Fifteen-year experience with 1678 Hancock porcine bioprosthetic heart valve replacements

Physiological basis for xenotransplantation from genetically modified pigs to humans

The collective efforts of scientists over multiple decades have led to advancements in molecular and cellular biology-based technologies including genetic engineering and animal cloning that are now being harnessed to enhance the suitability of pig organs for xenotransplantation into humans. Using organs sourced from pigs with multiple gene deletions and human transgene insertions, investigators have overcome formidable immunological and physiological barriers in pig-to-nonhuman primate (NHP) xenotransplantation and achieved prolonged pig xenograft survival. These studies informed the design of Revivicor's (Revivicor Inc, Blacksburg, VA) genetically engineered pigs with 10 genetic modifications (10 GE) (including the inactivation of 4 endogenous porcine genes and insertion of 6 human transgenes), whose hearts and kidneys have now been studied in preclinical human xenotransplantation models with brain-dead recipients. Additionally, the first two clinical cases of pig-to-human heart xenotransplantation were recently performed with hearts from this 10 GE pig at the University of Maryland. Although this review focuses on xenotransplantation of hearts and kidneys, multiple organs, tissues, and cell types from genetically engineered pigs will provide much-needed therapeutic interventions in the future.

A Biohybrid Material With Extracellular Matrix Core and Polymeric Coating as a Cell Honing Cardiovascular Tissue Substitute

Objective

To investigate the feasibility of a hybrid material in which decellularized pericardial extracellular matrix is functionalized with polymeric nanofibers, for use as a cardiovascular tissue substitute.

Background

A cardiovascular tissue substitute, which is gradually resorbed and is replaced by host's native tissue, has several advantages. Especially in children and young adults, a resorbable material can be useful in accommodating growth, but also enable rapid endothelialization that is necessary to avoid thrombotic complications. In this study, we report a hybrid material, wherein decellularized pericardial matrix is functionalized with a layer of polymeric nanofibers, to achieve the mechanical strength for implantation in the cardiovascular system, but also have enhanced cell honing capacity.

Methods

Pericardial sacs were decellularized with sodium deoxycholate, and polycaprolactone-chitosan fibers were electrospun onto the matrix. Tissue-polymer interaction was evaluated using spectroscopic methods, and the mechanical properties of the individual components and the hybrid material were quantified. In-vitro blood flow loop studies were conducted to assess hemocompatibility and cell culture methods were used to assess biocompatibility.

Results

Encapsulation of the decellularized matrix with 70 μm thick matrix of polycaprolactone-chitosan nanofibers, was feasible and reproducible. Spectroscopy of the cross-section depicted new amide bond formation and C–O–C stretch at the interface. An average peel strength of 56.13 ± 11.87 mN/mm2 was measured, that is sufficient to withstand a high shear of 15 dynes/cm2 without delamination. Mechanical strength and extensibility ratio of the decellularized matrix alone were 18,000 ± 4,200 KPa and 0.18 ± 0.03% whereas that of the hybrid was higher at 20,000 ± 6,600 KPa and 0.35 ± 0.20%. Anisotropy index and stiffness of the biohybrid were increased as well. Neither thrombus formation, nor platelet adhesion or hemolysis was measured in the in-vitro blood flow loop studies. Cellular adhesion and survival were adequate in the material.

Conclusion

Encapsulating a decellularized matrix with a polymeric nanofiber coating, has favorable attributes for use as a cardiovascular tissue substitute.

Long-Term Stability and Biocompatibility of Pericardial Bioprosthetic Heart Valves

The use of bioprostheses for heart valve therapy has gradually evolved over several decades and both surgical and transcatheter devices are now highly successful. The rapid expansion of the transcatheter concept has clearly placed a significant onus on the need for improved production methods, particularly the pre-treatment of bovine pericardium. Two of the difficulties associated with the biocompatibility of bioprosthetic valves are the possibilities of immune responses and calcification, which have led to either catastrophic failure or slow dystrophic changes. These have been addressed by evolutionary trends in cross-linking and decellularization techniques and, over the last two decades, the improvements have resulted in somewhat greater durability. However, as the need to consider the use of bioprosthetic valves in younger patients has become an important clinical and sociological issue, the requirement for even greater longevity and safety is now paramount. This is especially true with respect to potential therapies for young people who are afflicted by rheumatic heart disease, mostly in low- to middle-income countries, for whom no clinically acceptable and cost-effective treatments currently exist. To extend longevity to this new level, it has been necessary to evaluate the mechanisms of pericardium biocompatibility, with special emphasis on the interplay between cross-linking, decellularization and anti-immunogenicity processes. These mechanisms are reviewed in this paper. On the basis of a better understanding of these mechanisms, a few alternative treatment protocols have been developed in the last few years. The most promising protocol here is based on a carefully designed combination of phases of tissue-protective decellularization with a finely-titrated cross-linking sequence. Such refined protocols offer considerable potential in the progress toward superior longevity of pericardial heart valves and introduce a scientific dimension beyond the largely disappointing 'anti-calcification' treatments of past decades.

Durability of Mitral Valve Bioprostheses: A Meta-Analysis of Long-Term Follow-up Studies

BACKGROUND

Porcine and pericardial valves exhibited similar freedom from structural valve deterioration after aortic valve replacement. Limited data exist regarding their durability at long-term follow-up in the mitral position.

