The next generation of prosthetic heart valves needs a proven track record of patient outcomes at > or =15 to 20 years

The power of disruptive technological innovation: Transcatheter aortic valve implantation

We sought to evaluate the principles of disruptive innovation, defined as technology innovation that fundamentally shifts performance and utility metrics, as applied to transcatheter aortic valve implantation (TAVI). In particular, we considered implantation procedure, device design, cost, and patient population. Generally cheaper and lower performing, classical disruptive innovations are first commercialized in insignificant markets, promise lower margins, and often parasitize existing usage, representing unattractive investments for established market participants. However, despite presently high unit cost, TAVI is less invasive, treats a "new," generally high risk, patient population, and is generally done by a multidisciplinary integrated heart team. Moreover, at least in the short-term TAVI has not been lower-performing than open surgical aortic valve replacement in high-risk patients. We conclude that TAVI extends the paradigm of disruptive innovation and represents an attractive commercial opportunity space. Moreover, should the long-term performance and durability of TAVI approach that of conventional prostheses, TAVI will be an increasingly attractive commercial opportunity.

Hancock II bioprosthesis for aortic valve replacement: the gold standard of bioprosthetic valves durability?

BACKGROUND

This study examined the long-term durability of the Hancock II bioprosthesis (Medtronic, Minneapolis, MN) in the aortic position.

METHODS

From 1982 to 2004, 1134 patients underwent aortic valve replacement (AVR) with Hancock II bioprosthesis and were prospectively monitored. Mean patient age was 67 +/- 11 years; 202 patients were younger than 60, 402 were 60 to 70, and 526 were older than 70. Median follow-up was 12.2 years and 99.2% complete. Valve function was assessed in 94% of patients. Freedom from adverse events was estimated by the Kaplan-Meier method.

RESULTS

Survival at 20 and 25 years was 19.2% +/- 2% and 6.7% +/- 2.8%, respectively, with only 34 and 3 patients at risk. Survival at 20 years was 54.9% +/- 6.4% in patients younger than 60 years, 22.7% +/- 3.3% in those 60 to 70, and 2.4% +/- 1.9% in those older than 70 (p = 0.01). Structural valve deterioration developed in 67 patients aged younger than 60, in 18 patients aged 60 to 70, and in 2 patients older than 70. The freedom from structural valve deterioration at 20 years was 63.4% +/- 4.2% in the entire cohort, 29.2% +/- 5.7% in patients younger than 60 years, 85.2% +/- 3.7% in patients aged 60 to 70, and 99.8% +/- 0.2% in patients older than 70 (truncated at 18 years). Repeat AVR was performed in 104 patients (74 for structural valve failure, 16 for endocarditis, and 14 for other reasons). At 20 years, the overall freedom from AVR was 65.1% +/- 4% for any reason, 29.8% +/- 5.4% in patients younger than 60 years, 86.8% +/- 3.3% in patients 60 to 70, and 98.3% +/- 0.6% in patients older than 70.

CONCLUSIONS

Hancock II bioprosthesis is a very durable valve in patients 60 years and older and is probably the gold standard of bioprosthetic valve durability in this patient population.

Heart valve tissue engineering: concepts, approaches, progress, and challenges

Potential applications of tissue engineering in regenerative medicine range from structural tissues to organs with complex function. This review focuses on the engineering of heart valve tissue, a goal which involves a unique combination of biological, engineering, and technological hurdles. We emphasize basic concepts, approaches and methods, progress made, and remaining challenges. To provide a framework for understanding the enabling scientific principles, we first examine the elements and features of normal heart valve functional structure, biomechanics, development, maturation, remodeling, and response to injury. Following a discussion of the fundamental principles of tissue engineering applicable to heart valves, we examine three approaches to achieving the goal of an engineered tissue heart valve: (1) cell seeding of biodegradable synthetic scaffolds, (2) cell seeding of processed tissue scaffolds, and (3) in-vivo repopulation by circulating endogenous cells of implanted substrates without prior in-vitro cell seeding. Lastly, we analyze challenges to the field and suggest future directions for both preclinical and translational (clinical) studies that will be needed to address key regulatory issues for safety and efficacy of the application of tissue engineering and regenerative approaches to heart valves. Although modest progress has been made toward the goal of a clinically useful tissue engineered heart valve, further success and ultimate human benefit will be dependent upon advances in biodegradable polymers and other scaffolds, cellular manipulation, strategies for rebuilding the extracellular matrix, and techniques to characterize and potentially non-invasively assess the speed and quality of tissue healing and remodeling.

