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Publication:

Surgical Technology International XV - Cardiovascular Surgery

Article title:

Advanced Technologies for Cardiac Valvular Replacement, Transcatheter Innovations and Reconstructive Surgery

Contents:

 

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1. Article Information, Introduction, Background

2. Current Bioprostheses

3. Mechanical Prostheses

4. Transcatheter Heart Valve Therapies, Aortic Valve Replacement

5. Mitral Valve Reconstruction

6. Annuloplasty Prostheses For Valvular Reconstructive Surgery

7. Technological Advances, Clinical Performance, Summary of Experience

8. Indications for Prostheses Choice, Conclusion

9. References

Current BioProstheses

 

Biological valvular prostheses are formulated from porcine aortic valves or bovine pericardium

(see Table I).

 

The natural aortic valve possesses unique architectural and material characteristics consistent with functional requirements (Fig. 1).

Porcine bioprostheses have had tissue preservation at high pressure, low pressure, or pressure-free with glutaraldehyde to preserve bioprosthetic function and provide durability. The tissue preservation, together with stent designs, contribute to the anatomical characteristics and biomechanical properties of the leaflets. The first-generation porcine bioprostheses—Hancock standard and Carpentier-Edwards standard—had the porcine tissue fixed with glutaraldehyde at high pressure, 60 to 80 mmHg. The current generation porcine prostheses are primarily either low (<2 mmHg) pressure or zero pressure glutaraldehyde-fixed prostheses. The bovine pericardial prostheses have used pressure-free fixation with glutaraldehyde; the current generation has used advanced engineering to formulate the tissue-stent relationship.

The Carpentier-Edwards supra-annular (SAV) porcine bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) has a supra-annular configuration, mounted on a flexible Elgiloy™ wire frame for stress reduction

(Fig. 2). The prosthesis has a reduced stent profile and the tissue is preserved with glutaraldehyde at low pressure fixed at less than 4 mmHg. The tissue is treated with the calcium-mitigation agents, polysorbate-80, and ethanol (XenoLogiX). The supra-annular placement of the SAV yields the orifice area comparable to the patient’s annulus with no intra-annular component.

 

The Carpentier-Edwards PERIMOUNT pericardial bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) is biomechanically engineered and constructed with an Elgiloy™ stent at the orifice and commissures for flexibility. The prosthesis has an incomplete supra-annular configuration with intra-annular component. The pericardium is fixed by the Neutrologic stress-free process in glutaraldehyde. Leaflets are produced by computer-aided design for optimal leaflet to stent matching (Fig. 3a & 3b). The PeriMap pericardial thickness mapping technology, and tissue deflection testing enables the leaflets to be matched accurately. Leaflets achieve satisfactory coaptation without stent-post sutures. The tissue is treated with the calcium mitigation agents, polysorbate 80 and ethanol (XenoLogiX).

The Carpentier-Edwards Duraflex low-pressure mitral bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) is mounted on a flexible Eligiloy™ stent to reduce the loading on critical areas of tissue (Fig. 4). The porcine leaflets are preserved with glutaraldehyde at low- pressure fixation to preserve the natural flexibility of the valve leaflet tissue. The prosthesis has an extended sewing ring to provide a larger suture surface for mitral placement. The asymmetric orifice design accommodates the muscle shelf of the porcine valve. The tissue is treated with calcium mitigation agents, polysorbate-80, and ethanol in the XenoLogiX process.

The Carpentier-Edwards PERIMOUNT Magna aortic bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) has a true supra-annular design to achieve optimal hemodynamics and flow characteristics. The PERIMOUNT Magna is a redesign of the PERIMOUNT for total supra-annular configuration (Fig. 5a). Tissue treatment of the pericardium incorporates glutaraldehyde and the calcium-mitigation processes, namely, XenoLogiX and ThermaFix, to remove the two major calcium-binding sites, phospholipids and residual aldehydes. The ThermaFix is an extended heating process of the pericardium.
The Carpentier-Edwards PERIMOUNT Magna mitral bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) is a biomechanically engineered valve (Fig 5b). The tissue is treated and prepared in the same fashion as the Carpentier-Edwards PERIMOUNT Plus mitral pericardial bioprostheses with the addition of the ThermaFix advanced tissue processing to control major calcium-binding. The prosthesis has a low profile in support of minimally invasive procedures but a wide sewing cuff, which supports adequate suturing and covers mitral annulus irregularities. The anatomical saddle shape of this prosthesis provides a unique feature, which conforms to the native anatomy.

