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Interact CardioVasc Thorac Surg 2006;5:398-402. doi:10.1510/icvts.2005.122382
© 2006 European Association of Cardio-Thoracic Surgery
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Institutional report - Valves

Does the type of biological valve affect patient outcome?{star}

A. Pieter Kappeteina,*, Johanna J.M. Takkenberga, John P.A. Puvimanasinghea, W.R. Eric Jamiesonb, Marinus Eijkemansc and Ad.J.J.C. Bogersa

a Department of Cardio-Thoracic Surgery and the Erasmus MC, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands
b Division of Cardiovascular Surgery, Department of Surgery, University of British Columbia, Vancouver, British Columbia, Canada
c Center for Clinical Decision Sciences, Department of Public Health, Erasmus MC, Rotterdam, The Netherlands

Received 6 October 2005; received in revised form 12 April 2006; accepted 18 April 2006

{star} Presented at the joint 19th Annual Meeting of the European Association for Cardio-thoracic Surgery and the 13th Annual Meeting of the European Society of Thoracic Surgeons, Barcelona, Spain, September 25–28, 2005.

*Corresponding author. Tel.: +31 (0) 10 4635412; fax: +31 (0) 10 4633993.

E-mail address: a.kappetein{at}erasmusmc.nl (A.P. Kappetein).


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
Patient background mortality and excess mortality related to aortic valve disease may play a greater role than implanted valve type in explaining the observed survival differences after aortic valve replacement. This study attempts to identify the differences between the performance of selected biological valves, given similar patient characteristics and excess mortality. Four biological valve types, the Carpentier-Edwards pericardial and supra-annular valve, Medtronic Freestyle valve and allografts were used for this analysis. Primary data calculated observed patient-survival and median time to structural valvular deterioration. We then used a microsimulation model to calculate age-specific patient survival and reoperation- and event-free life expectancies. The model incorporated the US population mortality and a uniform excess mortality, while the hazards of valve-related events after implantation of the four valve types were estimated from corresponding meta-analysis and primary data. Observed 10-year survival (60–69)-year age group survival and median time to SVD for the different valve types did not differ. Microsimulation calculated, for a 65-year-old male for example, a 10-year survival of 51%, 51%, 53% and 56% for Carpentier-Edwards pericardial and Supra-annular valve, Freestyle and allografts, respectively. Patient life expectancy was 10.8, 10.8, 11.0 and 11.4 years, respectively. Assuming uniform patient characteristics and excess mortality, the observed difference in performance between the four biological valve types is less marked. Patient selection and the timing of operation may explain most of the observed differences in prognosis after aortic valve replacement with biological prostheses.

Key Words: Aortic valve replacement; Bioprosthesis; Microsimulation; Follow-up


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
Aortic valve replacement (AVR) has evolved into a safe operation for valvular pathology. Different prosthetic valves are available to select a prosthesis that will be most compatible with a patient's coexisting medical conditions and physiologic performance. Mechanical prostheses have the advantages of long-term durability but require lifelong anticoagulation. Bioprostheses do not require anticoagulation but will degenerate over time and may require replacement. Allografts do not require anticoagulation and have an excellent hemodynamic performance; however, these valves are more difficult to implant and will also degenerate over time. More recently, stentless xenografts have been introduced. These valves do not have prosthetic stents, allowing for larger valves to be implanted than if a stented bioprosthesis is used [1,2].

The optimum choice between a mechanical valve and a bioprosthesis for a given patient involves striking a balance between the risks and benefits of each valve type. In earlier studies we demonstrated that with the risk and benefit ratio comparing mechanical and biological prosthesis a bioprosthesis can be considered for patients over 60 years of age [3]. Little is known, however, about the outcome of the different types of biological valves. Microsimulation and associated simulation techniques can provide insight into these outcomes. We combined the data of several clinical studies with microsimulation to study patient outcome after AVR with a stented porcine bioprostheses, stentless prosthesis and allografts.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
2.1. Patients

We selected four biological valve types, the Carpentier-Edwards pericardial (CEP), Carpentier-Edwards supra-annular (CESAV) valve, Medtronic Freestyle valve and allografts for this analysis (Table 1).


