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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

 

 

Mechanical ProstheseS

 

 

The principle mechanical prostheses available primarily worldwide are listed in Table II. The original successful mechanical prosthesis was the Starr-Edwards caged-ball valve, the “gold standard” prosthesis for more than 20 years until the early 1980s. Mechanical prostheses subsequently were either monoleaflet or bileaflet prostheses with pyrolytic carbon leaflets, and titanium or pyrolytic carbon housing. Tungsten is used to facilitate radio-opacity of the leaflets, as well as the metallic-band reinforcement, if used. The housing is rotatable within the sewing ring in most prostheses. Retrograde washing facilitates prevention of blood stasis and thrombus formation. The monoleaflet prostheses have crossing bars or central guides to control leaflet travel, whereas bileaflet prostheses, in general, have pivot recesses in parallel flat segments of the orifice to control leaflet travel.

The St. Jude Medical mechanical prosthesis (St. Jude Medical, Inc., St. Paul, MN, USA) is a bileaflet prosthesis with pyrolytic carbon over graphite substrate for housing and leaflets (Fig. 40a). The leaflets are flat and impregnated with tungsten for radio-opacity. The two semicircular leaflets open to 85º, which result in central, near laminar flow. The leaflets are orifice-orientated and closing forces are supported by the pivot system. The pivot guards are raised above the housing, and leaflet motion is by rotation. Relatively high-velocity blood and approximately 10% to 15% regurgitant flow wash the pivot recesses. In the original prosthesis, the housing could not be rotated. The prosthesis has been altered in the Masters (Fig. 40b) series to rotate within the sewing ring and provide radio-opacity of the annular-rotating mechanism.
The St. Jude Medical Masters HP (Hemodynamic Plus) (Fig. 40c) and Regent™ (Fig. 40d) prostheses have been introduced and are designed to optimize hemodynamics. Development of the St. Jude Medical mechanical prosthesis has led to a progressively greater geometric orifice area while maintaining the same tissue annulus dimension. In the standard cuff St. Jude Medical mechanical prosthesis, part of the cuff fabric is intra-annular, whereas in the HP Series prosthesis this fabric has shifted to an entirely supra-annular position. The St. Jude Medical Regent™ prosthesis shifts the carbon rim from intra-annular to entirely supra-annular.

The CarboMedics mechanical prosthesis (Sorin-CarboMedics, Inc., Austin, TX, USA) is a bileaflet prosthesis with solid pyrolytic carbon housing and flat leaflets of pyrolytic carbon-coated over tungsten-loaded graphite substrate (Figs. 41a - 4e). The prosthesis has excellent radio-opacity with a radio-opaque titanium stiffening ring and increased tungsten content in the leaflet substrate. The opening angle of the leaflets is 78º, which encourages synchronous closure. The leaflet pivot retention mechanism is within the housing without pivot guards, struts, or orifice projections. Leaflet motion is by rotation. The housing can be rotated within the sewing ring. The CarboMedics Top-Hat™ prosthesis is designed for supra-annular aortic implantation and improved hemodynamic performance in small sizes (Fig. 41c). The CarboMedics Optiform™ mitral valve is a reconfiguration of the mitral prosthesis (Fig. 41d & e) with a generous, symmetrical polyester sewing cuff to allow either intra-annular or supra-annular implantation. The Optiform™ prosthesis is useful in small, hypertrophied, or both, left ventricles; double-valve replacement; and reoperative mitral surgery. The CarboMedics Orbis™ prosthesis configuration has a multipurpose cuff design for aortic implantation in the scarred and calcified annulus (Fig. 41f).

The Sorin Monoleaflet Allcarbon mechanical prosthesis (Sorin Biomedica, Saluggia, Italy) is a monoleaflet prosthesis constructed of a cobalt chromium alloy housing coated with a thin film of pyrolytic carbon (Carbofilm™), with a single monoleaflet of pyrolytic carbon (Fig. 42). The pyrolytic carbon disc has a graphite substrate coated with pyrolytic carbon. The strut mechanism is integral with the housing with no welds. The opening angle is 60o designed to minimize regurgitation and energy loss. The sewing ring of PTFE fabric is carbon coated to reduce and stabilize surface-tissue reaction.