The Carpentier-Edwards PERIMOUNT Plus mitral pericardial bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) is a biomechanically engineered valve (Fig. 6). The tissue is treated with stress-free Neutralogic fixation, Peri-Map pericardial thickness mapping technology, and tissue-deflection testing for leaflets to be matched accurately. The tissue is treated with the XenoLogiX calcium mitigation therapy.

The Carpentier-Edwards PERIMOUNT Theon mitral replacement system (Edwards Lifesciences, Irvine, CA, USA) is the PERIMOUNT Plus inclusive of the Carpentier-Edwards ThermaFix advanced tissue process to control both of the major calcium binding sites— phospholipids and residual aldehydes (Fig. 7).

The Edwards Prima™ Plus is a stentless porcine bioprosthesis (Edwards Lifesciences, Inc., Irvine, CA, USA) desig-ned as a versatile cylinder without prefashioned coronary openings (Fig. 8). The prosthesis has a Dacron™ mesh that covers the muscle shelf and forms a thin proximal cuff. The porcine tissue is glutaraldehyde fixed at low pressure with sinus-area dilatation. The tissue processing incorporates the XenoLogiX anticalcification technology. The prosthesis can be implanted as a freehand subcoronary, miniroot cylinder, or aortic root replacement technique. The Carpentier-Edwards Biophysio aortic bioprosthesis (Edwards Lifesciences, Irvine, CA, USA) is a trileaflet valve composed of bovine pericardium mounted on a highly flexible nitinol frame designed for supra-annular placement in the aortic root above the native aortic annulus below the coronary ostia (Fig. 9). The bioprosthesis is preserved in buffered glutaraldehyde solution and treated with the ThermaFix process, which involves heat treatment of the tissue in glutaraldehyde and uses ethanol and the surfactant, polysorbate-80. The bioprosthesis is packaged and terminally sterilized in glutaraldehyde. The mounting sizes of the bioprosthesis are 19 mm to 25 mm. The frame of the valve is designed to be secured within the aortic root and to be compliant at the orifice and commissures. The compliance is designed to optimize the orifice area, and reduce the closing loading shock at the commissures and free margins of the leaflets. A silicone sewing band covered with woven polytetrafluoroethylene (PTFE) cloth is attached to the nitinol frame, covered with polyester cloth. The Hancock II porcine bioprosthesis (Medtronic, Inc., Minneapolis, MN, USA) is a supra-annular prosthesis (Fig. 10). The prosthesis has an acetal homopolymer flexible stent, scalloped aortic sewing ring, and reduced stent profile, fixed with glutaraldehyde at low pressure, subsequently, for a prolonged period at high pressure. The prosthesis is treated with sodium dodecyl sulphate to retard calcification.
The sewing ring of the current Hancock II valve is mounted flush with the inflow edge of the scalloped stent. This refinement in design allows the new Hancock II aortic bioprosthesis to be positioned in the Supra-X position. Supra-X positioning refers to placement of the valve on the patient’s annulus—”supra” and “extra” annular. The prosthesis is placed, in effect, “up and out” of the annulus. Supra-X positioning allows blood flow through the annulus to encounter only tissue, not obstructive components such as the stent and sewing ring. This positioning increases the area available to flow over that of other “supra-annular” valves. Effectively, this means that a larger-size valve can be used with a given annulus.
The Medtronic Mosaic™ porcine bioprosthesis (Medtronic, Inc., Minneapolis, MN, USA) is a third-generation prosthesis (Fig. 11a). The prosthesis has a supra-annular configuration with an acetal homopolymer flexible stent, scalloped aortic sewing ring, and reduced stent profile. The tissue is pressure-free fixed with glutaraldehyde, and the aortic wall predilated to reduce deformation of the commissures. The prosthesis is treated with alpha oleic acid (AOA) to retard calcification.

