients.

Quantification of structural compliance of aged human and porcine aortic root tissues

The structural compliance of the aortic root has a significant implication for valve procedures such as transcatheter aortic valve implantation and valve-sparing aortic root replacement. However, a detailed quantification of human aortic root structural compliance, particularly in different regions, has been incomplete. In this study, the structural properties of human aortic roots (81 ± 8.74 years, n = 10) were characterized and compared with those of porcine ones (6-9 months, n = 10) using a vessel pressure-inflation test. The test involved tracking three-dimensional deformation of the markers affixed on the different surface regions of the aortic roots, including the three sinuses: the noncoronary sinus (NCS), the left-coronary sinus (LCS), and the right-coronary sinus (RCS), and at three regions along the longitudinal direction of each sinus: the upper sinus (US), the middle sinus (MS), and the lower sinus (LS), and the ascending aorta (AA) region above the NCS. We found that tissue stiffness in physiological pressure range was similar among the three human sinuses. A variation in regional structural stiffness of human aorta was observed. In the circumferential direction, the LS regions were the stiffest in the LCS and RCS, whereas NCS had relatively uniform stiffness. In the longitudinal direction, the human AA regions were more compliant than all sinuses. There was a significant difference in tissue stiffness between human and porcine aortic tissues, suggesting that the mechanical properties of porcine tissues may not be analogous to aged human ones.

Quantification of biomechanical interaction of transcatheter aortic valve stent deployed in porcine and ovine hearts

Success of the deployment and function in transcatheter aortic valve replacement is heavily reliant on the tissue-stent interaction. The present study quantified important tissue-stent contact variables of self-expanding transcatheter aortic valve stents when deployed into ovine and porcine aortic roots, such as the stent radial expansion force, stent pullout force, the annulus deformation response and the coefficient of friction on the tissue-stent contact interface. Braided Nitinol stents were developed, tested to determine stent crimped diameter vs. stent radial force from a stent crimp experiment, and deployed in vitro to quantify stent pullout, aortic annulus deformation, and the coefficient of friction between the stent and the aortic tissue from an aortic root-stent interaction experiment. The results indicated that when crimped at body temperature from 26 mm to 19, 21 and 23 mm stent radial forces were approximately 30-40% higher than those crimped at room temperature. Coefficients of friction leveled to approximately 0.10 ± 0.01 as stent wire diameter increased and annulus size decreased from 23 to 19 mm. Regardless of aortic annulus size and species tested, it appeared that a minimum of about 2.5 mm in annular dilatation, caused by about 60 N of radial force from stent expansion, was needed to anchor the stent against a pullout into the left ventricle. The study of the contact biomechanics in animal aortic tissues may help us better understand characteristics of tissue-stent interactions and quantify the baseline responses of non-calcified aortic tissues.

Development of transcatheter aortic valve implantation (TAVI): a 20-year odyssey

The development of transcatheter aortic valve implantation (TAVI) by our group has been a 20-year odyssey. In 1993, postmortem studies validated the concept of intravalvular stenting in calcific aortic stenosis. The first prototypes of balloon-expandable valves were tested in an animal model in 2000. The first-in-man implantation was performed in Rouen in 2002, rapidly followed by two prospective series in compassionate cases in our centre. TAVI took flight in 2004 in the hands of Edwards Lifesciences, with major improvements in devices and approaches. At the same time, the self-expanding CoreValve was launched. Thousands of high-surgical-risk patients were enrolled in feasibility studies, leading to the Conformité Européenne (CE) mark being granted in 2007 for the two devices. A number of postmarketing registries have shown dramatic improvements in procedural and midterm results and decreased complication rates, with more experience and improved technology. The results of the randomized PARTNER study in the USA recently confirmed the important place of TAVI in non-operable and high-surgical-risk patients. To date, more than 50,000 patients have benefited from TAVI worldwide (2300 patients in 33 centres in France in 2011) and the number is consistently increasing. An optimal multidisciplinary collaboration and formally trained experienced physicians are the keys to success. An extension of indications to lower-risk patients might be expected in the coming years but should be cautiously investigated. Ten years after the first-in-man case, TAVI is here to stay and the future is promising.