The Sorin Bicarbon™ mechanical prosthesis (Sorin Biomedica, Saluggia, Italy) is a bileaflet prosthesis with a titanium alloy housing coated with a thin film of pyrolytic carbon (Carbofilm™) (Fig. 43a). A titanium housing strengthens the prosthesis and the minimal thickness increases the effective orifice. The hinge cavity supports a constantly varying, single point of contact between pivot and housing, and two effluent passages provide continuous washing even in the closed position. The curved leaflets, made of pyrolytic carbon coated over a graphite and tungsten substrate, separate the orifice into three sections with similar resistance to flow, low-pressure gradients, and minimal turbulence. The hinge mechanism supports a rolling motion. The opening angle of both the aortic and mitral prosthesis is 80º, and both prostheses can be rotated within the sewing ring. The sewing ring is made with PET and carbon-coated PTFE. The Sorin Bicarbon Slimline™ prosthesis maintains all the design characteristics of the Bicarbon series while adding an improved orifice-to-annulus ratio by means of a reduced sewing cuff (Fig. 43b). The Bicarbon Slimline prosthesis is designed for supra-annular placement of the entire sewing cuff while the housing seats intra-annularly. Elimination of the sewing cuff material from the annulus allows the use of a larger titanium housing. The Bicarbon Overline™ prosthesis is designed for a totally supra-annular seating (Fig. 43c). This prosthesis supports the appropriate sewing cuff for each requirement and every suture technique. This prosthesis supports 100% orifice-to-annulus ratio.

The ATS Open-Pivot® mechanical prostheses (ATS Medical, Inc., Minneapolis, MN, USA) are bileaflet prostheses with pyrolytic carbon housing and pyrolytic carbon leaflets, with the housing and leaflets that contain graphite substrate (Figs. 44a & 44b). The prostheses have a convex hinge mechanism with protrusions on the inner aspect of the housing that supports the leaflets. The prostheses have no protruding struts with this hinge mechanism. The convex hinge mechanism is designed to facilitate retrograde washing. The opening angle is 85º. The aortic and mitral prostheses can be rotated within the sewing ring. The ATS Medical AP prosthesis is a supra-annular valve with a reduced sewing cuff applicable to the small tissue annulus..
The On-X mechanical prosthesis (Medical Carbon Research Institute, Austin, TX, USA) is a bileaflet prosthesis with a pure, non-silicon carbide alloyed pyrolytic-carbon housing and flat leaflets of pyrolytic carbon-coated over tungsten-loaded graphite substrate (Figs. 45a & 45b). The prosthesis design provides a curved housing in flow geometry and an orifice diameter-to-housing height ratio to minimize the vena contracta phenomenon and facilitate laminar blood flow. The leaflets of the mitral prosthesis are protected within the housing. The leaflet motion is by translation and rotation. The opening angle is no greater than 90º to the housing, but usually opens to an unstopped position of 85º. The leaflets travel an arc of 50º, and close at an angle of 40º. The regurgitant volume washes the pivot mechanism. The sewing ring is made of PTFE; the housing is rotatable within the sewing ring. Small titanium rings provide radio-opaque markers for location of the valve. The internal diameter of all mitral prosthesis sizes is 25 mm.
The Medtronic-Hall mechanical prosthesis (Medtronic, Inc., Minneapolis, MN, USA) is a monoleaflet prosthesis with a central guide for leaflet travel (Fig. 46a). The housing and central guide are made of titanium and the disc of pyrolytic carbon. The prosthesis can be rotated within the sewing ring; leaflet motion is by rotation and translation. The opening angle is 70º to 75º. The disc has a tungsten-loaded substrate for radio-opacity. The Medtronic-Hall Easy Fit is the supra-annular version of the prosthesis (Fig. 46b).

The Medtronic Advantage mechanical prosthesis (Medtronic Inc., Minneapolis, MN, USA) is a bileaflet prosthesis that consists of a pyrolytic carbon housing with two pyrolytic carbon leaflets and a rotatable PET sewing ring (Fig. 47a). The leaflets are widely spaced to increase the central-flow volume, reduce central-flow-velocity, and diminish the tendency of turbulence formation. The leaflets are radio-opaque and open to 86°. Washing of the hinge areas is facilitated by the enlarged central orifice and butterfly-hinge socket. The butterfly-hinge SureFlow™ pivot socket mechanism was designed to reduce areas of stasis and stagnant flow. This design was facilitated by the engineering techniques that incorporate laser Doppler velocimetry, computational fluid dynamics, and micro- scopic-flow visualization.

The Medtronic Advantage Supra™ mechanical prosthesis (Medtronic Inc., Minneapolis, MN, USA) is a full supra-annular model of the Advantage valve (Fig. 47b). The sewing cuff of the Supra™ is contoured to conform to the aortic complex. All functional mechanisms of the valve are not different from the standard Advantage prosthesis.
The Omnicarbon mechanical prosthesis (CV Medical, Inc., Inver Grove Heights, MN, USA) is a monoleaflet prosthesis with a pyrolitic carbon coating over a graphite substrate orifice and pyrolytic carbon disc (Fig. 48). The disc motion is controlled by short struts. The opening angle is 80º. The Omniscience mechanical prosthesis is similar except the housing is made of titanium.

