Valve Replacement Therapy: History, Valve Types, and Options

The Ideal Valve

Many acceptable substitutes exist today for the replacement of diseased human heart valves. The ideal valvular prosthesis as described by Harken remains the gold standard of cardiac surgery. According to Harken this valve would be durable, with a longevity approaching that of a native valve, thrombogenicity would not be a factor, and therefore no need for supplemental anticoagulation would exist. In addition, this valve would have no inherent gradient, thus allowing unimpeded outflow, and could be implanted with ease while being readily available. Lastly, the valve could grow commensurate with that of the recipient. While the technology of valve prostheses has evolved considerably over the past six decades, this lofty goal has yet to be met.

History

The first human heart valve operation was a digital valvotomy of a stenotic aortic valve performed by Tuffier in 1914. Cutler, Souttar, Brock, Swan, and Harken refined valvotomies and commissurotomies in the ensuing decades; however, the limited success of these techniques brought to light the need for an effective means of replacing the entire valve. The first step in the evolution of this technology came in 1950 when Hufnagel developed a ball valve that he placed in the descending thoracic aorta of a patient with severe aortic insufficiency. In 1956, Murray implanted an aortic homograft in the descending thoracic aorta of a patient with severe aortic insufficiency. The introduction of cardiopulmonary bypass opened the era of implanting valve prostheses in their native positions. In 1960, Braunwald and Harken successfully replaced the mitral and aortic valves using valves made of polyurethane. In 1961 Albert Starr, a surgeon, and Lowell Edwards, an engineer, developed a caged ball valve that resulted in acceptable long-term survival. Despite their success, the high profile of caged ball valves made implantation in patients with small ventricles and small aortic roots difficult. These valves also had inherently high gradients along with less favorable thromboembolic profiles, making them less desirable as new prostheses were introduced. Edwards Lifesciences (Irvine, CA) discontinued production of the Starr-Edwards valve in 2007.

The next generation of valve prosthesis used a tilting disc that would pivot into an open and close position according to the flow of blood across the valve. Wada was the first to introduce these tilting disc valves in 1966. The Lillehei-Kaster valve, introduced in 1967, was a hingeless valve with a freely rotating pivoting disc retained by struts. Björk, working with Shiley Laboratories, developed a similar version of a hingeless pivoting disc valve in 1969. Although the hemodynamic profile was improved relative to the caged ball valves, these early pivoting valves were subject to occasional thrombosis. The 60-degree convexoconcave Björk-Shiley valve was prone to catastrophic structural failure secondary to fracture of its welded struts, allowing escape of the occluder disc.

Seeking to improve on the durability and thrombogenicity problems of these early pivoting disc valves, Hall, Woien, Kaster, and the Medtronic Corporation (Minneapolis, MN) introduced the Medtronic-Hall valve in 1977. The valve housing was constructed from one piece of titanium alloy with no introduced welds or bends. The round central disc was made from tungsten-impregnated graphite with a pyrolytic carbon coating, and it had a central hole that allowed the disc to be retained by a curved central guide strut that was part of the housing. Valve washing was improved by a relatively larger minor orifice and a disc that lifted out of the housing and rotated with opening. It had a moderately high profile in the open position and a low transvalvular gradient. Occluder impingement was possible because its position at the equator of the valve housing made it susceptible to obstruction from retained valve elements, sutures cut too long, or pannus. Loss of structural integrity, however, was never reported. The valve could be rotated after implantation to achieve the desired orientation. Several studies reported a low incidence of valve-related morbidity and mortality. Svennevig and colleagues reported a 25-year experience of 816 patients that underwent an aortic valve replacement using the Medtronic-Hall valve. Linearized rates of thrombotic complications, warfarin-related bleeding, and endocarditis were 1.5%, 0.7%, and 0.16% per patient-year, respectively. Valve thrombosis was seen in only four patients. Seventy-nine percent of the patients were in New York Heart Association classes I or II. Despite these outcomes, Medtronic discontinued manufacturing the valve in September of 2009, removing the last of the tilting disc prosthesis available for clinical use.