METHODS

A literature search was performed through online databases. Papers reporting freedom from tissue valve deterioration after mitral valve replacement with a follow-up longer than 5 years were retrieved. Four porcine valves (Carpentier-Edwards [Edwards Lifesciences, Irvine, CA] and Hancock, Hancock II, and Mosaic [Medtronic, Inc, Minneapolis, MN]) and 1 pericardial prosthesis (Carpentier-Edwards) were the objects of the study. The structural valve deterioration (SVD) rate per year was calculated for each type of prosthesis. Kaplan-Meier curves and log-rank test analysis were performed to compare the long-term durability of porcine and pericardial valves.

RESULTS

Forty full-text papers including more than 15,000 patients were considered for the meta-analysis. Porcine valves were generally implanted in younger patients in the first period after their introduction. The mean age of the patients receiving a mitral bioprosthesis increased from 50 to 70 years over the decades. In patients operated after 1980 who had similar mean age at the time of implant, freedom from SVD was higher in the group of porcine valves with Mosaic prosthesis, showing the lowest rate of SVD. Long-term survival was higher for Mosaic porcine and Carpentier pericardial valves.

CONCLUSIONS

In surgical populations that underwent mitral valve replacement after 1980 with new generation tissue valves and similar mean age at the implant time, we found, at long-term follow-up, a higher freedom from SVD in the group of porcine prostheses.

In Search of the Ideal Valve: Optimizing Genetic Modifications to Prevent Bioprosthetic Degeneration

BACKGROUND

Bioprosthetic heart valves undergo structural degeneration and calcification. Similarities exist in the histopathologic features of explanted bioprosthetic valves and rejected pig tissues and organs after xenotransplantation into nonhuman primates. The development of more durable bioprosthetic valves, namely from genetically modified pigs, could negate the need for the insertion of mechanical prostheses in children and young adults with the requirement for life-long anticoagulation and might avoid the need for reoperation in elderly patients.

METHODS

We reviewed the literature (MedlinePlus, PubMed, Google Scholar) through September 1, 2018, under four key terms: (1) bioprosthetic heart valves, (2) xenograft antigens, (3) immunologic responses to bioprosthetic valves, and (4) genetic modification of xenografts.

RESULTS

Advances in tissue and organ xenotransplantation have elucidated important immunologic barriers that provide innovative approaches to prevent structural degeneration of bioprosthetic heart valves. The current evidence suggests that bioprosthetic valves derived from genetically modified pigs lacking xenogeneic antigens (namely Gal, Neu5Gc, and Sda), termed triple-knockout pigs, would function considerably longer than current wild-type (genetically unmodified) porcine valves in human recipients.

CONCLUSIONS

Preclinical and clinical studies to determine the safety and efficacy of triple-knockout porcine bioprosthetic valves will likely establish that they are more resistant to human immune responses and thus less susceptible to structural degeneration.

Current indications for stentless aortic bioprostheses

The best aortic prostheses have been debated for decades. The introduction of stentless aortic bioprostheses was aimed at improving hemodynamics and potentially the durability of aortic bioprostheses. Despite the good short- and long-term outcomes after implantation of stentless aortic bioprostheses, their use remains limited owing to the technically demanding implantation techniques. Nevertheless, stentless aortic bioprostheses might be of special benefit in certain indications, where they could be a valuable addition to the surgical armamentarium.

Heterotopic Implantation of Decellularized Pulmonary Artery Homografts In A Rodent Model: Technique Description and Preliminary Report

PURPOSE

Despite a substantial amount of literature on tissue-guided regeneration, decellularization process, repopulation time points and stem cell turnover, more in-depth study on the argument is required. Currently, there are plenty of reports involving large animals, as well as clinical studies facing cardiac repair with decellularized homografts, but no exhaustive rodent models are described. The purpose of this study was to develop such a model in rats; preliminary results are also herein reported.

MATERIAL AND METHODS

Fresh or decellularized pulmonary homografts from wild type rats were implanted in the abdominal aorta of green fluorescent protein positive rats. Three experimental groups were build up: sham, fresh homograft recipients and decellularized homograft recipients. The homograft decellularization process was performed with three cycles of detergent-enzymatic treatment protocol. Surgical technique of pulmonary homograft implantation and postoperative ultrasonographic evaluation were also reported; gross, histology and immunohistochemistry analysis on unimplanted and postoperative homografts were also carried out.

RESULTS

The median total recipient operating time was 148 minutes, with a surgical success rate of 82%. The decellularization protocol resulted effective and showed a complete decellularization with intact extracellular matrix. At 15 days from surgery, the implanted decellularized pulmonary homografts exhibited cell repopulation in the outer media wall and partial endothelial lining in absence of rejection.

CONCLUSIONS

Our technique is a feasible and reproducible model that can be fundamental for building a valid study for further exploitation on the field. Even in a short-term follow up, the decellularized pulmonary homografts showed autologous repopulation in absence of rejection.

Biomechanical Behavior of Bioprosthetic Heart Valve Heterograft Tissues: Characterization, Simulation, and Performance

The use of replacement heart valves continues to grow due to the increased prevalence of valvular heart disease resulting from an ageing population. Since bioprosthetic heart valves (BHVs) continue to be the preferred replacement valve, there continues to be a strong need to develop better and more reliable BHVs through and improved the general understanding of BHV failure mechanisms. The major technological hurdle for the lifespan of the BHV implant continues to be the durability of the constituent leaflet biomaterials, which if improved can lead to substantial clinical impact. In order to develop improved solutions for BHV biomaterials, it is critical to have a better understanding of the inherent biomechanical behaviors of the leaflet biomaterials, including chemical treatment technologies, the impact of repetitive mechanical loading, and the inherent failure modes. This review seeks to provide a comprehensive overview of these issues, with a focus on developing insight on the mechanisms of BHV function and failure. Additionally, this review provides a detailed summary of the computational biomechanical simulations that have been used to inform and develop a higher level of understanding of BHV tissues and their failure modes. Collectively, this information should serve as a tool not only to infer reliable and dependable prosthesis function, but also to instigate and facilitate the design of future bioprosthetic valves and clinically impact cardiology.