The Triflo medical mechanical heart valve (Triflo Medical, Inc., Irvine, CA, USA) is an experimental trileaflet prosthesis (Fig. 49). The leaflets are three-dimensionally (3-D) shaped and the valve orifice has a nozzle-shaped, streamlined configuration. The leaflet configuration provides a soft and early-closure mechanism, similar to the natural aortic valve, with minimal regurgitation and a low tendency for cavitation and high-intensity signal (HITS) generation. The streamlined design minimizes flow separation and is associated with a low gradient.

The Edwards Mira mechanical prosthesis (Edwards Lifesciences, Irvine, CA, USA) is the Sorin Bicarbon™ mechanical prosthesis with the unique StarRing sewing cuff (Fig. 50). The prosthesis features a curved-leaflet profile as well as a slim, Carbofilm™-coated titanium-alloy housing. The rolling hinge provides a constantly varying point of contact in the hinge area between the leaflet and housing. An open channel in the hinge cavity allows continuous hinge washing during the entire cardiac cycle. The prosthesis has unique sewing rings designed specifically for mitral and aortic applications, as well as special aortic versions for small annuli (Figs. 50a - 50d; Mira, Finesse and Ultra Finesse). Each sewing-ring design enhances the function of the prosthesis in its position and size, which includes the unique hyperbolic shape of the mitral valve and downstream extension of the aortic prosthesis. The hyperbolic shape of the mitral sewing ring enhances non-everting supra-annular placement, as well as everting intra-annular placement. Downstream extension of the aortic sewing ring is cus- tomized with smaller extension in smaller sizes. The sewing rings are formulated of seamless knitted polyester cloth surface with a silicone sponge insert to provide enhanced compliance to the status of all annular irregularities. The prosthesis is radio-opaque with the graphite and tungsten substrate. The opening angle of both the aortic and mitral prostheses is 80°, and both prostheses are rotatable within the sewing ring.

The Koehler Ultracor mechanical prosthesis (Koehler, Bellshill, Scotland, UK) is a monoleaflet prosthesis with a plano convex disc with pyrolytic carbon coating on a tungsten-impregnated graphite substrate (Figs. 51a & 51b). The prosthesis design eliminates flow impeding structures in the lesser orifice by the single strut. The orifice ring is machined from solid titanium, to eliminate welds. The opening angle is 73º in the aortic and 68º in the mitral. The central location of the disc pivot axis increases laminar blood flow. The sewing ring is made of knitted Teflon™ to promote rapid tissue ingrowth. The sewing ring allows in situ rotation of the housing. The disc is radiographic for imaging.

The caged-ball Starr-Edwards mechan- ical prosthesis (Edwards Lifesciences, Irvine, CA, USA) has been marketed in current version since 1968 (Figs. 52a & 52b). The Starr-Edwards silastic ball valve prosthesis is composed of a polished Stellite alloy cage with a combination of PTFE and polypropylene cloth sewing ring. The PTFE cloth is wrapped around a porous silastic sponge insert to facilitate tissue infiltration. The ball is made of silicone rubber and contains barium sulfate for radiopacity. The Stellite cage is made from single casting and is radiopaque with three struts in the aortic prosthesis and four struts in the mitral prosthesis. The ball can be removed from the aortic prosthesis (not the mitral prosthesis) for ease of implantation. The aortic prosthesis is model 1260 with a pediatric prosthesis model 1200. The mitral prosthesis is model 6120.

The St. Jude Medical Masters aortic valved graft (St. Jude Medical, Inc., St. Paul, Minnesota, USA) incorporates the St. Jude Medical valve and the Hemashield™ woven double velour graft (Meadox Medicals, Inc.) (Fig. 53). The woven graft is collagen impregnated to control homeostasis and reduce hemorrhagic complications. The gradual resorption rate of the collagen impregnation prolongs graft seal during the critical postoperative period. The collagen from bovine source promotes host-tissue integration. The graft has no pleats to facilitate coronary anastomoses and ease stress on the coronary buttons. The double velour cuff enhances implantability and conformation of the graft to the annulus. The valve is rotatable and supports reduction of interference between the leaflets and subvalvular structures. The graft length is of increased length from previous generations to provide greater versatility.

