Cardiac bioprostheses in the 1990s

Studying Xenograft Rejection of Bioprosthetic Heart Valves

Millions of patients with valvular heart disease have benefitted from heart valve replacement since the procedure was first introduced in the 1960s; however, there are still many patients who get early structural valve deterioration (SVD) of their bioprosthetic heart valves (BHV). BHV are porcine, bovine, or equine tissues that have been glutaraldehyde fixed to preserve the tissue and presumably make the tissue immunologically inert. These glutaraldehyde-fixed BHV with anti-calcification treatments last long periods of time in older adults but develop early SVD in younger patients. The consensus at present is that the early SVD in younger patients is due to more "wear and tear" of the valves and higher calcium turnover in younger patients. However, as younger patients likely have a more robust immune system than older adults, there is a new hypothesis that BHV xenografts may undergo xenograft rejection, and this may contribute to the early SVD seen in younger patients.At present, the technology to noninvasively study in vivo whether an implanted BHV in a human patient is undergoing rejection is not available. Thus, a small animal discordant xenotransplant model in young rodents (to match the young patient getting a pig/bovine/equine BHV) was developed to study whether the hypothesis that glutaraldehyde-fixed BHV undergo xenograft rejection had any merit. In this chapter, we describe our model and its merits and the results of our investigations. Our work provides clear evidence of xenograft rejection in glutaraldehyde-fixed tissue, and our small animal model offers an opportunity to study this process in detail.

Approach to the analysis of cardiac valve prostheses as surgical pathology or autopsy specimens

Pathologists are likely to encounter substitute heart valves with increasing frequency. Informed evaluation of such valves provides valuable information that contributes to both patient care and our understanding of the pathobiology of host interactions with mechanical devices. This article summarizes the most important considerations underlying such analyses-including valve identification, common morphologic features and modes of failure, technical details of evaluation, and potential pitfalls.

Triglycidyl amine crosslinking combined with ethanol inhibits bioprosthetic heart valve calcification

BACKGROUND

One of the most important factors responsible for the calcific failure of bioprosthetic heart valves is glutaraldehyde crosslinking. Ethanol (EtOH) incubation after glutaraldehyde crosslinking has previously been reported to confer anticalcification efficacy for bioprostheses. The present studies investigated the anticalcification efficacy in vivo of the novel crosslinking agent, triglycidyl amine (TGA), with or without EtOH incubation, in comparison with glutaraldehyde.

METHODS

The TGA crosslinking (±EtOH) was used to prepare porcine aortic valves for both rat subdermal implants and sheep mitral valve replacements, for comparisons with glutaraldehyde-fixed controls. Thermal denaturation temperature, an index of crosslinking, cholesterol extraction, and hydrodynamic properties were quantified. Explant endpoints included quantitative and morphologic assessment of calcification.

RESULTS

Thermal denaturation temperatures after TGA were intermediate between unfixed and glutaraldehyde-fixed. EtOH incubation resulted in almost complete extraction of cholesterol from TGA or glutaraldehyde-fixed cusps. Rat subdermal explants (90 days) demonstrated that TGA-EtOH resulted in a significantly greater level of inhibition of calcification than other conditions. Thus, TGA-ethanol stent mounted porcine aortic valve bioprostheses were fabricated for comparisons with glutaraldehyde-pretreated controls. In hydrodynamic studies, TGA-EtOH bioprostheses had lower pressure gradients than glutaraldehyde-fixed. The TGA-ethanol bioprostheses used as mitral valve replacements in juvenile sheep (150 days) demonstrated significantly lower calcium levels in both explanted porcine aortic cusp and aortic wall samples compared with glutaraldehyde-fixed controls. However, TGA-EtOH sheep explants also demonstrated isolated calcific nodules and intracuspal hematomas.

CONCLUSIONS

The TGA-EtOH pretreatment of porcine aortic valves confers significant calcification resistance in both rat subdermal and sheep circulatory implants, but with associated structural instability.

Evaluation of hemolysis in patients with prosthetic heart valves

The primary mechanism and most common cause of hemolytic disease in patients with prosthetic heart valves are mechanical trauma to red blood cells and paraprosthetic valvular regurgitation, respectively. Presenting features in patients with this condition include anemia, congestive heart failure, fatigue, jaundice, dark urine, and a regurgitant murmur. Various laboratory studies can be utilized to diagnose hemolytic anemia and to assess the severity of hemolysis. Transthoracic echocardiography, transesophageal echocardiography, and Doppler studies including color Doppler are useful imaging methods to assess valve function. Treatment is usually medical (oral iron); however, in patients with paravalvular regurgitation, surgery is often required to correct the anemia.