Successful matrix guided tissue regeneration of decellularized pulmonary heart valve allografts in elderly sheep

In vivo repopulation of decellularized allografts with recipient cells leads to a positive remodeling of the graft matrix in juvenile sheep. In light of the increasing number of heart valve replacements among older patients (>65 years), this study focused on the potential for matrix-guided tissue regeneration in elderly sheep. Pulmonary valve replacement was performed in seven-year old sheep using decellularized (DV), decellularized and CCN1-coated (RV), or decellularized and in vitro reendothelialized pulmonary allografts (REV) (n=6, each group). CCN1 coating was applied to support re-endothelialization. In vitro re-endothelialization was conducted with endothelial-like cells derived from peripheral blood. Echocardiograms of all grafts showed adequate graft function after implantation and at explantation 3 or 6 months later. All explants were macroscopically free of thrombi at explantation, and revealed repopulation of the allografts on the adventitial side of valvular walls and proximal in the cusps. Engrafted cells expressed vimentin, sm α-actin, and myosin heavy chain 2, while luminal cell lining was positive for vWF and eNOS. Cellular repopulation of valvular matrix demonstrates the capacity for matrix-guided regeneration even in elderly sheep but is not improved by in vitro endothelialization, confirming the suitability of decellularized matrix for heart valve replacement in older individuals.

Valve Configuration Determines Long-Term Results After Repair of the Bicuspid Aortic Valve

Background—

Reconstruction of the regurgitant bicuspid aortic valve has been performed for >10 years, but there is limited information on long-term results. We analyzed our results to determine the predictors of suboptimal outcome.

Methods and Results—

Between November 1995 and December 2008, 316 patients (age, 49±14 years; male, 268) underwent reconstruction of a regurgitant bicuspid aortic valve. Intraoperative assessment included extent of fusion, root dimensions, circumferential orientation of the 2 normal commissures (>160°, ≤160°), and effective height after repair. Cusp pathology was treated by central plication (n=277), triangular resection (n=138), or pericardial patch (n=94). Root dilatation was treated by subcommissural plication (n=100), root remodeling (n=122), or valve reimplantation (n=2). All patients were followed up echocardiographically (cumulative follow-up, 1253 years; mean, 4±3.1 years). Clinical and morphological parameters were analyzed for correlation with 10-year freedom from reoperation with the Cox proportional hazards model. Hospital mortality was 0.63%; survival was 92% at 10 years. Freedom from reoperation at 5 and 10 years was 88% and 81%; freedom from valve replacement, 95% and 84%. By univariable analysis, statistically significant predictors of reoperation were age (hazard ratio [HR]=0.97), aortoventricular diameter (HR=1.24), effective height (HR=0.76), commissural orientation (HR=0.95), use of a pericardial patch (HR=7.63), no root replacement (HR=3.80), subcommissural plication (HR=2.07), and preoperative aortic regurgitation grade 3 or greater. By multivariable analysis, statistically significant predictors for reoperation were age (HR=0.96), aortoventricular diameter (HR=1.30), effective height (HR=0.74), commissural orientation (HR=0.96), and use of a pericardial patch (HR=5.16).

Conclusions—

Reconstruction of bicuspid aortic valve can be performed reproducibly with good early results. Recurrence and progression of regurgitation, however, may occur, depending primarily on anatomic features of the valve.

Tissue-engineered heart valve prostheses: ‘state of the heart’

In this article, we will review the current state of the art in heart valve tissue engineering. We provide an overview of mechanical and biological replacement options, outlining advantages and limitations of each option. Tissue engineering, as a field, is introduced, and specific aspects of valve tissue engineering are discussed (e.g., biomaterials, cells and bioreactors). Technological hurdles, which need to be overcome for advancement of the field, are also discussed.

Prosthetic heart valves: Types and echocardiographic evaluation

In the last five decades multiple different models of prosthetic valves have been developed. The purpose of this article is to provide a comprehensive source of information for the types and the echocardiographic evaluation of the prosthetic heart valves.

Clinical results of Hancock II versus Hancock Standard at long-term follow-up

OBJECTIVE

We performed a multi-institutional study to compare the long-term structural valve deterioration of isolated Hancock Standard versus Hancock II bioprostheses.

METHODS

From 1983 to 2002, 714 Hancock Standard and 1293 Hancock II bioprostheses were implanted at hospitals of the Venetian territory (Padova, Treviso, and Venice). Follow-up on January 1, 2003, included 14,749 patient-years with a median of 12 years and was 96% complete: 115 Hancock Standard and 53 Hancock II bioprostheses were at risk at 15 years. The 2 series were nonconcomitant, and many covariates differed (Table 1). Survival was analyzed with Cox analysis, and durability was analyzed with Weibull analysis. Balancing analysis with the logistic propensity score model was performed.