The St. Jude Medical Masters HP valved graft prosthesis with Gelweave Valsalva™ technology (St. Jude Medical, Inc., St. Paul, MN, USA) incorporates St. Jude Medical Masters HP™ with the mechanical valve sewn into the base of the Vascutek Gelweave Valsava graft (Fig. 54). The valve incorporates an expanded HP cuff designed to be sutured above the patient’s annulus, which provides a larger orifice-to-annulus ratio. The graft incorporates a skirt region with a flared design to facilitate coronary artery anastomosis.

The Sorin-CarboMedics Carbo-Seal™ Aortic Valved Graft Prosthesis (Sorin-CarboMedics, Inc., Austin TX, USA) incorporates the CarboMedics mechanical prosthesis and low porosity, zero-preclot twill woven graft (Fig. 55). The woven graft is impregnated with gelatin and hydrolysis occurs over 14 days. The graft configuration minimizes interference and suture stress of coronary ostia implantation. Orientation markers provide easy suture positioning. The prosthesis has a pliable, cork-shaped sewing cuff that conforms to the annulus. The prosthesis incorporates a titanium-stiffening ring that allows rotatability in-situ and minimizes the possibility of leaflet lock-up or escape. The prosthesis has a full-sized orifice for improved hemodynamics. The woven graft enhances tissue ingrowth.
The CarboMedics Carbo-Seal™ Valsalva aortic valved graft prosthesis (Sorin-CarboMedics, Inc., Austin TX, USA) incorporates the CarboMedics mechanical prosthesis and the gelatin-impregnated polyester graft with sinuses of Valsalva (Fig. 56). The graft sinuses of Valsalva replicate the native sinuses, which facilitates the natural formation of systolic vortex, reduces stress on the coronary anastomoses, and enhances blood flow through the coronaries. The prosthesis has a titanium stiffening ring, which allows for in-situ rotatability and minimizes the possibility of leaflet lock-up or escape.

The Sorin Carbon Art™ Aortic Valved Graft Prosthesis (Sorin Biomedica, Saluggia, Italy) incorporates the Bicarbon™ bileaflet valve and a vascular conduit of seamless, knitted polyester double-velour PET fabric (Fig. 57). The Bicarbon™ heart valve and vascular conduit are both coated with Carbofilm™. The device, which features a modified Bicarbon™ aortic sewing ring, is intended for use as a replacement for the aortic valve and ascending aorta. The valve section of the prosthesis is coated with Carbo-film™ on the inflow surface side and surrounded by a soft, seamless, knitted polyester cuff. The conduit is tapered in the proximal portion. The sewing ring is attached securely to a woven polyester graft coated, both internally and externally, with Carbofilm™.

The Medtronic Hall valved conduit prosthesis (Medtronic Inc., Minneapolis, MN, USA) is a valve conduit with a standard Medtronic Hall mechanical valve sutured to a woven polyester fabric cylinder (Fig. 58). The valved conduit is recommended for aortic root replacement.

The Medtronic Hancock valved conduit prosthesis (Medtronic Inc., Minneapolis, MN, USA) is a valved conduit consisting of a standard unstented Hancock aortic porcine valve sutured into the centre of a woven fabric conduit (Fig. 59a). The Hancock conduit is recommended for reconstruction of congenital or acquired cardiac and great vessel abnormalities or pathology. The valved conduit is not recommended for aortic root replacement. Due to the Hancock bioprosthesis being unstented, the ratio of the conduit outer diameter to inner diameter of the bioprosthesis is optimized. The valved conduit incorporates Haynes alloy No. 25 annular ring, which prevents annular and leaflet distortion and preserves orifice shape. Also, a reinforcing ring, external to the conduit, prevents loss of leaflet coaptation and allows radiographic visualization.

The Medtronic left ventricular connector prosthesis (Medtronic Inc., Minneapolis, MN, USA) is a Hancock low-porosity valved conduit, which provides a method of relief of left ventricular hypertension in patients with severe left ventricular outflow tract obstruction such as hypoplasia of the aortic root, aortic annulus, or acquired problems secondary to aortic valve replacement, which cannot be relieved through conventional techniques (Fig. 59b).

The Carpentier-Edwards bioprosthetic valved conduit (Edwards Lifesciences, Irvine, CA, USA) is composed of a porcine valve designed for the pulmonary position. The flexible frame is composed of a corrosion-resistant cobalt chromium metal alloy and silicone rubber covered with PTFE cloth (Fig. 60). The majority of mechanical prostheses, bileaflet and monoleaflet, are provided as a valved conduit for aortic root reconstruction. Porcine aortic valve conduits were used previously, whereas porcine stentless aortic root bioprostheses are currently used together with homografts and autografts, for aortic root reconstruction.