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Eur J Cardiothorac Surg 2003;23:688-695
© 2003 Elsevier Science NL

Choice of a mechanical valve or a bioprosthesis for AVR: does CABG matter?

John P.A. Puvimanasinghea,b*, Johanna J.M. Takkenberga, Marinus J.C. Eijkemansb, Ewout W. Steyerbergb, Lex A. van Herwerdena, Gary L. Grunkemeierc, J. Dik F. Habbemab, Ad J.J.C. Bogersa

a Department of Cardio-thoracic Surgery, Erasmus Medical Center, Rotterdam, The Netherlands
b Center for Clinical Decision Sciences, Department of Public Health, Erasmus Medical Center, Rotterdam, The Netherlands
c Providence Health System, Portland, OR, USA

Received 2 October 2002; received in revised form 24 January 2003; accepted 27 January 2003.

* Corresponding author. Department of Cardio-thoracic Surgery, Erasmus Medical Center, Room Bd 162a, A.Z.R. Dijkzigt, Postbus 2040, 3000 CA Rotterdam, The Netherlands. Tel.: +31-10-463-5784; fax: +31-10-463-3993
e-mail: j.p.a.puvimanasinghe{at}erasmusmc.nl


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
Objective: Mechanical valves and bioprostheses are the commonly used devices in aortic valve replacement (AVR). Many patients with valvular disease also require concomitant coronary artery bypass grafting (CABG). We used a microsimulation model to provide insight into the outcomes of patients after AVR with mechanical valves and stented bioprostheses, with and without CABG, and to determine the age-thresholds or age crossover points in outcomes between the two valve types. Methods: We conducted a meta-analysis of published results after primary AVR with mechanical prostheses (nine reports, 4274 patients, 25,726 patient-years) and stented porcine bioprostheses (13 reports, 9007 patients, 54,151 patient-years) to estimate risks of valve-related events. A hazard ratio of 1.3 was used to incorporate the effect of CABG on long-term survival. Estimates were entered into a microsimulation model, which was then used to predict the outcomes of patients after AVR, with and without CABG. The model calculations were validated using a large data set from Portland, USA. Results: For a 65-year-old male without CABG, the life expectancy (LE) was 11.2 and 11.6 years and the event-free life expectancy (EFLE) was 8.2 and 8.9 years, respectively, after implantation with mechanical valves and bioprostheses. The lifetime risk of at least one valve-related event was 51 and 47%, respectively. The age crossover point between the two valve types, considering the above outcome parameters, was 59, 60 and 63 years, respectively. CABG reduced LE and consequently EFLE and lifetime risk of an event, but only minimally influenced the patient age crossover points. The model calculations showed good agreement with the Portland data. Conclusions: The currently recommended patient age for using a bioprosthesis (65 years) could be lowered further, irrespective of concomitant CABG. The trade-off between the reduced risks of bioprosthetic failure and of hemorrhage in mechanical valves, resulting from a lower LE, minimized the effect of CABG on the age crossover points between the two valve types.

Key Words: Aortic valve replacement • Coronary artery bypass grafting • Prognostic modeling • Mechanical valves • Bioprostheses


