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Eur J Cardiothorac Surg 2005;27:425-433
© 2005 Elsevier Science NL
a Division of Cardiac Surgery, University of Ottawa Heart Institute, 40 Ruskin Street, Suite 3403, Ottawa, Ont., Canada K1Y 4W7
b Department of Epidemiology and Community Medicine, University of Ottawa, Ottawa, Ont., Canada
Received 9 September 2004; received in revised form 22 November 2004; accepted 1 December 2004.
* Corresponding author. Address: Division of Cardiac Surgery, University of Ottawa Heart Institute, 40 Ruskin Street, Suite 3403, Ottawa, Ont., Canada K1Y 4W7. Tel.: +1 613 761 4893; fax: +1 613 761 4713. (E-mail: mruel{at}ottawaheart.ca).
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Abstract |
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 Top Abstract 1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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Key Words: Follow-up studies • Prognosis • Prosthesis • Valves
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1. Introduction |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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2. Methods |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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Patients were seen in a dedicated valve clinic six months postoperatively and on an annual basis thereafter. Of the 500 patients, 30 were lost to follow-up at a mean of 2.2±1.2 years after valve replacement. The remainder of the cohort was followed for a mean of 7.9±5.0 years postoperatively (maximum follow-up time: 26.7 years).
The preoperative characteristics of the cohort are presented in Table 1. The initial operation consisted of AVR in 309 patients (mechanical in 171, bioprosthetic in 138), MVR in 151 patients (mechanical in 109, bioprosthetic in 42), and DVR in 40 patients (mechanical in 36, bioprosthetic in 4). Table 2 shows the types of prostheses implanted.
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Warfarin anticoagulation was used at the discretion of the surgeon for a period of 3 months after operation in patients who underwent bioprosthetic valve replacement and who were in sinus rhythm. Warfarin was subsequently discontinued if sinus rhythm was maintained and no other indication for anticoagulation was present. Non-anticoagulated patients with a bioprosthetic valve were kept on 325mg of aspirin daily unless contraindicated, and the addition of dipyridamole was left to the decision of the patient's physician. Bioprosthetic valve patients in atrial fibrillation were anticoagulated at a prothrombin time or INR target range of 2.0–2.5x normal.
2.3. Outcomes
2.4. Statistical analyses
Data were imported and analyzed in Intercooled Stata 8.0 (Stata, College Station, TX). Continuous data are presented as mean±standard deviation, except for survival and events rates which are reported as mean±standard error. For actuarial analyses of the various outcomes in this study, patients were censored at the time of their last follow-up visit or at the time of death if the outcome of interest had not occurred, and censoring was assumed to be independent of predictors and outcomes. For actual analyses, patients were considered not to have experienced a given outcome by a specific time point if either (1) the time point had been reached and the outcome had not occurred, or if (2) death took place before the time point had been reached and the outcome had not occurred before death. Analyses were performed on the entire cohort, between subcohorts of mechanical versus bioprosthetic valves, and within mechanical or bioprosthetic valves according to 4 subclasses of valve models (Table 3). These 4 subclasses consisted of: (1) stented bioprostheses (Medtronic Hancock I, Medtronic Hancock II, or Edwards Perimount); (2) homografts (in the aortic position only); (3) tilting-disc mechanical valves (Medtronic Hall); and (4) bileaflet mechanical valves (St. Jude Medical, Carbomedics, or MCRI On-X).
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2.4.2. Multivariate analyses
2.4.2.1. Cox proportional hazards models
Actuarial analyses incorporated variables that had a P value of 0.20 or less on univariate Log-Rank testing in order to account for positive or negative confounding. No automated model selection procedure was used and all reported variables, unless collinear as arbitrarily determined by a Spearman's rank correlation coefficient 
0.30 and a P value <0.005, were used simultaneously. In addition, biologically important covariates (such as atrial fibrillation or left ventricular grade) were forced into the models to account for confounding and are reported as such in the text.
2.4.2.2. Logistic regression models
Actual outcome analyses at specific time points and binary outcomes analyses were performed by incorporating variables that had a P value of 0.20 or less on univariate analysis in a logistic regression model. As for Cox proportional hazards models, biologically important covariates were forced into the logistic regression models and are reported in the text.