The Medtronic Mosaic Ultra™ (Medtronic, Inc., Minneapolis, MN, USA) is an extended supra-annular prosthesis with a reduced profile acetal homopolymer flexible stent and reduced scallop aortic sewing ring (Fig. 11b). The tissue is pressure-free fixed with glutaraldehyde, and aortic wall is predilated to reduce deformation of the commissures. The prosthesis is treated with AOA to retard calcification.

The Medtronic Freestyle™ stentless porcine bioprosthesis (Medtronic, Inc., Minneapolis, MN, USA) is fashioned as a porcine aortic root for implantation using the subcoronary (allograft freehand-like), mini root cylinder, or aortic root technique (Fig. 12). Tissue is pressure-free fixed with glutaraldehyde and the aortic wall predilated to reduce deformation of the commissures. Tissue is treated with alpha amino oleic acid to retard calcification. Dacron™ mesh covers the muscle shelf and forms a fine proximal sewing cuff. The Medtronic-Venpro Contegra™ pulmonary valved conduit (Medtronic, Inc., Minneapolis, MN, USA) is a bioprosthesis that consists of a heterologous bovine jugular vein that has a tri-leaflet venous valve and possesses a natural sinus slightly larger in diameter than its lumen (Fig. 13). The conduit is preserved in buffered glutaraldehyde in low concentration to preserve the flexibility of the leaflet material. The conduit is available in both unsupported and supported models. In the supported model, two external cloth-covered polypropylene rings provide additional support on either side of the valve. The available sizes are 12 mm to 22 mm.

The St. Jude Medical-Biocor porcine bioprosthesis (St. Jude Medical, Inc., Belo Horizonte, MG, Brazil) is a <1mmHg pressure, glutaraldehyde-fixed porcine bioprosthesis (Fig. 14). The prosthesis is formulated as a triple-composite design, with the leaflets devoid of a muscle bar. The stent posts and rails are covered with a rim of bovine glutaraldehyde preserved pericardium to reduce risk of leaflet abrasion against the polyester fabric. The design of the prosthesis includes a polyacetal stent and polyester sewing ring.

The St. Jude Medical-Biocor Supra porcine bioprosthesis (St. Jude Medical, Inc., Belo Horizonte, MG, Brazil) is a standard Biocor porcine bioprosthesis with an extended supra-annular sewing-cuff configuration.

