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Ann Thorac Surg 2006;81:857-862
© 2006 The Society of Thoracic Surgeons

Original article: Cardiovascular

Valve Replacement Surgery in End-Stage Renal Failure: Mechanical Prostheses Versus Bioprostheses

Vincent Chan, MD a , W.R. Eric Jamieson, MD a , * , Arlen G. Fleisher, MD b , David Denmark, MPH b , Florence Chan a , Eva Germann, MS a

a University of British Columbia, Vancouver, British Columbia, Canada
b Westchester Medical Center, Valhalla, New York

Accepted for publication September 6, 2005.

* Address correspondence to Dr Jamieson, 486 Burrard Building, St. Paul's Hospital, 1081 Burrard St, Vancouver, BC V6Z 1Y6, Canada (Email: wrej{at}interchange.ubc.ca).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
BACKGROUND: The 1998 American College of Cardiology/American Heart Association Guidelines recommend mechanical prostheses for valve replacement in patients with end-stage renal disease requiring dialysis. The aim of the study is to evaluate the combined experience at two academic centers.

METHODS: Sixty-nine valve replacements (aortic 40; mitral 22; multiple 7; 47 bioprostheses, 22 mechanical prostheses) were performed. Total follow-up was 128.7 patient-years (bioprostheses, 68.4; mechanical prostheses, 60.4).

RESULTS: Patient populations were homogeneous, except for age (bioprostheses greater than mechanical prostheses, p = 0.012), previous myocardial infarction (bioprostheses greater than mechanical prostheses, p = 0.040), and concomitant CABG (bioprostheses greater than mechanical prostheses, p = 0.019). A survival advantage was observed in favor of mechanical prostheses (p = 0.0299) at 5 years. Freedom from valve-related complications at 5 years was calculated for thromboembolism plus thombosis plus hemorrhage (bioprostheses, 93.0% ± 3.9%; mechanical prostheses, 76.4% ± 12.7%), thromboembolism excluding thombosis (bioprostheses, 93.0% ± 3.9%; mechanical prostheses, 88.9% ± 10.5%), and hemorrhage (bioprostheses, 100%; mechanical prostheses, 95.2% ± 4.7%). One case of structural valve deterioration occurred in the bioprostheses group at 95 months after surgery. Five-year freedom from all valve-related complications was 82.8% ± 8.1% for bioprostheses and 76.4% ± 12.7% for mechanical prostheses.

CONCLUSIONS: Overall survival was poor. Differences between populations were related to age at operation and coronary artery disease. Structural valve deterioration was not accentuated with bioprostheses. Considering lack of homogeneity between prostheses groups there was no superiority of mechanical prostheses over bioprostheses in terms of freedom from composites of complications. Bioprostheses should be considered in the management of valvular disease in end-state renal disease patients.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 
Patients receiving renal dialysis have unique cardiac care needs. Chronic uremia, hypertension, and hyperlipidemia are just several conditions associated with end-stage renal disease (ESRD) that predispose to cardiac valvular abnormalities [1]. Frequent vascular access sites and impaired immunity lead to a heightened risk of endocarditis. It is therefore not surprising that cardiac disease is the major cause of morbidity and mortality among patients with ESRD [2]. Surgical intervention may not necessarily benefit these patients based on their poor general health and truncated life expectancy. The choice of valve prostheses is also subject to debate.

The traditional teaching recommended by the American College of Cardiology/American Heart Association is that bioprostheses will likely undergo accelerated calcification in patients with ESRD; therefore, mechanical valves have been the mainstay of treatment for many years [3]. More recent literature challenges this notion based on the increased risk of stroke and bleeding associated with life-long anticoagulation therapy [4–6]. The Canadian Cardiovascular Society Consensus on Surgical Management of Valvular Heart Disease has recommended bioprostheses for valvular replacement surgery [7].

These well-designed studies are limited by small sample sizes and limited long-term follow-up data that is essential to determine the true risk of developing valve-related complications. The low prevalence of ESRD requiring dialysis in the general population [8, 9] means that few will present for valve surgery. Also, much investigation into ESRD patients has looked at cardiac surgery as a whole, with a relatively small number of patients presenting for valve replacement [10–12].