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3. Results |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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3.1.2. Long-term
Fig. 1 displays the long-term survival of patients in the cohort. The overall five, 10, and 15-year survival by implant site was 92.7±1.7, 88.3±2.4 and 80.1±4.7% after AVR, 93.1±2.3, 79.5±4.3 and 71.5±5.4% after MVR, and 83.1±6.3, 78.9±7.2 and 69.1±11.2% after DVR, respectively. Long-term survival was significantly worse after double valve replacement than after either aortic or mitral replacement (HR: 2.2; 95% CI: 1.1, 4.5; P=0.03). On the other hand, there was no significant difference in survival between patients who underwent AVR versus those who underwent MVR, no survival difference between patients implanted with a mechanical versus a bioprosthetic valve in either implant position, and within mechanical or bioprosthetic valves in either implant position there was no survival difference between the 4 subclasses of prostheses examined (Table 3).
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3.1.3.2. Mitral
Independent risk factors for late death after MVR were preoperative atrial fibrillation (HR: 5.5; 95% CI: 1.5, 19.9; P=0.01), preoperative left atrial diameter (HR: 3.0 per cm increase; 95% CI: 1.0, 9.1; P=0.04), preoperative NYHA class (HR: 2.1 per class increase; 95% CI: 1.1, 4.1; P=0.02), and the need for concomitant coronary artery bypass grafting at the time of MVR (HR: 5.7; 95% CI: 1.0, 32.3; P=0.05). Prosthesis type or subclass, age at the time of surgery, gender, left ventricular grade, and the type of prosthesis had no significant effect.
3.1.3.3. Double valve
In the limited number of young patients who underwent DVR in the cohort, the only independent risk factor for reduced survival was preoperative atrial fibrillation (HR: 7.2; 95% CI: 1.3, 41; P=0.03).
3.2. Stroke
3.2.1. Embolic
Four strokes occurred in the early postoperative period in the cohort; 2 involved AVR patients (0.6%) and 2 occurred in MVR patients (1.3%). In the chronic phase, the 10-year cumulative incidence of late postoperative embolic stroke was 6.3±2.4% for mechanical AVR patients, 6.4±2.9% for bioprosthetic AVR patients, 12.7±3.9% for mechanical MVR patients, 3.1±3.1% for bioprosthetic MVR patients, and 16.1±9.4% for mechanical DVR patients. No strokes occurred in the 4 bioprosthetic DVR patients.
3.2.2. Risk factors
In the aortic position, there was no difference in embolic stroke risk between mechanical and bioprosthetic valves. In the mitral position, mechanical prostheses were a risk factor for stroke on univariate analysis (HR: 2.2±0.9; P=0.04); however, this lost significance on multivariate analysis as atrial fibrillation and smoking entered the model. The only independent risk factors for embolic stroke in MVR patients were atrial fibrillation (HR: 2.8; 95% CI: 1.1, 7.2; P=0.04) and smoking (HR: 4.0; 95% CI: 1.4, 11; P=0.008). No significant independent effect was observed with respect to prosthesis type or subclass (Table 3). The addition of aspirin to warfarin anticoagulation had no significant effect on the incidence of embolic stroke in patients with mechanical valves, regardless of implant position or valve type.
3.2.3. Bleeding events
Three intracranial bleeding events occurred in the cohort during the follow-up period. There were an additional 26 patients who experienced bleeding at extracranial sites during the follow-up period, 12 of whom required hospital admission, and 6 for whom surgical intervention was necessary. All patients denoted above except two (one who had a spontaneously bleeding intracranial aneurysm and one who had a minor bleeding episode) were on warfarin anticoagulation. The linearized rates of intracranial, major, and minor bleeding events in anticoagulated patients from the cohort were respectively, 0.1% per year, 0.4% per year, and 0.9% per year.
The presence of a mechanical prosthesis, non-dissociable from the use of warfarin in the series, was a significant risk factor for bleeding events in either implant position (Table 3). Within mechanical valves, tilting disc prostheses were also associated with significantly more bleeding events than bileaflet prostheses in the mitral position.
3.3. Reoperation
Reoperation took place in 8 mechanical aortic valve patients, 11 aortic bioprosthesis valve patients, 3 mechanical mitral valve patients, and 20 mitral bioprosthesis patients. All patients reoperated for aortic or mitral mechanical valve failure, as well as patients reoperated for mitral bioprosthesis failure received a mechanical valve at reoperation. Although the decision was individualized, patients reoperated for aortic bioprosthesis failure more than 8 years after initial implantation received another bioprosthetic valve in the series, while the remainder, including early failing homografts, were re-implanted with an aortic mechanical valve. The overall mortality associated with redo-AVR was 6.0%; that of redo-MVR was 11.1%.