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  		Table 1 Baseline characteristics of the four different patient cohorts (CESAV=Carpentier-Edwards supra-annular valve; CEP=Carpentier-Edwards pericardial valve)

 
Datasets were obtained from different sources. The 267 patients who received a CEP were operated between September 1981 and December 1983 and conceive a premarket approval cohort which is followed yearly. These patients were also described in an earlier study [4]. The data on the Carpentier-Edwards supra-annular (CESAV) valve came from a patient cohort operated from 1981 to 1998 in Canada and comprises 1847 patients [5]. The Freestyle data were obtained from a multicenter evaluation of the Freestyle stentless valve from eight different centers in North America during the period 1992–2001 [1]. The 137 patients who received an allograft, are patients selected on the basis of age (>50 years) from our ongoing prospective cohort study and operated in our own center during the period 1988–2003 [6]. Patient characteristics are given in Table 1.

2.2. Analysis of primary data to estimate hazard of SVD

Primary data were used to calculate observed patient-survival and median time to reoperation for structural valvular deterioration (SVD) [7,8]. The risk of SVD in a bioprosthesis depends on the age of the patient at implantation and on the time elapsed since valve replacement. Risk decreases with implantation age, but increases with time since implantation. The estimate of the hazard of SVD was obtained by fitting age-dependant Weibull curves on primary data. The Weibull formula for the freedom from SVD is: SVD: S(t) = e–(t/{sigma})ß where S(t) indicates the freedom from SVD at time t while {sigma} and ß denote the scale and shape parameters of the model.

The value of the scale ({sigma}) parameter of the Weibull model depends on age and the shape parameter (ß) reflects the changing risk of SVD over time. For the four different valve types these are given in Table 2.


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  		Table 2 Specification of the Weibull models that estimate freedom from reoperation for structural valvular deterioration (SVD) for each of the four valve types

 
2.3. Analysis of other valve-related event rates

Previously reported meta-analyses on the occurrence rates of other valve-related events with the four valve types were used to model the events in the microsimulation model [7,8]. In Appendix A the occurrence rates and their consequences are displayed.

2.4. The microsimulation model

We then used a microsimulation model to calculate survival and life expectancies with the various valve types. The model incorporated the US population mortality and a uniform excess mortality, while the hazards of valve-related events after implantation of the four valve types were estimated from previous meta-analyses and primary data. The microsimulation model is a computer application that simulates the life of a patient after AVR with a given valve type, taking into account the morbidity and mortality events that the patient may experience. The mortality of a patient is composed of the mortality experience of the general population, mortality due to valve-related events and an ‘additional mortality’ component that is associated with underlying valve pathology, left ventricular function, and valve replacement procedure, respectively [9].

The mortality experience of the general population was incorporated into the model by means of the US population life tables. The US population life tables were chosen since the majority of included patients was from North America. We previously estimated age-specific and sex-specific hazard ratios to represent the effect of additional mortality. They were 2.9, 1.8, 1.2, and 0.8 for male patients aged 45, 55, 65, and 75 years, respectively [10]. Operative mortality was estimated at 1.5% for a 40-year-old patient, increasing with odds ratios of 1.022 per additional year of age and 1.7 per reoperation. The model calculates patient outcomes by superimposing the morbidity and mortality estimates of valve-related events on the other two mortality components. For each calculation, 10,000 simulations were performed. In principle, the model can be applied for any valve type and for a patient of either sex. For this analysis, the model was used to calculate outcomes for the four different valve types. A detailed account of the microsimulation structure and methodology has been given previously [11,12].


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
The age at implantation of the 267 patients who received a bovine pericardial aortic valve ranged from 21 to 86 years (mean 65±12 years). Of these, 64% were men. Coronary artery disease (n=133, 50%), congestive heart failure (n=58, 22%), and previous myocardial infarction (n=45, 18%) were the most common preexisting conditions. The native aortic valve lesions were pure aortic stenosis (n=174, 65%), pure aortic regurgitation (n=46, 17%), and mixed stenosis and regurgitation (n=39, 15%); 8 (3%) additional patients had a previous AVR.

