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J Thorac Cardiovasc Surg 2008;135:885-893
© 2008 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease |
a Department of Thoracic and Cardiovascular Surgery, Cleveland Clinic, Cleveland, Ohio
b Department of Quantitative Health Sciences, Cleveland Clinic, Cleveland, Ohio
c Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, Ohio
Received for publication May 2, 2007; revisions received October 15, 2007; accepted for publication November 26, 2007. * Address for reprints: A. Marc Gillinov, MD, Department of Thoracic and Cardiovascular Surgery, Cleveland Clinic, 9500 Euclid Avenue/F24, Cleveland, OH 44195. (Email: gillinom{at}ccf.org).
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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Methods: From 1985 to 2005, 3286 patients underwent isolated primary operation for degenerative mitral valve disease. Valve repair was performed in 3051 patients (93%), and valve replacement was performed in 235 patients (7.2%). A propensity model and score developed for fair comparison of outcomes yielded 195 matched pairs.
Results: Patients undergoing replacement were older (70 ± 12 years vs 57 ± 13 years) and had more complex valvar pathology, symptoms, and left ventricular dysfunction. Thus, the characteristics of the propensity-matched patients undergoing repair more resembled those of the patients undergoing replacement (older, complex valvar pathology) than patients undergoing typical repair. Eight patients died in the hospital (0.26%) after repair and 5 patients (2.1%) died after replacement (P = .001). Unadjusted survival at 5, 10, and 15 years was 95%, 87%, and 68% after repair and 80%, 60%, and 44% after replacement, respectively (P < .0001); however, among propensity-matched patients, survival was similar (P = .8): 86% versus 83% at 5 years, 63% versus 62% at 10 years, and 43% versus 48% at 15 years. Freedom from reoperation among propensity-matched patients was 94% at 5 and 10 years after repair and 95% and 92% at 5 and 10 years after replacement, respectively (P = .6).
Conclusion: It is reasonable to perform valve repair in elderly patients with complex degenerative mitral valve pathology because it can eliminate the need for anticoagulation and risk of prosthesis-related complications. However, when valve pathology is so complex that repair is infeasible, this study demonstrates that valve replacement does not diminish long-term outcomes.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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The reported advantages of mitral valve repair over mitral valve replacement include preservation of left ventricular function; greater freedoms from endocarditis, thromboembolism, and anticoagulant-related hemorrhage; and, most important, improved survival.1-5
For these reasons, valve repair is preferred to valve replacement in patients with degenerative mitral valve disease.6 However, there are few data available to clarify the relative effects of patient factors and choice of valve procedure (repair vs replacement) on outcome after surgery for mitral regurgitation (MR) caused by degenerative disease. Selected patients with rheumatic and ischemic MR seem to have equal, and in some cases better, survival with valve replacement as with valve repair, illustrating the importance of patient characteristics on outcome.7,8 In patients with degenerative MR, we sought to 1) identify characteristics differentiating those undergoing valve replacement from those undergoing valve repair, 2) use this information to compare, among matched patients, survival and reoperation after each procedure, and 3) contrast these outcomes with those of typical patients undergoing valve repair.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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Concomitant tricuspid valve repair for functional tricuspid regurgitation was performed in 171 patients (5.2%), and ablation of atrial fibrillation was performed in 153 patients (4.6%). Preoperative MR was graded by echocardiography using standard techniques; all patients had moderately severe (3+, 8.2%) or severe (4+, 92%) MR. Data were extracted from the Cardiovascular Information Registry, a repository of extensive clinical and surgical data entered concurrently with patient care. Use of these data for research was approved by the institutional review board, with patient consent waived.
