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J Thorac Cardiovasc Surg 2003;125:1350-1362
© 2003 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease |
From the Departments of Thoracic and Cardiovascular Surgerya and Biostatistics and Epidemiology,b The Cleveland Clinic Foundation, Cleveland, Ohio.
Received for publication May 10, 2002. Revisions requested July 18, 2002; revisions received Aug 21, 2002. Accepted for publication Aug 27, 2002. Address for reprints: Marc Gillinov, MD, The Cleveland Clinic Foundation, 9500 Euclid Ave/Desk F24, Cleveland, OH 44195 (E-mail: gillinom{at}ccf.org).
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Abstract |
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 Top Abstract IntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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1-4 Purported advantages of mitral valve repair over replacement include greater freedom from reoperation and endocarditis, better preservation of left ventricular function, and improved survival. 1-9 These advantages have been investigated when degenerative mitral valve disease exists in isolation. 1 However, particularly in aging populations with a limited life expectancy, it often coexists with ischemic heart disease. When a prolonged combined coronary artery and valve operation is contemplated, the appropriate valvular surgical strategy (mitral valve repair vs expeditious replacement) is unclear. Therefore we have compared long-term survival in patients with ischemic heart disease undergoing coronary artery bypass grafting (CABG) with either mitral valve repair or replacement for degenerative disease. Because selection of the valve repair or replacement procedure was not randomized, comparison required (1) identifying patient characteristics that were more likely to lead to repair than replacement at this center, (2) determining whether survival was better after repair or replacement once those characteristics were taken into account, and (3) discovering which patients were predicted to benefit from repair and which from replacement.
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Patients and methods |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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1,10 If microscopic pathologic examination revealed myxomatous degeneration, the valve was classified as degenerative (although we recognize that myxoid material might represent a final common pathway for possible diverse causes). When pathology reports were unavailable, valves were classified as degenerative if on echocardiography or inspection they had typical findings of leaflet prolapse caused by chordal elongation or rupture and thick floppy leaflets. Finally, those rare patients with annular dilatation and thick billowing leaflets but without frank leaflet prolapse were judged to have degenerative mitral valve disease.
Particular care was taken to exclude patients with ischemic mitral regurgitation. In the setting of ischemic heart disease, mitral valve regurgitation is caused by ischemic heart disease in about half of patients and coexists with it in the other half. 11 Ischemic mitral regurgitation is caused by papillary muscle infarction and elongation, papillary muscle rupture, or failure of leaflet coaptation caused by leaflet restriction after myocardial infarction. 12 Patients in the latter group, who have functional ischemic mitral regurgitation, are distinguished from patients with degenerative disease by the presence of leaflet restriction after myocardial infarction and lack of excess leaflet tissue.
Patient identification
By using these definitions, potential patients operated on from 1973 to 1999 were identified for this study by query of the Cardiovascular Information Registry. This registry contains detailed demographic, clinical, pathologic, operative, and outcome variables on all patients having cardiac surgery at The Cleveland Clinic Foundation abstracted from clinical records concurrently with patient care. Data from this registry has been approved for use in research by The Cleveland Clinic Foundation's Institutional Review Board. Because definitions of valve cause have evolved and because of the need to clearly separate degenerative disease from ischemic disease, search criteria were intentionally broad to cast a wide net that we believed would capture all instances of degenerative disease and CABG. Medical records of the 1500 patients so identified were reviewed to verify valve cause, and this netted 679 patients.
Among these 679 patients, the mitral valve was repaired in 447 and replaced in 232. All had at least 2+ (moderate) mitral regurgitation. Patients undergoing tricuspid valve repair were included, but those undergoing aortic valve or Maze procedures were not.
The mean age of patients undergoing mitral valve repair was 67 ± 9.1 years, which was similar to that of patients undergoing mitral valve replacement (67 ± 9.4 years, P = .4). Patient characteristics overall and according to whether repair or replacement was performed are given in Tables 1 and 2.