This study utilizes the clinical experience of two medical centers to ascertain whether there are differences in morbidity and mortality among patients with ESRD requiring dialysis who have received either bioprostheses or mechanical heart valve prostheses.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 Acknowledgments
 References
 
Valve replacement surgery (aortic 40, mitral 22, multiple 7) was performed in 69 patients with ESRD requiring dialysis from January 1975 to June 2002 at the affiliated teaching hospitals of the University of British Columbia (UBC), Canada (St. Paul's Hospital, Vancouver General Hospital, and Royal Columbian Hospital), and at Westchester Medical Center in Valhalla, New York. Patients were included in this study only if they were chronically on either hemodialysis or peritoneal dialysis preoperatively.

The University of British Columbia had approval for this study through the UBC Clinical Research Ethics Board that annually reviews the UBC Cardiac Surgery Valve Database and associated longitudinal follow-up. For Westchester Medical Center, this study was Internal Review Board exempt as they included the personal patients of the involved surgeon.

The overall mean age was 61.8 ± 14.3 years (range, 23 to 84). There were 47 bioprostheses replacements (mean age, 64.7 ± 14.1; range, 23 to 84) and 22 mechanical prostheses replacements (mean age, 55.5 ± 12.9; range, 32 to 83). Bioprostheses and mechanical prostheses populations were compared through analysis of preoperative (n = 29), operative (n = 9), and postoperative (n = 4) variables listed in the Appendix.

Of the 69 total patients in this study, 36 (bioprostheses = 28, mechanical prostheses = 8) were operated on in New York, whereas 33 (bioprostheses = 19, mechanical prostheses = 14) were operated on in British Columbia. Within the UBC group, 19 received bioprostheses (12 aortic, 6 mitral, 1 multiple) and 14 received mechanical prostheses (7 aortic, 6 mitral, 1 multiple). Within the Westchester Medical Center group, 28 received bioprostheses (15 aortic, 8 mitral, 5 multiple) and 8 received mechanical (6 aortic, 2 mitral, 0 multiple).

The total follow-up was 128.7 patient-years (bioprostheses, 68.4; mechanical prostheses, 60.4). Late follow-up was 100% complete. Patient status was determined through telephone interviews with the patient or family, documented medical records, or governmental vital statistic registries.

Statistical Analysis
Statistical significance was evaluated at {alpha} = 0.05 level. The {chi}2 statistic, with Yates' correction or when it was appropriate Fisher's exact tests, was applied on categorical variables. Continuous variables were presented as mean ± SD and range. Independent samples (Student's) t tests were used on continuous variables to determine if the patients receiving bioprostheses or mechanical prostheses were heterogeneous for the variables of clinical interest. Patient survival by valve prostheses and concomitant coronary artery bypass graft surgery (CABG) were analyzed by the nonparametric Kaplan-Meier method, and the log-rank test was applied for the overall comparison of the two survival curves. Preoperative, operative, and postoperative risk factors were defined according to The Society of Thoracic Surgeons adult cardiac database definition of terms, version 2.41. Pulmonary artery hypertension was defined as mean pulmonary artery pressure greater than 20 mm Hg or systolic pressure greater than 30 mm Hg. Valve-related complications were defined according to the "Guidelines for Reporting Morbidity and Mortality after Cardiac Valvular Operations" and include structural valve deterioration, nonstructural dysfunction, thromboembolism, hemorrhage, and prosthetic valve endocarditis [4]. Hemorrhagic events were considered valve related if the patient was maintained on anticoagulant or antiplatelet therapy. Valve-related residual morbidity was defined as residual neurologic or functional impairment. Freedom from composites of valve-related complications was assessed by Kaplan-Meier methodology.

Univariate analysis can act as a screen for selecting risk factors to be considered in multivariate regression. The predictors of survival and composites of valve-related complications were identified with multivariate Cox hazard regression. Preoperative, operative, and postoperative variables that were of clinical interest were used in the univariate Cox hazard regression models. The multivariable Cox hazard regression models were built with those independent predictors that were found significant univariately or were of clinical importance to assess predictors of overall mortality and composites of complications, namely, valve-related mortality and residual morbidity.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 Acknowledgments
 References
 
The bioprostheses and mechanical prostheses groups were homogeneous except for age, previous myocardial infarction, concomitant coronary artery bypass, and preoperative management with immunosuppressive drugs (Table 1).