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
Despite new procedures and advances in the design and construction of prosthetic heart valves, mechanical valves and xenograft bioprosthetic valves remain the two most commonly used devices in aortic valve replacement (AVR) [1]. Both mechanical valves and bioprostheses have their inherent advantages and disadvantages [2] and the choice between these devices for an individual patient remains difficult. The choice may be further complicated by the presence of coronary artery disease (CAD), which is a common finding in patients with valvular disease [3]. The American College of Cardiology/American Heart Association (ACC/AHA) task force recommends coronary artery bypass grafting (CABG) in the presence of significant CAD in patients requiring AVR [3]. Insight into the outcomes of patients after AVR will help in the selection of the optimal prosthesis. We combined meta-analysis of published data and other data sources with microsimulation, to provide insight into the outcomes of patients after AVR with bileaflet mechanical valves and stented porcine bioprostheses, respectively, with and without concomitant CABG. The age crossover points in outcomes between the two valve types were also estimated.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
2.1. Selection of reports for meta-analysis
We conducted a literature search of the Medline database using the PubMed search interface for the period January 1990–October 2001 in order to estimate the hazards of post-operative valve-related events and their outcomes. The St. Jude Medical (SJM) bileaflet valves, models ‘standard’ and ‘hemodynamic plus’ (St. Jude Medical Inc., MN, USA) were selected to represent the mechanical valves. The bioprostheses were represented by one or more of the following stented porcine bioprostheses: Carpentier–Edwards ‘standard’ and ‘supra-annular’ valves (Baxter Healthcare Corp., CA, USA) and Hancock ‘standard’, ‘modified orifice’ and ‘Hancock II’ valves (Medtronic Inc., MN, USA). The MeSH terms in combination with the text words ‘St. Jude’ for the mechanical valves and ‘stented’, ‘Hancock’, ‘Carpentier–Edwards’ or ‘modified orifices’ for the bioprostheses, respectively, were used for the search, which was limited to the English language. The titles and abstracts of these reports were screened for those that examined outcomes following AVR, which were selected and perused. References in these reports were cross-checked for other potentially relevant studies. This resulted in 76 published reports for mechanical valves and 68 for bioprostheses, respectively. We then stipulated the following criteria for each valve type in order to obtain relatively homogenous groups of studies:

Studies that had overlapping patient populations were excluded. Finally, nine reports on St. Jude Medical mechanical valves and 13 reports on stented porcine bioprostheses were selected (Appendix A). The authors of some of the selected papers were contacted for clarifications and additional information.

2.2. Estimation of model parameters and assumptions made
Data required to parameterize the microsimulation model were obtained from the results of the meta-analysis (Table 1) and from other data sources [6–8]. The annual hazards of valve thrombosis, thrombo-embolism and non-structural dysfunction (NSD) were considered to be constant. Weighted pooling was used to calculate the linearized annual occurrence rates (LOR) for these events. The risk of endocarditis was assumed to take two phases of constant hazard, with the hazard during the first 6 months greater than the subsequent period. Therefore, we fitted two-period exponential models to the pooled freedom-from-endocarditis curves of the two valve types. Taking into account the increasing hazard with age, hemorrhage after AVR with a mechanical valve was modeled using the Gompertz distribution, incorporating data from another study [6]. The risk of structural valvular deterioration (SVD) in a bioprosthesis depends on the age of the patient at valve implantation and the time elapsed since valve replacement. This relationship is well described by a Weibull distribution [9]. The Weibull distribution is a generalization of the exponential curve that accommodates the increasing risk of SVD over time. We estimated the shape parameter of the Weibull model from the pooled freedom from SVD curves obtained from the selected reports and calculated the age effect from another selected study [10]. Mortality and re-operation rates associated with individual valve-related events were also estimated.


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  		Table 1. Pooled incidence of valve-related events and their outcomes after AVR with mechanical valves and bioprostheses

 
As depicted in Fig. 1 , there are three components of mortality in patients who survive AVR, namely background mortality, mortality due to valve-related events and ‘additional mortality’. The microsimulation model incorporates the mortality experience of the general population, the so-called background mortality, by means of life tables of the relevant population (for example, American males). The mortality of a patient, who remains alive after AVR, is greater than that of a matched individual in the general population. This excess mortality in the patient, compared to a matched person in the general population, is due to the mortality caused by valve-related events and to ‘additional mortality’ that may be associated with the underlying valve pathology, left ventricular function and the valve replacement procedure per se [11]. The ‘additional mortality’ component is not clearly defined and estimated at present. Therefore, we calculated age- and sex-specific hazard ratios to represent this effect in the model. This was done by approximating age- and sex-specific survival curves obtained from the microsimulation model, which contained the background mortality and mortality due to valve-related events, to the corresponding ‘true’ survival curves obtained from the literature, which contained all three components of mortality. Hazard ratios of 2.9, 1.8, 1.2 and 0.8 were calculated for male patients' aged 45, 55, 65 and 75 years, respectively. Further, a hazard ratio of 1.3 was incorporated into the microsimulation model to represent a patient who required concomitant CABG [7]. Results obtained from analysis of the Society of Thoracic Surgeons (STS) National Cardiac Surgery Database [8] was used to estimate operative mortality in the model. For a 65-year-old patient, for example, the operative mortality was 5.2 and 3.3%, respectively, with and without concomitant CABG.



