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J Thorac Cardiovasc Surg 1994;107:381-0393
© 1994 Mosby, Inc.
Surgery for Acquired Heart Disease |
Durham, N.C.
From the Departments of Surgery and Community and Family Medicine, Duke University Medical Center, Durham, N.C.
Address for reprints: Donald D. Glower, MD, Box 3851, Duke University Medical Center, Durham, NC 27704.
Abstract
During the period of 1977 to 1990, 960 Carpentier-Edwards standard prostheses (Baxter Healthcare Corp., Santa Ana, Calif.) were placed in 875 operations. Freedom from reoperation at 10 years was 57% ± 4%, 76% ± 3%, and 95% ± 5% for mitral, aortic, and tricuspid valve replacement, respectively. Age was the only independent determinant of reoperation for both aortic and mitral valves. Likelihood of reoperation decreased with age, with freedom from reoperation after 10 years in patients aged less than 60 years versus 60 or more years being 65% ± 5% versus 90% ± 4% after aortic valve replacement and 48% ± 5% versus 75% ± 6% after mitral valve replacement. For mitral valve replacement, larger valve size made reoperation more likely, with freedom from reoperation at 10 years being 71% ± 6% for sizes less than 31 mm and 57% ± 5% for sizes 31 mm or larger. For aortic valve replacement, prior median sternotomy reduced freedom from reoperation at 10 years from 80% ± 3% to 25% ± 5%. The low prevalence of reoperation affirms the suitability of the Carpentier-Edwards prosthesis for selected elderly patients and for tricuspid valve replacement. Because of their influence on the probability of reoperation, valve size and prior cardiac procedures also merit consideration in the choice of valvular prosthesis. (J THORAC CARDIOVASC SURG 1994;107:381-93)
The incidence of reoperation after valve replacement has been frequently reported and is probably a function of time, of patient characteristics, and of the valvular prosthesis itself. However, little information exists to clearly document the determinants of reoperation after valve replacement, especially as concerns those patient characteristics that might influence the likelihood of subsequent reoperation.
1-4 Yet, the determinants of reoperation are quite important in patient selection, in choice of prosthesis, and in design of a given operative procedure. Because relevant data regarding determinants of reoperation are lacking, these decisions have often been difficult and have been quite controversial in recent years. 5, 6 Specifically, bioprostheses were generally favored 10 years ago, but now mechanical prostheses have gained more favor, in part because of an apparently lower risk of reoperation. Because much of this confusion results directly from lack of data regarding the influence of patient characteristics and choice of valvular prosthesis on reoperation, this debate and others will not be resolved until studies better document the actual determinants of reoperation after valve replacement.
A retrospective study was therefore designed to examine in a multivariable fashion the determinants of reoperation in patients who received a standard Carpentier-Edwards bioprosthesis (Baxter Healthcare Corp., Santa Ana, Calif.).
METHODS
The study population included all patients who received a Carpentier-Edwards standard valvular prosthesis during the period of 1977 through 1990 at Duke University Medical Center. In these patients, 960 standard Carpentier-Edwards prostheses were placed in 875 operations (366 aortic, 370 mitral, 60 tricuspid, 1 pulmonic, 58 aortic and mitral, 1 aortic and tricuspid, 12 mitral and tricuspid, 7 aortic and mitral and tricuspid). The study included patients who underwent multiple valve replacement so that the impact of concurrent cardiac procedures on subsequent reoperation could be examined. By retrospective medical record review, data were collected regarding patient demographics, previous cardiac operations, cardiovascular risk factors, noncardiac comorbid conditions, cardiac symptoms, cardiac catheterization, operative procedures, postoperative in-hospital course, subsequent procedures, complications after discharge, and symptoms at last follow-up. Preoperative comorbidity was quantified by the comorbidity index of Jollis and associates. 7
Follow-up data were obtained from medical records, local physicians, direct telephone contact, patient questionnaires, or the National Death Index, and follow-up was complete as of 1990 in 798 of 875 patients (91%). Mean follow-up was 5.8 ± 4.6 years, and a total of 5611 valve-years of follow-up were available for study. With the use of both reoperation and reoperation for structural deterioration as end points, Cox proportional hazards models were constructed with preoperative and intraoperative patient characteristics. Those variables obtaining univariate significance at the 0.10 level were incorporated into a multivariable model that used stepwise backward elimination of variables not attaining multivariable significance at the 0.05 level. Estimates of freedom from reoperation were constructed by the methods of Kaplan and Meier, and Kaplan-Meier curves were compared by the log-rank and Wilcoxon tests. All data were presented as mean plus or minus standard deviation unless otherwise specified.