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.

Biomechanics of engineered heart valve tissues

The vast majority of prosthetic valve designs are either mechanical prosthesis and bioprosthetic heart valves (BHV). Mechanical prostheses are fabricated from synthetic materials, mainly pyrolytic carbon leaflets mounted in a titanium frame. Tissue engineering (TE) offers the potential to create cardiac replacement structures containing living cells, which has the potential for growth and remodeling, overcoming the limitations of current pediatric heart valve devices. The purpose of this paper is to present a review of the structure-strength relationships for native and engineered heart valve tissues.

Regulation of endothelial cell phenotype by biomimetic matrix coated on biomaterials for cardiovascular tissue engineering

One major weakness that all cardiovascular replacements have in common is the lack of endothelial cell (EC) growth and post-implant remodeling of the device. The emerging field of tissue engineering focuses on the in vitro generation of functional organ replacements using living endothelial cells and other vascular cells for which nondegradable or biodegradable scaffold base materials are used. In this paper, it is demonstrated that some of the cardiovascular device materials in clinical use lack the ability to promote endothelial cell growth in vitro. We previously established a biomimetic matrix composition which supports the growth of human umbilical vein endothelial cells (HUVECs) while maintaining normal physiology in vitro. Here the effectiveness of the same coating to preserve the normal antithrombotic phenotype of endothelial cells grown on biomaterials was evaluated. The up/down-regulation of two prothrombotic and two antithrombotic molecules by HUVECs grown on bare material surfaces were compared with that on composite-coated materials. The suitability of this approach for blood-contacting applications was investigated by in vitro blood compatibility studies as recommended in ISO10993 part 4, by putting an EC-seeded surface in contact with human whole blood. It is demonstrated that EC-seeded bare material surfaces are prothrombotic, whereas surfaces pre-coated with biomimetic molecules facilitated maintenance of the normal EC phenotype and reduced the risk of platelet adhesion and activation of blood coagulation. The results presented here suggest that matrix composed of biomimetic adhesive proteins and growth factors is suitable for cardiovascular tissue engineering to improve biological function, irrespective of the material chosen to meet the mechanical properties of the device.

Effects of collagen fiber orientation on the response of biologically derived soft tissue biomaterials to cyclic loading

In the present study, the effects of initial collagen fiber orientation on the medium-term (up to 50 x 10(6) cycles) fatigue response of heart valve soft tissue biomaterials was investigated. Glutaraldehyde treated bovine pericardium (GLBP), preselected for uniform structure and collagen fiber orientation, was used as the representative heart valve biomaterial. Using specialized instrumentation, GLBP specimens were subjected to cyclic tensile loading to maximum stress levels of 500 +/- 50 kPa at a frequency of 22 Hz. Two sample groups were examined, one with the preferred collagen fiber direction parallel (PD) and perpendicular (XD) to the direction of applied strain. The primary findings indicated that GLBP fatigue response was highly sensitive to the direction of loading with respect to fiber orientation. Specifically, when loading perpendicular to the preferred collagen fiber orientation, fiber reorientation is the dominant mechanism. In contrast, when loaded parallel to the preferred fiber direction a reduction in both collagen fiber crimp and fiber reorientation occurred. Moreover, alterations in the degree and direction of mechanical anisotropy can be inducted by cyclic loading when specimens are loaded perpendicular to the preferred fiber direction. Fourier Transform Infrared Spectroscopy (FT-IR) results indicate that molecular-level damage to collagen occurs in both groups after only 20 x 10(6) cycles. Taken as a whole, the results of this study suggest that initial collagen orientation plays a critical role in bioprosthetic heart valve biomaterial fatigue response.

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.