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Tricuspid valve repair was performed in 15 (3%) patients having mitral valve repair and 10 (4%) having mitral valve replacement.
Follow-up
Patients were followed systematically at 2-year intervals with a mailed questionnaire, a telephone interview, or examination at the Cleveland Clinic. Mean follow-up among survivors was 5.2 ± 3.6 years, with 25% followed for more than 6 years and 10% for more than 10 years; 3568 patient-years of information were available for analysis. Nonparametric survival estimates were considered reliable to 11 years. 13
Data analysis
Overview
The primary challenge in comparing long-term survival after CABG and either mitral valve repair or replacement is that selection of repair or replacement was not allocated on the basis of a randomized process. Thus data analysis first addressed the following question: "Were characteristics of patients undergoing mitral valve repair similar to those of patients undergoing replacement?" Lack of similarity necessitated use of methods specific for nonrandomized comparisons. We then asked, "Is long-term survival better after mitral valve repair than after replacement?" A simple comparison was not possible, and therefore both risk adjustment and adjustment for nonrandom treatment assignment were used. Finally, we asked, "Which patients benefit from which procedure?" Multivariable simulation was used to answer this question.
Were characteristics of patients undergoing mitral valve repair similar to those of patients undergoing replacement? Multivariable logistic regression analysis was used to identify factors associated with valve repair rather than replacement. In this analysis demographic characteristics, symptoms and clinical status, mitral valve pathology, cardiac comorbidity, noncardiac comorbidity, operative details, and experience were considered (Appendix Table 1).
The process of identifying these factors was similar in all multivariable analyses. Initial screening of variables was performed to ensure that at least 5 events were associated with each factor considered. Continuous and ordinal variables were examined by means of decile analysis to discover possible linearizing transformations of scale that best met model assumptions. Noninformative imputation of sporadic missing values was used.
Selection of risk factors used bootstrap bagging, with automated analysis of 1000 random data sets by using a P value of .05 or less as the criterion for retention of factors in each model. This was followed by tabulation of the frequency of occurrence at a P value of .05 or less of both single factors and closely related clusters of factors. 14,15 In the final model only factors occurring in at least 50% of the analyses were considered statistically significant for the parsimonious model.
This parsimonious model was amplified into a propensity model by adding factors from each class of variables not already represented (see Appendix Table 1 for these classes). 16,17 The propensity model was solved to generate a propensity score for each patient, representing the probability of undergoing repair. It was used in 3 ways in this study: (1) to stratify patients by quintiles to demonstrate differential survival between repair and replacement 17,18; (2) to form propensity-matched pairs by means of greedy matching for comparison 19; and (3) to adjust the multivariable time-related comparison for not only risk factors but also selection bias. 20,21 Results of all 3 types of propensity matching were similar, and only the results of method 3 are presented.
Is long-term survival better after mitral valve repair than after replacement? Overall nonparametric estimates of survival were obtained by using the Kaplan-Meier method. 22 A parametric method was used to resolve the number of phases of instantaneous risk of death (hazard function) and to estimate its shaping parameters. 23* Thereafter, multivariable analysis was performed in the hazard-function domain by using the strategies discussed above.
In all analyses we forced in the variable "mitral valve repair versus mitral valve replacement" and the propensity score to obtain an overall estimate of the benefit of repair versus that of replacement. This was followed by an intense investigation of factors interacting with type of operation to discover modulating factors.
Which patients benefit from which procedure? The overall multivariable survival equation was solved twice for each patient, once as though the patient's mitral valve had been replaced and once as though a repair had been performed (simulation). The difference between predicted survivals for these 2 strategies at 10 years was compared. A positive difference was interpreted as a repair benefit and a negative difference as a replacement benefit.
Multiple linear regression of the 10-year survival differences was performed by using the strategies discussed above. From this, an algorithm for predicting the strategy for mitral valve repair versus that for replacement was devised.