Nomenclature were defined according to the guidelines for reporting morbidity and mortality after cardiac valvular operations. 8 Operative mortality included any death that occurred within 30 days after operation or before discharge from the hospital. Valvular structural deterioration included any abnormality that caused stenosis or regurgitation intrinsic to the valve and exclusive of thromboembolism or infection. Valvular dysfunction as a result of perivalvular leak, inappropriate sizing, or clinically significant hemolytic anemia was considered to be nonstructural dysfunction. Reoperation was defined as any procedure that altered, repaired, or replaced a previously placed prosthesis.
RESULTS
Since the first standard Carpentier-Edwards prosthesis was implanted in 1977 at this institution, the number of operations in which the standard Carpentier-Edwards prosthesis was used increased rapidly up to 1980 when the Carpentier-Edwards valve represented 78% of all valve prostheses used at this center. Subsequent to 1980, the use of the standard Carpentier-Edwards prosthesis declined and then stabilized at 12% of all prostheses implanted in the years 1988 to 1990 (Fig. 1). Of the 821 aortic or mitral valve operations done with standard Carpentier-Edwards prostheses, 509 operations (62%) involved a single valve replacement without concurrent procedures (Table I). In 78 operations (9%), two or more standard Carpentier-Edwards prostheses were implanted. Prostheses other than the standard Carpentier-Edwards prosthesis were concurrently placed in 54 operations; 22 prostheses in the aortic position (2 Starr-Edwards, 7 Ionescu-Shiley 
), 28 in the mitral position (11 Starr-Edwards, 11 St. Jude Medical, 1 Björk-Shiley, 4 Hancock, 1 Ionescu-Shiley), and 4 in the tricuspid position (4 Hancock). Additional concurrent procedures (Table I) included coronary artery bypass grafting in 169 operations (19%), other valve repair in 12 operations (1.4%), and repair of ascending aortic aneurysms in 13 patients (1.5%).
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Table II). Operations before aortic valve replacement were isolated aortic valve repair or replacement in 20 (61%) of 33, and operations before mitral valve replacement were isolated mitral valve commissurotomy, repair, or replacement in 59 (70%) of 84 operations. Increased Jollis comorbidity score was associated with decreased survival (p < 0.05), and the mean Jollis comorbidity scores were 2.1 ± 1.5 and 2.0 ± 1.4 for aortic and mitral valve replacement, respectively.
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Table III. Structural deterioration accounted for 128 (81%) of the 159 reoperations, with perivalvular leak and infection accounting for only 13% and 4% of reoperations, respectively. At reoperation, 5 (3%) of 159 patients underwent replacement of normal Carpentier-Edwards aortic valves as part of a concurrent operation. Six patients had hemodynamic evidence of structural deterioration by cardiac catheterization or echocardiography, but these six patients did not undergo reoperation because of patient refusal or overriding comorbid conditions. The mode of valve failure in patients who required reoperation for structural deterioration was stenosis in 10%, regurgitation in 59%, and mixed stenosis and regurgitation in 31% for aortic valves. For mitral valves, the mode of failure was stenosis in 19%, regurgitation in 56%, and mixed stenosis and regurgitation in 25%.
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Table IV lists the variables examined as potential determinants of reoperation by Cox model analysis. Multivariable analyses were not done on the 80 tricuspid valve replacements because the total number of reoperations was small. For all patients who underwent Carpentier-Edwards aortic valve replacement, age, previous median sternotomy, and valve size were the only independent variables that affected likelihood of reoperation. For mitral valve replacement, age and mitral valve size were the only independent variables that obtained multivariable significance. A second multivariable analysis that examined freedom from reoperation for structural deterioration as the dependent variable found that only young age and prior median sternotomy increased risk of structural deterioration in the aortic position, whereas young age and large valve size increased risk of structural deterioration in the mitral position (Table V). As a check to ensure that the results in Table IV were not biased by concurrent operations, a similar analysis was conducted that examined the 250 patients with isolated aortic valve replacement and the 259 patients with isolated mitral valve replacement. From this analysis, the independent determinants of reoperation after isolated aortic or mitral valve replacement were the same variables identified as significant in Table IV. Thus patient age was the strongest predictor of reoperation after Carpentier-Edwards valve replacement, with young age increasing the likelihood of reoperation for both aortic and mitral valve replacements (Fig. 5). Age less than 60 years decreased freedom from reoperation at 10 years from 90% ± 4% to 65% ± 5% for aortic valve replacement (p = 0.0001) and from 75% ± 6% to 48% ± 5% for mitral valve replacement (p = 0.01).