Cyclic loading response of bioprosthetic heart valves: effects of fixation stress state on the collagen fiber architecture

Biologically derived, chemically modified collagenous tissues are being increasingly used to fabricate cardiac valve prostheses and as biomaterials in cardiovascular repair. A stress-free state during chemical modification has been shown to preserve the collagen fiber architecture of the native tissue, potentially preserving native mechanical properties and improving prostheses durability. However, it is not known if the native collagen fiber architecture is stable during long-term in vivo operation. To address this question, we obtained porcine aortic valves chemically treated at (i) 0 mmHg transvalvular pressure (with 40 mmHg aortic pressure) and (ii) 4 mmHg transvalvular pressure, then subjected the valves to 0, 1 x 10(6), 50 x 10(6), and 200 x 10(6) in vitro accelerated wear testing (AWT) cycles. The resulting changes in collagen fiber architecture were quantified using small angle light scattering analysis (SALS). SALS measurements indicated that collagen fibers in the 0 mmHg pressure-fixed leaflets became more aligned between 1 x 10(6) and 50 x 10(6) AWT cycles. In contrast, only minor changes (not statistically significant) in collagen fiber orientation occurred in the 4 mmHg pressure-fixed valvular tissue with cycling. It was also noted that although the 0 mmHg group was fixed without transvalvular pressure, distention of the root induced significant changes in collagen structure of the leaflets. Overall, our observations suggest that the native collagen fiber crimp of the 0 mmHg pressure-fixed leaflets were rapidly lost after only 50 x 10(6) AWT cycles (equivalent to approximately 1.6 patient years) and thus may not be maintained over a sufficient period of time to be clinically beneficial. Further, the collagen structure of the native aortic valve is exquisitely sensitive to dimensional change in the aortic root-independent of the presence of transvalvular pressure. Our findings also suggest that without in vivo remodeling, any collagenous tissue used to fabricate BHV may undergo similar degenerative, irreversible changes in vivo.

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.

Response of heterograft heart valve biomaterials to moderate cyclic loading

We have recently demonstrated that noncalcific tissue damage can lead to significant collagen degradation in clinically explanted bioprosthetic heart valves (BHVs). In the present study we quantified the early response of glutaraldehyde treated bovine pericardium (GLBP) to cyclic tensile loading to begin to elucidate the mechanisms of noncalcific tissue degeneration in BHV biomaterials. GLBP specimens were cycled at 30 Hz to a maximum uniaxial strain of 16% (corresponding to approximately 1-MPa peak stress), with the loading direction parallel to the preferred collagen fiber (PD) direction. After 30 x 10(6) cycles, specimens were subjected to biaxial mechanical testing, then cycled until 65 x 10(6) cycles. The results indicated a permanent change in the unloaded tissue dimensions of +7.1% strain in the PD direction and -7.7% strain in the cross fiber direction (XD) after 65 x 10(6) cycles and an increase of the collagen crimp period from 40.6 to 45.2 microm by 65 x 10(6) cycles (p = 0.05). Fourier transform IR spectroscopy analysis indicated that cyclic fatigue of GLBP leads to both collagen conformational changes and early denaturation. Furthermore, no significant changes in areal strain were found under 1-MPa equibiaxial stress, indicating that cyclic loading changed the collagen fiber orientation but not the overall tissue compliance. These observations suggest that while deterioration of collagen begins immediately, fiber straightening and reorientation dominates the changes in the mechanical behavior up to 65 x 10(6) cycles. The present study underscores the complexity of the response of biologically derived biomaterials to cyclic mechanical loading. Improved understanding of these phenomena can potentially guide the development of novel chemical treatment methods that seek to improve BHV durability by minimizing these degenerative processes.

Acellular scaffold implantation--no alternative to tissue engineering

OBJECTIVE

Degradation mechanisms of cardiovascular bioprostheses may play an important role in bioartificial implants. The fate of acellular implanted and cellular cardiovascular scaffolds was examined in an in vivo model.

METHODS

Decellularized or native ovine carotid artery (CA, n=42) and aorta (AO, n=42) were implanted subcutaneously into rats for 2, 4 and 8 weeks. Immunohistochemical methods were used to monitor repopulation. Desmin-vimentin, CD31-, CD4- and CD18-antibodies for myocytes, endothelium, and inflammatory cell-infiltration, respectively. Calcification was detected by von-Kossa staining. Cell density was quantified by DNA-isolation.

RESULTS

Acellular AO and CA matrices showed progressive calcification. Cellular AO and CA matrices trigger a strong inflammatory reaction which subsides after two weeks. CA scaffolds are revascularized progressively, whereas AO biocomposites degenerate. Calcification is less pronounced in cellular AO scaffolds and lacking in CA.

CONCLUSION

Acellular bioartificial implants demonstrate degradation mechanisms similar to currently applied cardiovascular bioprostheses. Cellularized viable implants are promising clinical alternatives.