3.3.1. Bioprostheses
The actuarial and actual cumulative incidences of reoperation for bioprosthetic valves are shown on Fig. 2. Structural valve deterioration was the primary indication in 83% of bioprosthetic valve reoperations. There was an opposite discrepancy between actuarial and actual reoperation rates in aortic versus mitral bioprosthesis patients due to lower long-term survival and longer follow-up in the mitral patients (Fig. 1).
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3.3.3. Mechanical valves
Mechanical valves had a cumulative incidence of reoperation of 5.4±2.2% at 10 years in the aortic position and of 4.2±2.4% at 10 years in the mitral position. These rates correspond to the 15 year reoperation rates in this series, as no event led to the reoperation of a mechanical heart valve after 10 or more years had elapsed since the initial operation. No difference in reoperation rates was observed between tilting disc and bileaflet prostheses in either implant position (Table 3).
3.4. Heart failure
Heart failure appeared more frequent in patients implanted with a aortic mechanical valve than in those with a aortic bioprosthesis (HR: 2.7; 95% CI: 0.8, 9.0; P=0.12), but the trend was not significant (Table 3). This relationship was independent of atrial fibrillation (HR: 18.6±32.6 for recurrent NYHA III or IV status; P=0.10), left ventricular grade (OR: 1.3±0.8 per grade increase; P=0.6), and aortic prosthesis size (OR: 0.7±0.2 per size increase; P=0.2). Although a similar trend was observed in MVR patients (Table 3), there was also no significant difference in the crude and adjusted incidence of recurrent heart failure symptoms between mechanical and bioprosthetic MVR and DVR patients.
3.5. Quality of life
3.5.1. Short form-12 health status instrument
Fig. 4 shows the mean physical and mental component scores of the short form (SF)-12 health status instrument. Quality of life was good to very good in all groups. Physical component scores for AVR patients were significantly higher in patients with aortic bioprostheses than in those with mechanical aortic valves (by 9.9%; 95% CI: 2.7, 17.1; Bonferroni-adjusted P=0.02). This difference of aortic bioprostheses over mechanical valves was observed irrespectively of the use of homografts versus stented bioprostheses (Fig. 4A). There was no other significant difference in SF-12 physical or mental component scores between prosthesis types and subclasses in either implant site.
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3.5.3. Disease perception
A higher proportion of AVR patients with a mechanical prosthesis answered ‘yes’ to the question ‘did your valve disease or prosthesis significantly affect your work, career, or income?’ than bioprosthetic AVR patients (35.2 versus 23.0%, mechanical versus bioprosthetic AVR patients, respectively; adjusted OR: 2.2; 95% CI: 1.02, 5.1; P=0.04). This difference was observed with the use of either aortic homografts or aortic stented bioprostheses, and was independent of atrial fibrillation, age, left ventricular function, and coronary artery disease. This relationship was also observed in mechanical versus bioprosthetic MVR patients (55.6 versus 18.2% answered ‘yes’, mechanical versus bioprosthetic MVR patients, respectively; adjusted OR: 6.3; 95% CI: 1.1, 37; P=0.04), with no differences between valve subclasses.
3.5.4. Marital status
There was no difference in marital status between implant sites, prosthesis types and subclasses in the cohort, with a cumulative incidence of divorce of 32.7% at a mean age of 48.6±8.4 years at last follow-up. Valve replacement did not appear to constitute a major factor, as 75.5% of patients who experienced a divorce separated at a mean of 9.0±6.6 years before valve replacement. In only 24.6% of divorced patients did the separation occur after surgery, at a mean of 5.1±3.7 years postoperatively.
3.5.5. Mood
The reported cumulative incidence of depression in the cohort was 24.1%, with no difference according to prosthesis type or subclass, implant site, left ventricular function, atrial fibrillation, coronary disease, or age. The point prevalence of depression at latest follow-up was 9.8%, with no significant difference between subgroups.