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  		Fig. 1. Basic structure of the microsimulation model.

 
2.3. Microsimulation
The microsimulation model is a computer application that simulates the remaining lifetime of a patient after AVR, taking into account all morbidity and mortality events that the patient might experience. The basic structure of the model is depicted in Fig. 1. In principle, the model can be applied for any valve type and for either sex. For this analysis, the model was used to predict the life expectancy (LE), event-free life expectancy (EFLE) and lifetime risks of valve-related events for male patients undergoing AVR with bileaflet mechanical valves and stented porcine bioprostheses, with or without concomitant CABG.

The model simulates the lifetime of a patient, with given characteristics, by aging the individual and updating the status of the individual with the incidence of various valve-related events that may occur. The valve-related events are simulated by random draws from distributions describing the probability of an event. The model calculates patient outcome by superimposing the occurrence and mortality estimates of valve-related events, on the background mortality and ‘additional mortality’ incorporated in the model. Ten thousand simulations of any given patient create a ‘virtual’ patient population, i.e. a cohort of patients with identical characteristics but with many random outcomes after AVR. The number of simulations conducted was chosen arbitrarily, but was the same for each combination of risk factors. From this large cohort of identical patients, the model calculates the average life expectancies and lifetime risks of valve-related events for that given patient.

2.4. Validation
To assess the agreement between age-specific model outputs and the corresponding true life experience of AVR patients, we compared the model outputs with the long-term outcomes of patients in a large data set from Portland, OR, USA [12]. The Portland data set, from Providence Health System, Portland, USA, contains 25 years of follow-up data on patients who underwent AVR with the Starr–Edwards mechanical prosthesis and the Carpentier–Edwards ‘standard’ bioprosthesis and includes data on age, gender and concomitant CABG.


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 Appendix A
 Appendix B. Conference...
 References
 
3.1. Meta-analysis
The nine reports selected on St. Jude mechanical aortic valves contained 4274 patients undergoing AVR with a cumulative follow-up of 25,726 patient-years. Males accounted for 64% of the patients and the mean age of the population was 59 years. Thirty percent of the patients had concomitant CABG. The 13 reports on stented porcine bioprostheses consisted of 9007 patients, with 65% males, and had a follow-up of 54,151 patient-years. The mean age was 65 years and 37% had concomitant coronary re-vascularization.

3.2. Model parameters and assumptions
The risks of the valve-related events and their outcomes, obtained from the meta-analysis, are given in Table 1. A Gompertz model estimated the increasing hazard of hemorrhage with advancing age associated with the mechanical valves. The lambda and gamma parameters of this model were -8.874 and 0.076, respectively. The average incidence of SVD in a bioprosthesis was estimated using a Weibull model (Fig. 2 ). The probability of remaining free from SVD at time t (S(t)) is given by the formula:

where {sigma} and ß denote the scale and shape parameter of the model. The value of {sigma} depends on age: {sigma}=exp(2.21+0.0112xage) while ß=3.35. The estimated median time to SVD was 15.1, 16.8 and 18.8 years, respectively, for 55-, 65- and 75-year-old male patients.



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  		Fig. 2. Average freedom from SVD estimated from the literature (pooled) and with the Weibull model.