The St. Jude Medical Epic porcine bioprosthesis (St. Jude Medical, Inc., St. Paul, MN, USA) is a minimal pressure, glutaraldehyde-fixed porcine bioprosthesis (Fig. 15a). The prosthesis is formulated as a triple-composite design devoid of muscle bar, and is a low-profile design in both aortic and mitral positions. The stent-posts and rails are covered with a rim of glutaraldehyde-preserved bovine pericardium to reduce risk of leaflet abrasion against the polyester fabric. The prosthesis has a polyacetal stent and polyester sewing ring. In the Linx™ technology, ethanol is used to prevent calcification.
The St. Jude Medical Epic Supra porcine bioprosthesis (St. Jude Medical, Inc., St. Paul, MN, USA) is a standard Epic porcine bioprosthesis with an extended supra-annular sewing-cuff configuration (Fig. 15b). The St. Jude Medical-Toronto SPV stentless porcine bioprosthesis (St. Jude Medical, Inc., St. Paul, MN, USA) is a subcoronary stentless porcine bioprosthesis with an external surface, including a muscle shelf covered with fine Dacron™ mesh (Fig. 16). The proximal sewing ridge is covered with fine Dacron™. The porcine tissue is preserved with low-pressure glutaraldehyde fixation. The second generation of the Toronto SPV bioprosthesis incorporates the BiLinx™ technology with ethanol for calcium mitigation and is called the St. Jude Medical-Toronto SPV II The St. Jude Medical-Toronto Stentless Root™ porcine bioprosthesis (St. Jude Medical, Inc., Minneapolis, MN, USA) is a new-generation porcine aortic root for implantation as a subcoronary, free-hand valve insertion or an aortic root replacement (Fig. 17). The proximal sewing ridge is covered with fine Dacron™, and the muscle shelf is also covered with fine Dacron™ mesh. The porcine tissue is preserved with low-pressure glutaraldehyde fixation. The tissue is treated with the BiLinx™ anticalcification technology, which has been identified to reduce calcification on the aortic wall tissue, as well as the aortic leaflet. The Toronto SPV Root™ is used in procedures in which aortic root disease accompanies valve disease. The St. Jude Medical-Biocor pericardial bioprosthesis (St. Jude Medical, Inc., Belo Horizonte, MG, Brazil) is a zero-pressure, glutaraldehyde-fixed pericardial bioprosthesis with the stent-posts and rails covered with pericardium (Fig. 18). The design incorporates a polyacetal stent and polyester ring. The St. Jude Medical-Biocor stentless porcine bioprosthesis (St. Jude Medical, Belo Horizonte, MG, Brazil) is a stentless prosthesis with individual porcine cusps to mount a composite bioprosthesis, and avoids leaflets with muscular bands (Fig. 19). The leaflets are treated under no pressure and tanned with different glutaraldehyde solutions for three months. The leaflets are sutured to a conduit of glutaraldehyde-treated bovine pericardium; the conduit is then shaped in a scalloped manner to mimic the natural aortic valve. The St. Jude Medical Trifecta™ pericardial bioprosthesis (St. Jude Medical, Inc., St. Paul, MN, USA) is a tri-leaflet stented bovine pericardial bioprosthesis designed for supra-annular placement in the aortic position (Fig. 20). The Trifecta™ is a tricuspid bovine bioprosthesis designed from three bovine pericardial leaflets from a single sheet of pericardium preserved pressure-free in glutaraldehyde. The polyester components of the bioprosthesis are covered with porcine pericardial tissue. The Trifecta™ bioprosthesis is processed using a proprietary Linx™ anticalcification technology. This bioprosthesis is currently an investigational device under regulatory control. The Sorin Pericarbon™ MØRE pericardial bioprosthesis (Sorin Biomedica, Saluggia, Italy) is made with two sheets of pressure-free fixed pericardium over a semiflexible polymeric stent covered with polyester fabric (Fig. 21). One sheet forms the three cusps with reduced stress on the commissures and a cylindrical shape in the open position. The other sheet coats the inner surface of the stent. The prosthesis is low profile, has a radio-opaque metal wire marker and Carbofilm™ coated polyester fabric sewing ring (to control pannus overgrowth). The sewing ring in the aortic position is designed for supra-annular positioning. The tissue is submitted to detoxification post- glutaraldehyde aimed at neutralizing residues of unbound aldehyde groups. The valve is stored in a solution free from aldehyde. The soft, reduced sewing ring is coated with Carbofilm™. The Sorin Pericarbon™ Freedom stentless pericardial bioprosthesis (Sorin Biomedica, Saluggia, Italy) is a stentless pericardial valve made of two separate sheets of low-pressure, glutaraldehyde-treated bovine pericardium (Fig. 22). The first sheet is shaped to form the three leaflets by means of a process of atraumatic tissue fixation without the use of molds, and then sutured to the second sheet using a Carbofilm™-coated suture. The suture line is designed especially to minimize the mechanical stress at the level of the commissures. The tissue is submitted to detoxification post-glutaraldehyde with homocysteic acid aimed at neutralizing residues of unbound aldehyde groups. The valve is stored in a solution free from aldehyde after detoxification. The stentless bioprosthesis is entirely free of any fabric reinforcement. The Freedom Stentless bioprosthesis provides superior hemodynamic performance due to the thinness of the pericardium and optimized design. The Sorin Pericarbon™ Freedom Solo stentless pericardial bioprosthesis (Sorin Biomedica, Saluggia, Italy) is a stentless pericardial valve implanted with one suture line instead of two (Fig. 23). The Freedom Solo stentless valve does not require trimming, as the pericardium is already