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  		Table 1. Patient Characteristics for Bioprostheses (BP) and Mechanical Prostheses (MP) Groups
 
Early mortality (30-day) was 29.0% (20 of 69). Early mortality for the bioprostheses group (36.2%; 17) was higher than that of the mechanical prostheses group (13.6%; 3); however, this difference was not statistically significant.

Survival of all patients in this study at 5 years was 31.2% ± 6.7%. At 5 years, survival within the mechanical prostheses group (52.0% ± 12.9%) was higher than in the bioprostheses group (21.9% ± 7.1%; p = 0.0299).

No statistically significant difference in survival was observed, at 5 years, between the two prostheses groups when comparing patients receiving concomitant CABG (bioprostheses, 24.4% ± 9.1%; mechanical prostheses, 50.0%±20.4%; p = 0.7515). A survival advantage was observed for mechanical prostheses over bioprostheses in patients who did not receive concomitant CABG (bioprostheses, 19.1% ± 10.4%; mechanical prostheses, 53.6 ± 15.4%; p = 0.0254).

The univariate predictors of composites of complications and overall mortality are listed in Table 2. The only significant multivariate predictor for all cause mortality was age at operation (p = 0.05; Table 3).


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  		Table 2. Univariate Predictors of Composites of Complications and Overall Mortality
 

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  		Table 3. Multivariate Predictors of Composites of Complications and Overall Mortality
 
The freedom from thromboembolism, thrombosis, and hemorrhage are described in Figure 1. The 5-year freedom for bioprostheses and mechanical prostheses groups was 93.0% ± 3.9% and 76.4% ± 12.7%, respectively. For the two instances of thromboembolism in mechanical prostheses patients, one was a thrombosis that developed 19.0 months after prosthesis valve implantation. The incidence of thrombosis was not treated with thrombolytic therapy, but through surgical resection of thrombus in the left femoral artery and arteriovenous fistule. The patient that developed nonthrombotic thromboembolism did so 25.2 months after cardiac surgery. Both patients in the mechanical group who developed thromboembolism were less than 60 years of age at operation. For the bioprostheses group, two instances of thromboembolism occurred in patients receiving isolated aortic valve replacement whereas one occurred in an patient receiving a combined aortic and mitral valve replacement. Preoperatively, all 3 patients did not receive anticoagulation therapy. One had a history of intermittent atrial fibrillation. All had thromboembolism within 2 weeks of cardiac surgery and were 70 years of age and older at operation. The single fatal thromboembolism event occurred in a patient who was 77 years of age at time of operation.


Figure 1
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  		Fig 1. Actuarial freedom from valve-related thromboembolism, thrombosis, and hemorrhage, overall (solid line) and for bioprostheses (BP [long-dash line]) and mechanical prostheses (MP [short-dash line]). (NS = not significant.)

 
The freedom from valve-related hemorrhage is described in Figure 2. Freedom from valve-related hemorrhage at 5 years was 100% for bioprostheses and 95.2% ± 4.7% for mechanical prostheses. The lone bleeding event occurred in a patient in the mechanical group. This patient was 32 years of age at the time of operation and developed bleeding 0.3 months after surgery. It should be noted that there were three major bleeding events in the biological prostheses population, but these patients were not maintained on anticoagulants and, in our center, this type of patient has not been included in our valve analyses.


Figure 2
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  		Fig 2. Actuarial freedom from valve-related hemorrhage, overall (solid line) and for bioprostheses (BP [long-dash line]) and mechanical prostheses (MP [short-dash line]). (NS = not significant.)

 
Structural valve deterioration in the form of calcific mitral prosthesis stenosis developed in one patient in the bioprostheses group. Successful reoperation was conducted 95.5 months after the patient's initial surgery. Extensive calcification of the native mitral valve was the pathology at the initial surgery. The resultant 5-year freedom from structural valve deterioration in the bioprostheses group was 50.0% ± 35.4%. No structural valve deterioration occurred in patients with mechanical prostheses.

The freedom from prosthetic valve endocarditis in the bioprostheses and mechanical prostheses groups was 75.5% ± 11.7% and 100% at 5 years, respectively. Of the 4 cases of prosthetic valve endocarditis in the biological group, 1 patient involved had previous native valve endocarditis. Both of these patients were more than 65 years of age, with the lone fatal event occurring in a patient more than 70 years of age. None of the cases of prosthetic valve endocarditis developed in patients less than 60 years of age. These instances of prosthetic valve endocarditis occurred 1.5, 6.9, 14.6, and 23.8 months after surgery.

