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| Newer Concepts in the Surgical Treatment of Valvular Heart Disease |
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| Edward Y. Sako, MD, PhD |
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| 2004,
6:100-105 Current Science, Inc. ISSN Copyright © 2004 by Current Science, Inc. |
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| The search for the ideal therapy for valve replacement continues. The major options include mechanical or tissue valves, with an increasing variety of tissue valves becoming available. The key factor continues to be thrombogenicity versus durability. Aortic valve surgery primarily consists of replacement. This is aided by the increased variety of options allowing tailoring of the procedure to the patient's native valve disease. Mitral valve surgery has greater potential for repair, which affords preservation of the native valve, optimizing function and reducing long-term complications. An increasingly popular concept is treatment of secondary or functional mitral valve regurgitation in the setting of depressed left ventricular function. The routine use of intraoperative transesophageal echocardiography and a trend toward the use of minimally invasive procedures are altering the conduct of valve operations. |
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| Introduction |
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| The field of valvular surgery continues to be an evolving and challenging one for the cardiac surgeon. The growing number of options for valve replacement therapy is testament to the problem of finding the perfect answer for valve replacement. These options do, however, allow for improved tailoring of the operation for a given patient. |
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| Valve Replacement Options |
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| The major dichotomy in valve replacement therapy continues to be between mechanical and bioprosthetic (tissue) valves. Given the rigors of regulation surrounding such materials, the current available valves largely represent variations on well-proven prostheses as opposed to radically different designs. Although there were a variety of mechanical valves in the past, the most widely used mechanical valves in recent years have utilized the bileaflet valve popularized by the St. Jude's (St. Paul, MN) prosthesis. The basic material is pyrolite carbon and the design includes two hinged semicircular leaflets. Several manufactures have developed variations on this design, but none has been proven clearly superior. Based primarily on historic data, all continue to share a propensity to possible thrombosis and embolism. A recent meta-analysis of two popular mechanical valves showed thromboembolism, valve thrombosis, and bleeding rates in the 0.5% to 2% per year range [1]. Therefore, the need for long-term warfarin anticoagulation of the mechanical valve still exists. The tendency for thrombosis continues to be higher in mechanical prosthesis in the mitral position as compared with the aortic position [1, 2]. Overall improved valve design has allowed generally lower levels of anticoagulation. Anecdotal series in non-US countries have suggested the possibility of cessation of anticoagulation with warfarin for selected mechanical valves in the aortic position, but these continue to be viewed as preliminary rather than definitive data. |
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| Bioprosthetic (tissue) valves are known to be less thrombogenic but also less durable. Though most consensus guidelines still recommend short-term (4-12 weeks) warfarin therapy (often with aspirin) for the newly implanted tissue valve, long-term therapy usually consists of daily aspirin use only. A variety of bioprosthetic valves exist that differ in types of tissue used, preparation of the tissue leaflets, and construction of the valve leading to different implantation techniques [3*]. The three major tissue types are human, porcine valves that use porcine aortic valve leaflets, and bovine valves in which leaflets are constructed of bovine pericardium stamped out and sewn into a stent (Table 1). The two manufacturers of the most widely used stented tissue valves, Medtronic (Minneapolis, MN; porcine) and Edwards (Irvine, CA; bovine pericardium) tout these as "third-generation" valves with average durability of 10 to 15 years [4*]. It is also of interest that durability appears to increase with age of the patient at the time of implantation [2, 5]. |
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| The major types of tissue valve construction are stented, stentless, homograft, and autograft (Table 1). Stented valves are self-contained and are placed with fairly routine and reproducible techniques involving suturing the sewing ring to the annulus of the valve to be replaced. The bulk of the stent results in an effective orifice area that is commonly less than that of the original, predisease valve but in the vast majority of patients is sufficient. |
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| Valve | Prosthesis category | Prosthesis type | Commercial examples | |
| Aortic | Mechanical | Bileaflet | St. Jude, CarboMedics, ATS, On-X | |
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Tilting disc | Medtronic Med Hall, Bjork-Shiley | |
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Tissue | Stented | Edwards Bovine Pericardial | |
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Medtronic Porcine Mosaic | |
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Stentless | Medtronic Freestyle | |
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St. Jude Toronto | |
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Homograft | CryoLife | |