Significant differences in the material properties between aged human and porcine aortic tissues

OBJECTIVE

Currently, percutaneous aortic valve (PAV) replacement devices are being investigated to treat aortic stenosis in patients deemed to be of too high a risk for conventional open-chest surgery. Successful PAV deployment and function are heavily reliant on the tissue-stent interaction. Many PAV feasibility trials have been conducted with porcine models under the assumption that these tissues are similar to human; however, this assumption may not be valid. The goal of this study was to characterize and compare the biomechanical properties of aged human and porcine aortic tissues.

METHODS

The biaxial mechanical properties of the left coronary sinus, right coronary sinus, non-coronary sinus, and ascending aorta of eight aged human (90.1 ± 6.8 years) and 10 porcine (6-9 months) hearts were quantified. Tissue structure was analyzed via histological techniques.

RESULTS

Aged human aortic tissues were significantly stiffer than the corresponding porcine tissues in both the circumferential and longitudinal directions (p < 0.001). In addition, the nearly linear stress-strain behavior of the porcine tissues, compared with the highly nonlinear response of the human tissues at a low strain range, suggested structural differences between the aortic tissues from these two species. Histological analysis revealed that porcine samples were composed of more elastin and less collagen fibers than the respective human samples.

CONCLUSIONS

Significant material and structural differences were observed between the human and porcine tissues, which raise questions on the validity of using porcine models to investigate the biomechanics involved in PAV intervention.

History of percutaneous aortic valve prosthesis

This review describes the development of percutaneous transluminal catheter-mounted heart valves for permanent implantation. The time period from the first surgically implanted valve in 1952, through catheter- mounted valves inserted for temporal relief, until the conception of the percutaneous transcatheter heart valve for permanent implantation is summarized. The process involved in the construction of the new valve is detailed in Figure 1, and the future of this new treatment modality is discussed.

Development and evaluation of a novel artificial catheter-deliverable prosthetic heart valve and method for in vitro testing

BACKGROUND

This work presents a novel artificial prosthetic heart valve designed to be catheter or percutaneously deliverable, and a method for in vitro testing of the device. The device is intended to create superior characteristics in comparison to tissue-based percutaneous valves.

METHODS

The percutaneous heart valve (PhV) was constructed from state-of-the-art polymers, metals and fabrics. It was tested hydrodynamically using a modified left heart simulator (Lhs) and statically using a tensile testing device.

RESULTS

The PhV exhibited a mean transvalvular pressure gradient of less than 15 mmhg and a mean regurgitant fraction of less than 5 percent. It also demonstrated a resistance to migration of up to 6 N and a resistance to crushing of up to 25 N at a diameter of 19 mm. The PhV was crimpable to less than 24 F and was delivered into the operating Lhs via a 24 F catheter.

CONCLUSION

An artificial PhV was designed and optimized, and an in vitro methodology was developed for testing the valve. The artificial PhV compared favorably to existing tissue-based PhVs. The in vitro test methods proved to be reliable and reproducible. The PhV design proved the feasibility of an artificial alternative to tissue based PhVs, which in their traditional open-heart implantable form are known to have limited in vivo durability.

The role of the out-of-operating room anesthesiologist in the care of the cardiac patient

Modern invasive cardiovascular procedures require patients to be both comfortable and cooperative. In addition, these procedures demand the complete attention of the attending cardiovascular specialist, and, to a large degree, the outcomes of these procedures depend on the amount of focus and concentration the cardiovascular specialist can give to performing the procedure itself. A team approach using the specialized skills of a cardiologist and an anesthesiologist frequently is required to optimize results. This article clearly delineates the procedures cardiologists perform that might involve anesthesiologists. Mutual knowledge, understanding, and respect are fundamental requirements for integration of cardiology and anesthesia services to optimize patient outcomes.

Transcatheter Valve Repair and Replacement

There is significant interest in developing transcatheter therapy for valvular heart disease (VHD). Numerous devices have been developed for the percutaneous treatment of pulmonary and aortic stenosis as well as mitral regurgitation. Several of these devices have progressed to randomized clinical trials. These ongoing trials for aortic stenosis and mitral regurgitation will provide important insights into the durability of these therapies as well as the results following standard surgical repair. The field of transcatheter valve therapy is rapidly evolving, and this review aims to summarize the current status of the field.