Collagen fiber disruption occurs independent of calcification in clinically explanted bioprosthetic heart valves

The durability of bioprosthetic heart valves (BHV) is severely limited by tissue deterioration, manifested as calcification and mechanical damage to the extracellular matrix. Extensive research on mineralization mechanisms has led to prevention strategies, but little work has been done on understanding the mechanisms of noncalcific matrix damage. The present study tested the hypothesis that calcification-independent damage to the valvular structural matrix mediated by mechanical factors occurs in clinical implants and could contribute to porcine aortic BHV structural failure. We correlated quantitative assessment of collagen fiber orientation and structural integrity by small angle light scattering (SALS) with morphologic analysis in 14 porcine aortic valve bioprostheses removed from patients for structural deterioration following 5-20 years of function. Calcification of the explants varied from 0 (none) to 1+ (minimal) to 4+ (extensive), as assessed radiographically. SALS tests were performed over entire excised cusps using a 0.254-mm spaced grid, and the resultant structural information used to generate maps of the local collagen fiber damage that were compared with sites of calcific deposits. All 42 cusps showed clear evidence of substantial noncalcific structural damage. In 29 cusps that were calcified, structural damage was consistently spatially distinct from the calcification deposits, generally in a distribution similar to that noted in porcine BHV subjected to in vitro durability testing. Our results suggest a mechanism of noncalcific degradation dependent on cuspal mechanics that could contribute to porcine aortic BHV failure.

Aortic valve replacement: current clinical practice and opportunities for quality improvement

This is a review of the current clinical practice and opportunities for quality improvement in aortic valve replacement surgery. The topics include trends and regional variation in procedure rates, and changes in the use of aortic valve replacement among the elderly. Recent developments guiding the choice of prosthetic valves and trends in in-hospital mortality rates for aortic valve surgery are summarized. Lastly, a discussion of topics relevant to clinical practice improvement including the implementation of clinical practice guidelines, the need for consensus on risk adjustment, better understanding of volume-outcome effects, and the opportunities for comprehensive assessment of aortic valve surgery.

Prosthetic valve type for patients undergoing aortic valve replacement: a decision analysis

BACKGROUND

In two large, randomized, clinical trials long-term survival after aortic valve replacement (AVR) was similar for patients receiving tissue and mechanical aortic heart valve prostheses. Higher bleeding rates among patients with mechanical valves, who must receive permanent oral anticoagulation to prevent thromboembolism, were offset by higher reoperation rates for valve degeneration among patients with tissue valves. Because the average age of patients undergoing AVR and clinical practices have changed considerably since the randomized clinical trials were conducted, we performed a decision analysis to reassess the optimal valve type for patients undergoing AVR.

METHODS

We used a Markov state-transition model to simulate the occurrence of valve-related events and life expectancy for patients undergoing AVR. Probabilities of clinical events and mortality were derived from the randomized clinical trials and large follow-up studies.

RESULTS

Although the two valve types were associated with similar life expectancy in 60-year-old patients (mean age of patients in the randomized clinical trials), tissue valves were associated with greater life expectancy than mechanical valves (10.7 versus 11.1 years) in 70-year-old patients (currently mean age of AVR patients). For 70-year-old patients, the effects of major bleeding complications (24%) with mechanical valves substantially outweighed those of reoperation for valve failure (12%) with tissue valves at 12 years. Of the clinical practice changes assessed, the recommended valve type was most sensitive to changes in bleeding rates with anticoagulation. However, bleeding rates would have to be 68% lower than those reported in the European randomized clinical trial to affect the recommended valve type for 70-year-old patients. Reoperation rates would have to be five times higher, and mortality rates at reoperation would have to be four times higher to affect the recommended valve type for 70-year-old patients.

CONCLUSIONS

Although mechanical valves are preferred for AVR patients less than 60 years old, most patients currently undergoing AVR are elderly and would benefit more from tissue valves.

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.

Manual debridement of the aortic valve in elderly patients with degenerative aortic stenosis

OBJECTIVE

We prospectively analyzed the short- and long-term results of manual debridement of the aortic valve in elderly patients with severe degenerative aortic stenosis.

METHODS

Between September 1988 and January 1997, 103 patients aged 73.7 +/- 6 years with degenerative aortic stenosis underwent the manual debridement technique. All had symptoms (angina or dyspnea, or both). Peak systolic gradient was 89 +/- 28 mm Hg. Forty-one patients (39.8%) had associated coronary artery disease necessitating revascularization.