RESULTS

Perioperative mortality was 6% in Hancock II and 12% in Hancock Standard operations. The overall unadjusted 15-year survival was identical (39.7% +/- 2.3% vs 39.9% +/- 2.4%, respectively), but age-adjusted survival at 15 years was 46% versus 25% (P < .001). Late survival was unrelated to the prosthetic model, whereas it was adversely affected by older age, previous operations, aortic regurgitation, male sex, higher New York Heart Association class, atrial fibrillation, and coronary artery bypass grafting. In Hancock II patients aged 65 years and older, the cumulative hazard of structural valve deterioration at 15 years was 6%, versus 17.5% in Hancock Standard patients. In younger patients, it was 18% and 37%, respectively. Analysis of 541 propensity-balanced patients showed a hazard ratio of the Hancock Standard prosthesis of 2 and a risk reduction of older age of approximately 10% every 10 years.

CONCLUSION

After balancing risk factors and calibrating age effects, Hancock II propensity-matched bioprostheses showed similar survival but definitely increased durability.

Application of tissue-engineering principles toward the development of a semilunar heart valve substitute

Heart valve disease is a significant medical problem worldwide. Current treatment for heart valve disease is heart valve replacement. State of the art replacement heart valves are less than ideal and are associated with significant complications. Using the basic principles of tissue engineering, promising alternatives to current replacement heart valves are being developed. Significant progress has been made in the development of a tissue-engineered semilunar heart valve substitute. Advancements include the development of different potential cell sources and cell-seeding techniques; advancements in matrix and scaffold development and in polymer chemistry fabrication; and the development of a variety of bioreactors, which are biomimetic devices used to modulate the development of tissue-engineered neotissue in vitro through the application of biochemical and biomechanical stimuli. This review addresses the need for a tissue-engineered alternative to the current heart valve replacement options. The basics of heart valve structure and function, heart valve disease, and currently available heart valve replacements are discussed. The last 10 years of investigation into a tissue-engineered heart valve as well as current developments are reviewed. Finally, the early clinical applications of cardiovascular tissue engineering are presented.

Calcification of Tissue Heart Valve Substitutes: Progress Toward Understanding and Prevention

Calcification plays a major role in the failure of bioprosthetic and other tissue heart valve substitutes. Tissue valve calcification is initiated primarily within residual cells that have been devitalized, usually by glutaraldehyde pretreatment. The mechanism involves reaction of calcium-containing extracellular fluid with membrane-associated phosphorus to yield calcium phosphate mineral deposits. Calcification is accelerated by young recipient age, valve factors such as glutaraldehyde fixation, and increased mechanical stress. Recent studies have suggested that pathologic calcification is regulated by inductive and inhibitory factors, similar to the physiologic mineralization of bone. The most promising preventive strategies have included binding of calcification inhibitors to glutaraldehyde fixed tissue, removal or modification of calcifiable components, modification of glutaraldehyde fixation, and use of tissue cross linking agents other than glutaraldehyde. This review summarizes current concepts in the pathophysiology of tissue valve calcification, including emerging concepts of endogenous regulation, progress toward prevention of calcification, and issues related to calcification of the aortic wall of stentless bioprosthetic valves.

Complications of prosthetic heart valves

Treatment of native valvular heart disease has resulted in an increasing number of patients with prosthetic valves. Although an improvement over the diseased native valve removed at surgery, prosthetic valves have suboptimal hemodynamics; mechanical valves require anticoagulation and tissue valves wear out over time. Serious complications of prosthetic valves occur at a rate of about 2% to 3% per patient-year. Complications include thromboembolism, prosthesis-patient mismatch, structural valve dysfunction, endocarditis, and hemolysis. Prosthetic valve endocarditis is a lethal disease with mortality rates of 50% to 80% even with appropriate therapy. Echocardiography now provides detailed information on valve function and hemodynamics, allowing early detection of complications. Many of these complications can be prevented by choosing the optimal valve at the time of surgery, rigorous control of anticoagulation and adherence to established anticoagulation guidelines, dental hygiene and endocarditis prophylaxis, and periodic echocardiographic monitoring by a cardiologist.

Transplantation of Cultured Human Corneal Endothelial Cells

PURPOSE

To investigate the feasibility of corneal reconstruction utilizing cultured human corneal endothelial cells (HCECs).

METHODS

We cultivated HCECs using culture dishes pre-coated with bovine corneal endothelial extracellular matrix. The effect of donor age on HCECs was investigated. We reconstructed corneas using cultured HCECs and human corneal stroma, then examined their functioning. The possibility of porcine corneal stroma as a carrier of cultured HCECs was investigated.

RESULTS

The older the donor, the more frequently large senescent cells appeared in the passaged HCECs. The density of HCECs on the reconstructed cornea reached 2500 cells/mm2. The potential difference in the reconstructed and normal corneas was 0.30 mV and 0.40 mV, respectively; this indicates that the pump function of the reconstructed corneas is 75% of that of normal corneas. Porcine corneal stroma expressing little xenosugar antigen alpha-gal epitope induced no superacute rejection but mild cellular rejection when transplanted into corneas of animals possessing natural antibody to alpha-gal epitope.

CONCLUSIONS

To reconstruct corneas that are the same as, or superior to, normal corneas, innovation is necessary in the methods used for culturing and seeding HCECs. Porcine corneal stroma is promising as a carrier of HCECs instead of human corneal stroma, the supply of which is limited. The validity of porcine corneal stroma, acellularized to prevent retrovirus infection, should be evaluated.

