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J Thorac Cardiovasc Surg 2004;128:278-283
© 2004 The American Association for Thoracic Surgery
Surgery for acquired cardiovascular disease |
a Division of Cardiac Surgery, Ottawa, Ontario, Canada
b Department of Epidemiology, University of Ottawa, Ottawa, Ontario, Canada
Received for publication September 3, 2003; revisions received November 5, 2003; accepted for publication November 10, 2003.
* Address for reprints: Marc Ruel, MD, MPH, University of Ottawa Heart Institute, 40 Ruskin Street, Suite 3403, Ottawa, Ontario, Canada K1Y 4W7
mruel{at}ottawaheart.ca
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Abstract |
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METHODS: Patients who underwent mitral valve replacement with contemporary prostheses (N = 708) were followed with annual clinical assessment and echocardiography. Cox proportional hazard models were developed to evaluate the impact of demographic, comorbid, and valve-related variables on the occurrence of congestive heart failure after mitral valve replacement, defined as the composite outcome of New York Heart Association class III or IV symptoms or death caused by congestive heart failure postoperatively. Factors associated with all-cause mortality were also examined. Models were bootstrapped 1000 times.
RESULTS: The total follow-up was 3376 patient-years (mean 4.8 ± 3.7 years, range 60 days to 17.1 years). Freedom from New York Heart Association III or IV symptoms or death caused by congestive heart failure was 96.1% ± 0.8%, 82.7% ± 1.7%, 66.4% ± 3.0%, and 38.8% ± 6.9% at 1, 5, 10, and 15 years, respectively. Preoperative New York Heart Association class, left ventricular grade, atrial fibrillation, coronary artery disease, smoking, persistent tricuspid regurgitation, and redo status predicted congestive heart failure postoperatively (all P < .05). Patients who underwent mitral valve replacement for pure mitral stenosis had less congestive heart failure events after surgery than those with regurgitation or mixed disease. Prosthesis size and elevated transprosthesis gradients were not predictive of freedom from congestive heart failure after mitral valve replacement. Atrial fibrillation, persistent tricuspid regurgitation, and surgical referral for mitral valve replacement at an advanced functional stage were also risk factors for all-cause mortality.
CONCLUSIONS: This study identifies the incidence of and risk factors for congestive heart failure and death late after mitral valve replacement. Although prosthesis size has no effect, other potentially modifiable factors such as atrial fibrillation, persistent tricuspid regurgitation, and late surgical referral have a negative impact on freedom from congestive heart failure and overall survival after mitral valve replacement.
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Methods |
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18 years) who underwent MVR between 1976 and 2001 at our institution were followed annually in a dedicated valve clinic with clinical and laboratory examinations. The preoperative characteristics of the cohort are presented in Table 1.
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Statistical analyses
Data were imported and analyzed in Intercooled Stata 8 (Stata, College Station, Tex). Patients were censored at the time of their last follow-up visit if they had not experienced at least 1 episode of NYHA functional class III or IV for 4 weeks or more, or had died from a CHF-related event. Deaths from an unknown cause were not considered to result from CHF. Crude, stratified, and risk-adjusted survival, heart failure event rates, and failure rates are reported as mean ± SE or as mean (95% confidence interval [CI] lower bound, 95% CI upper bound).
Cox proportional hazards models were developed by incorporating variables that had a P value of .10 or less on univariate analysis and by forcing into each model patient- and prosthesis-related variables (eg, age, gender, comorbidities, atrial fibrillation, and valve type) that constituted potential confounders regardless of their univariate P value. Variables used in the models are presented in Tables 3 and 4. To account for positive or negative confounding, no automated model selection procedure was used, and reported variables, unless collinear with a Spearman's rank correlation coefficient of 0.30 or greater and a P value less than .01, were used simultaneously. Each model was evaluated with a score test and rejected if the P value was .05 or greater. Final models were subjected to 1000 bootstrap replications, and bias-corrected estimates of 95% CIs were tabulated for significant covariates.
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Results |
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Prosthesis-related factors
In contrast with patients with aortic prostheses,2 prosthesis size did not significantly predict freedom from heart failure after MVR, regardless of whether body surface area was accounted for in the model.
The median transprosthesis peak and mean gradient for patients with a mitral prosthesis were 11 mm Hg and 4 mm Hg, respectively, and the 90th percentile values for peak and mean aortic gradients were 19 mm Hg and 7 mm Hg, respectively. Peak and mean transprosthesis gradients had no significant impact on the freedom from heart failure after MVR either as a linear relationship or as a dichotomous predictor defined by a gradient at or above the 90th percentile value of the cohort.