Engineering complex tissues

This article summarizes the views expressed at the third session of the workshop "Tissue Engineering--The Next Generation," which was devoted to the engineering of complex tissue structures. Antonios Mikos described the engineering of complex oral and craniofacial tissues as a "guided interplay" between biomaterial scaffolds, growth factors, and local cell populations toward the restoration of the original architecture and function of complex tissues. Susan Herring, reviewing osteogenesis and vasculogenesis, explained that the vascular arrangement precedes and dictates the architecture of the new bone, and proposed that engineering of osseous tissues might benefit from preconstruction of an appropriate vasculature. Jennifer Elisseeff explored the formation of complex tissue structures based on the example of stratified cartilage engineered using stem cells and hydrogels. Helen Lu discussed engineering of tissue interfaces, a problem critical for biological fixation of tendons and ligaments, and the development of a new generation of fixation devices. Rita Kandel discussed the challenges related to the re-creation of the cartilage-bone interface, in the context of tissue engineered joint repair. Frederick Schoen emphasized, in the context of heart valve engineering, the need for including the requirements derived from "adult biology" of tissue remodeling and establishing reliable early predictors of success or failure of tissue engineered implants. Mehmet Toner presented a review of biopreservation techniques and stressed that a new breakthrough in this field may be necessary to meet all the needs of tissue engineering. David Mooney described systems providing temporal and spatial regulation of growth factor availability, which may find utility in virtually all tissue engineering and regeneration applications, including directed in vitro and in vivo vascularization of tissues. Anthony Atala offered a clinician's perspective for functional tissue regeneration, and discussed new biomaterials that can be used to develop new regenerative technologies.

Fifteen-year results with the Hancock II valve: A multicenter experience

OBJECTIVES

The purpose of this multi-institutional study was to review the 15-year outcome of patients who received isolated aortic or mitral valve replacement with the Hancock II bioprosthesis.

METHODS

From 1983 through 2002, 1274 patients underwent 1293 isolated valve replacements, 809 aortic valve replacements and 484 mitral valve replacements, at hospitals in the Venetian area (Padova, Treviso, and Venice). Mean age was 68 +/- 8 years in patients undergoing aortic valve replacement and 66 +/- 9 years in patients undergoing mitral valve replacement; 52% of patients undergoing aortic valve replacement and 63% of patients undergoing mitral valve replacement were in New York Heart Association class III or greater. Coronary artery disease was present in 32% of patients who had undergone aortic valve replacement and 18% of patients who had undergone mitral valve replacement. Follow-up included 8520 patient-years, with a median of 12 years, and was 97% complete.

RESULTS

Overall 15-year survival was 39.7% +/- 2.4%, similar in both the aortic and mitral positions. Multivariable analysis of late survival showed the incremental risk of male sex, higher New York Heart Association class, coronary artery disease, and mitral position. Freedom from embolism was higher in the aortic position (81% +/- 2.9% in aortic vs 72% +/- 4.7% in mitral valve replacements). Freedom from endocarditis was similar in the aortic and mitral position (95% +/- 1.2% vs 94% +/- 1.7%). Freedom from reoperation (82% +/- 3.7% vs 71% +/- 5.0%) and from valve-related morbidity-mortality (52% +/- 3.6% vs 36% +/- 4.4%) was higher in patients who had undergone AVR. Actual freedom from structural valve deterioration for patients 60 years and older who had undergone aortic valve replacement was 96.5% +/- 1.3% versus 88% +/- 3.2% for patients who had undergone mitral valve replacement and 70% +/- 7.5% versus 77.5% +/- 5.3%, respectively, in younger patients. Multivariable Weibull analysis showed structural valve deterioration related to younger age and preoperative valve incompetence and inversely related to coronary artery disease.

CONCLUSION

Optimal 15-year durability can be expected in male patients 60 years and older who have undergone aortic valve replacement and in male patients 65 years and older who have undergone mitral valve replacement, extending safely the age limits for the use of this valve.

New frontiers in the pathology and therapy of heart valve disease: 2006 Society for Cardiovascular Pathology, Distinguished Achievement Award Lecture, United States–Canadian Academy of Pathology, Atlanta, GA, February 12, 2006

This review summarizes several areas relative to the pathology of heart valve disease in which there has been rapid and ongoing evolution, namely, our understanding of: (a) the dynamic functional biology of cardiac valves; and (b) the pathology/pathobiology of valvular heart diseases; (c) new developments in valve repair and substitution using percutaneous approaches; and (d) progress toward the exciting potential of therapeutic valvular tissue engineering and regeneration, including the challenges that will need to be overcome before such therapeutic advances can become clinically useful.

Novel approaches to clinical trials: device-related infections

The explosive growth in the use of cardiac devices and the continued large number of thoracic operations produce a significant number of costly infectious complications. These infections represent a leading cause of death and disability after device implantation or surgery. Unfortunately, few objective data are available to validate the clinical epidemiology of surgical and device-related infections, and although the number of randomized trials is increasing, too few have tested strategies for prophylaxis or treatment, particularly in the cardiac arena. Because of the expected increase in invasive vascular procedures and device implantations, it is timely to consider innovative approaches to clinical research that will hasten the translation of effective therapeutic strategies and technologies into clinical practice. Because of the multidisciplinary nature of the care of patients undergoing thoracic surgery or device implantation, bringing together existing networks and several arms of the Federal government could rapidly advance this field to provide a definitive base of evidence to guide clinical practice and improve clinical outcomes. The remainder of the articles in this supplement discuss specific issues on the diagnosis and treatment of device-related or surgical infection. The purpose of this manuscript is to discuss issues about the design of studies and their organization.