RESULTS

Follow-up time was 42 +/- 21 months (range 3-98 months). The Kaplan-Meier estimated survival at 98 months was 50% (95% CI: 30%-70%). In-hospital mortality was 5.8% (6 patients), and late mortality was 21% (21 patients). No predictors of in-hospital mortality or of late mortality were detected. Nonfatal postoperative complications appeared in 25 patients (24%). At 8 years, freedom from endocarditis was 98% (95% CI: 95%-100%) and freedom from thromboembolic events was 99% (95% CI: 96%-100%). No patient required long-term anticoagulation as a result of the procedure. Fourteen patients (14%) required reoperation for aortic insufficiency (n = 5), restenosis (n = 8), and mitral regurgitation (n = 1). The probability of reoperation at 98 months was 23% (95% CI: 12%-35%).

CONCLUSION

Manual aortic valve debridement has low rates of in-hospital mortality, perioperative complications, and thromboembolic and infectious events and it offers freedom from anticoagulation. However, the incidence of restenosis and reoperation is high in the long term. It may therefore be regarded as an alternative in aged patients with favorable valve anatomy (no distortion and calcium deposits only on the aortic surface of the cusps), especially in those with a small aortic anulus, associated coronary artery disease, and/or contraindication for anticoagulation.

Comparison of different anticalcification treatments for stentless bioprostheses

BACKGROUND

New anticalcificant treatments have been developed because tissue calcification is a major contributing factor for bioprosthetic valve failure.

METHODS

Aortic valve leaflet and aortic root tissue samples from stentless bioprostheses treated with No-React (Biocor, Belo Horizonte, Brazil), AOA (Medtronic freestyle, Minneapolis, MN), and BiLinx (St. Jude Medical, St. Paul, MN) were compared to a control group by subcutaneous implantation in 60 male weanling Sprague-Dawley rats.

RESULTS

Calcium levels were in the range of 0.3 to 2.2 mg/g dry tissue at 3 and 12 weeks in all three treated aortic valve leaflet implants. The BiLinx treatment proved anticalcificant effectiveness on aortic root samples as well. There were statistically significant differences for valve leaflet tissue samples: No-React = AOA < BiLinx < < Control and for aortic root tissue samples: BiLinx < < AOA < Control = No-React.

CONCLUSION

Calcification of aortic valve leaflets was significantly reduced by all new anticalcificant treatments. Inhibition of cellular calcification (BiLinx) resulted in additional reduction of aortic root calcification. Maximum anticalcificant properties upon both leaflet and aortic root is important as these are considered a functional unit in stentless bioprostheses.

Valvular heart disease in pregnancy. A contemporary perspective

Valvular heart disease may have a significant impact on the course and outcome of pregnancy with implications for fetal as well as maternal health. Optimally, serious symptomatic valvular heart disease should be detected and treated before pregnancy. Whether a pregnant woman is known to have valvular heart disease or is diagnosed during pregnancy, it is imperative that she is managed by an experienced multidisciplinary team. Although medical therapy may alleviate symptoms of heart failure in some patients, definitive intervention either with percutaneous balloon valvuloplasty or with surgical valve replacement may be necessary.

Clinical, echocardiographic, and pathologic features of aortic wall dehiscence of porcine bioprosthetic valves: a cause of rapidly progressive mitral regurgitation and heart failure after bioprosthetic mitral valve replacement

The aim of this study was to define the clinical, echocardiographic, and pathologic correlates of commissural dehiscence of aortic wall from the stent post of the porcine bioprostheses in the mitral position. This form of valve degeneration was found in 5 of 23 explanted mitral bioprostheses. A thickened, separated aortic wall at multiple commissural sites along with other evidence of valve degeneration was identified in the three patients who had chronic congestive heart failure. A large dehiscence at a single commissural site with otherwise normal valve morphology was present in the two patients who had acute heart failure. Two dimensional/Doppler echocardiography showed a prolapsing or a flail anteriorly positioned leaflet and an eccentric posteriorly directed mitral regurgitation jet in all patients. These echocardiographic findings in patients with a porcine bioprosthetic mitral valve should suggest commissural dehiscence from the aortic wall as a possible mechanism of valve failure. Exclusive involvement of the porcine aortic bioprosthesis placed in the mitral position along with involvement of strut of the bioprosthesis facing the aortic root in all cases suggests excessive hemodynamic stress on the valve in the mitral position and in particular on the anteriorly placed strut as the potential cause of this form of valve degeneration.