The freedom from all valve-related complications was not statistically different between the bioprostheses and mechanical prostheses groups (Fig 3). At 5 years after cardiac surgery, freedom from all valve complications was 82.8% ± 8.1% for bioprostheses patients and 76.4% ± 12.7% for mechanical prostheses patients.


Figure 3
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  		Fig 3. Actuarial freedom from all valve-related complications, overall (solid line) and for bioprostheses (BP [long-dash line]) and mechanical prostheses (MP [short-dash line]). (NS = not significant.)

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
Acknowledgments
 References
 
There is much controversy regarding prostheses valve selection in patients with ESRD requiring dialysis. These patients bring complications and risk to surgery based on their renal and cardiovascular disease. This series highlights the precarious nature of these patients' health. The overall early mortality in this series was found to be 29.0%. This is comparable with the in-hospital mortality of 20.7% determined by Herzog and colleages [13] from the analysis of 5,858 dialysis patients undergoing prostheses heart valve implantation in the United States. That well-designed study advocated use of bioprostheses valves based on the fact that no survival advantage was observed from mechanical prostheses valves in ESRD patients. The survival at 2, 5, and 10 years for bioprostheses was 40%, 14%, and 5%, respectively; and for mechanical prostheses, it was 40%, 15%, and 4%, respectively [13]. Given the nature of the study, valve-related complications were not analyzed, thereby basing prostheses recommendations solely on survival data.

In this study, a survival advantage in favor of mechanical valves was observed at 5 years after operation. This finding is in contrast to current literature, which has thus far found no survival difference between bioprostheses and mechanical prostheses patients [1, 5, 6, 13]. This survival advantage is difficult to interpret as patients receiving bioprostheses in our series were older, suffered more previous myocardial infarction, and had a greater incidence of concomitant revascularization procedures. Previous myocardial infarction and concomitant CABG have been shown to be strong predictors of mortality [14]. In this series, age at operation was found to be predictive of overall mortality upon univariate and multivariate analyses. Prosthesis type was not a significant predictor, meaning that, statistically, its impact is overshadowed by the consideration of age. A survival advantage was also observed between bioprostheses and mechanical prostheses groups who underwent valve replacement surgery without concomitant procedures. That no survival difference was observed between the two groups who received concomitant CABG may owe to the aforementioned fact that concomitant procedures drastically increase mortality risk [14]. Because more patients received concomitant procedures in the bioprostheses group compared with the mechanical group, survival differences may have been masked. The overall 5-year survival was comparable with that of dialysis patients in the general population [15]; therefore, in terms of survival, patients were no worse off having had valve replacement surgery.

The freedom from all valve-related complications, including individual valve-related complications, was not significantly different between the bioprostheses and mechanical prostheses groups. That was observed even though the patients in the bioprostheses group were significantly older than those in the mechanical prostheses group. All of the instances of thromboembolism in patients receiving bioprostheses, including the single fatal event, occurred in patients who were 70 years of age or older at the time of operation. The two instances of thromboembolism (including thombosis) in the mechanical group, however, occurred in patients less than 60 years at operation. Because older patients are at increased risk of embolic events, the increased frequency of thromboembolism may be a result of age as opposed to prosthesis type. Also, the single case of hemorrhage in the mechanical prostheses group occurred in a patient who was 32 years of age at operation.

It is important to note that only one incidence of calcific structural valve deterioration was observed in this series. The observed rarity of this event suggests that the 1998 guidelines [3] may be incorrect, whereas the 2004 Canadian guidelines [7] are correct. In fact, this observation also supports the research that suggests that accelerated calcification in patients on chronic renal dialysis is rare [5, 6].

Notwithstanding, there are clear limitations of this study. The small sample size is an obvious hindrance. This study also encompasses data from four hospitals over a timeline of 27 years. Variability such as surgical technique can influence outcomes. Further, patients receiving mechanical prostheses and bioprostheses in this study were significantly different thereby making comparisons between them complex. But valve replacement surgery in ESRD patients is rare, and the major studies conducted thus far have consisted of fewer patients or did not evaluate valve-related complications [1, 5, 6, 13].