The 1847 patients with implantation of a Carpentier-Edwards supra-annular (CESAV) valve were operated from 1981 to 1998 in Canada. Of these 69% were men. Mean age was 68 years with a range from 20 to 90 years. Of the total population, 3% (56 patients) had previous coronary artery bypass (CABG) and 6% (110 patients) had previous valve repair or replacement. Concomitant CABG was performed in 42% (756 patients). Early mortality was 6%.

Between August 1992 and November 2001, 725 patients underwent AVR with the Freestyle bioprosthesis. The mean age at operation was 72 years (range 36–92). The population included 402 (55%) males. Thirty-day mortality was 5% (n=38). The implant technique was subcoronary in 509 (70%), total root in 178 (25%), and root inclusion in 38 (5%) patients.

From 1988 until 2003, 137 patients over 50 years of age received an allograft. The native aortic valve lesions were pure aortic stenosis (n=29, 21%), pure aortic regurgitation (n=86, 63%), and mixed stenosis and regurgitation (n=22, 16%); Concomitant CABG was performed in 16% (22 patients). Kaplan–Meier estimates of observed cumulative survival in the 4 datasets are shown in Fig. 1.


Figure 1
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  		Fig. 1. Kaplan–Meier curves; observed cumulative survival for all valve types.

 
3.1. Microsimulation

The microsimulation model calculated total life expectancy, reoperation-free life expectancy (RFLE), event-free life expectancy (EFLE), and life time risk of at least one reoperation following AVR with the different bioprosthesis and allografts for male patients of different ages.

For a 65-year-old man, for example, 10-year survival was 51% for Carpentier-Edwards pericardial valve, 51% for Carpentier supra-annular valve, 53% for the Freestyle valve and 56% for allografts. Life expectancy was 10.8, 10.8, 11.0 and 11.4 years, respectively, after implantation.

The Weibull estimates of freedom from reoperation for SVD for a 65-year-old patient are shown in Fig. 2.


Figure 2
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  		Fig. 2. The Weibull estimates of freedom from reoperation for structural valve deterioration for a 65-year-old male.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
Appendix A
 Appendix B. Conference...
 References
 
The most proper way to evaluate differences in outcomes between different valve types is by a prospective randomized trial. However, conducting such a trial would be very costly and it would take many years before the endpoints would be met and a comparison can be made. A microsimulation model, like we used in the present and in previous studies, can also provide insight into the age- and sex-related life expectancy and lifetime risks of valve-related events after AVR with different types of valves [11–13]. Simulation techniques, by modeling complex outcome paths that result from many competing risks, provide a useful adjunct to standard statistical methods in calculating the outcomes of patients after AVR. In earlier studies, it proved that the survival outputs of the microsimulation model for males of different ages compared favorably with the corresponding curves of the two separate datasets from the Providence Health System in Portland, Oregon experience, through 25 years postimplantation [13,14].

The Carpentier-Edwards pericardial aortic valve was introduced after several design changes, which included improved tissue preservation, a more flexible stent, a modified shape of the cusps, and modified tissue-mounting of the pericardium in the stent. Since the introduction in 1981 the Carpentier-Edwards pericardial valve has shown perfect long-term results and in many centers it became the biological valve of choice in the aortic position. With the Carpentier-Edwards supra-annular valve, the mounting structure of the aortic valve had been redesigned for the positioning above rather than within the annulus. The fixation treatment and the stent had also been modified in an attempt to improve leaflet durability. The sewing ring was reconfigured to increase the effective orifice of the valve. The more recently introduced bioprosthesis that aims at increasing the effective orifice area is the Medtronic Freestyle aortic root bioprosthesis. This is a stentless porcine aortic root prepared by using low-pressure and zero-pressure fixation processes and leaflet anticalcification treatment, with the aim of optimizing both hemodynamics and bioprosthesis durability. The use of allografts valve was initiated by Ross in 1962. Several changes in surgical techniques have been attempted to improve durability, and different preservation techniques have been employed to increase shelf half-life time and improve durability. Allografts yield adequate midterm results, with low thromboembolism rates and seem to produce the best results with a short harvest and implantation time [6,15].