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Autograft | | |
| Mitral | Mechanical | Bileaflet | St. Jude, CarboMedics, ATS, On-X | |
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Tilting disc | Medtronic Med Hall, Bjork-Shiley | |
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Tissue | Stented | Edwards Bovine Pericardial | |
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Medtronic Porcine Mosaic | |
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Annuloplasty rings and bands | |
Edwards Physio, Cosgrove Band | |
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(for repair) | |
Medtronic Future Band | |
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St. Jude Seguin Ring | |
| Tricuspid | Mechanical (rarely used) | Bileaflet | St. Jude, CarboMedics, ATS | |
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Tilting disc | Medtronic Med Hall, Bjork-Shiley | |
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Tissue | Stented | Edwards Bovine Pericardial | |
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Medtronic Porcine Mosaic | |
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Annuloplasty rings and bands | |
Edwards Cosgrove Band | |
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(for repair) | |
Medtronic Duran Ring | |
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St. Jude Tailor Ring | |
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| Device manufacturers: ATS--Minneapolis, MN; Bjork-Shiley--Pfizer, New York, NY; CarboMedics--Austin, TX; CryoLife--Kennesaw, GA; Edwards--Irvine, CA; Medtronic--Minneapolis, MN; OnX--Medical Carbon Research Institute, Austin, TX; St. Jude Medical--St. Paul, MN. | ||||
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| Stentless valves are currently applicable for aortic valve replacement. They are typically porcine aortic roots that have been modified with a sewing cuff. They may be implanted within the native aortic root or some versions may be placed as a "mini-root" replacement. In general, the technical demands for implantation are significantly greater with increased potential for variable results such as postoperative aortic regurgitation. The advantage is that in most cases the effective orifice area is maintained to a greater degree than with stented versions. Durability, however, appears to be similar [6, 7, 8]. |
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| Homografts are similar to stentless valves with regard to implant techniques. They are human valves that are harvested from cadavers and treated to maintain tissue flexibility and reduce antigenicity. The most common treatment is cryopreservation. They typically have no attached artificial material. In most cases of aortic valve homografts, they consist of a generous amount of ascending aorta and the attached anterior leaflet of the mitral valve. This may be advantageous in selected cases in which additional reconstruction of the aorta or patching of the mitral valve is required. Pulmonary homografts are also available, although their durability is less than that of aortic homografts. In general, they are reserved for reconstruction of the right ventricular outflow tract in infants, children, and young adults [9, 10]. The major drawback for all homografts is availability in numbers and sizes [11]. |
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| Autografts imply the transfer of the pulmonary valve to the aortic position, typically as a root replacement with replacement of the pulmonary valve with a homograft (Table 1). Commonly referred to as the Ross procedure and named for the surgeon who first developed it, this represents the most technically demanding of the procedures for aortic valve replacement. Its use is generally reserved for aortic valve disease in the pediatric or young adult population in whom there is a desire to avoid long-term anticoagulation with the hope of increased durability when compared with most other tissue valve replacements [10, 12, 13]. Homografts for mitral valve replacement have been described by selected centers but the technical demands, short- and medium-term reliability concerns have prevented widespread use at this point [14]. |
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| Aortic Valve Disease |
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| Most aortic valve disease in adults continues to be treated with leaflet excision followed by replacement. At this point, the wide variety of options comes into play with choices made in relation to a number of factors, including patient age, comorbidities, need for concomitant procedures, availability of a given replacement, technical expertise of the surgeon, and patient compliance. Numerous articles are available to aid in this choice [3*, 4*, 15, 16, 17, 18, 19]. A mechanical prosthesis represents the most durable, technically easiest valve to implant, with ready availability in a variety of sizes. This is usually considered the valve of choice for adults up to approximately age 65. The two major drawbacks are the need for long-term anticoagulation with warfarin and the potential for so-called valve mismatch, which results in a valve that is too small for a given patient, leading to a residual pressure gradient that is too high. Though an enlargement procedure can be done to accommodate a larger valve if a small annulus is encountered, this adds to potential for perioperative complications. The problems of long-term warfarin use are well documented, and include inadequate monitoring leading to under or over anticoagulation, and tetragenic considerations. |