The next step in the evolution of valve prostheses came in 1977 when St. Jude Medical (Minneapolis, MN) introduced a bileaflet mechanical valve. The design has undergone several refinements since its introduction. Its advantage over the caged ball valves or the tilting disc valves are its greater effective orifice area and therefore improved gradients, along with reduced thrombogenicity.

In light of the thrombogenic potential of mechanical valves and the need for lifelong anticoagulation, development of tissue-based valves was undertaken in parallel with mechanical prosthesis. In 1962, Ross reported the use of aortic homografts for aortic valve replacement (AVR) and subsequently developed the Ross procedure, which uses a pulmonary autograft for replacement of the aortic valve. In 1969, Carpentier and Hancock developed the first porcine xenografts, and Ionescu developed the first glutaraldehyde-preserved bovine pericardial valve in 1971. Limited long-term durability secondary to leaflet calcification and subsequent valve failure plagued the early generation of bioprostheses. Significant progress has been made in improving the durability of these valves through improved fixation strategies and overall valve design. State-of-the-art anticalcification methods are now being used in an effort to improve valve longevity. Given the inherent gradients with stented bioprostheses, stentless xenografts were introduced in 1986, and they have remained an effective option for a tissue-based prosthesis.

Morbidity and Mortality Guidelines for Valve Operations

Clinical studies are crucial for determining outcomes after cardiac valve operations and precise definitions of outcomes are critical in comparing valve prostheses. To address this need, the councils of the Society of Thoracic Surgeons (STS) and the American Association of Thoracic Surgery (AATS) formulated the Ad Hoc Liaison Committee for Standardizing Definitions of Prosthetic Heart Valve Morbidity. The initial report of this committee was issued in 1988 with an update in 1996. The report strictly defines types of morbidity and mortality that can occur after valvular surgery. An understanding of these definitions is crucial for interpreting studies dealing with valvular prostheses.

The guidelines distinguish two types of mortality: hospital mortality and 30-day mortality. Hospital mortality refers to death occurring at any time before discharge during a patient's initial hospitalization. Thirty-day mortality, also referred to as operative mortality, is death that occurs at any time or place within 30 days of the procedure. There are several precise definitions of valve-related morbidity. Structural valve deterioration (SVD) refers to “any change in function of an operated valve resulting from an intrinsic abnormality of the valve that causes stenosis or regurgitation.” It includes “changes intrinsic to the valve, such as wear, fracture, poppet escape, calcification, leaflet tear, stent creep and suture line disruption of components … of an operated valve.” Thrombotic or infectious causes of valve dysfunction are not included.

Nonstructural dysfunction includes nonthrombotic and noninfectious causes of valvular stenosis or regurgitation that are not intrinsic to the valve itself. “Examples … include entrapment by pannus, tissue, or suture; paravalvular leak; inappropriate sizing or positioning; residual leak or obstruction from valve implantation or repair; and clinically important hemolytic anemia.” Morbid events are often reported as the composite linearized rate, or the number of events divided by the number of patient-years of follow-up (events/patient-years). The composite linearized rate for nonstructural dysfunction of the commonly available mechanical valves is 0.2 to 0.8 (events/patient-years) for the aortic position and 0.3 to 1.4 (events/patient-years) for the mitral position. Valve thrombosis is defined as thrombus in or about the valve that is not associated with infection and that interferes with valve function or obstructs blood flow through the valve. The composite linearized rate of thrombosis of mechanical valves is 0 to 0.2 (events/patient-years) in the aortic position and 0.4 to 0.8 (events/patient-years) for the mitral position.

Embolism refers to any embolic event not associated with endocarditis that occurs after the immediate perioperative period and after the emergence from anesthesia. Embolic events are further delineated into neurologic events and peripheral embolic events. The composite linearized rate of thromboembolism ranges from 1.4 to 2.5 (events/patient-years) for the aortic position and 1.8 to 3.6 (events/patient-years) for the mitral position.

A bleeding event refers to any clinically significant bleed requiring hospitalization or transfusion or causing death. A patient does not have to be taking an anticoagulant to sustain a bleeding event. Composite linearized rates vary from 0.8 to 2.5 (events/patient-years) for the aortic position and 1.2 to 2.2 (events/patient-years) for the mitral position.