Surgical Technique
Surgical approach was minimally invasive in 1726 patients, full sternotomy in 1552 patients, and right thoracotomy in 4 patients. The minimally invasive technique included a 6- to 8-cm skin incision and partial upper sternotomy.9 The most common repair techniques included posterior leaflet resection with (1244) or without (1466) sliding repair and chordal transfer (423). Anuloplasty techniques included Cosgrove-Edwards anuloplasty band (Edwards Lifesciences LLC, Irvine, Calif) (2254, 74%), Carpentier-Edwards classic ring (Edwards Lifesciences LLC) (411, 13%), and posterior bovine pericardial strip (296, 9.7%); 90 patients (2.9%) had leaflet repair without anuloplasty. Among 235 patients undergoing mitral valve replacement, prostheses were bioprosthetic in 179 (76%) and mechanical in 56 (24%). At mitral valve replacement, the posterior leaflet and its attached subvalvar apparatus were routinely preserved; the anterior leaflet generally was excised.
Follow-up
Patients were followed routinely at 2, 5, 10, 15, and 20 years. At each follow-up, patients were contacted by mailed institutional review board-approved questionnaire or telephone interview, with patient consent. Follow-up for mitral valve reoperation depended entirely on this active follow-up. Of the 3286 patients, 897 were not yet due for follow-up. Of the remaining 2389 patients, 303 (13%) were considered lost to follow-up (269 US and 29 foreign patients were untraced, and 5 patients did not consent to follow-up). The median active follow-up was 2.6 years, with 25% followed more than 5.6 years, 10% followed 
10 years, and 3% followed 12 years; 11,689 patient-years of data were available for analyses of reoperation. Information on vital status was supplemented by data from the Social Security Death Index10,11 (cross-sectional passive follow-up), yielding a total of 18,244 patient-years of data for analysis. Passive follow-up averaged 5.6 ± 4.4 years, with 15% of living patients followed 10 years and 5% followed 14 years. Graphs of reoperation were truncated at 12 years, and graphs of survival were truncated at 14 years.
Data Analysis
Factors Associated With Mitral Valve Replacement Versus Repair
Multivariable logistic regression was performed to identify factors associated with mitral valve replacement versus repair. Variables considered are listed in Appendix 1. Bagging was the method for variable selection, with automated analysis of 500 resampled data sets, followed by tabulating the frequency of occurrence at P 
.05 of both single factors and closely related clusters of factors.10,11 Factors with occurrence of 50% or more were retained in the model.
Time-related Events
Nonparametric time-to-event estimates were obtained by the Kaplan–Meier method. For mortality, a parametric method was used to resolve the number of phases of instantaneous risk (hazard function) and estimate shaping parameters.12 (For additional details, see http://www.clevelandclinic.org/heartcenter/hazard.) Thereafter, multivariable analyses were performed in the hazard function domain. Variable selection used bagging, as described earlier.
Outcomes in Propensity-matched Pairs
Because the characteristics of patients receiving mitral valve replacement rather than repair were different (
Table 1), propensity score methods were used to reduce selection bias in comparing outcomes.13,14 First, logistic regression analysis was used to identify risk factors for valve replacement rather than repair, using bagging as described earlier in the text. Second, this parsimonious model was amplified by nonstatistically significant variables representing every class of variable available, 28 in all. Third, by using the resulting propensity model, a propensity score representing the probability of having a replacement was estimated for each patient (Figure E1). Fourth, on the basis of the propensity scores, 195 matched pairs were identified.15 Finally, time-related outcomes were compared between matched patients receiving repair and patients receiving replacement.
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Accounting for Attempted Repairs
The influence of attempted valve repair, converted to replacement in the same operation, was assessed in 2 ways. First, among propensity-matched pairs, the variable "attempted repair" (crossover from repair to replacement in same operative session) was added to the multivariable survival model used to compare valve repair versus replacement. Second, matched patients were compared as strictly intent-to-treat.
Presentation
Mortality, survival, and freedom from reoperation estimates are accompanied by asymmetric 68% confidence limits equivalent to ± 1 standard error. Categoric data are summarized by frequencies and percentages, and continuous variables are summarized by means ± 1 standard deviation.