Our present study shows that there is actually no significant difference between the four types of biological valves in terms of survival, or structural valve deterioration, or thromboembolism rate. Co-morbidities seem to be the most important predictors of survival after AVR. The older the patient at the time of valve implantation, the lower the 10- to 20-year survival because older patients are more likely to have associated comorbid conditions that adversely affect survival after AVR. Several other studies have also addressed the issue and have shown that co-morbidities play the most important role in determining the outcome of patients after AVR than the type of valve itself. Advanced age, male sex, left ventricular dysfunction, coronary artery disease, and NYHA functional class are independent predictors of mortality after AVR [16,17].

Mortality of an AVR patient who survives the operation is greater than that of a matched person in the general population. This excess mortality is due to valve related mortality and an additional mortality. The additional mortality, which may be related to underlying valve pathology, left ventricular residual hypertrophy, and functional abnormality and the valve replacement procedure, is not clearly defined and estimated at present. Hence, we had previously estimated age- and sex-specific hazard ratios to represent the effect of additional mortality in the model [13].

Our results suggest that for the different biological valves patient survival and valve complications were comparable. Considering our model calculation for the lifetime risk of reoperation, a lowering of the 65-year age threshold for each of these valves may be considered, especially in patients whose life expectancy is reduced by concomitant disease. Thus, if the patient accepts a ‘small’ increased risk of structural valve deterioration if a biological valve were to be implanted for the benefit of not needing anticoagulant treatment with use of mechanical valve, then the decision to insert a bioprosthesis at that age may be reasonable.


   Appendix A
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
Appendix B. Conference...
 References
 
Occurrence rates of valve-related events for the 4 valve types used as input for the microsimulation model:

CE-P: Thrombo-embolism 1.35%/patient year; Valve thrombosis 0.03%/patient year; Endocarditis 0.62%/patient year; Major bleeding 0.43%/patient year; Non-structural dysfunction 0.13%/patient year

CE-SAV: Thrombo-embolism 1.76%/patient year; Valve thrombosis 0.02%/patient year; Endocarditis 0.39%/patient year; Major bleeding 0.46%/patient year; Non-structural dysfunction 0.61%/patient year

Freestyle: Thrombo-embolism 2.9%/patient year; Valve thrombosis 0.04%/patient year; Endocarditis 0.45%/patient year; Major bleeding 0.95%/patient year; Non-structural dysfunction 0.28%/patient year

Allograft: Thrombo-embolism 0.6%/patient year; Valve thrombosis 0.00%/patient year; Endocarditis 0.48%/patient year; Major bleeding 0.05%/patient year; Non-structural dysfunction 0.50%/patient year


   Appendix B. Conference discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
References
 
Dr A. Moritz (Frankfurt, Germany): You have such diligent data. Why did this patient have such a higher mortality over the normal population? It is not the rate of valve complications that cause this higher mortality over the long run. So why do they die?

Dr Kappetein: You mean in the younger age group, patients have a worse survival than the normal population? It is because in the younger patient population prevalence of aortic regurgitation is high, most of the times they already have a dilated ventricle, which is a predictor for their survival. But besides that, there are some intrinsic abnormalities in the ventricle of the patient. For example the arrangement of myofibrils are different in these kinds of patients.

Dr Moritz: Did they die of heart failure or did they die of sudden death or is it simply unknown, or what are the reasons?

Dr Kappetein: One of the reasons is they die of heart failure; that's the most important reason. Another abnormality is that, they also have differences in aortic lamellae and they sometimes form an aneurysm of the aorta, that are the kind of morbidities that they may develop.

We incorporated the results of nine studies in the model, and if you look at these nine studies, they all showed the same effect in the younger patient population.

Dr F. Mohr (Leipzig, Germany): Just let me ask a question. We both think if we don't know we should randomize following Grüntzig in another study, and as you have seen in our randomized trial at eight years, Freestyle and Toronto showed a better survival as compared to a stented bioprosthesis. What would you prefer, actually, the modeling or the randomization?