 
3.3. Microsimulation
Fig. 3A shows the calculated LE and EFLE for male patients of different ages after implantation with a mechanical valve and a bioprosthesis, respectively, without concomitant CABG. For a 65-year-old patient, for example, the LE was 11.2 and 11.6 years while the EFLE was 8.2 and 8.9 years, respectively. Considering LE and EFLE, the age crossover point between the two valve types was 59 and 60 years, respectively. At implantation ages below the age crossover point, mechanical valves had a better outcome than the bioprostheses, whereas above the crossover point the bioprostheses performed better. Concomitant CABG resulted in a decrease of LE and EFLE. For the 65-year-old patient, the LE was 9.9 and 10.2 years and EFLE was 7.4 and 8.1 years, respectively, after implantation with a mechanical valve and a bioprosthesis. The age crossover points were 58 and 59 years considering the LE and EFLE, respectively (Fig. 3B).



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  		Fig. 3. (A) Comparison of LE and EFLE in males after AVR with mechanical valves and bioprostheses, without concomitant CABG. (B) Comparison of LE and EFLE in males after AVR with mechanical valves and bioprostheses, with concomitant CABG.

 
We also estimated the lifetime risks of valve-related events following implantation of both valve types. The lifetime risk of SVD with a bioprosthesis was seen to decrease with advancing age of valve implantation, consequent to a decrease in LE. For a 75-year-old patient with and without CABG, for example, the risk was 8.9% and 12.4%, respectively. Conversely, advancing age of implantation of a mechanical valve was associated with a greater risk of hemorrhage. For a 75-year-old patient with and without CABG, this risk was 35.5 and 41.2%, respectively (Fig. 4 ). The risk of thrombo-embolism reduced with advancing age of implantation for both valve types. When considering the lifetime risk of any valve-related event, the age crossover point between the two valve types was 63 years for a patient without CABG. It was 62 years when the patient required coronary re-vascularization.



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  		Fig. 4. Lifetime risk of SVD with bioprostheses and hemorrhage with mechanical valves, respectively, after AVR with and without concomitant CABG.

 
3.4. Validation
We compared the microsimulation model outputs for male patients of varying ages, who had undergone AVR with and without concomitant CABG, with the corresponding long-term data from Portland, OR, USA [12]. Although the model predicted slightly higher survival for bioprostheses in most age groups, there was reasonably good agreement with the Portland data (Figs. 5 and 6 ).



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  		Fig. 5. Comparison of microsimulation model output and corresponding Portland data for 50-, 60- and 70-year-old males after AVR with a mechanical valve and concomitant CABG.

 


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  		Fig. 6. Comparison of microsimulation model output and corresponding Portland data for 50-, 60- and 70-year-old males after AVR with a bioprosthesis and concomitant CABG.

 

   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
Appendix A
 Appendix B. Conference...
 References
 
Simulation techniques, by allowing modeling of complex outcome paths resulting from many simultaneous risks, provide a useful adjunct to standard statistical methods in predicting outcomes of individual patients after AVR. These models have been used previously to predict outcome after AVR and to support prosthetic valve choice [13,14]. Birkmeyer and colleagues [14] used a Markov state-transmission model to simulate the prognosis after AVR. Although the Markov model and microsimulation have similar assumptions, they encompass important differences between them. The Markov model follows a virtual population over time and has no ‘memory’, which translates to the assumption that subjects in a particular state are a homogenous group. In microsimulation, individual life histories are simulated. Further, it permits adjusting of hazards for the individual patient depending on prior events, thereby accommodating the variability with groups of subjects [15]. We used the microsimulation model to predict, for a 65-year-old male without CABG, a LE of 11.2 and 11.6 years and an EFLE of 8.2 and 8.9 years, respectively, after implantation with a mechanical valve and a bioprosthesis. Considering LE, the age crossover point between either valve type was 59 years. This concurs well with the results of Birkmeyer and colleagues who obtained a similar LE for 60-year-old patients receiving mechanical valves and bioprostheses [14]. CABG resulted in a decrease in the age crossover point to 58 years.