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| The next most popular choice in replacement is stented tissue valves (Table 1). They share with mechanical valves the properties of ease of implantation and ready availability in a variety of sizes. There is less thrombogenicity with no need for long-term anticoagulation. Durability remains a problem, as noted above. They are considered the valve of choice for elderly patients. The cutoff age may also be influenced by factors that may affect expected life expectancy, such as associated coronary artery disease. They may also be a consideration in younger patients in whom anticoagulation may be relatively contraindicated. Continued improvements in technique and perioperative care have resulted in improved results for reoperations to the extent that limited durability of a valve should not completely preclude its use. |
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| Stentless valves (Table 1) are relatively new, implying that long-term data in large numbers are yet to be determined. In terms of availability and durability, they should still be considered equivalent to the stented tissue valves. The major advantage over a stented valve is the improvement in effective orifice size for any given annulus. At least one form of this group of valves has the added ability to be implanted as an aortic root with subsequent reimplantation of the coronary arteries. This is at the cost of increased technical requirements and associated increased perioperative complications such as bleeding, heart block, and valve dysfunction. The possible need for associated cardiac procedures such as concomitant coronary artery bypass may also be a factor. At this point, indications seem to be similar to those of stented tissue valves with the addition of use when the annulus size is smaller, leading to increased potential for mismatch if a stented or mechanical valve is used. They would be considered an alternative to annular enlarging procedures. |
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| As mentioned, homografts are human aortic valves that are typically cryopreserved and usually come as an entire aortic root. Currently they are considered much in the way stentless valves are, with very similar modes of implantation, the preferred being root replacement. The major drawbacks are limited durability and limited availability. Pulmonary homografts are also now available but used primarily for replacement in the right ventricular outflow tract. |
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| Autografts as used in the Ross procedure represent the most technically demanding of the aortic replacement procedures. This procedure is rather uniquely suited for the pediatric population in that growth of the autograft has been noted, there is no need for warfarin anticoagulation, and durability is rather good though also limited. |
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| Aortic valve repair may be possible in selected circumstances (Table 1). Isolated perforation of the leaflet may be patched. Leaflets may be intact and the pathology may lie in dilation of the sinotubular junction. Appropriate-sized graft replacement of the ascending aorta may correct the insufficiency. Aortic valve repair is limited in part by the technical demands but more commonly by the lack of appropriate pathology [20]. |
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| Mitral Valve Disease |
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| Replacement therapy for mitral valve disease follows much the same guidelines as for aortic valve disease, although the options are commonly limited to stented tissue valves or mechanical prosthesis. In the course of mitral valve replacement, the concept of chordal preservation is now generally accepted. Maintaining a connection between the valve, usually the annulus, and the papillary muscle has been felt to improve long-term left ventricular (LV) function. A variety of techniques have been described, including imbrication of portions of the leaflet with the chorda still attached to the papillary muscle, or placement of artificial chordae from the annulus to the muscle. |
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| Repair of the mitral valve, however, has much greater applicability compared with aortic valve surgery and should be considered the first choice when possible. Many more variables are involved, including the exact nature of the valve pathology, the experience of the surgeon and the availability of methods to assess the immediate results, such as intraoperative transesophageal echocardiography (TEE). Many of the techniques of valve repair are well described [21, 22]. |
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| A major trend in mitral valve surgery in recent years has been the treatment of what may be thought of as secondary mitral valve disease (Table 1). Advancements in mitral valve repair techniques and myocardial protection have prompted reconsideration of the concept of correcting mitral regurgitation (MR) in the setting of severe ventricular dysfunction. Specifically, the group of patients under discussion here are those felt to have MR secondary to changes in the ventricle with relatively normal-appearing leaflets. |
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| Radio opaque marker studies of components of the mitral valve in vivo demonstrate the dynamic nature of each component and suggest that the valve may have a role other than just maintaining one way flow from the atria to the ventricle. |