Antigenicity of porcine cornea as xenograft

PURPOSE

To investigate the antigenicity of porcine corneal stroma as xenograft to man.

METHODS

The localization of alpha-gal epitope in the porcine eye was determined using biotinylated Griffonia simplicifolia 1 isolectin B4. Porcine corneal stromal was inserted into corneal stromal pockets of cynomolgus monkeys. Immunohistochemistry was performed to analyze the immunological reaction in the monkey.

RESULTS

Immunohistochemistry showed no alpha-gal epitope in the porcine cornea except for several keratocytes in the anterior-most part. Haze and keratic precipitates developed in two corneas out of three corneas that were followed up until 6 months after the surgery. In these two corneas, infiltrating cells included CD4+, CD8+, or HAM56+ cells, suggesting that haze and keratic precipitates were induced by cellular rejection to porcine corneal stroma.

CONCLUSIONS

Porcine corneal stroma induces no hyperacute rejection but mild cellular rejection when transplanted in the cornea of cynomolgus monkeys.

The evolution of mitral valve surgery: 1902-2002

The evolution of the surgical therapy of mitral valve disease emanates from original statements by British cardiologists in 1902 and anecdotal individual surgical cases in 1923 and 1925. Considerable amounts of experimental investigation during these years and after World War II in 1948 finally resulted in the widespread use of closed mitral commissurotomy, a successful therapy for noncalcified mitral stenosis. The history of mitral valve surgery then rapidly progressed with a variety of prosthetic and bioprosthetic valve devices, ultimately, to a considerable number of successful valve repair operations with prosthetic ring annuloplasty. The authors conclude with a discussion of the current status of minimally invasive mitral valve surgery, both by direct vision and robotic assistance. The entire evolution of thought and technique of mitral valve surgery is summarized in this paper from 1902-2002.

Over twenty-year follow-up of the standard Hancock porcine bioprosthesis implanted in the mitral position

BACKGROUND

To define the long-term results of 331 standard Hancock porcine bioprostheses implanted in the mitral position between 1973 and 1980.

METHODS

Of 331 patients (225 male patients, 68%), mean age 49+/-10 years (range 14 to 69 years), 88% were in New York Heart Association functional class III or IV and 77% were in atrial fibrillation. Follow-up time extended more than 20 years (mean 13.9 years, range 0.3 to 24.7 years) for a total of 4,601 patient-years.

RESULTS

Overall operative mortality was 6.3%. At 5, 10, 15, and 20 years, the actuarial survival rate of patients were 71%+/-2%, 46%+/-3%, 30%+/-3%, and 22%+/-2%, respectively. Actuarial estimates of freedom from structural valve deterioration were 95%+/-1%, 67%+/-3%, 32%+/-3%, and 14%+/-3%; from reoperation were 96%+/-1%, 72%+/-3%, 36%+/-4%, and 18%+/-4%; from thromboembolism were 89%+/-2%, 82%+/-3%, 74%+/-4%, and 51%+/-2%; and from anticoagulant-related hemorrhage were 98%+/-1%, 96%+/-1%, 91%+/-1%, and 86%+/-4%. Estimates of freedom from all valve-related mortality at 5, 10, 15, and 20 years were 89%+/-2%, 76%+/-3%, 64%+/-4%, and 48%+/-4%. Multivariate analysis showed younger age to be a significant risk factor for reoperation. Age at operation did not correlate with structural valve deterioration.

CONCLUSIONS

The long-term results with the standard Hancock bioprosthesis implanted in the mitral position appear satisfactory, particularly up to 15 years from implantation. Protection from stroke, anticoagulant hemorrhage, and endocarditis was good.

Are the indications for tissue valves different in 2001 and how do we communicate these changes to our cardiology colleagues?

The indications for tissue valves in the aortic and mitral positions are becoming better defined with advances in valve design, valve preservation, and management of reoperations. Although some patients who require cardiac valve replacement clearly benefit more from one type of valve than from another, not infrequently one encounters a patient who is in the "gray zone," where the optimal choice is difficult. At present, bioprostheses for the diseased aortic valve include stented porcine and pericardial valves, stentless porcine valves, aortic homograft, and pulmonary autograft. For patients with mitral valve disease, options for tissue valve replacement are a stented porcine or pericardial prosthesis. Generally, factors to consider in choosing the appropriate valve substitute include the patient's age, expected life expectancy, coexisting medical problems, lifestyle, and socioeconomics; the etiology of the valve disease, annular size, and physician and patient preference are also relevant. Despite the known finite durability of tissue valves, which is the main limitation in their use, the long-term results have been satisfactory, particularly in older patients, patients with a limited life expectancy, and those undergoing valve replacement in the aortic position. Distillation of available information and ongoing communication between the surgeon and the cardiologist will enable us to assist the patient in choosing the best valve substitute.

Reoperative surgery for degenerated aortic bioprostheses: predictors for emergency surgery and reoperative mortality

OBJECTIVE

The long-term outcome of patients with aortic bioprosthetic valves could be improved by decreasing the reoperative mortality rate.

METHODS

Predictors of emergency reoperation and reoperative mortality were identified retrospectively in 172 patients who had the first bioprosthetic aortic valve replacement between 1975 and 1988 (mean age 46+/-13 years) and were subjected to replacement of the degenerated bioprostheses between 1978 and 1997 (mean age 56+/-14 years). Emergency reoperation had to be performed in 31 patients (18%).