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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Figure 1, A). Patients undergoing replacement were older (70 ± 12 years vs 57 ± 13 years, Figure 1, B) and had more advanced symptoms, with 29% showing New York Heart Association functional class III or IV versus 14% of patients undergoing repair (Table 1). Advanced age, mitral valve calcification, anterior or bileaflet prolapse, operation earlier in the experience, and surgeon identity were associated with an increased probability of replacement rather than repair (
Table 2). These characteristics of patients undergoing valve replacement were not typical of most patients presenting for management of degenerative mitral valve disease, as illustrated by the more favorable profile of unmatched patients undergoing repair (
Table 3).
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Figure 3). This finding was corroborated by propensity-adjusted multivariable analysis (Table E1). Among these propensity-matched groups, survival was similar to that of the age and sex-matched US population after a period of higher risk early after operation in both groups.
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Figure 4); these represent typical patients undergoing repair (Table 3): young with no or mild symptoms, generally in sinus rhythm, and having isolated posterior leaflet prolapse without valve calcification. Survival was lowest in unmatched patients undergoing replacement, who were older (75 ± 8.1 years), were more symptomatic, were more likely to be in atrial fibrillation and have noncardiac comorbidities, and rarely had isolated posterior mitral leaflet prolapse (7.5%), but rather anterior or bileaflet prolapse and mitral valve calcification. These comparisons were similar by multivariable analysis of attempted repair (P > .5, Table E1) and intent-to-treat analyses (P > .6).
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Figure 5).
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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Factors Associated With Mitral Valve Replacement versus Repair
The primary objective of this study was to determine the impact of mitral valve repair versus replacement on survival and reoperation in patients with degenerative disease. However, examination of the data revealed important differences between these patient groups. Patients undergoing valve replacement were more likely to have complex valvar pathology, including calcification and anterior or bileaflet prolapse; these factors increase the difficulty of valve repair. Although most replacements occurred in this group, our data also demonstrate that the majority of such valves are repairable, and previous studies document excellent long-term durability after repair.2,3,16,17 Patients with this complex valvar pathology represent a distinct subgroup of those presenting for surgical management of degenerative mitral valve disease; they are older and have more symptoms and comorbidities, including atrial fibrillation for which they are already receiving warfarin, and more likely to have left ventricular dysfunction, as previously shown by David and colleagues.3 It is only in these patients that we could compare outcomes after mitral valve repair and replacement. In particular, our data do not enable comparison of outcomes after valve repair versus replacement in the typical young patient in sinus rhythm with isolated posterior leaflet prolapse, few symptoms, and no comorbidity, because few patients with this profile undergo replacement at our institution.
The wide disparity of characteristics of patients undergoing repair and replacement, particularly in settings such as ours that are committed to repair, calls into question unadjusted comparisons of outcomes after surgery for degenerative mitral valve disease.2,4,18,19 For example, analyzing 1411 patients with mitral valve prolapse undergoing repair (83%) or replacement (17%), Suri and colleagues focused on the site of prolapse and claimed to demonstrate a survival benefit of repair over replacement in patients with isolated posterior or bileaflet prolapse.2 Patients in that study were older and more symptomatic than the typical patient undergoing valve repair, and many also had coronary artery disease. The presence of coronary artery disease introduces complex confounding of results, complicating analyses.20 Risk-adjusted comparison of repair and replacement in that setting indicated that repair usually (89%) conferred a survival advantage.21
Mitral Repair versus Replacement: Outcomes
Surgical correction of degenerative MR, whether by repair or replacement, was associated with long-term survival either better than (repair) or similar to (replacement) that of the general US population. Although unadjusted survival was better after repair than replacement, propensity-matched groups undergoing repair and replacement had similar survival and freedom from reoperation. This finding does not negate the generally accepted tenet that mitral valve repair is preferable to replacement in most patients with degenerative mitral valve disease and has excellent long-term durability.1-6 Rather, these data enhance our understanding of the roles of mitral valve repair and replacement in the subgroup of patients with complex valvar pathology. When a valve either appears unrepairable or attempts to repair fail, neither survival nor reoperation is adversely affected by replacement.