Endocarditis involving an operated valve is designated operated valvular endocarditis. “Morbidity associated with active infection, such as valve-thrombosis, thrombotic embolus, bleeding event, or paravalvular leak, is included under this category and is not included in other categories of morbidity.” Composite linearized rates for prosthetic valve endocarditis range from 0.4 to 0.7 (events/patient-years) for both the aortic and mitral positions.

Consequences of morbid events are also defined by the guidelines. A reoperation is any operation on “a previously operated valve.” The composite linearized rate for reoperation ranges from 0.3 to 1.8 (events/patient-years) for the aortic position and 0.6 to 1.6 (events/patient-years) for the mitral position.

Valve-related mortality is any death after a valve operation caused by a morbid event that is not related to progressive heart failure in patients with functioning valves. Unexplained deaths are just that, and they should be listed as such. Cardiac deaths include valve-related deaths, sudden deaths, and non–valve-related cardiac deaths. Total deaths refer to any and all deaths after a valve operation. Permanent valve-related impairment refers to any “permanent neurologic or functions deficit” caused by a morbid event.

Prosthetic Heart Valves

The following section lists and describes prosthetic heart valves available worldwide. The valves are grouped according to their structural type (i.e., mechanical vs. bioprosthetic), manufacturer, and design specifications. The order in which they appear in no way delineates a preference by the authors. For a summary of clinically available valves, implantation positions, and sizes please see Tables 76-1 and 76-2 .

TABLE 76-1

Mechanical Valve Choices

Valve Type	Manufacturer	Name	Position	Available Sizes (mm)
Bileaflet	Medtronic	Open Pivot AP360	Aortic	16-26
		Open Pivot AP	Aortic	16-26
		Open Pivot AP	Mitral	16-26
		Open Pivot Standard	Aortic	19-31
		Open Pivot Standard	Mitral	25-33
	St. Jude Medical	Masters	Aortic	19-31
		Masters	Mitral	19-33
		Masters HP	Aortic	17-27
		Masters HP	Mitral	17-27
		Regent	Aortic	19-27
	Sorin Group	Bicarbon Fitline *	Aortic	19-31
		Bicarbon Fitline *	Mitral	19-33
		Bicarbon Overline *	Aortic	16-24
		Bicarbon Slimline *	Aortic	17-27
		Carbomedics Top Hat	Aortic	19-27
		Carbomedics OptiForm	Mitral	23-33
		Carbomedics Reduced	Aortic	19-29
		Carbomedics Standard	Aortic	19-31
		Carbomedics Standard	Mitral	21-33
		Carbomedics Standard Pediatrics	Aortic	16-18
		Carbomedics Standard Pediatrics	Mitral	16, 18, 21
		Carbomedics Orbis *	Aortic	19-31
		Carbomedics Orbis *	Mitral	21-33
	On-X	Standard Sewing Ring	Aortic	19-27/29
		Standard Sewing Ring	Mitral	23-31/33
		Conform-X Sewing Ring	Aortic	19-27/29
		Conform-X Sewing Ring	Mitral	25/33
		Anatomic Sewing Ring	Aortic	19-27/29

* Available only outside the United States.