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| In this specific subset of patients, the regurgitation is a result of and not the cause of the cardiomyopathy. Selected subsets of cardiomyopathic hearts regardless of the etiology (idiopathic, ischemic) remodel toward a dilated state. The two major effects of the cardiomyopathy on the mitral valve are dilation of the annulus (primarily posterior) and tethering of the leaflets by the chordae and papillary muscle toward the apex. The leaflets and chordae themselves are generally not altered. The effect is malcoaptation of the leaflets resulting in progressive regurgitation. This corresponds to a type I and III defect in the Carpentier classification [21]. In years past, conventional wisdom was that correction of MR (typically via replacement) in the setting of severe LV dysfunction was contraindicated because of the poor results. The theory was that the "pop-off" mechanism of the regurgitant mitral valve was disrupted leading to overt cardiac failure. |
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| In 1995, Bolling et al. [23*, 24] reported surgical results on 16 patients with LV ejection fraction (LVEF) 9% to 25% in functional New York Heart Association (NYHA) class IV with severe MR. All underwent ring mitral annuloplasty and, where indicated, tricuspid valve annuloplasty and coronary artery bypass. There were no perioperative deaths and the 1-year actuarial survival was 75%. On medium-term follow-up, the survivors were in NYHA class I or II with a mean LVEF of 25% and overall reduction in hospitalization when compared with their preoperative status. Subsequent longer-term follow-up as well as reports by others have shown similar results [25]. In general, operative morbidity and mortality have been low and there has been functional improvement in this group of chronically ill patients. |
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| The typical patient under consideration for this type of therapy is in NYHA class III-IV under poor control, with LVEF generally less than 30%; there is severe MR with normal-appearing leaflets, no evidence of perforation, significant thickening, or prolapse. One caveat concerns the assessment of the MR, and generally it has been a combination of catheterization, TEE and transthoracic echocardiography. Optimization of the patient's congestive failure is recommended prior to surgery. |
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| The primary procedure involves an undersized annuloplasty with one of the many commercially available rings or bands (Table 1). Undersizing means the usual methods of determining ring size by the intracommissural distance or the area of the anterior leaflet are replaced by taking the ring one to two sizes smaller than that determined by the above methods, or by simply using the smallest of the commercial rings available [26]. |
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| Intraoperative use of TEE is essential to evaluate the procedure, although one is cautioned regarding the intraoperative assessment of MR prior to annuloplasty. As the MR can be very dynamic in nature in these patients, the conditions of general anesthesia including alterations in preload and afterload may reduce the severity of the regurgitation. Provocative maneuvers such as aggressively increasing the afterload may help in this assessment. More important is the knowledge of the status of the valve in the awake, ambulatory setting. |
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| Subsequent mitral stenosis has been rare, in part because the rings or bands used are still within a reasonable size range and the leaflets themselves usually are normal. The incidence of systolic anterior motion is also very low even though the smaller rings are used. This is related to the altered ventricular geometry in these patients, which increases the angle between the aortic and mitral valve. |
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| There is evidence that annuloplasty or other valve repair is superior to replacement in a variety of ways, including improved short- and long-term function. Further support lies in the historic reports of the poor results of mitral valve replacement in the setting of severely depressed function. However, it is believed some of this was related to the then-traditional method of total excision of the valve and subvalvar apparatus. Improved perioperative management and replacement with chordal preservation has prompted some to revisit this issue. A recent report assessed 44 patients with MR and LV dysfunction (EF < 35%) over a 9-year period; 27 (61%) were in NYHA class III-IV. The etiology was ischemia (30%), valvar (40%), or dilated cardiomyopathy (30%). Mitral valve repair was performed in 80%; the remainder underwent mitral valve replacement. Of the replacement group, most were done for primary valve pathology, all with chordal preservation. In this study, mitral valve replacement was not demonstrated to increase mortality over repair [25]. The experience of other centers appears to confirm this [27]. |
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| Improved recognition of the role the mitral valve plays in overall ventricular function has led some to adopt a more aggressive approach to moderate mitral valve regurgitation in those patients with coronary artery disease undergoing coronary artery bypass [27, 28, 29]. Experience and improved perioperative care, together with the ability to correct the regurgitation without replacement, has resulted in significant reductions in short- and long-term morbidity and mortality. As always, these studies suggest trends that ultimately may require randomized studies to confirm [30, 31]. These should be considered early data in the growing options for surgery in the treatment of cardiomyopathy and heart failure [32]. |
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| Tricuspid Valve Disease |