The actuarial method and the Kaplan–Meier analysis are commonly used in studies to estimate survival of patients after AVR. However, when applied to a non-fatal event such as SVD, it estimates the freedom from event by censoring patients who had not yet experienced that event, including those who had died and will therefore never experience it. Consequently, Kaplan–Meier analysis estimates a higher percentage of events than will actually occur. An alternative method, the ‘actual’ analysis (cumulative incidence) modifies this estimate to exclude future events attributed to already deceased persons and answers the more pertinent question, "what is the lifetime risk of the event?" [16]. The microsimulation model provides estimates of the lifetime risk of each of the valve-related events and the overall risk of an event, following AVR. For the 65-year-old patient, the overall lifetime risk of any event was 51 and 47%, respectively, for a mechanical valve and a bioprosthesis.

There is uncertainty as to whether coronary re-vascularization of patients with CAD undergoing AVR leads to a long-term survival similar to that of patients without CAD requiring AVR [17]. The influence of concomitant CABG on long-term survival is complex and theoretically can be viewed in two aspects [18]. Concomitant CABG may be associated with increased long-term survival compared to those who had mild coronary disease that did not require re-vascularization at the time of surgery, whose atherosclerotic disease progressed subsequently. Further, patients having concomitant CAD have less severe aortic valve disease in general. These factors may lend support to the view that concomitant CABG returns those patients with concomitant aortic valve disease and CAD to a prognostic curve determined by the valvular disease. Nunley and colleagues [19] found that patients who had AVR with concomitant CABG had similar survival to those without CAD, who had isolated AVR. Conversely, it has been postulated that patients who had concomitant CABG had atherosclerotic disease that increased the risk even after CABG, compared to those who only required AVR. Studies have shown that patients, who had concomitant CABG, still had survival rates inferior to those without CAD who underwent AVR [7,20]. Assuming the latter possibility, we incorporated a hazard ratio of 1.3 to the survival curve estimates of patients to represent those who had concomitant CABG. This hazard ratio was in good agreement with the Portland data [12].

Does CABG matter in the choice of a valve for AVR? The main difference in outcomes between the two valve types is due to the high risk of hemorrhage in the mechanical valves and the high risk of SVD in the bioprosthesis. The lifetime risk of hemorrhage with mechanical valves and SVD with bioprostheses, for patients with different implantation ages are given in Fig. 4. It shows that the age crossover point in overall valve complications follows the increasing risk of hemorrhage in mechanical valves and decreasing risk of SVD in the bioprostheses, with advancing age of implantation. Considering the overall risk of any valve-related event, the age crossover point was 63 years. Concomitant CABG results in a reduced LE compared to those who only require AVR (Fig. 3A, B). In a patient with concomitant CABG, the trade-off between the reduced risks of SVD and hemorrhage resultant from a lowered LE, minimizes the effect of CABG on the age crossover point, which was then 62 years.

The American College of Cardiology and the American Heart Association guidelines [3] recommend a bioprosthesis for patients >=65 years of age, who do not have risk factors for thrombo-embolism, based on the reduced risk of SVD and the increasing risk of hemorrhage at this age. Considering the patient age crossover points calculated by our model for total LE, EFLE and the lifetime risk of a valve-related event, we suggest that a bioprosthesis may be considered for patients under 65 years of age. New strategies being developed to retard mineralization of xenograft valves and evidence that pericardial aortic valves have a better durability than porcine valves further supports reduction of the 65-year-old limit. However, our suggestion needs to be considered in the context of the narrow age difference between the LE for both valve types (Fig. 3A, B) and the present inability of the microsimulation model to estimate the uncertainty of the input data. The influence of age on the risk of anticoagulation-related bleeding is disputed in the literature [6,21]. We assumed an exponentially increasing risk of hemorrhage with advancing age for the mechanical valves, based on a large study that assessed the risk of bleeding complications in patients treated with oral anti-coagulants [6]. However, an alternative assumption of a constant hazard for hemorrhage or consideration of anti-coagulation strategies which aim for lower INR ranges will push the age crossover point towards the 65-year limit. When considering the lifetime risk of a valve-related event, equal weight was given to the severity and outcomes of all events. Patient preference is also important in clinical decisions about valve prostheses.