3.5.6. Satisfaction with the prosthesis
In AVR patients, 30.3% of mechanical valve patients versus 20.2% of patients with a bioprosthesis either expressed dissatisfaction with their prosthesis or were uncertain whether they would choose the same prosthesis again (multivariate adjusted OR for prosthesis non-satisfaction: 1.8, mechanical versus bioprosthetic AVR, respectively; 95% CI: 0.8, 4.0; P=0.13). This relationship was not statistically significant, however, and the only independent predictor of non-satisfaction with the chosen aortic prosthesis was whether a patient had experienced reoperation (OR: 4.7; 95% CI: 1.0, 23; P=0.05). Within aortic mechanical valves, there was a trend towards patients implanted with a tilting disc valve more often expressing dissatisfaction with the prosthesis than those who received a bileaflet prosthesis (OR: 2.4, 95% CI: 0.9, 6.3; tilting disc versus bileaflet; P=0.07). No predictor of dissatisfaction with the prosthesis(es) was identified in MVR and DVR patients.
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4. Discussion |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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While this follow-up study represents one of the largest series of young patients implanted with contemporary heart valve prostheses to date, it also illustrates the difficulties in examining these patients’ outcomes with adequate statistical power. Fewer young patients require valve replacement compared to older subjects, and event rates are lower than in regular valve patient cohorts. Young valve patients also constitute a relatively heterogeneous population compared to regular valve patients, with some presenting with endocarditis and marginal lifestyle, Marfan's syndrome, rheumatic fever, premature coronary disease, congenital defects, etc..., while the remainder are generally healthy. Compliance issues add to this biologic heterogeneity, as age under 55 years is a known risk factor for poor compliance with warfarin therapy [6]. Consequently one should exercise caution at drawing strong conclusions on the choice of valve for a given patient from the present study, and instead see these data as useful prognostic information for surgeons, cardiologists, and patients. For instance, these results refute the commonly held belief that mechanical AVR patients are at significantly greater embolic stroke risk than patients with a bioprosthetic aortic valve. The study also illustrates the need for multicenter prospective studies and databases to better understand the important problem of valve replacement in the young adult. As the present data indicate, young patients with modern prosthetic valves continue to have a higher mortality risk than if they did not have valve disease, indicating that this health issue remains far from resolved.
This results of this study suggest that aortic bioprostheses may constitute a viable alternative to mechanical valves in young patients in need of AVR who wish to avoid anticoagulation. Aortic bioprostheses, in the form of stented bioprotheses or homografts (which have equivalent performance) appear to be associated with better physical capacity, social functioning, and prosthesis satisfaction. On the other hand, a bioprosthetic mitral valve offers no clear advantage compared to a mechanical MVR with the exception of warfarin avoidance (a crucial aspect for women contemplating childbirth), and may be actually more hazardous as late survival is poor and reoperation for redo-MVR carries significant risk. Although a higher rate of embolic stroke is seen in mechanical MVR patients, this is confounded by the higher co-prevalence of atrial fibrillation, itself a stroke risk. In the future, less thrombogenic mechanical prostheses, newer forms of anticoagulation, and the routine performance of concomitant atrial fibrillation surgery when indicated may constitute a good option for the occasional young patient whose mitral valve is not amenable to repair and who is not contemplating pregnancy.
4.1. Previous related work
4.1.1. Survival, stroke, and reoperation
Other studies have also indicated that in young patients, survival does not appear to be affected by the type of prosthesis [7,8]. A high incidence of thromboembolic and bleeding complications in patients with mechanical valves of nearly 3% per patient-year has previously been reported with mechanical prostheses [9]. However, the present series and previous work from our group indicate that thromboembolism rates are reduced in younger patients, as age is a risk factor [2]. Emery et al. reported that in patients under the age of 50 who had AVR with a St. Jude Medical valve, freedom from mortality was 89% at 10 years and 87% at 18 years, with a freedom from thromboembolism of 96.5% at 10 years [10]. Other risk factors for death and thromboembolism, such as coronary artery disease, atrial fibrillation and poor ventricular function, are less common in young patients [2,10].
Several mechanisms have been proposed to explain the process of early calcification of bioprostheses in young patients, including primary collagen degeneration, discrete immunologic reaction, increased turnover of calcium, and fatigue-induced lesions [11]. More recently, with the advent of the latest generation bioprostheses employing newer fixation and anti-mineralization processes [12], more promising long-term results of bioprostheses in young patients have been published. Carpentier's group reported encouraging results with the high-temperature fixed valvular bioprostheses in young patients, illustrating 95% actuarial survival, 92% freedom from structural failure, 87.6% freedom from reoperation (91.7% for AVR, 80% for MVR) at 9 years. In a follow-up study of young adults aged 15–58 undergoing AVR with the Carpentier-Edwards supra-annular porcine bioprosthesis, Yamak et al. reported a freedom from SVD of 92% at 5 years and 44% at 12 years [13].