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| In many cases of MR secondary to cardiomyopathy, associated tricuspid regurgitation may also be seen as a consequence of ventricular dilation and elevated pulmonary artery pressures. Aggressive concomitant therapy for tricuspid valve regurgitation is recommended. It has been felt in the past that with correction of the MR, the pulmonary pressures should fall resulting in the improvement of the tricuspid insufficiency. This is not immediate, and in some cases does not occur. Therefore, a tricuspid annuloplasty should be performed if moderate to severe regurgitation exists [33]. |
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| In other cases of tricuspid disease, many of the same principles apply as with mitral disease. Often, annular dilation leading to regurgitation is amenable to one of several annuloplasty techniques. Replacement, if needed, is usually limited to either a mechanical or stented tissue valve. In general, the preference is for tissue valves. The lower pressure involved as well as the lower flow for a given area create increased risk for thrombosis with a mechanical valve. These factors may also contribute to less stress and increased durability for the tissue valves [34*]. |
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| Transesophageal Echocardiography |
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| A key to the discussion of current valve surgery is the use of intraoperative TEE. In many centers, its use has become routine for cardiac surgical procedures. Specific for valve surgery, it can provide an improved visualization of the valves in the functioning state as an aid to assessing pathology. Following any valve procedure, repair or replacement, it can provide immediate feedback on the functioning of the new or repaired valve prior to completion of the operation. It can also be an aid in assessing the amount of retained intracardiac air to help guide appropriate measures [35*, 36, 37]. |
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| One caveat for the use of TEE is the need for experienced operators. In selected cases, cardiologists are called on to assist in interpretation in the operating room. With increasing frequency, cardiac anesthesiologists are being trained in many aspects of TEE use. One also needs to be cognizant of the changes in hemodynamics in the anesthetized patient that may alter the appearance of valve function. The most common example is in the subset of patients with functional MR. In some cases, decreased afterload may lead to apparent improvement in the degree of regurgitation. Maneuvers such as volume loading or pharmacologically increased afterload may allow better assessment of the pathology. |
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| Minimally Invasive Surgery |
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| Another issue that has garnered increasing interest in cardiac surgery and in particular, valve procedures, has been that of minimally invasive surgery. In general, this refers to techniques that are intended to reduce the short- and long-term effects of the surgical procedure. In most cases of valve surgery, this involves smaller or alternative incisions or approaches to the valve coupled with additional technology [38, 39]. Examples include a partial sternotomy for aortic or mitral valve surgery, limited right thorocotomy aided by video/endoscopic assistance with alternative means of providing cardiopulmonary bypass, and robotic assistance in mitral valve surgery as the pinnacle of technologic assistance [40, 41]. |
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| Limitations to this trend include the increased technical demands; increased costs related to the technology and limitations on what concomitant procedures can be performed. Further study possibly including randomized protocols or propensity studies will be needed to determine the true benefit to the patient over that of cosmesis alone, demonstration of physiologic and anatomic results that are at least equivalent, as well as a cost benefit analysis. |
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| Conclusions |
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| There continues to be a growing number of options available for the treatment of valvular heart disease. Although the search for the ideal replacement continues, the variety currently available has improved the options. There is an increasing appreciation of the interrelationship between the mitral valve and the ventricle that go beyond the issues of stenosis or regurgitation alone. The increasing use and value of intraoperative TEE makes this modality almost mandatory. Finally, improvements are being sought to alter the approach to the operation with the hope of improving patient comfort and outcome. |
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| References and Recommended Reading |
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| Recently published papers of particular interest have been highlighted as: | |
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| * | Of importance |
| ** | Of major importance |
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| 1. |
Grunkemeier GL: "Our complication rates are lower than theirs": statistical critique of heart valve comparisons. J Thorac Cardiovasc Surg 2003, 125:290-300. | |
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Starr A: Heart valve replacement surgery: past, present and future. Clin Exp Pharmacol Physiol 2002, 29:735-738. | |
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| 3. * |
Schoen FJ: Future directions in tissue heart valves: impact of recent insights from biology and pathology. J Heart Valve Dis 1999, 8:350-358. | |
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| A nice review of the biology of tissue valves. | ||
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View the PubMed
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| 4. * |
Wernley JA: Choosing a prosthetic heart valve. Cardiol Clin 1998, 16:491-504. | |