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Table IV), but large valve size significantly increased the likelihood of reoperation for structural deterioration only after mitral and not aortic valve replacement (Table V, Fig. 6). Freedom from reoperation for structural deterioration 10 years after mitral valve replacement was 71% ± 6% for sizes 25 to 29 mm and was 57% ± 5% for sizes 31 to 35 mm (p < 0.03). Ten years after aortic valve replacement, freedom from reoperation for structural deterioration was 87% ± 5% for sizes 19 to 23 mm and was 79% ± 4% for sizes 25 to 31 mm (p = 0.06). When aortic and mitral valves of similar sizes (25 to 29 mm) were compared, freedom from reoperation for structural deterioration at 10 years was quite similar (79% ± 4% aortic versus 71% ± 6% mitral; Fig. 6), which suggests that the earlier valvular dysfunction in the mitral position versus aortic position may in large part result from differences in mitral versus aortic valve sizes (Fig. 3). Valve size did not correlate with mode of valve failure (stenosis versus regurgitation) in aortic valves (r2 = 0.00, p = 0.9), but smaller mitral valve sizes did correlate with valve failure caused by stenosis (r2 = 0.23, p = 0.001; Fig. 7).
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2 = 10.1, p < 0.01). In addition, patients undergoing aortic valve replacement with prior median sternotomy were more likely to have rheumatic fever (13 of 29 versus 55 of 348, 2 = 19.8, p < 0.01) or endocarditis (5 of 29 versus 23 of 380, 2 = 5.9, p = 0.01) as the valve disease etiology. On the other hand, median sternotomy before mitral valve replacement was not associated with concurrent valve procedure or with a rheumatic or infectious valve disease etiology (p > 0.1). Thus, in patients with aortic valve replacement but not in those with mitral valve replacement, prior median sternotomy tended to be a marker for patients with multivalve disease caused by rheumatic fever or endocarditis, and the increased rate of reoperation among these patients was associated with increased likelihood of reoperation on multiple valves. Of note, prior median sternotomy did not affect the prevalence of reoperation for perivalvular leak after aortic or mitral valve replacement.
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The rates of reoperation observed in the current study parallel those reported in most large studies of reoperation 5, 9, 10 and of structural deterioration. 9 The greater prevalence of reoperation and structural deterioration for mitral valve replacement relative to aortic valve replacement has been described for the standard Carpentier-Edwards bioprosthesis. 3, 5, 9, 10 Although no direct comparisons have been made between the Carpentier-Edwards standard prosthesis and other bioprostheses such as the Hancock valve, the rates of reoperation and structural deterioration have been similar for the Carpentier-Edwards and Hancock prostheses, 11, 12 prompting many authors to combine Carpentier-Edwards and Hancock prostheses. 1, 13, 14 Operative mortality 10,15-17 and the prevalence of perivalvular leak 15, 18 in previous reports did not differ significantly from the rates observed in the current study.
Relatively few studies have used multivariable analysis to seek determinants of reoperation or structural deterioration for Carpentier-Edwards or Hancock prostheses. 1-4 However, since the original report of Magilligan and associates, 1 many authors have observed premature prosthetic dysfunction associated with younger patient age. 2-4, 10, 13, 17, 19-22Although Magilligan and associates 1 found that age less than 35 years and incrementally younger accelerated prosthetic dysfunction, age has subsequently been seen to have a continuous effect on prosthetic dysfunction, with prosthetic dysfunction rarely being seen in patients over the age of 70 years. 19 The current study confirmed that, for the Carpentier-Edwards prosthesis in either the aortic or mitral position, patient age is the most significant predictor of reoperation and of structural deterioration that necessitates reoperation. Although the current study contained few patients less than 40 years old, the likelihood of prosthetic dysfunction and reoperation was a continuous function of age as described by Jamieson and colleagues. 19 This effect of age on the rate of reoperation and prosthetic dysfunction was not a result of decreased survival in the elderly, inasmuch as the estimates of freedom from reoperation were calculated only for those living patients at risk for reoperation. Moreover, other factors such as comorbidity score were associated with diminished survival but were not associated with increased prosthetic longevity. Exactly why young age accelerates degeneration of bioprostheses remains unclear but may include such factors as calcium metabolism and greater cardiac output in the young. Of interest, Pansini and associates 4 found no effect of serum calcium or phosphate levels on structural deterioration, whereas Magilligan and associates 2 observed accelerated valvular dysfunction in patients with cardiac indexes greater than 2.0 L/min/m2.