scalloped. The bioprosthesis seats in a supra-annular position that provides superior hemodynamic performance with alignment of the valve orifice to the patient’s tissue annulus. The Soprano supra-annular aortic pericardial bioprosthesis (Sorin Biomedica, Saluggia, Italy) is designed for total supra-annular seating, which allows a precise alignment of the valve orifice to the patient’s tissue annulus, and results in a maximization of blood flow with 100% orifice-to-annulus ratio (Fig. 24). The Soprano prosthesis is constructed from glutaraldehyde-treated bovine pericardium. The prosthesis has a unique two-pericardial sheet design with no direct contact between polyethylene terephthalate (PET) and leaflets. The tricuspid-shaped pericardium sheet is sutured to a second sheet that covers the internal part of the stent. The semi-flexible polymeric stent is creep resistant. When the leaflets open, they recover the original cylindrical configuration, hence, they are completely stress-free. The unique design creates a chain of smooth linkages with increasing elasticity among stent/PET fabric/pericardium, the ideal condition for minimizing the concentration of tensional stress—especially during the closure phase. During the opening phase, only pericardium-to-pericardium contact occurs, which avoids abrasion of the pericardial leaflet’s impact against the PET polyester fabric. The tissue is submitted to detoxification post-glutaraldehyde with homocysteic acid aimed at neutralizing residues of unbound aldehyde groups. The valve is stored in a solution free from aldehyde. The soft, reduced sewing ring is coated with Carbofilm™. The labelled valve size refers to the orifice diameter, equivalent to the patient’s tissue annulus diameter. The Mitroflow pericardial bioprosthesis (Sorin-Mitroflow, Richmond, British Columbia, Canada) is formulated with an acetyl homopolymer stent for flexibility and pericardium pressure-free fixed with glutaraldehyde (Fig. 25). Pericardium is used as a single component without critical stent-post sutures. The Dacron™ cloth of the prosthesis (current version) has the smooth, rather than ribbed, PET in contact with the pericardium. The prosthesis has maximum valve opening and optimum blood flow due to unique mounting of the pericardium on the outside of the stent. The tiny and soft streamlined sewing cuff optimizes placement for the increased blood flow area. The pulmonary autograft is used to replace, and/or reconstruct, the aortic root. Pulmonary allograft is usually used to replace the pulmonary root; stentless porcine root is another alternative (Fig. 26). The CryoValve Aortic valve with or without conduit (Cryolife International, Inc., Kennesaw, GA, USA) is a cryopreserved human cadaveric aortic allograft for aortic root replacement or freehand aortic valve (Fig. 27a & 27b). The aortic valve is transected from the left ventricle that contains the muscle band with or without the anterior mitral leaflet. The aortic allograft (homograft) also is available from institutional or regional tissue banks. The allograft aortic valve is acceptable for pediatric and adult valve replacement, small aortic root, women of childbearing age, and infective endocarditis. The CryoValve pulmonary valve with conduit is a cryo-preserved human cadaveric pulmonary allograft for pulmonary root replacement. CryoValve Mitral valve (Cryolife International, Inc., Kennesaw, GA, USA) is a cryopreserved mitral valve (Fig. 28). The mitral valve is transected from the left ventricle that contains the muscle band and anterolateral and posteromedial papillary muscles, with the chordae tendineae attached. The mitral valve prosthesis is used for both mitral and tricuspid valve replacements. The allograft valve is accepted for adult and pediatric valve replacement, women of childbearing age, infective endocarditis, and contraindication for anticoagulation therapy. The Cryolife-O’Brien stentless porcine bioprosthesis (Cryolife, Inc., Kennesaw, GA, USA) is a stentless, composite-design prosthesis with three non-coronary leaflets, which eliminates the ventricular muscle shelf (Fig. 29). The prosthesis is designed only for distal suture line implantation, above the annulus with the scalloped design and absence of xenograft tissue below the leaflet hinge, in contrast to other stentless porcine bioprostheses that require two suture lines. The prosthesis is fixed in glutaraldehyde at <2 mmHg pressure. The Cryolife-O’Brien stentless porcine bioprosthesis also is fashioned as an aortic root for implantation using the subcoronary, mini root cylinder or aortic root technique. The Shelhigh Skeletonized Super-Stentless™ (Shelhigh, Inc., Union, NJ, USA) aortic porcine bioprosthesis is a composite porcine bioprosthesis (Fig. 30a). The valve is mounted on a super-flexible ring (skeleton), preserved with glutaraldehyde, detoxified, and heparin-treated with the No-React® anti-calcification treatment. The No-React® treatment is a tissue-detoxification and stabilization process that makes cross-linking permanent and prevents the toxic glutaraldehyde molecules from leaching out of the tissue. Endothelial cells have been documented on glutaraldehyde, No-React® treated tissue by Factor VIII immunoassay. The Shelhigh Super-Stentless™ valve has stentless hemodynamics and the implantation is as easy as that of a stented valve. The valve has a “volume-less” annulus that facilitates upsizing by one size. Also available from Shelhigh is the BioMitral™ valve (Model NR-900) (Figs. 30b, 30c). As with the Super-Stentless, it is treated with the No-React® process and is the first stented, totally biological valve. The BioMitral™ valve contains no fabric material. Internally, it employs a