Dr Kappetein: A very good question. I think ideally is to randomize. But to find two companies or three companies that want to compare different bioprostheses, that is very difficult. It would also be a very costly trial, and besides that, you have to wait a very long time before you have the results. And you know like industry is, at the time you have the results there will be another valve on the market. But ideally you are right, a randomized trial gives you the best evidence.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 

  1. Bach DS, Kon ND, Dumesnil JG, Sintek CF, Doty DB. Eight-year results after aortic valve replacement with the Freestyle stentless bioprosthesis. J Thorac Cardiovasc Surg 2004; 127:1657–1663.[Abstract/Free Full Text]
  2. Kappetein AP, Braun J, Baur LH, Prat A, Peels K, Hazekamp MG, Schoof PH, Huysmans HA. Outcome and follow-up of aortic valve replacement with the freestyle stentless bioprosthesis. Ann Thorac Surg 2001; 71:601–607.[Abstract/Free Full Text]
  3. Puvimanasinghe JP, Takkenberg JJ, Edwards MB, Eijkemans MJ, Steyerberg EW, Van Herwerden LA, Taylor KM, Grunkemeier GL, Habbema JD, Bogers AJ. Comparison of outcomes after aortic valve replacement with a mechanical valve or a bioprosthesis using microsimulation. Heart 2004; 90:1172–1178.[Abstract/Free Full Text]
  4. Banbury MK, Cosgrove DM 3rd, Thomas JD, Blackstone EH, Rajeswaran J, Okies JE, Frater RM. Hemodynamic stability during 17 years of the Carpentier-Edwards aortic pericardial bioprosthesis. Ann Thorac Surg 2002; 73:1460–1465.[Abstract/Free Full Text]
  5. Jamieson WR, Janusz MT, MacNab J, Henderson C. Hemodynamic comparison of second- and third-generation stented bioprostheses in aortic valve replacement. Ann Thorac Surg 2001; 71:S282–S284.[Abstract/Free Full Text]
  6. Takkenberg JJ, van Herwerden LA, Eijkemans MJ, Bekkers JA, Bogers AJ. Evolution of allograft aortic valve replacement over 13 years: results of 275 procedures. Eur J Cardiothorac Surg 2002; 21:683–691.[Abstract/Free Full Text]
  7. Puvimanasinghe JP, Takkenberg JJ, Eijkemans MJ, van Herwerden LA, Jamieson WR, Grunkemeier GL, Habbema JD, Bogers AJ. Comparison of Carpentier-Edwards pericardial and supraannular bioprostheses in aortic valve replacement. Eur J Cardiothorac Surg 2006; 29:374–379.[Abstract/Free Full Text]
  8. Takkenberg JJM, Eijkemans MJC, van Herwerden LA, Steyerberg EW, Lane MM, Elkins RC, Habbema JDF, Bogers AJJC. Prognosis after aortic root replacement with cryopreserved allografts in adults. Ann of Thorac Surg 2003; 75:1482–1489.[Abstract/Free Full Text]
  9. Sand ME, Naftel DC, Blackstone EH, Kirklin JW, Karp RB. A comparison of repair and replacement for mitral valve incompetence. J Thorac Cardiovasc Surg 1987; 94:208–219.[Abstract]
  10. Puvimanasinghe JP, Takkenberg JJ, Eijkemans MJ, Steyerberg EW, van Herwerden LA, Grunkemeier GL, Habbema JD, Bogers AJ. Choice of a mechanical valve or a bioprosthesis for AVR: does CABG matter? Eur J Cardiothorac Surg 2003; 23:688–695.[Abstract/Free Full Text]
  11. Takkenberg JJ, Puvimanasinghe JP, Grunkemeier GL. Simulation models to predict outcome after aortic valve replacement. Ann Thorac Surg 2003; 75:1372–1376.[Free Full Text]
  12. Puvimanasinghe JP, Steyerberg EW, Takkenberg JJ, Eijkemans MJ, van Herwerden LA, Bogers AJ, Habbema JD. Prognosis after aortic valve replacement with a bioprosthesis: predictions based on meta-analysis and microsimulation. Circulation 2001; 103:1535–1541.[Abstract/Free Full Text]
  13. Puvimanasinghe JP, Takkenberg JJ, Eijkemans MJ, Steyerberg EW, van Herwerden LA, Grunkemeier GL, Habbema JD, Bogers AJ. Prognosis after aortic valve replacement with the carpentier-edwards pericardial valve: use of microsimulation. Ann Thorac Surg 2005; 80:825–831.[Abstract/Free Full Text]
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