Unlike patient age, valve size has not been examined as a determinant of bioprosthetic deterioration. In the 70-degree convexoconcave Björk-Shiley valve, large valve size has been associated with increased risk of strut fracture. 23 In series of mixed Carpentier-Edwards and Hancock bioprostheses, small valve size correlated with inward post bending, 24 increased calcification, 25 and increased stenotic failure. 26 The current study examined structural deterioration leading to either stenosis or regurgitation, and accelerated valve deterioration with large rather than small valve size was clearly demonstrated for mitral valves. An association between small valve size and valve failure caused by stenosis was noted only for mitral prostheses. In the current study, large valve size did increase the likelihood of reoperation in aortic valves, but large valve size was not a significant independent determinant of reoperation for structural deterioration. This differing effect of valve size between aortic and mitral valves may have resulted from inadequate patient numbers to detect a weaker effect of valve size on aortic prostheses, or some of the excess reoperations on large aortic valves may have resulted from associations with young age, Marfan's syndrome, or factors other than structural deterioration. As suggested by Figs. 4 and 6, the earlier valvular deterioration in the mitral position versus aortic position may in large part result from differences in mitral versus aortic valve sizes. Inherently greater mechanical stresses placed on the leaflets of larger bioprostheses may be one mechanism for greater valve longevity in the smaller bioprostheses.
As with valve size, prior or concurrent operations have not previously been examined as determinants of reoperation or prosthetic dysfunction. Of note, patients with prior operation and those undergoing concurrent operation tended to be the same patients in the present study. This suggests that prior or concurrent operation did not in fact accelerate prosthetic dysfunction, but merely accelerated the interval to reoperation in which the aging bioprosthesis was replaced for lesser degrees of dysfunction. Of note, prior or concurrent operation did not affect the incidence of perivalvular leak, thus perivalvular leak did not explain the increased reoperation rate in patients with prior or concurrent operations.
The only remaining factor that has been examined as a determinant of prosthetic dysfunction or reoperation is gender. Jamieson and associates 3 and Magilligan and associates 2 both found that female gender accelerated structural degeneration of bioprosthetic valves, although this effect was not statistically significant in the smaller study of Pansini and associates. 4 In the current study, female gender tended to increase structural deterioration in mitral valves, yet the effect of gender was not statistically significant. Because differences related to gender have only been observed in studies of more than 1000 patients, the gender effect appears to be small and will require much larger studies for possible confirmation.
The current study has several inherent limitations. Although only two other institutions have reported larger numbers of standard Carpentier-Edwards prostheses than the current study, 3, 27 other weaker determinants of structural deterioration or reoperation might have been missed because of inadequate numbers of patients. Small patient numbers especially limit the applicability of this study to patients less than 40 years old and to valves of extremely small or extremely large sizes. The small number of patients who required reoperation for reasons other than structural deterioration (such as perivalvular leak, endocarditis) similarly prohibits any conclusions from this study in these small patient subsets. More important, the current study is subject to the limitations of retrospective analyses. Specifically, uncontrolled bias linking age, prior or concurrent operations, valve size, or undetermined factors could have confounded the present study. The fact that age, valve size, and prior operation were significant determinants in both multivariable and univariate analyses should minimize any biases involving those variables. Similarly, the reproducibility of Table IV with the use of either the entire population or only isolated valve replacements suggests that the data shown in Table IV were not confounded by concurrent operations in a heterogeneous population.