Risk factors for all-cause death
Table 4 displays the risk factors for all-cause death late after MVR in the study cohort. Significant independent predictors were age, atrial fibrillation, preoperative functional class, left ventricular grade, coronary artery disease, number of pack-years smoked, and persistent tricuspid insufficiency at follow-up. Again, no significant effect of prosthesis size on crude survival was detected.
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Discussion |
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These data have practical relevance in light of some of the current controversies related to the operative management of patients with mitral valve disease. First, patients with atrial fibrillation have an increased risk of persistent or recurrent CHF after MVR, raising the question of whether the use of a concomitant maze procedure might modify this risk. Previous data have demonstrated that all-cause mortality after mitral valve surgery is lower for patients in sinus rhythm than for those in atrial fibrillation3 and that, as expected, freedom from atrial fibrillation after MVR is higher in patients who concomitantly undergo a maze procedure.4,5 Our data support the premise that the maze procedure may be beneficial with respect to CHF outcomes and all-cause mortality after MVR, and may provide the basis for a randomized, controlled trial that would examine the impact of this procedure not only on electrophysiologic, anticoagulation, and stroke outcomes but also on CHF end points and functional capacity after MVR and mitral valve repair.
Another finding of relevance in this study is that persistent tricuspid insufficiency at follow-up was independently associated with an increased risk of CHF and all-cause death after MVR, regardless of the severity of symptoms preoperatively. Although this significant finding was not robust on bootstrap resampling simulations because of the relatively small number of linked events, it nevertheless suggests that the commonly held view stipulating that the performance of tricuspid valve repair in patients after MVR is dictated by the presence of congestive symptoms may be unfounded, and that an aggressive approach toward repair of tricuspid insufficiency in patients after MVR might positively impact on freedom from CHF late postoperatively. In this regard, other investigators have also suggested that even asymptomatic, functional tricuspid insufficiency may warrant tricuspid valve repair, because tricuspid insufficiency may not improve and even worsen with time, especially in the presence of atrial fibrillation.6
Other aspects of patient management were also identified as potential CHF risk modifiers in this study. For example, it is possible that newer trends in the management of patients with mitral valve disease, such as the referral of patients for valve surgery before symptom development, may have an independent positive impact on the freedom from CHF after MVR.
An important negative finding of this study was that mitral prosthesis size, within the usual range used for MVR in adults, did not correlate with functional outcome, freedom from CHF death, or overall survival after MVR. These findings are in contrast with recent work from our group that examined similar outcomes after AVR and that showed aortic prosthesis size had a significant independent effect on freedom from CHF.2 Yazdanbakhsh and colleagues7 indicated that a small valve area index is a risk for early mortality after MVR (with congestive failure being the main cause of death), but these authors, as those in the present study, found no impact of mitral prosthesis size on late mortality after MVR. In this regard, it is plausible that early outcomes of surgeries such as MVR may be particularly susceptible to selection bias, which can persist despite rigorous multivariate analysis.8
Smoking was another potentially modifiable risk factor for CHF after MVR that was identified in this study. Although smoking and its associated impairments in functional capacity may have resulted in more pseudo-CHF symptoms reported from smokers than nonsmokers, a recent study from our group indicated that smoking is an independent risk factor for structural bioprosthesis degeneration, which may help explain the impact of smoking on CHF outcomes observed in the present study.9 Additional evidence pertaining to native valves previously suggested that cigarette-derived toxins play a biologic role on the structural integrity of valves through premature calcification.10,11
It is noteworthy that within the number of risk factors identified, a history of stroke may have been a risk factor for subsequent stroke12 or a marker of advanced cardiovascular disease and thus a potential positive confounder of poor functional status that could not be fully discriminated from advanced NYHA class symptoms during the follow-up period.
Finally, the results of this study also indicate that patients with pure mitral stenosis who undergo MVR have a significantly better long-term functional outcome than those with mitral insufficiency or mixed disease and that MVR provides relatively good functional results in patients for whom mitral commissurotomy is not feasible. This issue may warrant further research to determine whether MVR is better than a suboptimal mitral valve repair in a patient with advanced mitral stenosis whose valve is poorly amenable to commissurotomy.
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Limitations |
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Patients lost to follow-up may have had important subsequent outcomes that were not accounted for in the analyses, and the mean follow-up of the study, although extending to 19.9 years, was only 4.8 years. Inferences therefore apply mostly to intermediate-term outcomes.
Some entries were incomplete in the database. Although no data were imputed and the sample size of each analysis was floated with respect to the number of complete entries, this approach may have prevented the demonstration of some associations by increasing type II statistical error, because some potential predictors were evaluated with subtotal samples.
Other than for a general consensus to preserve the subvalvular mitral apparatus in patients of the cohort who underwent operation after 1990, specific details pertaining to the preservation technique used in each patient were not available from the database. Their impact on CHF outcomes could therefore not be examined in this study.
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Conclusions |
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Acknowledgments |
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References |
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