Presentation
Mortality and survival estimates are accompanied by an asymmetric 68% confidence interval, which is comparable to ±1 SE. Throughout, model coefficients are given with their SEs rather than either odds ratios (logistic) or hazard ratios (time-related analyses). This is because hazard ratios lose simple meaning in the setting of transformations of scale of continuous variables to obtain appropriate calibration and a time-related events model that is one of nonproportional hazards.
Both logistic regression and hazard-function models were solved for specific sets of values for variables to illustrate the results in a risk-adjusted fashion.
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Results |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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and 2). Factors associated multivariably with a greater likelihood of repair included isolated posterior chordal rupture, more recent date of operation, and younger age. Factors associated multivariably with replacement were bileaflet prolapse and previous cardiac surgery (Table 5). There was a striking increase in the prevalence of mitral valve repair in more recent experience (Figure 1, A). Increasing prevalence of repair in recent years corresponds to the era during which ITA grafting became increasingly routine (Figure 1, B); this explains the higher ITA use among patients undergoing repair (Table 4). Figure 2 shows the relationship of age and probability of repair in patients with and without isolated posterior chordal rupture.
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Non-risk-adjusted survival comparison: early mortality
Thirty (4.4%; confidence limit [CL], 3.6%-5.4%) patients died in the hospital: 16 (3.6%; CL, 2.7%-4.7%) after mitral valve repair and 14 (6.0%; CL, 4.4%-8.1%) after mitral valve replacement (P = .14). Thirty-day mortality was 3.1% after mitral valve repair and 5.6% after replacement (P = .12), and operative mortality (hospital mortality and patients dying within 30 days) was 4.0% and 6.5% (P = .16), respectively.
Non-risk-adjusted survival comparison: time-related survival
For the entire group, unadjusted survival was 76% at 5 years and 46% at 10 years. For the repair group, survival was 79% and 59% at 5 and 10 years, and for the replacement group, it was 70% and 37%, respectively (Figure 3, A). The unadjusted survival curves diverged at about 4 years because of earlier divergence (less than 2 years) of the late rising phase of the hazard (Figure 3, B), with patients undergoing mitral valve replacement having a marked increase in mortality risk compared with those undergoing repair.
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) indicated that 89% of patients would have better 10-year survival after repair compared with after replacement of the mitral valve (Figure 4). Linear regression produced a clinical algorithm useful for suggesting whether repair or replacement should be used in a patient (Appendix 2). For example, Figure 5, A, shows predicted time-related survival in a 70-year-old patient coming to operation in New York Heart Association (NYHA) class II, with no other cardiac or noncardiac risk factors. Such a profile is typical of patients referred in the current era. Predicted survival after mitral valve repair and replacement diverges at about 4 years, with better survival after repair. In contrast, Figure 5, B, shows predicted survival in a 70-year-old diabetic patient in NYHA class IV with severe left ventricular dysfunction from previous myocardial infarcts. Survival is limited after a mitral valve operation and concomitant CABG, with no advantage of either strategy for managing the mitral valve.
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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Implications of differences among patients undergoing mitral valve repair versus replacement
Patients who underwent mitral valve repair differed in important respects from many patients who underwent replacement. As a group, elderly patients have more advanced degenerative disease with more prolapse than do younger patients with isolated mitral valve degeneration. 1 In the analysis of mitral valve repair versus replacement, we approached the potential confounding of outcome from these differences by using propensity score adjustment. 16-18
In our institution patients with complex mitral valve pathology, such as bileaflet prolapse, were more likely to have their valves replaced. Other investigators have noted a similar experience. 5,6,8,9 Although repair of anterior or bileaflet prolapse is challenging, multiple surgical techniques can provide reliable and durable results. 1-4 With current surgical techniques, most patients with anterior leaflet prolapse can be offered durable valve repair. 1,10
Mitral valve repair versus replacement
In elderly patients with ischemic heart disease, surgeons might be tempted to replace rather than repair the mitral valve, presuming that the choice of procedure will have little or no effect on survival. In addition, valve replacement is easily and reliably completed, generally requiring less time than repair.