Because prosthetic dysfunction and reoperation are morbid events potentially affected by choice of valve prosthesis, this study has important implications for clinical decisions regarding selection of valve prosthesis. Indeed, concerns regarding reoperation have been largely responsible for the shift toward mechanical prostheses in the last decade. 5, 6 First of all, this study confirms the suitability of the standard Carpentier-Edwards prosthesis in elderly patients or in other patients in whom the valve longevity of 10 to 12 years exceeds the longevity expected for the patient. Especially in the elderly, the primary advantage of bioprostheses remains the avoidance of fatal (0.5% per patient-year) and nonfatal (2% to 4% per patient-year) anticoagulant-related hemorrhage. 28 Even though other factors such as comorbid illness may limit patient longevity without affecting valve longevity (Tables IV and V), relatively young patients may be reasonable candidates for the Carpentier-Edwards prosthesis if significant comorbidity reduces life expectancy to less than that of the prosthesis. Thus comorbidity does not affect likelihood of reoperation on an incidence per patient-year basis, but life-limiting comorbidity may well decrease the absolute probability of reoperation and thus favor choice of a bioprosthesis.
As in elderly patients, the Carpentier-Edwards valve demonstrated excellent longevity and freedom from reoperation in the tricuspid position (Fig. 4). Superb durability in the tricuspid position has been reported for other bioprostheses. 29 The reasons for the durability of tricuspid bioprostheses despite the larger valve sizes used in the tricuspid position may result from the lower pressures and lower mechanical leaflet stress. Because of excellent durability and a low incidence of valve thrombosis, the Carpentier-Edwards valve and other bioprostheses remain the prostheses of choice for tricuspid valve replacement.
Just as mechanical prostheses have become favored in young patients, bioprostheses are seeing less use in the mitral position because of concerns of decreased valve longevity in the mitral position and because of data that suggest that 36% or more of patients who undergo mitral valve replacement will ultimately require anticoagulation because of atrial fibrillation or atrial enlargement. 5 The current study provides important information that much of the decreased valve survival in the mitral position occurs only in the larger valve sizes. Thus, anticoagulation concerns aside, an older patient with a life expectancy of less than 10 years and needing a small-sized prosthesis could be a reasonable candidate for a Carpentier-Edwards mitral prosthesis.
Finally, the current study implies that previous cardiac operations are additional factors to consider in choosing a valve prosthesis, especially in patients with aortic valve disease who have had prior mitral valve procedures. Because reoperation is more likely in patients with aortic valve disease who have had a previous operation, a mechanical prosthesis may be preferable in these patients barring other considerations such as age, valve size, and anticoagulation. This strategy presumes that the life span of a mechanical prosthesis will exceed the likely time interval to reoperation for concurrent mitral valve disease.
In summary, review of a large, single institutional experience with the standard Carpentier-Edwards prosthesis has confirmed previous reports of the durability of this valve generally being 8 to 12 years. Choice of a valve prosthesis should be individualized for each patient using such considerations as need for anticoagulation, patient age, patient life expectancy, valve size, valve position, and other cardiac disease. Advanced age, life expectancy less than 8 to 12 years, smaller valve size, tricuspid valve position, and absence of other previous cardiac disease all favor choice of a bioprosthesis such as the standard Carpentier-Edwards valve in patients who do not require anticoagulation for other reasons. With a new generation of bioprostheses becoming available, the standard Carpentier-Edwards prosthesis remains a gold standard for future comparison. Further studies with even larger patient numbers are needed to clarify the roles of more subtle or less prevalent factors such as gender or dialysis-dependent renal failure on the choice of a valvular bioprosthesis.
* 4 St. Jude Medical,
7 Björk-Shiley, 2 Hancock,§
Appendix: DISCUSSION
Dr. Alain Carpentier (Paris, France)
Inasmuch as I have some indirect responsibility in these reoperations I think it is only fair that I rise to speak. I congratulate the authors for this superb series and for allowing us to discuss this important problem of reoperation. This study confirms what we already know, that the durability of a bioprosthesis is linked with both the age of the patient and the position of the valve.
But the study brings something new, that is, the relationship between durability and the size of the prosthesis. I am not sure that we can say that an aortic valve is more durable than a mitral valve just because of the difference in size; the very different hemodynamic conditions play probably a more important role. If we talk about the mitral valve only, having in mind what you have shown, I would like to ask the authors whether they have the tendency to downsize the valve in their current practice, for example, to use more 27 and 29 mm valves than the 31 or 33 mm valves that we used in the past, knowing that the transvalvular gradient is still acceptable with these smaller sizes.