Limitations of the model include certain structural and parameter uncertainties, respectively. Several assumptions were necessary in structuring the microsimulation model. For example, valve thrombosis, thrombo-embolism and NSD were assumed to carry constant hazards. These events may have an increased hazard during the early period (<30 days), but was not incorporated into the model. The risk of endocarditis was assumed to be greater during the first 6 months than the subsequent period, but was assumed to be constant during these two phases. These hazards may in fact be time- and age-dependant, and hence, further knowledge is necessary to address these assumptions. Further, an ‘additional mortality’ after AVR has been incorporated into the model by means of hazard ratios. As previously described, this was necessitated by the observation that the excess mortality in patients after AVR, compared to the general population, can only in part be explained by valve-related events. We used one set of hazard ratios to represent this ‘additional mortality’. The possibility that ‘additional mortality’ varies according to valve type, operative procedure and cross-clamp time needs also to be considered further. Parameter uncertainties relate to the quality of the input of the model. The estimated hazards obtained from clinical literature, which are used to parameterize the model carry some uncertainty.

Survival after AVR has also been shown to depend on pre-operative cardiac rhythm, type of valve lesion and New York Heart Association (NYHA) functional status. Although the model incorporates these factors non-specifically by means of the hazard ratios, the model cannot determine the individual influence of these factors on overall survival. At present, the model can only predict outcome for an average risk profile.

In conclusion, we have described the combination of meta-analysis and microsimulation to provide insight into age- and gender-specific long-term prognosis after AVR, with and without concomitant CABG. Based on the age crossover points for patient outcomes between the two valve types, we suggest that the currently recommended age for implanting a bioprosthesis could be lowered further, irrespective of concomitant coronary re-vascularization.


   Acknowledgments
 
The authors acknowledge Dr Tirone David, Dr Steven Khan and Dr Jose Bernal for providing additional information on their publications.


   Footnotes
 
Presented at the 16th Annual Meeting of the European Association for Cardio-thoracic Surgery, Monte Carlo, Monaco, September 22–25, 2002.


   Appendix A
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
Appendix B. Conference...
 References
 
The nine reports selected on St. Jude mechanical valves are as follows:

  1. Khan SS et al. J Thorac Cardiovasc Surg 2001;122:257–69.
  2. Peterseim DS et al. J Thorac Cardiovasc Surg 1999;117:890–7.
  3. Smith JA et al. Circulation 1993;88:II49–54.
  4. Lund O et al. Ann Thorac Surg 2000;69:1459–65.
  5. Zellner JL et al. Ann Thorac Surg 1999;68:1210–8.
  6. Horstkotte D et al. J Heart Valve Dis 1993;2:291–301.
  7. Aoyagi S et al. J Thorac Cardiovasc Surg 1994;108:1021–9.
  8. Baudet EM et al. J Thorac Cardiovasc Surg 1995;109:858–70.
  9. Ibrahim M et al. J Thorac Cardiovasc Surg 1994;108:221–30.

The 13 reports selected on stented porcine bioprostheses are as follows:

  1. Peterseim DS et al. J Thorac Cardiovasc Surg 1999;117:890–7.
  2. Cohn LH et al. Ann Thorac Surg 1998;66:S30–4.
  3. Wilson ES et al. J Heart Valve Dis 1996;5:40–4.
  4. Logeais Y et al. Ann Thorac Surg 1999;68:421–5.
  5. Hurle A et al. J Heart Valve Dis 1998;7:331–5.
  6. Fann JI et al. Ann Thorac Surg 1996;62(5):1301–11; discussion 1311–2.
  7. David TE et al. J Thorac Cardiovasc Surg 2001;121:268–278.
  8. Bernal JM et al. Ann Thorac Surg 1995;60:S248–52.
  9. Westaby S et al. Ann Thorac Surg 2000;70:785–90; discussion 790–1.
  10. Jamieson WR et al. Ann Thorac Surg 1995;60:999–1006; discussion 1007.
  11. Jamieson WR et al. Ann Thorac Surg 2001;71:S224–7.
  12. Orszulak TA et al. Ann Thorac Surg 1995;59:462–8.
  13. Akins CW et al. Circulation 1990;82:IV65–74.