We documented several risk factors for early and late death after surgical treatment of degenerative mitral valve and ischemic heart diseases. These included general factors, such as older age, advanced NYHA functional class, severe left ventricular dysfunction, preoperative atrial fibrillation, and renal dysfunction. Mitral valve replacement emerged as a risk factor for late death after adjustment for these factors and the propensity score.
It is generally accepted that mitral valve repair rather than replacement confers a survival advantage. Although Akins and colleagues 7 and Enriquez-Sarano and associates 9 found that repair was associated with reduced hospital mortality, we and others 5,24 did not. Sand and coworkers 5 found that mitral valve replacement might be a risk factor for late death. In a study limited to patients with degenerative disease, Lee and colleagues 6 concluded that surgical procedure (mitral valve repair, replacement with subvalvular preservation, or replacement without subvalvular preservation) did not affect 6-year survival.
The previously mentioned studies suffer from small numbers of patients 5,6 and populations that include multiple causes for mitral valve dysfunction. 5,7-9 It is particularly important to distinguish patients with ischemic mitral regurgitation from those with concomitant degenerative mitral valve and ischemic heart diseases. Patients with ischemic mitral regurgitation have a poor prognosis. 12
Which patients benefit from repair?
Eighty-nine percent of patients with degenerative mitral valve and ischemic heart diseases were projected to derive a survival benefit from mitral valve repair versus replacement. Even in elderly patients with ischemic heart disease, repair is desirable. However, patients in NYHA class IV with extreme left ventricular dysfunction have poor survival, regardless of mitral valve procedure, and present a contemporary surgical challenge.
Limitations
This was a nonrandomized clinical study. By using the propensity score, we attempted to adjust the multivariable analyses of outcomes for nonrandom selection bias related to the choice of valvular procedure.
The end point of this study was death. 25 We did not analyze other valve-related complications, all of which have been thoroughly documented in the literature on mitral valve repair and replacement. For similar reasons, we did not examine valve durability or reoperation. 1,10,26
We were unable to determine from review of the operative reports which patients with mitral valve replacement had preservation of all or part of the subvalvular apparatus. Thus we could not analyze the effect of this surgical technique directly. However, because the procedure became standard practice at the Clinic in 1988, we analyzed the interaction between the date of operation and valve replacement as a surrogate and did not identify a statistically significant relationship.
Clinical inferences and decision making
Choice of surgical procedure affects late survival in patients with degenerative mitral valve disease coexisting with ischemic heart disease. Most patients benefit from mitral valve repair.
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Appendix 1 |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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Age (years)
Body size: height (centimeters), weight (kilograms), body mass index, body surface area (square meters)
Sex
Symptoms and clinical status
NYHA class, emergency surgery
Mitral valve pathology
Prolapse of the anterior leaflet, prolapse of the posterior leaflet, elongated chordae to the anterior leaflet, elongated chordae to the posterior leaflet, rupture of the anterior chordae, rupture of the posterior chordae, dilated annulus, leaflet retraction
Cardiac comorbidity
Previous cardiac surgery, family history of coronary artery disease, preoperative atrial fibrillation, left ventricular dysfunction (graded as none, mild, moderate, or severe), history of myocardial infarction, coronary artery disease (maximum stenosis in left main trunk, left anterior descending, circumflex, and right coronary trunk systems), number of coronary systems with greater than 50% stenosis (0-3)
Noncardiac comorbidity
Blood urea nitrogen, creatinine, renal disease, cholesterol, bilirubin, treated diabetes, smoking, hypertension, chronic obstructive pulmonary disease, peripheral vascular disease
Operative details
Mitral valve replacement versus repair
Mitral prosthesis: bioprosthesis, mechanical
Mitral repair: site of repair (annulus, posterior leaflet, anterior leaflet); use of annuloplasty (type of ring: Carpentier-Edwards, Cosgrove, Edwards; bovine pericardial annuloplasty); leaflet resection (partial or complete, sliding or not); chordal resection; chordal shortening or transfer
CABG: ITA grafting, single versus bilateral ITA grafting; number of grafts; complete revascularization
Experience
Date of operation expressed on a continuous scale as years from January 1, 1973.