TABLE 76-2

Bioprosthetic Valve Choices

Valve Type	Manufacturer	Name	Position	Available Sizes (mm)
Stented porcine	Medtronic	Hancock II	Aortic	21-29
		Hancock II	Mitral	25-33
		Hancock II Ultra	Aortic	21-29
		Mosaic	Aortic	19-29
		Mosaic	Mitral	25-33
		Mosaic Ultra	Aortic	19-29
	Edwards Lifesciences	Carpentier-Edwards Standard Porcine (2625 and 6625)	Aortic	19-31
		Carpentier-Edwards Standard Porcine (2625 and 6625)	Mitral	25-33
		Carpentier-Edwards S.A.V. Porcine (2650)	Aortic	19-31 *
		Carpentier-Edwards S.A.V. Porcine (2650)	Mitral ^†	25-33
		Carpentier-Edwards Duraflex Low Pressure Porcine ^‡ (6625LP)	Mitral	27-35
		Carpentier-Edwards Duraflex Low Pressure Porcine with Extended Sewing Ring ^‡ (6625-ESR-LP)	Mitral	27-35
	St. Jude Medical	Epic	Aortic	21-29
		Epic	Mitral	25-33
		Epic Supra	Aortic	19-27
		Biocor	Aortic	21-29
		Biocor	Mitral	25-33
		Biocor Supra	Aortic	19-27
Stented bovine pericardial	Edwards Lifesciences	Carpentier-Edwards PERIMOUNT (2700 and 2700TFX)	Aortic	19-29
		Carpentier-Edwards PERIMOUNT RSR (2800 and 2800TFX)	Aortic	19-29
		Carpentier-Edwards PERIMOUNT Plus (6900P and 6900PTFX)	Mitral	25-33
		Carpentier-Edwards PERIMOUNT Magna (3000 and 3000TFX)	Aortic	19-29
		Carpentier-Edwards PERIMOUNT Magna Ease (3300TFX, 7300TFX)	Aortic	19-29
		Carpentier-Edwards PERIMOUNT Magna Ease (3300TFX, 7300TFX)	Mitral	25-33
	Sorin Group	Mitroflow	Aortic	19-29
		Soprano Armonia ^†	Aortic	19-33
		Pericarbon More ^†	Mitral	19-33
	St. Jude Medical	Trifecta	Aortic	19-29
Stentless	Medtronic	Freestyle	Aortic	19-29
	Medtronic	3f	Aortic	19-29
	Sorin Group	Pericarbon Freedom ^†	Aortic	15-29
	Sorin Group	Freedom Solo ^†	Aortic	19-27
	Edwards Lifesciences	Prima Plus	Aortic	21-29
Sutureless bovine pericardial	Medtronic	3f Enable ^†	Aortic	19-29
	Sorin Group	Perceval S ^†	Aortic	S, M, L, XL
	Edwards Lifesciences	Edwards Intuity ^†	Aortic	19-27
Transcatheter	Edwards Lifesciences	Sapien	Aortic	23, 26
		Sapien XT	Aortic	23, 26, 29
	Medtronic	CoreValve	Aortic	23, 26, 29, 31
	St. Jude Medical	Portico ^†	Aortic	25

RSR, Reduced sewing ring.

* Sizes 19, 29, and 31 available only outside the United States.

† Available only outside the United States.

‡ Available only in the United States.

Mechanical Valves

Bileaflet Prostheses

Medtronic

The Medtronic Open Pivot Mechanical Heart Valve ( Fig. 76-1 A ) is a bileaflet valve that was originally developed and owned by ATS Medical, Inc. (Minneapolis, MN). The valve is made of a solid pyrolytic carbon orifice and a titanium strengthening band that provides it with added durability. Its unique design eliminates shallow recesses in the hinge area where clots may form. These design features lead to a continuous gentle flow of blood across the valve, resulting in low levels of clotting while helping to prevent damage to blood cells. Furthermore, with the Open Pivot design, the unimpeded flow of blood provides for a continuous passive washing of the valve. Within the Open Pivot Series, there are three subtypes, each geared toward different potential clinical needs. The AP360 is an aortic valve prosthesis with a supra-annular flanged cuff configuration designed for added flexibility and conformability, and it is available in sizes from 16 to 26 mm. The AP valve has a supra-annular compact cuff configuration for ease of suturing and overall conformability. The valve can be placed in either the aortic or mitral position and is also available in sizes from 16 to 26 mm. The Standard valve is designed for intra-annular placement and has a generous and compliant cuff. The valve is available in sizes from 19 to 31 mm in the aortic position and 25 to 33 mm in the mitral position. All the Open Pivot valves are rotatable in situ.

FIGURE 76-1, Mechanical bileaflet valves. A, Open Pivot Mechanical Valve. B, The Regent mechanical valve. C, The Top Hat mechanical valve. D, The On-X Heart Valve.