composite construction using three carefully matched non-coronary porcine leaflets. The stent is completely covered externally with pericardium, which is extended to form a strong, small, volume sewing ring. The Shelhigh BioMitral™ valve is currently available in four sizes: 27, 29, 31 and 33 mm, with smaller sizes available. The current generation Shelhigh porcine pulmonic valve conduit (Shelhigh, Inc., Union, NJ, USA) is a glutaraldehyde-fixed porcine pulmonic valve and (pulmonary artery) pericardial sleeve extension to formulate the conduit (Fig. 31). The conduit is treated with the No-React® tissue-detoxification process to prevent the onset of or attenuate (reduce or delay the onset of) calcification. The porcine pulmonic valve conduit has segments of bovine pericardial tissue to allow trimming to fit. The valve conduit is available in sizes 11-19, 21 and 23 mm in the U.S.A. and up to 29 mm outside the U.S.A. The Koehler Aspire porcine bioprosthesis (Koehler, Bellshill, Scotland) is a low-pressure (<2 mmHg) glutaraldehyde-fixed stented porcine bioprosthesis (Fig. 32). The bioprosthesis is formulated by a process of “fresh mounting” to allow correct alignment of the commissures. Dilation of the valve during reparation allows correct functional sizing. Dilation in conjunction with low-pressure fixation increases the angle of inclination of the leaflet and produces a reduction in open leaflet bending deformation. The valve tissue is selected to ensure minimal size of the muscle shelf. The unique fresh mounting optimizes the animal tissue to the mounting frame. The leaflets closely approximate the natural leaflet geometry, which reduces opening commissural bending stresses and provides a solution to structural failure from calcification and tears. The Koehler Elan stentless aortic porcine bioprosthesis (Koehler, Bellshill, Scotland) is a stentless valve with handling characteristics similar to a homograft (Fig. 33). The Koehler core technology of bioengineering ensures a stentless valve with handling and functional characteristics similar to the native aortic valve. The unique, one-piece sizer gauges the sizer of the sinotubular junction to determine the correct bioprosthesis. The Elan size also measures the aortic annulus to ensure the valve is neither too large nor too small. No cloth is on the prosthesis, which makes it a reasonable consideration in the presence of endocarditis. The Koehler Root Elan stentless aortic porcine bioprosthesis (Koehler, Bellshill, Scotland) is a glutaraldehyde low-pressure bioprosthesis designed to maintain natural tissue integrity and function (Fig. 34). The valve annulus is reinforced with porcine pericardium for secure suturing. The anatomical shape is retained and conformed to the native aorta. The Root Elan is designed for adult patients who require replacement of the aortic valve and/or root. The porcine adult roots can be provided with an anterior mitral cusp. The sizing is conducted the same as for the Koehler Elan stentless aortic porcine bioprosthesis. The 3F Therapeutics™ bioprosthesis (3F Therapeutics Inc., Lake Forest, CA, USA) is composed of three equal sections of equine pericardium that have been processed by fixation with a buffered formulation of glutaraldehyde, and are assembled together to form a tubular structure (Fig. 35). The glutaraldehyde formulation is of concentration sufficiently low to preserve much of the flexibility of the raw material, and fully crosslink the collagenous structure to preserve its strength, minimize its immunogenic and thrombogenic potentials, and provide lengthened durability when implanted in the heart of the patient. In contrast with bovine pericardium, equine pericardium comes from a source that has not been implicated in transmissible spongiform encepha-lopathies. The inflow aspect of the bioprosthesis is fitted with a woven polyester cuff to facilitate suturing of the device to the orifice created by removal of the diseased heart valve, and allow fibrous ingrowth to help in prevention of perivalvular leakage. The junctions of the three pericardial sections that form the leaflets become the three commissures of the bioprosthetic valve. These commissural attachment sites are integral tabs of pericardium backed by woven polyester material. The polyester material serves to reinforce the tissue and firmly affix the commissural attachment sites near the sino-tubular junction of the native aorta during surgical implantation of the bioprosthesis. 3F Therapeutics have a bi-leaflet, mitral, equine pericardial bioprosthesis currently under investigation. The Labcor stented porcine bioprosthesis (Labcor, Inc., Belo Horizonte, MG, Brazil) is a stented, tri-composite prosthesis of low-profile design (Fig. 36). The tri-composite prosthesis has three non-coronary leaflets preserved in glutaraldehyde at zero-pressure fixation. The three non-coronary leaflets with no muscle shelf provide a large, effective blood-flow area. The Labcor stented pericardial bioprosthesis (Labcor, Inc., Belo Horizonte, MG, Brazil) is a tri-composite prosthesis with precisely determined individual cusp shape and with the tissue selected for mounting of uniformity and thickness (Fig. 37). The prosthesis is formulated with a copolymer scalloped flexible stent to reduce stress on the tissue. The fabrication technique produces uniformity and consistency in valve function. Attachment of the pericardium at the stent post facilitates stress reduction and reinforces apposition of the leaflets. The prosthesis also is constructed to avoid contact of the pericardial membrane with the polyester and reduction of abrasion by means of pericardial padding of the inner surface of the valve at the post.