Differential calcification of cusps and aortic wall of failed stented porcine bioprosthetic valves

In this study, we examined separately calcification of cusps (C) and associated aortic wall (AW) of 38 (13 aortic and 25 mitral) porcine bioprosthetic heart valves explanted from 37 patients (ages 25-80 years, mean 59) for structural dysfunction, following 54-210 months (mean 125 months aortic, 119 months mitral). Valves were sectioned into C and corresponding AW components; calcification was assessed by atomic absorption spectroscopy for calcium and histologic examination. Overall, AW calcification was half that of C (33.3 +/- 5.4 vs. 65.9 +/- 6.3 microg/mg, mean +/- standard error of the mean respectively, p = 0.002). Correlation of calcification in individual C/AW pairs was weak (r2 = 0.34). Calcification in C was nodular, largely in the valve fibrosa, but AW calcification predominated in the cells between elastic lamellae; large nodules were sparse. We conclude that since AW calcification in these failed porcine valves was neither prominent nor clinically significant, this process should rarely if ever be a limiting factor in the function of stented porcine valves, and that development of anticalcification therapies directed toward the AW of stented valves should be of low priority. However, in stent-free valves, the AW is not covered by prosthetic material, and the level of calcification could be greater and more likely to cause clinical problems through stiffening, embolism, and/or protrusion into the lumen of calcific masses.

Clinical and echocardiographic follow-up after aortic valve reconstruction with bovine or autologous pericardium

Eighty-six patients, mean age 29 +/- 15 years, underwent aortic valve reconstruction with bovine or autologous pericardial tissue. Mean clinical follow-up was 35 months. Echocardiographic data were assessed in 65 patients with follow-up > or = 6 months. There were two in-hospital and three late deaths. Warfarin was not given, and no thromboembolic events occurred. Five (6%) patients needed reoperation because of severe aortic regurgitation. Peak aortic valve gradients remained low (26 +/- 14 mm Hg for the bovine group and 16 +/- 16 mm Hg for the autologous group). One patient is awaiting surgery for aortic stenosis after 76 months. Leaflet thickening at latest follow-up was marked in six (9%) patients. Left ventricular dimensions normalized postoperatively and showed only insignificant increase during follow-up. This technique is a promising alternative to valve prosthesis in selected patients; however, longer follow-up is necessary to assess long-term results.

Bioprosthetic mitral valve thrombosis: clinical profile, transesophageal echocardiographic features, and follow-up after anticoagulant therapy

Cardiac bioprosthetic valve thrombosis is frequently found on pathologic examination, but preoperative diagnosis is rarely performed. Four hundred six patients with mitral porcine xenograft bioprostheses were examined by transthoracic echocardiography. Transesophageal echocardiography (TEE) was performed in 161 of the patients, with clinical or echocardiographic criteria of prosthetic malfunction. Fairly homogeneous and echodense masses, attached to the ventricular surface of the mitral bioprosthetic cusps, were detected by TEE in 15 patients. Only 10 patients, in whom diagnosis of bioprosthetic thrombosis was confirmed, are included in this study. After TEE, two patients underwent prosthetic replacement and eight patients received anticoagulants. A new TEE was performed 85.6 +/- 29.8 days after anticoagulation in these eight patients. Clinical follow-up was continued for 13.6 +/- 8.6 months, and one additional patient underwent surgery during the follow-up. Pathologic examination of removed grafts (three cases) identified these masses as being thrombotic tissue. TEE examination after therapeutic anticoagulation demonstrated complete disappearance of the echogenic masses on bioprosthetic cusps and normal mobility of all leaflets in six cases. In the other two cases, cusp masses were notably reduced, but partially restrictive mobility of affected leaflets persisted, suggesting incomplete resolution of thrombi. Mitral valve prosthetic mean gradient decreased from 11.8 +/- 4.5 to 7.6 +/- 3.7 mm Hg (p < 0.001), and mitral valve area increased from 1.13 +/- 0.3 to 1.72 +/- 0.6 cm2 (p < 0.001). Long-term symptomatic improvement after anticoagulation was obtained in seven patients. Thus this study shows that mitral bioprosthetic thrombosis is a relatively frequent cause of valve dysfunction, TEE is useful for detecting thrombus in relation to mitral bioprosthetic valves, and oral anticoagulation is effective in resolving thrombosis on bioprostheses.