Several studies have demonstrated good hemodynamics and an overall low complication rate with these valves. Bernet and colleagues reported their outcomes for a series of 1161 patients that received either the SJM valve or the Open Pivot Mechanical Valve. Cumulative survival and freedom from valve-related mortality at 10 years for the SJM valve and Open Pivot Mechanical Valve were 66% ± 3% versus 68% ± 5% ( P = 0.84) and 96% ± 1% versus 97% ± 1% ( P = 0.36), respectively. No structural valve failure was encountered for both valve types. The linearized rates for valve-related adverse events for the SJM valve and Open Pivot Mechanical Valve were, respectively: thromboembolism, 0.9% and 1.1% per patient-year; major bleeding requiring transfusion, 0.3% and 0.5% per patient-year; prosthetic endocarditis, 0.03% and 0.1% per patient-year; paravalvular leak, 0.1% and 0.6% per patient-year.

St. Jude Medical

The St. Jude Medical (SJM) Standard valve prosthesis was approved by the U.S. Food and Drug Administration (FDA) in 1977, and more than 2.3 million valves have been implanted worldwide. The SJM leaflets and ring orifice are constructed with pyrolytic carbon and are highly durable. The 85-degree leaflet opening angle provides improved laminar flow and reduces turbulence. The Hemodynamic Plus (HP) series was developed to address the inherent gradient in smaller valves and the potential for patient–prosthesis mismatch. With the small annulus in mind, the sewing cuff was reduced and redesigned to allow supra-annular placement of the valve, leading to an increased effective orifice area (EOA). The Masters Series was later introduced, providing the ability to rotate the valve to the desired orientation after implantation. The Standard and HP valves are offered only within the Masters Series. The available Standard valve sizes are 19 to 31 mm for the aortic position and 19 to 33 mm for the mitral position, whereas the available HP valve sizes are 17 to 27 mm for both the aortic and mitral positions. The Regent valve (see Fig. 76-1 B ) is the most recent evolution of the bileaflet design, developed to improve hemodynamic performance. In addition to a supra-annular cuff, the carbon rim was shifted to the supra-annular position. As with the Masters Series it is fully rotatable as well. This redesign allows the valve to achieve an increased EOA and an up to 84% orifice-to-annulus ratio. The Regent valve is available only for the aortic position and for sizes ranging from 19 to 27 mm.

Several reports have documented the outcomes of the various valve series produced by SJM. Tool and colleagues reported their 25-year experience in which 946 valve recipients were followed prospectively at 12-month intervals from 1979 to 2007. The series included implants using all SJM designs, with the original Standard valve being the most widely used. Among aortic valve recipients, 25-year freedom from reoperation, thromboembolism, bleeding, and endocarditis was 90% ± 2%, 69% ± 5%, 67% ± 3%, and 92% ± 3%, respectively. Among mitral valve recipients, 25-year freedom from reoperation, thromboembolism, bleeding, and endocarditis was 81% ± 10%, 52% ± 8%, 64% ± 6%, and 97% ± 1%, respectively. Freedom from valve-related mortality was 66% ± 8% and 87 ± 3% for aortic and mitral valve replacement (MVR), respectively.

Head-to-head comparisons between the standard and HP designs have also been reported. Vitale and colleagues reported results from the Multicenter Study Group for the SJM HP aortic valve prosthesis. This prospective randomized study included 140 patients with 21- and 23-mm–annulus diameters and who received either the SJM Standard valve or the HP valve. Postoperatively and at 6 months, echocardiographic hemodynamic variables such as ejection fraction, cardiac output, peak gradient, mean gradient, EOA, indexed EOA (iEOA), and performance index were calculated. Decreased peak and mean gradients and increased EOA, iEOA, and performance indexes were found for the HP valve. The authors concluded that use of the HP valve allows implantation of smaller prostheses without patient–prosthesis mismatch (PPM) and with avoidance of the additional morbidity associated with root enlargement procedures. Ismeno and colleagues similarly reported their results comparing the 19-mm standard and HP valve in the aortic position after 5 years. Those who received the HP valve had statistically better hemodynamics with lower peak and mean gradients and larger EOAs. There was no difference, however, in terms of 5-year survival, late complications, or left ventricular mass reduction between the two groups.