In addition to this question, I would like to make a comment. I would like to take this opportunity to share with you our most recent results with a new-generation bioprosthesis that we introduced in France 12 years ago and that became available in this country only recently.
This new bioprosthesis took advantage of the research done in my laboratory in the past 20 years and the lessons learned from our clinical practice both in terms of biology and hemodynamics. The stent, the mounting technique, and the preservation method have been improved. Pericardium has been preferred to porcine valve tissue to eliminate the aortic sheath and therefore minimize the transvalvular gradient. The tissue is mounted on a fully flexible stent with a unique configuration that renders unnecessary commissural stitches. The pericardial tissue is carefully selected, oriented, and preserved. The results we have had after 12 years of experience with this new valve are quite surprising: the freedom from valve-related thromboembolism is only slightly superior to that of the existing bioprosthesis but freedom from valve reoperation was 94% and freedom from structural valve deterioration is 96% at 12 years.
Thus progress continues to be made in this field so as to achieve better valve durability.
Dr. Robert A. Guyton (Atlanta, Ga.)
A question that has certainly been addressed in the past is whether or not in looking at valves and structural deterioration we need to consider a little more carefully freedom from death or reoperation. With a 75-year-old patient whose valve is beginning to deteriorate, our chance of doing a reoperation is maybe 50/50, whereas with a 55-year-old patient with valve deterioration, our chance of doing a reoperation is 100%. Is it really true that we can look at the rate of reoperation and compare 70-year-old patients with 55-year-old patients and, looking just at these raw rates, claim that the structural valve deterioration is less in the 70-year-old patient? A 75-year-old patient who is frail and not a candidate for reoperation is likely to die without an operation. Our curves show that the freedom from reoperation is less in 70-year-olds. I would like Dr. Glower to address this question.
Dr. Glower
Dr. Carpentier, although these results are relatively new, I expect that they will encourage us to downsize some valves slightly or to have a lower threshold for implanting a bioprosthesis in patients who require a smaller valve size.
We will certainly look forward to seeing this kind of analysis repeated in the new prostheses that you have described. I expect that the standard Carpentier-Edwards valve will be a good gold standard for such future bioprostheses.
Dr. Guyton, your point differentiating death or likelihood of reoperation by Cox model analysis from the overall probability of an elderly versus a young patient actually undergoing reoperation is an important one. These data do show that Carpentier-Edwards valves really do last longer in older patients if all patients live the same period of time, but the lesser life expectancy in older patients is itself an important factor in choosing a bioprosthesis versus a mechanical prosthesis. It is, therefore, our current practice to use bioprostheses primarily in elderly patients or patients in whom there are specific contraindications to anticoagulation.
Acknowledgments
We gratefully acknowledge the assistance of Rob DeVoe with the illustrations and the secretarial assistance of Louise Leighton.
Footnotes
Read at the Seventy-third Annual Meeting of The American Association for Thoracic Surgery, Chicago, Ill., April 25-28, 1993. 
*Baxter Healthcare Corp., Santa Ana, Calif.
St. Jude Medical, Inc., St. Paul Minn.
§Johnson & Johnson Cardiovascular, King of Prussia, Pa.
References
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 |
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 D. D. Potter, T. M. Sundt III, K. J. Zehr, J. A. Dearani, R. C. Daly, C. J. Mullany, C. G. A. McGregor, F. J. Puga, H. V. Schaff, and T. A. Orszulak Risk of repeat mitral valve replacement for failed mitral valve prostheses Ann. Thorac. Surg., July 1, 2004; 78(1): 67 - 72. [Abstract] [Full Text] [PDF]
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|
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 R Z Omar, L S Morton, D A Halliday, E M Danns, M T Beirne, W J Blot, and K M Taylor Outlet strut fracture of Bjork-Shiley convexo concave heart valves: the UK cohort study Heart, July 1, 2001; 86(1): 57 - 62. [Abstract] [Full Text] [PDF]
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I. R.A. Goldsmith, T. J. Spyt, M. Boehm, S. Kendall, and M. D. Rosin Midterm evaluation of the Tissuemed (Aspire) porcine bioprosthesis: 493 patients, 506 bioprostheses Ann. Thorac. Surg., May 1, 2001; 71(5): 1471 - 1476. [Abstract] [Full Text] [PDF]
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|
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 |
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|
|
|
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|
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|
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