Minimally invasive transventricular implantation of pulmonary xenograft

Minimally invasive valve replacement is now a clinical reality. A number of ingenious techniques have been described for percutaneous aortic and pulmonary valve replacement as well as transventricular aortic valve replacement. We describe a technique for transventricular pulmonary valve replacement utilizing off-the-shelf bovine tissue valve, vascular stents, and simplified delivery system. After median sternotomy with limited exposure of the right ventricle, Contegra 200 pulmonary valve (Medtronic, Inc., Minneapolis, MN, USA) is transfixed inside a CP stent (NuMed, Inc., Hopkinton, NY, USA) using multiple 5/0 prolene sutures. The valve/stent composite is crimped on a Cristal balloon catheter (Balt, Montmorency, France). The valve/stent and the balloon are then introduced via a small purse-string placed at the RVOT. The stent/valve composite is then expanded in the pulmonary valve position.

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.

Transcatheter aortic valve replacement in patients with critical aortic stenosis: rationale, device descriptions, early clinical experiences, and perspectives

The development of lesser invasive transcatheter techniques for aortic valve replacement (AVR) to treat high surgical risk patients with severe aortic stenosis (AS) has engendered controversy among traditional cardiovascular therapists. Presently, there are two catheter-based treatment systems (the Cribier-Edwards Aortic Bioprosthesis and the CoreValve Revalving System) utilizing either a balloon-expandable or a self-expanding stent (or cage) platform which unfolds a pericardial tissue valve within the displaced diseased aortic valve. After ex vivo durability testing and animal studies, several clinical registries with these transcatheter AVR systems in almost 300 patients worldwide have demonstrated the following: (1) good acute hemodynamic performance with reduction in mean aortic valve gradients to <10 mm Hg; (2) frequent para-valvular regurgitation, which has improved with self-expanding devices and the use of larger (26 mm) valve sizes; (3) acceptable periprocedural (30-day) mortality (<10%) with the newest generation devices and improved operator techniques. Enlightened interdisciplinary treatment teams incorporating surgeons, interventionalists, and medical therapists as well as rigorously conducted randomized clinical trials will be required to determine if these innovative transcatheter AVR approaches will represent a viable therapy for high-risk patients with severe AS in the future.

Percutaneous Technique for Creation of Tricuspid Regurgitation in an Ovine Model

Experimental models of tricuspid regurgitation (TR) are needed to study the percutaneous placement of prosthetic atrioventricular valves. The purpose of this study was to develop an appropriate simple and reproducible percutaneous experimental model for creation of tricuspid regurgitation. Tricuspid regurgitation was successfully created through papillary muscle avulsion using a guide-wire loop in seven sheep with regurgitation documented on right ventricular angiograms and a significant increase in heart rate and right atrial pressures. Acute onset of tricuspid regurgitation was poorly tolerated in one animal that died. Autopsy examinations showed avulsion of one papillary muscle in four animals and two papillary muscles in three animals.

Percutaneous implantation of the pulmonary and aortic valves: indications and limitations

Percutaneous transcatheter intervention for valvular heart disease is the new horizon in transcatheter therapeutics. Balloon dilatation has been used successfully for treatment of congenital and acquired stenotic lesions of semilunar and atrio-ventricular valves. Although attempts have been made to repair and replace cardiac valves without cardiopulmonary bypass and through percutaneous techniques, this has only recently become a reality. The semilunar valves have preceded atrioventricular valves in successful application in animals and humans. Morphological features play an important role in determining the design of the valve and technique and site of implantation. The major deviations in research and development in artificial or tissue valves have included attempts at delivery of these valves to the site of implantation without open heart surgery. Successful implantation needs long-term follow-up for the durability of the valve and freedom from re-intervention.

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.

Surgery Insight: current advances in percutaneous heart valve replacement and repair

Several advances have been made in interventional cardiology, particularly in the field of valvular heart disease. Among the procedures for which technologies are available, percutaneous replacement of the pulmonary and aortic valves, and percutaneous repair of the mitral valve, via annuloplasty or the Alfieri method, are the best known. Along with the excitement generated by these new subspecialties, however, there has also been skepticism. In this article we focus on the current innovations that have been applied to the procedures in humans, and discuss the advantages and disadvantages of the different strategies.

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.