Biological valves beyond fifteen years: the Wessex experience

Between 1975 and 1979, 443 biological valves (298 Carpentier-Edwards, 134 homograft, and 11 Hancock valves) were implanted in 415 patients (age, 16 to 77 years; mean, 59 years) with an operative mortality of 2.9%. Total follow-up was 4,248 patient-years. Overall event-free survival was 60% +/- 1.5% (standard deviation) at 10 years and 29% +/- 1.4% at 15 years. Ten-year and 15-year event-free survival were 72% +/- 3.4% and 41% +/- 3.3% for aortic homografts, 62% +/- 3% and 33% +/- 2.8% for isolated aortic xenografts, and 43% +/- 3.5% and 14% +/- 3.0% for isolated mitral xenografts. Freedom from structural valve degeneration was 87% +/- 1.3% and 63% +/- 2.5% for all patients at 10 and 15 years, respectively, 86% +/- 2.7% and 58% +/- 4.1% for aortic homografts, 93% +/- 1.8% and 76% +/- 5.1% for aortic xenografts, and 75% +/- 4.0% and 47% +/- 7.4% for mitral xenografts. Of the 110 remaining patients, echocardiography was performed in 61 patients (23 aortic xenograft, 24 aortic homograft, 9 mitral xenograft, and 5 tricuspid xenograft) between 14 and 17 years after implantation. An early diastolic murmur was heard in 57% of all aortic valve replacements (AVRs) 62.5% of homograft AVRs, and 52% of xenograft AVRs. Echocardiographically, aortic regurgitation was detected in 79%, 83%, and 74% of all AVRs, homografts, and xenografts, respectively. Aortic stenosis was present clinically in 11% of all AVRs, 4% of homograft AVRs, and 17% of xenograft AVRs.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial and transient relief of conduit obstruction by low-pressure balloon dilation in patients with congenital heart disease

Seven patients underwent attempted low pressure balloon dilation of stenotic conduits or homografts from right ventricle to pulmonary artery (n = 5), in the aortic valve position (n = 1), or from right atrium to left pulmonary artery (n = 1). In the right ventricle to pulmonary artery group, mean gradient reduction was only 17%. At follow-up, two patients underwent surgical conduit replacement, one had a stent implanted at cardiac catheterization, the other two are awaiting surgical intervention. The patient with a homograft in the aortic valve position had a good initial result but restenosed within 1 year and underwent a pulmonary autograft operation. The patient with the Fontan homograft stenosis had transient obstruction relief but subsequently required stent implantation. Low-pressure balloon dilation of conduits or homografts is only partially and transiently successful. Whether stent implantation will offer better long-term results remains to be determined.

Pathology of substitute heart valves: new concepts and developments

All types of contemporary cardiac valve substitutes suffer deficiencies and complications that limit their success. Mechanical and bioprosthetic valves are intrinsically obstructive, especially in small sizes. Mechanical valves are associated with thromboembolic problems; the chronic anticoagulation used in virtually all mechanical valve recipients causes hemorrhage in some. Calcification limits the success of porcine and pericardial bioprostheses, allograft valves, and the yet experimental trileaflet polymeric prostheses. The predominant mechanism of calcification in porcine, pericardial, and allograft valves is cell mediated, being nucleated at the membranes and in organelles of the transplanted cells. In polymeric leaflet valves, calcification is both extrinsic (in adherent thrombus) and intrinsic (subsurface and acellular in the solid elastomer). Nevertheless, except for a few notable exceptions, contemporary mechanical valves are durable. Other important potential complications of prosthetic and bioprosthetic valves include paravalvular leak, endocarditis, or extrinsic interference with function. Moreover, aortic valvular allografts undergo progressive noncalcific degeneration, tearing, sagging, and/or retraction. Studies of retrieved long-term cryopreserved allograft explants demonstrate severe degeneration, with distortion of normal architectural detail, loss of endothelial and deep connective tissue cells, and variable inflammatory cellularity. Thus, they are morphologically nonviable valves, whose structural basis for function seems primarily related to the largely preserved collagen, and they are unlikely to have the capacity to grow, remodel, or exhibit active metabolic functions. Since calcification intrinsic to the cusps is the major pathologic process necessitating bioprosthetic valve reoperations, efforts to prevent formation of mineral deposits are active.(ABSTRACT TRUNCATED AT 250 WORDS)