RESULTS

The operative mortality was 5.2% (9/172), 22.6% for emergency (odds ratio 11.17; 95%-confidence limit 4.33-28.85) and 1.4% for elective replacement of the degenerated aortic bioprosthesis (P<0.0001; OR=20.3). Patients who died at reoperation had higher transvalvular gradients before the primary aortic valve replacement (P=0.007), received smaller bioprostheses at the first operation (P=0.03), had later recurrence of symptoms after the first aortic valve replacement (P=0.04), a higher pre-reoperative New York Heart Association (NYHA) class (P=0.02), and a higher incidence of coronary artery disease (P=0.001) and pulmonary artery hypertension (P=0.009). Endocarditis before the primary aortic valve replacement (P=0.004), postoperative pneumonia at the first operation (P=0.005), pulmonary hypertension (P=0.0004) acquired during the interval, later recurrence of symptoms (P=0.04) after the first operation, a lower ejection fraction at the time of reoperation (P=0.03) and acute onset of bioprosthetic regurgitation (P=0.00002) were predictors for emergency surgery. Higher transvalvular gradients at the primary aortic valve replacement (P=0. 006), coronary artery disease (P=0.003) acquired during the interval, the need for concomitant coronary artery revascularization (P=0. 001), sex (P=0.02) and size (P=0.05) and type of the bioprostheses used (P=0.007) were incremental predictors for reoperative mortality which were independent of emergency surgery.

CONCLUSIONS

Elective replacement of failed aortic bioprostheses is safe. Patients undergoing emergency reoperation have a considerably higher mortality. They can be identified by a history of native aortic valve endocarditis, higher transvalvular gradients at primary aortic valve replacement, smaller bioprostheses, and pulmonary hypertension or coronary artery disease acquired during the interval. A failing bioprosthesis must be replaced at its first sign of dysfunction.

Founder's Award, 25th Annual Meeting of the Society for Biomaterials, perspectives. Providence, RI, April 28-May 2, 1999. Tissue heart valves: current challenges and future research perspectives

Substitute heart valves composed of human or animal tissues have been used since the early 1960s, when aortic valves obtained fresh from human cadavers were transplanted to other individuals as allografts. Today, tissue valves are used in 40% or more of valve replacements worldwide, predominantly as stented porcine aortic valves (PAV) and bovine pericardial valves (BPV) preserved by glutaraldehyde (GLUT) (collectively termed bioprostheses). The principal disadvantage of tissue valves is progressive calcific and noncalcific deterioration, limiting durability. Native heart valves (typified by the aortic valve) are cellular and layered, with regional specializations of the extracellular matrix (ECM). These elements facilitate marked repetitive changes in shape and dimension throughout the cardiac cycle, effective stress transfer to the adjacent aortic wall, and ongoing repair of injury incurred during normal function. Although GLUT bioprostheses mimic natural aortic valve structure (a) their cells are nonviable and thereby incapable of normal turnover or remodeling ECM proteins; (b) their cuspal microstructure is locked into a configuration which is at best characteristic of one phase of the cardiac cycle (usually diastole); and (c) their mechanical properties are markedly different from those of natural aortic valve cusps. Consequently, tissue valves suffer a high rate of progressive and age-dependent structural valve deterioration resulting in stenosis or regurgitation (>50% of PAV overall fail within 10-15 years; the failure rate is nearly 100% in 5 years in those <35 years old but only 10% in 10 years in those >65). Two distinct processes-intrinsic calcification and noncalcific degradation of the ECM-account for structural valve deterioration. Calcification is a direct consequence of the inability of the nonviable cells of the GLUT-preserved tissue to maintain normally low intracellular calcium. Consequently, nucleation of calcium-phosphate crystals occurs at the phospholipid-rich membranes and their remnants. Collagen and elastin also calcify. Tissue valve mineralization has complex host, implant, and mechanical determinants. Noncalcific degradation in the absence of physiological repair mechanisms of the valvular structural matrix is increasingly being appreciated as a critical yet independent mechanism of valve deterioration. These degradation mechanisms are largely rationalized on the basis of the changes to natural valves when they are fabricated into a tissue valve (mentioned above), and the subsequent interactions with the physiologic environment that are induced following implantation. The "Holy Grail" is a nonobstructive, nonthrombogenic tissue valve which will last the lifetime of the patient (and potentially grow in maturing recipients). There is considerable activity in basic research, industrial development, and clinical investigation to improve tissue valves. Particularly exciting in concept, yet early in practice is tissue engineering, a technique in which an anatomically appropriate construct containing cells seeded on a resorbable scaffold is fabricated in vitro, then implanted. Remodeling in vivo, stimulated and guided by appropriate biological signals incorporated into the construct, is intended to recapitulate normal functional architecture.

Valvular disease in the elderly

As the incidence of valvular disease in the elderly is increasing, understanding of its pathogenesis and natural progression as well as surgical approaches and device technologies are improving. Future studies are needed to develop medical interventions that slow or halt the degenerative valvular processes associated with aging. In addition, mechanical approaches with lower operative risks should be explored and the search should continue for a valve substitute that is durable, hemodynamically efficient, easy to implant, and does not require anticoagulation. Hopefully, future intervention trials will include quality of life assessments such as symptoms, functional capacity and perceptions of well being. At present, the degenerative valvular processes must be followed closely by the clinician, and individual management decisions for the elderly based on the type and severity of valve disease, comorbid medical conditions, and the risks and benefits of intervention, along with patient preferences, rather than on the chronologic age of the patient. It is becoming clear that both survival and quality of life outcomes can improve by consideration of surgery at the onset of indications, before further deterioration eliminates the opportunity to provide benefit for the elderly patient with valvular disease.