The Regent valve has also demonstrated good in vivo hemodynamics and clinical outcomes. Bach and colleagues reported the results of a multicenter study from North America and Europe of 361 patients that underwent aortic valve replacement using the Regent valve. The mean gradient at 6 months was 9.7 ± 5.3 mm Hg for the 19-mm valve, with the larger valves having progressively lower gradients. The iEOA was equal to or greater than 1.0 cm ² /m ² for all valve sizes and left ventricular mass index decreased significantly between early postoperative (165.9 ± 57.1 g/m ² ) and 6-month follow-up (137.9 ± 41.0 g/m ² ; P < 0.0001).

Sorin Group

The Sorin Group (Milan, Italy) manufactures two mechanical valve series: the Bicarbon Product Line, developed internally by Sorin, and the CarboMedics Product Line, acquired through the purchase of Sulzer CarboMedics. Within each series there are multiple subtypes geared toward a variety of clinical needs. As a whole, the mechanical valves in their catalog are bileaflet. For Bicarbon, the leaflets are constructed from pyrolytic carbon deposited on a graphite substrate and a housing made of titanium alloy treated with a proprietary Carbofilm coating for enhanced hemo-biocompatibility. For the Carbomedics valve the leaflets are constructed from pyrolytic carbon deposited on a graphite substrate, like those of the Bicarbon valve. The housing of the Carbomedics valve is fabricated from nonsubstrated pure pyrolytic carbon reinforced with a titanium reinforcing ring.

The Bicarbon series features the Fitline valve, which is designed for intra-annular implantation and is available for both aortic and mitral valve replacement. It will fit annular sizes of 19 to 31 mm for the aortic position and 19 to 33 mm for the mitral position. The Bicarbon Overline maintains the same design as the Fitline while improving hemodynamics through its supra-annular seating and 100% orifice-to-annulus ratio. These design features make the valve suitable for small annuli and create the potential benefit of decreasing the need for annulus enlargement. The Overline valve is available only for the aortic position and for 16- to 24-mm sizes. The Bicarbon Slimline is designed for partial supra-annular seating and therefore improved hemodynamics, while maintaining the same design features as the Fitline. The Slimline valve is available only for the aortic position and for sizes from 17 to 27 mm. All the Bicarbon valves are rotatable in situ and are available only outside the United States.

The CarboMedics mechanical valve series has six different valve designs within its portfolio. The Top Hat valve (see Fig. 76-1 C ) is designed for supra-annular implantation in the aortic position. By virtue of the design, the valve has no ventricular protrusions and leaves no valve components in the annulus. In turn, this design allows for improved seating in a smaller annulus with the advantage of reducing the need for a root enlargement along with a potential 100% orifice to annulus match. The Top Hat is available for sizes ranging from 19 to 27 mm. The OptiForm valve has a symmetrical cuff design that allows the valve to be placed in a supra-annular, intra-annular or subannular position simply by varying suture entry and exit sites. This valve is available for the mitral position only and for sizes from 23 to 33 mm. The Reduced Series valve is an intra-annular valve and was designed primarily for a smaller annulus and root size. The small external diameter and the smaller, pliable cork-shaped sewing cuff allows for improved seating and once again provides the potential advantage of reducing the need for root enlargement. This valve is available for the aortic position only and for sizes from 19 to 29 mm. The Standard valve offers a generous sewing cuff and is available for the aortic and mitral position. Its low-profile pivot design reduces the risk of coronary obstruction for aortic valve replacements and limits protrusion into the atrium for mitral valve replacements, thus reducing potential thrombus formation. The valve is available in sizes from 19 to 31 mm in the aortic position and 21 to 33 mm in the mitral position. The Standard Pediatric valve was designed for small adults or pediatric patients and is available for both the aortic and mitral position. The placement of the aortic valve can be supra- or intra-annular, and the valve available in sizes from 16 to 18 mm. The mitral valve is available in 16 and 18 mm for either supra- or intra-annular placement, while a 21-mm valve is designed for intra-annular placement only. The Orbis valve, available only outside the United States, has a multipurpose cuff design that allows for a variety of implantation techniques. This valve is offered for both aortic and mitral valve replacement and will fit sizes from 19- to 31-mm in the aortic position and 21- to 33-mm in the mitral position. All CarboMedics valves are rotatable in situ.