Labcor Stentless Porcine Bioprosthesis
The Labcor stentless porcine bioprosthesis (Labcor, Inc., Belo Horizonte, MG, Brazil) is a stentless prosthesis of tri-composite design with three non-coronary leaflets (Fig. 38). The leaflets are preserved in glutaraldehyde at no pressure. The tri-composite design provides a large, effective blood-flow area.

The Glycar Quattro™ mitral bioprosthesis (Glycar, Inc., Johannesburg, South Africa) is a stentless bovine pericardial mitral prosthesis (Fig. 39). The pericardium is preserved with glutaraldehyde and treated with polyol technology to reduce calcification. The prosthesis is composed of a “D-shaped” sewing cuff, with one large anterior leaflet and one posterior leaflet that contains three scallops. Chordal support for both leaflets on the anterolateral (left) side of the prosthesis is brought together, which forms one anterolateral papillary flap. Similarly, the chordae on the posteromedial (right) side are brought together to form another papillary flap. The valve components are held together by aligning stitches to form a four-leaflet stentless mitral prosthesis. The implantation technique incorporates anchoring of each papillary flap to the corresponding papillary muscle with two horizontal or longitudinal pledgetted mattress sutures. The aligning sutures in the prosthesis sewing ring and papillary flaps guide the placement of sutures during implantation. The Quattro™ prosthesis is available in mitral sizes 26, 28 and 30 mm.