   Appendix B. Conference discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 Appendix A
 Appendix B. Conference...
References
 
Dr M. Antunes (Coimbra, Portugal): I have doubts about this conclusion of yours because the decreasing risk for structural valve disease, the line going down, crossing with the line going up for hemorrhagic events, is somewhere between 60 and 65. So, it doesn't really give substance to your conclusion when you say that we should implant biological valves after 65, 63 or 67, it makes no difference. Can you comment?

Dr Puvimanasinghe: Actually, it depends on the different parameters considered. If you consider the life expectancy, or the event-free life expectancy, the crossover point is at about 60 years, but if you consider different valve-related events or the actual lifetime risk of any valve-related event, as you say, the crossover is then at 62, or 62.5 years. So it depends on the parameter you consider. But many would consider the life expectancy as a hard parameter, and that gives you a crossover point of 60 years. A study conducted previously by Birkmeyer and colleagues in the United States, who used different data sets and used a Markov model, also obtained a crossover point of 60 years considering life expectancy. So it depends on the parameters.

And if I may go just a bit further, if you considered reoperation-free life expectancy, as you see, there were no structural deterioration in the mechanical valves, the crossover point is at 67 years.

Dr Antunes: Does it depend on sex?

Dr Puvimanasinghe: That is possible because females have a better life expectancy compared to males and the additional mortality could vary between males and females, but at present we only give the results for males.

Dr H. Oelert (Mainz, Germany): I don't see the impact of coronary artery bypass in your study. What does it have to do with life expectancy or event-free survival time? And if you consider bypass as an impact factor on survival, what do you use, do you use vein grafts or mammary artery?

Dr Puvimanasinghe: There are different assumptions in the literature regarding CABG. Some have found that following CABG the patient follows the same survival as a comparable person in the general population. Other studies show that there is an increased hazard following CABG. Now, we assume an increased hazard of 1.3 for a patient who receives CABG against a patient who does not. So the effect of CABG was a reduction in life expectancy. We did not consider the type of vessel that was used for CABG. In general, data obtained from the literature just commented on CABG. So we couldn't be more specific on that point.

Dr C. Yankah (Berlin, Germany): My question is whether there are some other factors which might influence the life expectancy in these patients, because you didn't include diabetic patients, dialysis patients, hypertensive patients and other risk factors which might influence coronary microcirculation and subsequently the life of these patients despite functional valves.

Dr Puvimanasinghe: Definitely, that's right. As I mentioned, at present we just consider a basic profile of the patient: age, sex and CABG. We are working at present to include other important factors which have been shown to be risk factors for survival and life expectancy like for example pre-op atrial fibrillation, NYHA status and diabetic status. But at the moment we are just speaking about a basic risk profile.

Dr E. Baudet (Bordeaux, France): For your aortic mechanical patients what was the level of INR you recommended, first? In addition, in your bioprosthetic patients, how many of them were on anticoagulants because of atrial fibrillation, not at the time of operation but further?

Dr Puvimanasinghe: Regarding the first question on mechanical valves, as I mentioned, we stipulated many criteria, and one was the target range of INR. All selected studies had a range between 2 and 4.5. The range was wide, but we were forced to consider that.

Regarding the second question about bioprostheses, in the meta-analysis we tried to collect studies with patients who did not have long-term anticoagulation, but this is not clearly mentioned and I admit there could be some patients who did receive long-term anticoagulation. But we were unable to separate that from the literature used.


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

  1. Edmunds L.H., Jr. Evolution of prosthetic heart valves. Am Heart J 2001;141(5):849-855.[CrossRef][Medline]
  2. Khan S.S., Chaux A., Blanche C., Kass R.M., Cheng W., Fontana G.P., Trento A. A 20-year experience with the Hancock porcine xenograft in the elderly. Ann Thorac Surg 1998;66(6 Suppl):S35-S39.
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