Ten-Year Results with Liotta Porcine Bioprostheses in the Mitral Position

The Liotta porcine bioprosthesis is a third generation bioprosthesis with a very low profile supraannular configuration with low-pressure glutaraldehyde-fixed tissue. Between May 1986 and December 1990, 670 patients underwent isolated mitral valve replacement with Liotta porcine bioprosthesis. There were 403 (60%) females and 267 (40%) males; the mean age was 39.03 ± 4.57 years (range, 16 to 75 years). The predominant lesion was combined mitral stenosis and mitral insufficiency in 46% of the patients. The operative mortality rate was 5.9% and the most frequent cause of the mortality was low cardiac output. Total follow-up was 3193.5 patient-years. The average follow-up period was 6.1 ± 2.5 years (range, 1 to 10 years). During the late period, 44 patients (1.4% per patient-year) died. The long-term survival estimate at 10 years was 84.8% ± 2.7%. Structural valve deterioration developed in 198 patients (6.2% per patient-year). Actuarial estimates of freedom from structural valve deterioration at 5 and 10 years were 87.6% ± 1.5% and 28.5% ± 4.5% and it was unrelated to sex or age. Most patients (88%) who developed bioprosthesis dysfunction underwent repeat valve replacement. The period between the implantation and development of structural valve deterioration was 5.9 ± 1.8 years for female patients and 6.2 ± 1.8 years for males (no statistically significant difference). We concluded from the early and high rates of structural valve deterioration in this young age group that the Liotta porcine bioprosthesis has limited long-term durability for mitral valve replacement.

A 20-year experience with the Hancock porcine xenograft in the elderly

BACKGROUND

The availability of 20 years of follow-up data on the Hancock porcine valve (Medtronic Inc, Irvine, CA) allows determination of long-term actual and actuarial failure rates in the elderly.

METHODS

We analyzed outcomes after mitral or aortic valve replacement with the Hancock porcine valve in 491 consecutive patients, comparing actual and actuarial valve failure rates in the elderly (age 65 or older) with those in younger patients.

RESULTS

The average age of aortic valve replacement recipients was 68+/-14 years (N = 243) and of mitral valve replacement recipients, 64+/-12 years (N = 248). Average follow-up was 7.0 years (1,673 patient-years) for aortic valve replacement and 7.3 years (1,781 patient years) for mitral valve replacement recipients. The median time to reoperation or structural failure was 15.9 years for aortic valve replacement patients and 14.3 years for mitral valve replacement patients. However, few elderly patients survived to 15 years (22% of the elderly aortic valve replacement and 13% of the older mitral valve replacement patients). The 15-year actual reoperation rate was therefore only 10% in the elderly aortic valve replacement compared to 30% in the younger aortic valve replacement patients. For mitral valve replacement, the 15-year actual reoperation rate was 11% in the elderly and 36% in the younger patients. The lifetime reoperation risk (the maximum potential number of patients who might ever undergo reoperation during their lifetime) is the sum of actual survival and actual reoperation rates. The lifetime reoperation risk was 20% or less for elderly aortic valve replacement patients and 18% or less for elderly mitral valve replacement patients.

CONCLUSION

These data suggest that about 1 in 10 elderly patients (65 years or older) receiving a Hancock valve will require reoperation within 15 years and less than one in five will ever require reoperation in their lifetimes.

Determinants of 15-year outcome with 1,119 standard Carpentier-Edwards porcine valves

BACKGROUND

The determinants of long-term outcome 15 years or more after porcine valve replacement are poorly documented.

METHODS

A retrospective review was performed of patients undergoing valve replacement with standard Carpentier-Edwards aortic (n = 531), mitral (n = 492), and tricuspid (n = 96) valves.

RESULTS

Patient survival was 26%+/-3%, 23%+/-2%, and 31%+/-8% 15 years after aortic, mitral, and tricuspid valve replacements, respectively. Independent determinants of impaired long-term survival for aortic or mitral valve replacement were multiple valve replacement, older age, renal disease, lung disease, or coronary disease. Actual (versus actuarial) freedom from reoperation at 15 years was 86%+/-2%, 76%+/-2%, and 95%+/-2% after aortic, mitral, and tricuspid valve replacement, respectively. Risk factors for reoperation were young age for aortic or mitral valve replacement, previous operation for aortic valve replacement, and large valve size for mitral valve replacement. Freedom from thromboembolism was 77%+/-4%, 62%+/-9%, and 80%+/-5%; from hemorrhage, 95%+/-5%, 87%+/-4%, and 82%+/-6%; and from endocarditis, 94%+/-1%, 96%+/-1%, and 89%+/-5% 15 years after aortic, mitral, and tricuspid valve replacement, respectively. Risk factors for thromboembolism or hemorrhage were multiple valve replacement and age.

CONCLUSIONS

The standard Carpentier-Edwards bioprosthesis continues to provide relatively low complication rates at 15 years, especially in the aortic and tricuspid positions, and especially in patients older than 60 years or with significant comorbdity.

Twenty-year follow-up of the Hancock modified orifice porcine aortic valve

BACKGROUND

The entire experience with the Hancock modified orifice porcine bioprosthetic aortic valve from 1976 to 1996 at the Brigham and Women's Hospital has been reviewed. Eight hundred forty-three patients received this valve with a total follow-up of 61,114 months, and a mean follow-up of approximately 72.5 months. There were 490 men and 353 women, and the predominate lesion was aortic stenosis (636 of 843); 365 (43%) patients required a concomitant coronary artery bypass graft operation.