Percutaneous pulmonary valve placement in a 10-month-old patient using a hand crafted stent-mounted porcine valve

Percutaneous replacement of the pulmonary valve in a right ventricle to pulmonary artery (RV-PA) conduit using bovine jugular valves has recently been described as an alternative to surgical options in selected patients weighing >or=20 kg. We report the first case of transcatheter pulmonary valve implantation in an infant and the first use of "off the shelf" components. A 12-mm (Hancock) porcine valve was sutured into a predilated Genesis 2510b stent. The valved stent was manually crimped and mounted on a 12-mm balloon. Snare-assisted deployment in the middle of the RV-PA conduit was accomplished without the use of a long sheath. After the initial deployment, a 14-mm balloon was used to further approximate the stent to the walls of the conduit. Short-term (11 month) follow-up has demonstrated continued valve integrity, markedly decreased right ventricular size and improved function and symptomatic improvement. At 10 months of age, this case represents the youngest patient to undergo percutaneous valve placement and documents the technical feasibility of the procedure.

Transcatheter aortic valve implantation and mitral valve repair: state of the art

Surgical replacement of cardiac valves evolved significantly since its first use. Evolution of techniques and valves used was driven by the frequent complications encountered with surgically implanted valves. Transcatheter implantation of valves is a new technique which continues to be under investigation and promises to perform a task with less risk and potentially better outcome. In addition, new techniques are being developed to address minimizing mitral regurgitation. Progress in transcatheter valve implantation and catheter mitral annuloplasty is reviewed in this article.

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.

Percutaneous Valve Replacement: Current State and Future Prospects

Percutaneous valve implantation is the development of a foldable heart valve that can be mounted on an expandable stent delivered percutaneously through standard catheter-based techniques and implanted within a diseased valve annulus. In cases with severe aortic stenosis, the diseased valve has to be pre-dilated. To perform a true replacement the diseased valve has to be ablated and removed. In this article, we review the development of percutaneous valve replacement technology and discuss future prospects in this field.

Future Horizons in Surgical Aortic Valve Replacement: Lessons Learned During the Early Stages of Developing a Transluminal Implantation Technique

The aim of this study was to develop a heart valve prosthesis that could be transluminally inserted through the infrarenal aorta in pigs and the femoral artery in humans. Therefore, this valve prosthesis had to be foldable to a diameter of approximately 8 mm, self-expandable when released in the vascular system, and equipped with an anchoring mechanism. For implantation, a suitable catheter delivery system for insertion via the abdominal aorta in pigs also was designed. Furthermore, an operation method, including positioning of the catheter delivery system and deployment of the valved stent under fluoroscopic and echocardiographic control, was developed. A series of different prototypes of the valved stents and catheter delivery systems was produced to optimize design and handling. These prototypes were tested in vitro in a circulation model, and those showing satisfying hemodynamic properties were implanted in pigs as in vivo studies afterwards. The valved stents had a good hemodynamic function in vitro and in vivo with no more than a mild regurgitation or stenosis. Valve movements were satisfying, and the design proved to be generally feasible. However, positioning and anchoring were still difficult; some stents were tilted in the lumen or migrated after implantation.

Percutaneous stent-mounted valve for treatment of aortic or pulmonary valve disease

The objective of this study was to develop a prosthetic cardiac valve designed for percutaneous transcatheter implantation. Percutaneous catheter-based therapies play a limited role in the management of cardiac valve disease. Surgical implantation of prosthetic valves usually requires thoracotomy and cardiopulmonary bypass. The stent-valve is constructed of a rolled sheet of heat-treated nitinol. Although malleable when cooled, once released from a restraining sheath at body temperature the stent unrolls, becomes rigid, and assumes its predetermined cylindrical conformation. A ratcheting lock-out mechanism prevents recoil and external protrusions facilitate anchoring. Valve leaflets are constructed of bovine pericardium. The feasibility of catheter implantation, prosthetic valve function, and survival were investigated in an animal model. In vitro and pulse duplicator testing documented valve durability. Endovascular delivery of the prototype stent-valve to the aortic or pulmonary position was feasible. Accurate positioning was required to ensure exclusion of the native valve leaflets and, in the case of the aortic valve, to avoid compromise of the coronary ostia or mitral apparatus. Oversizing of the stent in relation to the valve annulus was desirable to facilitate anchoring and prevent paravalvular insufficiency. Stent-valve implantation proved feasible and compatible with survival in an animal model. Transcatheter implantation of prosthetic valves is possible. Further evolution of this technology will involve lower-profile devices with design features that facilitate vascular delivery, visualization, positioning, deployment, and valvular function.