A number of reports have been published demonstrating good clinical outcomes using the Bicarbon and CarboMedics Series. The specific types of Bicarbon or CarboMedics valves used, however, are not detailed in these reports. Azarnoush and colleagues reported the 15-year clinical outcomes of the Sorin Bicarbon prosthesis from a multicenter European study where 1704 patients received aortic valve replacement, mitral valve replacement, or both. Actuarial freedom from valve-related deaths at 15 years was 76.4%, and actuarial freedom from thromboembolism, hemorrhage, and endocarditis at 15 years was 88.8%, 77.5%, and 96.8%, respectively. No cases of structural failure were observed. Bouchard and colleagues reported their 20-year experience with 3297 patients who received a CarboMedics valve as an aortic valve replacement or mitral valve replacement. At 20 years, freedom from valve-related mortality for AVR and MVR was 78.3% and 74.6%, respectively. Freedom from thromboembolic events, reoperation, and bleeding were 91.6%, 89.2%, and 89.5% for AVR and 88.5%, 80.3%, and 88% for MVR, respectively. Freedom from endocarditis was 97.3% for both AVR and MVR. In a direct comparison, Bryan and colleagues reported the 10-year follow-up of their prospective randomized trial where 485 patients received either the CarboMedics valve or the SJM mechanical valve in either the aortic position, mitral position or both. Freedom at 10 years from valve-related mortality was 95.0% in the CarboMedics group and 93.0% in the SJM group. Linearized rates per patient-year were 1.1% in the CarboMedics group and 0.8% in the SJM group for thromboembolism; 2.3% in the CarboMedics group and 3.2% in the SJM group for bleeding events; and 0.72% in the CarboMedics group and 0.47% in the SJM group for nonstructural valve dysfunction.

On-X Life Technologies

The On-X Heart Valve (On-X Life Technologies, Austin, TX; see Fig. 75-1 D ) is a bileaflet valve constructed completely of pyrolytic carbon. The manufacturer claims that the lack of silicon doping in the valve's carbon construction potentially decreases its thrombogenicity. Its design includes a tall, flared inlet that increases the orifice area and decreases the ability of retained valve tissue to interfere with opening and closing. In addition, the stasis-free pivot design allows the valve to wash itself, and the 90-degree leaflet opening provides improved laminar flow and reduced turbulence. The On-X Heart Valve is available for both aortic and mitral valve replacement. There are three different sewing rings available, each catered to a particular clinical setting. The valve construct within the three sewing rings is the same. The Standard ring is available in sizes from 19 to 27/29 mm in the aortic position and 23 to 31/33 mm in the mitral position. The Conform X model provides a more flexible sewing ring and is available in sizes from 19 to 27/29 mm in the aortic position, whereas for the mitral position it offers one size that is intended to fit an annular size ranging from 25 to 33 mm. The Anatomic sewing ring is designed to fit the contours of the aortic valve annulus and is available in sizes ranging from 19 to 27/29 mm.

Under FDA investigational device exemption, the Prospective Randomized On-X Anticoagulation Clinical Trial (PROACT) has been testing the safety of less aggressive anticoagulation than recommended by the American College of Cardiology and American Heart Association guidelines after implantation of the On-X valve. In the first limb of the PROACT, Puskas and colleagues reported their results of 375 patients with elevated risk factors for thromboembolism who underwent an aortic valve replacement. While receiving 81 mg of aspirin daily, patients received either low-dose warfarin with a target international normalized ratio (INR) of 1.5 to 2 or standard warfarin dosing targeting an INR of 2 to 3. The mean INR was 2.50 ± 0.63 for the control group and 1.89 ± 0.49 for the low dose group ( P < 0.0001). The low-dose group experienced significantly lower major (1.48% vs. 3.26% per patient-year; P = 0.047) and minor (1.32% vs. 3.41% per patient-year; P = 0.021) bleeding rates. The incidence of stroke, transient ischemic attack, total neurologic events, and all-cause mortality were similar between the two groups. Enrollment for the low-risk aortic and mitral valve replacement arm of the PROACT was completed in 2013.

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