METHODS

Patients were followed prospectively in the Brigham Cardiac Valve Data Registry, and the data were analyzed by the SAS statistical package, using actuarial survival curves and incidence per patient-year of morbidity and mortality.

RESULTS

The overall operative mortality was 45 of 843 (5.3%) with 23 of 478 (4.8%) for isolated aortic valve replacement and 22 of 365 (6.0%) for aortic valve plus coronary artery bypass graft operation. The major morbidity of this valve was structural valve dysfunction, which was significantly related to the age of the patient in whom the valve was placed. Actuarial probability of freedom from structural valve degeneration at 5, 10, and 15 years overall was 99%+/-1%, 79%+/-3% and 57%+/-4%, at 15 years, respectively. In patients younger than 50 years, freedom from structural valve dysfunction was 16%+/-8%, whereas in the age group older than 70 years it was 87%+/-5% (p = 0.0005). Thromboembolism at 10 and 15 years was 81%+/-3% overall, 84%+/-2% in patients in normal sinus rhythm, and 57%+/-13% in patients with chronic atrial fibrillation.

CONCLUSIONS

The Hancock modified orifice aortic valve, despite its more complicated fabrication, has been a reliable porcine bioprosthetic valve and can be used reliably in patients older than 70 years because of its low structural valve degeneration rate, and protection from stroke and anticoagulant hemorrhage in those patients in sinus rhythm.

Long-term Doppler echocardiographic results of aortic or mitral valve replacement with Biocor porcine bioprosthesis

OBJECTIVES

Our objectives were to evaluate the long-term bioprosthetic and cardiac functional outcome after insertion (over a 10-year period) of a new-generation porcine zero pressure-fixed Biocor bioprosthesis, as well as to determine the echocardiographic accuracy for selection of patients requiring reoperation. The long-term systematic Doppler echocardiographic assessment after valve replacement with this bioprosthesis is lacking.

METHODS

Between January 1983 and January 1993, we inserted 756 Biocor prostheses in the aortic (619) or mitral (137) positions. All 51 patients who had a reoperation during the follow-up time were evaluated echocardiographically before reoperation. Additionally, 263 of 446 patients (59%) with aortic bioprostheses and 42 of 74 patients (57%) with mitral bioprostheses who were alive in January 1993 had long-term echocardiographic follow-up.

RESULTS

Group A: Normally functioning bioprostheses were found in the aortic position in 242 of 263 patients and in the mitral position in 33 of 42 patients. Group B: Thirty patients had abnormal bioprosthetic function. Eleven patients had regurgitation, 3 had a combined lesion, and signs of calcification appeared in 16 patients with aortic valves, all with a peak gradient of above 60 mm Hg. Group C: Patients who had a reoperation (41 aortic and 10 mitral) within the follow-up period were followed up echocardiographically from the detection of a possible valve dysfunction until reoperation, and the findings accorded well with those at operation in 49 of 51 patients.

CONCLUSIONS

These findings suggest that, during a long-term follow-up, most bioprostheses function normally, facilitating improved heart function. Abnormalities in a bioprosthesis usually develop gradually, enabling their detection by Doppler echocardiographic evaluations performed regularly or in case of any symptomatic deterioration.

Characterization of abnormalities responsible for immediate rejection of porcine aortic valves for the manufacture of bioprostheses

Gross observation at the slaughterhouse determines the primary selection of porcine aortic valves for the manufacture of bioprostheses. This step is critical because only valves with significant abnormalities are rejected. The present study validated this selection process by investigating the pathological characteristics of one series of accepted valves and one series of rejected valves. Macroscopy, x-ray examination, light microscopy, and scanning electron microscopy (SEM) were performed on 5 initially rejected valves, 3 leaflets from 3 other initially rejected valves, and 6 valves that successfully passed this first step in the selection process. Abnormalities were macroscopically visible only on the rejected valves and were described as thick white areas, heavy white striations, thin spots, white plaques, and nodules. Individual variability in the structure of each leaflet was more significant in the rejected valves than in the valves that had passed the first inspection. The leaflets of the rejected valves were also irregularly thick with a lack of consistency in the position and prominence of the different layers. The formation of nodules and the presence of white plaques in the inner fibrosa layer were among the pathological features. The initially accepted valves considered defect free under gross observation continued to display some weaknesses, and not all of the valves selected during the first step of the process were suitable to become bioprostheses. Because the manufacturer carries out further quality control inspections at every step of preparation resulting in additional rejections, it is therefore anticipated that all valves with defects will be rejected. None of the rejected valves were defect free, and rejection was fully justified.

Aortic stenosis. Clinical evaluation and optimal timing of surgery

Aortic valve disease is common in the elderly with recent data suggesting that aortic sclerosis and stenosis are the end-stage of an active disease process. Aortic atenosis may be diagnosed at symptom onset (angina, heart failure or syncope) but often the diagnosis is suspected in an asymptomatic patient with a systolic murmur. The diagnosis can be confirmed and disease severity evaluated reliably using Doppler echocardiography. Symptomatic severe aortic stenosis is treated with valve replacement, even in the elderly, due to the extremely poor prognosis without relief of outflow obstruction. Management is controversial when there is coexisting moderate aortic stenosis and left ventricular systolic dysfunction.