Data from this series clearly describe the complexity associated with prosthetic heart valve selection in patients with ESRD requiring dialysis. It is clear that the overall survival of ESRD patients was poor. Differences in survival between patients receiving bioprostheses or mechanical prostheses were related to age at operation and not to prosthesis type. There was no superiority of freedom from all valve-related complications and individual valve-related complications with mechanical prostheses or bioprostheses. Bioprostheses should not be contraindicated in ESRD patients given the observed rarity of accelerated calcification [7], as well as the poor intermediate-term survival. Bioprostheses also offer a distinct advantage over mechanical valves as they allow patients the opportunity to circumvent long-term anticoagulation therapy. This is important given the associated issues of chronic care related to routine dose adjustments and nonmorbid bleeding events included in the standard definition of valve-related hemorrhage, but not necessarily reported by all investigators [4].


   Appendix
 


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  		Variables Analyzed
 


   Acknowledgments
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
References
 
The authors would like to thank Kevin Shillitto for his efforts related to the word processing of this manuscript. This work would not have been completed without his efforts.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Brinkman WT, Williams WH, Guyton RA, et al. Valve replacement in patients on chronic renal dialysisimplications for valve prosthesis selection. Ann Thorac Surg 2002;74:37-42.[Abstract/Free Full Text]
  2. US Renal Data System. Annual data report. National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, 2001. Available at: http://www.usrds.org/adr.htm (accessed Aug 2002)..
  3. Bonow RO, Carabello B, deLeon Jr AC, et al. Guidelines for the management of patients with valvular heart disease: executive summary. A report of the American College of Cardiology / American Heart Association Task Force on Practice Guidelines Circulation 1998;98:1949-1984.[Free Full Text]
  4. Edmunds Jr LH, Clark RE, Cohn LH, et al. Guidelines for reporting morbidity and mortality after cardiac valvular operations Ann Thorac Surg 1996;62:932-935.[Abstract/Free Full Text]
  5. Lucke JC, Samy RN, Atkins BZ, et al. Results of valve replacement with mechanical and biological prostheses in chronic renal dialysis patients Ann Thorac Surg 1997;64:129-133.[Abstract/Free Full Text]
  6. Kaplon RJ, Cosgrove DM, Gillinov AM, Lytle BW, Blackstone EH, Smedira NG. Cardiac valve replacement in patients on dialysisinfluences of prosthesis on survival. Ann Thorac Surg 2000;70:438-441.[Abstract/Free Full Text]
  7. Jamieson WRE, Cartier PC, Burwash IG, et al. Canadian Cardiovascular Society. Surgical management of valvular heart disease Can J Cardiol 2004;20E:1-120.
  8. Schaubel DE, Morrison HI, Desmeules M, Parsons DA, Fenton SSA. End-stage renal disease in Canadaprevalence projections to 2005. Can Med Assoc J 1999;160:1557-1563.[Abstract]
  9. Pork FK. Worldwide demographics and future trends in end-stage renal disease Kidney Int 1993;43(Suppl 41):4-7.
  10. Penta de Peppo A, Nardi P, De Paulis R, et al. Cardiac surgery in moderate to end-stage renal failureanalysis of risk factors. Ann Thorac Surg 2002;74:378-383.[Abstract/Free Full Text]
  11. Horst M, Mehlhorn U, Hoerstrup SP, Suedkamp M, de Vivie R. Cardiac surgery in patients with end-stage renal disease10-year experience. Ann Thorac Surg 2000;69:96-101.[Abstract/Free Full Text]
  12. Frenken MF, Krian A. Cardiovascular operations in patients with dialysis-dependent renal failure Ann Thorac Surg 1999;68:887-893.[Abstract/Free Full Text]
  13. Herzog CA, Ma JZ, Collins AJ. Long-term survival of dialysis patients in the United States with prosthetic heart valvesshould the ACC/AHA practice guidelines on valve selection be modified?. Circulation 2002;105:1336-1341.[Abstract/Free Full Text]
  14. Edwards FH, Peterson ED, Coombs LP, et al. Prediction of operative mortality after valve replacement surgery Am J Coll Cardiol 2001;37:885-892.[Abstract/Free Full Text]
  15. Byrne C, Vernon P, Cohen JJ. Effect of age and diagnosis on survival of older patients beginning chronic dialysis JAMA 1994;271:34-36.[Abstract/Free Full Text]



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