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| A good, detailed summary of most of the currently available valves with a reasonable algorithm for selection. | ||
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| 5. |
Fann JI: Are the indications for tissue valves different in 2001 and how do we communicate these changes to our cardiology colleagues? Curr Opin Cardiol 2001, 16:126-135. | |
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| 6. |
David TE: Aortic valve replacement with stentless porcine bioprostheses. J Card Surg 1998, 13:344-351. | |
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Park SZ: Current status of stentless aortic xenografts. Curr Opin Cardiol 2000, 15:74-81. | |
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Kouchoukos NT: Aortic allografts and pulmonary autografts for replacement of the aortic valve and aortic root. Ann Thorac Surg 1999, 67:1846-1848;. | |
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Dacey LJ: Pulmonary homografts: current status. Curr Opin Cardiol 2000, 15:86-90. | |
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Staab ME: Aortic valve homografts in adults: a clinical perspective. Mayo Clin Proc 1998, 73:231-238. | |
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Elkins RC: Ross operation in children: late results. J Heart Valve Dis 2001, 10:736-741. | |
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Gatzoulis MA: Ross procedure: the treatment of choice for aortic valve disease? Int J Cardiol 1999, 71:205-206. | |
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| 14. |
Reardon MJ: Evolving experience with cryopreserved mitral valve allografts. Curr Opin Cardiol 1998, 13:85-90. | |
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| 15. |
Thamilarasan M: Choosing the most appropriate valve operation and prosthesis. Cleve Clin J Med 2002, 69:688-690. | |
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| 16. |
Sapirstein JS: The "ideal" replacement heart valve. Am Heart J 2001, 141:856-860. | |
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| 17. |
Chatterjee S: Factors determining selection of valve prosthesis--tissue or mechanical: current status. Adv Cardiol 2002, 39:189-194. | |
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| 18. |
Birkmeyer NJ: Aortic valve replacement: current clinical practice and opportunities for quality improvement. Curr Opin Cardiol 2001, 16:152-157. | |
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Braunwald E: Aortic valve replacement: an update at the turn of the millennium. Eur Heart J 2000, 21:1032-1033. | |
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David TE: Aortic valve repair for management of aortic insufficiency. Adv Card Surg 1999, 11:129-159. | |
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| 21. |
Espada R: New developments in mitral valve repair. Curr Opin Cardiol 1998, 13:80-84. | |
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| 22. |
Lawrie GM: Mitral valve repair vs replacement. Current recommendations and long-term results. Cardiol Clin 1998, 16:437-448. | |
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| 23. * |
Bolling SF: Surgery for acquired heart disease: early outcome of mitral valve reconstruction in patients with end stage cardiomyopathy. J Thorac Cardiovasc Surg 1995, 109:676-683. | |
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| One of the early reports of the approach to secondary or functional MR associated with cardiomyopathy. | ||
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View the PubMed
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| 24. |
Bolling SF: Intermediate-term outcome of mitral reconstruction in cardiomyopathy. J Thorac Cardiovasc Surg 1998, 115:381-388. | |
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| 25. |
Bishay ES, et al.: Mitral valve surgery in patients with severe left ventricular dysfunction. Euro J Cardiothorac Surg 2000, 17:213-221. | |
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| 26. |
Bolling SF: Mitral reconstruction in cardiomyopathy. J Heart Valve Disease 2002, II(Suppl I):S26-S31. | |
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| 27. |
Byrne JG: Repair versus replacement of mitral valve for treating severe ischemic mitral regurgitation. Coron Artery Dis 2000, 11:31-33. | |
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Adams DH: Surgical treatment of the ischemic mitral valve. J Heart Valve Disease 2002, II(Suppl I):S21-S25. | |
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| 29. |
Dreyfus G: Mitral valve repair in cardiomyopathy. J Heart Lung Transplant 2000, 19(Suppl 8):S73-S76. | |
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| 30. |
Lachmann J: Mitral ring annuloplasty: an incomplete correction of functional mitral regurgitation associated with left ventricular remodeling. Curr Cardiol Rep 2001, 3:241-246. | |
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| 31. |
Tittle SL: Concomitant mitral repair at the time of coronary artery bypass grafting--the ‘con' point of view. Adv Cardiol 2002, 39:157-163. | |
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| 32. |
Zeltsman D: Surgical management of heart failure: an overview. Annu Rev Med 2002, 53:383-391. | |
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| 33. |
Trichon BH: Secondary mitral and tricuspid regurgitation accompanying left ventricular systolic dysfunction: is it important, and how is it treated? Am Heart J 2002, 144:373-376. | |
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| 34. * |
Blaustein AS: Tricuspid valve disease. Clinical evaluation, physiopathology, and management. Cardiol Clin 1998, 16:551-572. | |
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| A very complete summary of the topic. | ||
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