Limitations
This is a single-institution study of operations performed during a 20-year time span. However, repair techniques have remained nearly constant, and valve replacement has included chordal sparing since the late 1980s. This study addresses survival and, to a lesser extent, reoperation after surgery for degenerative mitral valve disease; we did not seek to examine effects of mitral procedure on other outcomes, such as freedom from prosthesis-related morbidity.
This is not a randomized trial. At this point in the history of mitral valve surgery, such a trial involving patients with typical degenerative disease is likely infeasible. Rather, the choice of surgical procedure and its conduct were surgeon-dependent; for this reason, surgeon identity was included in the analyses. This revealed that even in our institution some surgeons are somewhat more likely than others to elect valve replacement over valve repair.
The small number of valve replacements among typical younger patients with degenerative disease prohibited assessing the effect of repair versus replacement in that group. Therefore, comparative survival analyses may apply only to patients with complex valvar pathology, who tend to be older and have greater comorbidity.
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Conclusions |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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However, when valvar pathology is so severe that repair is infeasible, valve replacement does not diminish long-term survival. |
Appendix 1 |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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Demography
Age (y), sex, height (cm), weight (kg), body surface area (m2), body mass index (kg/m–2)
Preoperative Status
New York Heart Association functional class, Canadian angina class, emergency operation
Mitral Valve Pathology
Leaflet prolapse (posterior, anterior, bileaflet), valve fibrosis or thickening, valve calcification, elongated chordae (posterior, anterior), chordal rupture (posterior, anterior), elongated papillary muscle, dilatation of mitral anulus, dilated left ventricle, regurgitation grade (0 to 4+ scale), left atrial diameter, and volume
Left Ventricular Structure and Function
LV mass (g/m–2), LV inner diameter in diastole (cm), LV end-diastolic volume (mL), LV inner diameter in systole (cm), LV end-systolic volume (mL), posterior wall thickness (cm), intraventricular septal thickness (cm), LV relative wall thickness, LV dysfunction grade (0 = none, 1 = mild, 2 = moderate, 3 = severe), previous myocardial infarction, LV ejection fraction (%)
Other Cardiac Comorbidity
Atrial fibrillation, coronary artery stenosis (50%, any) (left main trunk, left anterior descending coronary artery, circumflex coronary artery, right coronary artery), number of coronary systems with > 50% stenosis, family history of coronary artery disease, ventricular arrhythmia, complete heart block, history of endocarditis, history of heart failure
Noncardiac Comorbidity
History of hypertension, treated diabetes (insulin treated/not insulin treated), stroke, smoking; peripheral arterial disease, chronic obstructive pulmonary disease, renal failure, blood urea nitrogen (mg/dL–1), creatinine (mg/dL–1), bilirubin (mg/dL–1), cholesterol (mg/dL–1) (total, high-density lipoprotein, low-density lipoprotein), triglycerides (mg/dL–1), hematocrit (%)
Details of Procedure
Surgical approach (minimally invasive), mitral valve repair details (posterior/anterior/bileaflet repair, leaflet resection, sliding leaflet repair, chordal resection, cleft repair, leaflet suture, leaflet debridement, type of anuloplasty ring), mitral valve replacement details (mechanical or bioprosthetic, propensity for replacement), tricuspid valve repair
Experience
Date of operation, surgeon
LV, Left ventricular.
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Figure E1 |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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Table E1 |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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LV, Left ventricular; MV, mitral valve; NYHA, New York Heart Association; SE, standard error. No reliable factors were found in constant hazard phase.
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Acknowledgments |
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Footnotes |
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Read at the Eighty-seventh Annual Meeting of The American Association for Thoracic Surgery, Washington, DC, May 5–9, 2007.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionConclusionsAppendix 1Figure E1Table E1References |
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