4.1.2. Quality of life
Young patients after valve replacement surgery face a full lifespan and need to lead an active lifestyle, including school or work attendance, regular physical activity, and normal social relations, with the possibility of marriage and pregnancy. Although long-term anticoagulation does cause some degree of discomfort from blood tests and disruption of daily life [14], warfarin is well tolerated by most patients and does not have an important effect on quality of life [14,15]. Following mechanical MVR, van Doorn et al. reported that young adults perceived their quality of life and level of functioning as normal or near normal in most areas compared with a reference population [14]. Similarly, good quality of life was reported by young patients several years after mechanical AVR [16,17]. Other authors have also found that the majority of young patients return to work after valve replacement, reporting an employment rate of 67–73% one year after surgery [18,19].
4.2. Limitations
4.2.1. Censoring and follow-up
The Cox proportional hazards regression method requires an assumption of independent censoring which may not always be met. In this regard, it is possible that patients lost to follow-up after a number of visits may have had subsequent outcomes that were not accounted for in the analyses.
4.2.2. Selection bias and generalizability
Like that of other observational cohorts, the results of these analyses may not be generalizable to all young adult patients who have undergone prosthetic valve replacement at other centers. Demographic and valve selection factors unique to the study cohort could have resulted in leverage from statistically influential patients. For example, the observation within mitral mechanical valves that tilting disc prostheses were associated with significantly more bleeding events than bileaflet prostheses despite a similar anticoagulation regimen may have reflected differences in referral patterns, patient compliance, or others. Confounding by indication, a form of selection bias that cannot be fully accounted for by multivariate analyses [20], might also have led to certain associations.
4.3. Conclusions
Despite the above limitations, the findings of this study allow patients and clinicians to better understand and quantify long-term survival, risks of adverse events, and quality of life after heart valve replacement in young adults. One important finding amongst others identified in this study is that the avoidance of smoking in young valve patients decreases thromboembolism and bioprosthesis reoperation hazards after valve replacement. As in the past, decisions on the choice of prosthesis need to be individualized and discussed between the patient and the treatment team, as no prosthesis is without major drawbacks in this age group.
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Appendix. Conference discussion |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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Dr Mesana: Yes.
Dr Cicek: Then in your conclusion you say all these models may result in suboptimal long-term results. Do you consider changing your practice and using more Ross procedure for these kinds of patients, or what is your comment on this?
Dr Mesana: We don't have many Ross procedures in this study. We have homografts that were used as a homograft reimplantation technique. I don't think that this question addresses the Ross operation. It is addressing that we offer suboptimal solutions for now with patients requiring AVR, and mechanical valves are probably not the best option even if there is a need for reoperation with a tissue valve.
Dr P. Kolh (Liege, Belgium): Can you elaborate a little bit on why the patients with mechanical valves are in worse physical condition? I assume it is not only because they have had thromboembolic events. There must be other reasons for that. Do you have any insights into that information?
Dr Mesana: Actually you have to understand that the number of strokes or bleeding complications are really low, in fact. But to elaborate on your question, we had the SF-12, the short form 12, which is a very simple questionnaire that we did through the phone, because not all patients were available, because Canada is a big country, and in Ontario we sometimes have a patient who lives a 20-h drive from our center, but we have almost a complete follow-up through the phone, and this is how they answered the question.
Dr Kolh: So it is a subjective assessment?
Dr Mesana: Yes.
Dr R. Dion (Leiden, Netherlands): What do you think is the reason why the mechanical valve would lead more often to a recurrence of congestive heart failure?
Dr Mesana: I cannot answer this question. This was just the result of our study. I think we have to go into more detail and try to find this out. It is a good question. I have no answer, to be honest.
Dr Dion: Do you think it is still true that the adjunction of coronary bypass to a mitral valve or an aortic valve multiplies the risk of congestive heart failure by five?
Dr Mesana: I think it is well known data, but in our population that is how the univariate odds ratio showed up.
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Acknowledgments |
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Footnotes |
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References |
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TopAbstract1. Introduction2. Methods3. Results4. DiscussionAppendix. Conference discussionReferences |
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