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Appendix 2 |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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Appendix: Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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What is evident to me, however, is that your patients who had mitral valve replacement were operated on much earlier in your experience than those who had mitral valve repair. Actually, 62% of your patients who had mitral valve replacement were operated on before 1990, and 73 of those who had mitral valve repair were operated on after 1990. This alone suggests to me a change in approach at your institution, that the surgeons who are facing the problem decided to change the way they manage their problem. In addition, patients who had mitral valve replacement were much older, they are much more symptomatic, and they had worse ventricular function than patients who had mitral valve repair.
There was no mention in your presentation or your manuscript that I reviewed, thanks to you, as to whether the papillary muscles and chordae tendineae were preserved during mitral valve replacement. Years ago we published an article showing that mitral valve repair or replacement with the preservation of the chordae tendineae had similar 10-year survival if the patients had isolated mitral valve regurgitation caused by myxomatous disease.
I have a couple of questions for you, Dr Faber. Were the papillary muscles preserved in any of your patients, and if they were, was the result the same?
The second question is related to the ITA. We have shown over and over that revascularization of the internal descending artery with the left ITA enhances life span. Forty-five percent of your mitral valve repairs used the ITA, whereas this was the case in only 15% of the replacements. Could this difference alone account for most of the difference found in survival?
Finally, there must be a number of patients in whom, even after 1990, when your surgeons were more experienced in mitral valve repair, your surgeons attempted to repair the mitral valve, and then, after a while, 30 minutes or an hour, they abandoned the procedure and replaced the valve. Those patients, if they were lumped together with the elective mitral valve replacements, had a much worse prognosis than those who had mitral valve replacement to start with.
Dr Faber. Dr David, thank you very much for your kind comments, and those are very important issues that you pointed out. I would like to say that we did not have the information about the preservation of the subvalvular apparatus on the operative reports of the patients, so we could not say which ones we preserved and which ones we did not preserve. I know about the results of your article, and I agree with them, but we could not analyze that data, and that probably could be accounting for some of the differences that we saw.
Dr David. I am sorry to dwell on this issue. Did you take a look at temporal response of mitral valve replacement as well? In other words, of the patients who were operated on after 1990 and had mitral valve replacement, did those patients do better than those operated on in 1973?
Dr Faber. I do not know the answer for this. We did not look into that. The only thing we know is that after we gained more experience with repair, we started doing more and more of those, but we did not look specifically at the time frame of those. Therefore I could not answer this question for you.
About the ITA differences in survival, yes, I agree with that, and it has been shown that there is a difference in survival. Still, this, in the beginning of our experience, was based on the decision of the surgeon. Therefore I could not say why they used that. But I agree with your comments, and lately, that is what we use for the revascularization of the LAD.
What was your last question?
Dr David. The issue of attempting mitral valve repair. Because it is a long procedure because the patient also needs myocardial revascularization, after whatever each one of us allows ourselves for repair—30 minutes, 60 minutes—some of us then abandon the procedure and perform mitral valve replacement instead. Those patients are at a disadvantage because of the long operative procedure.
Dr Faber. Sure. Those patients we analyzed with intention to treat, which means that if they were in for repair and they had their valves replaced at the end, they would count as the repair patients in the repair group. That is the way we looked into that data.
Dr David H. Adams (New York, NY). I just had one comment about your data and that was that it looked like age was one of the predictors of valve replacement and anterior leaflet prolapse was one of the predictors of valve replacement, and, at least in your conclusion, it looks like if you have poor ventricular function, you might be more likely to go straight to valve replacement. Therefore given those 3 variables, I am sure all of us are interested to understand today in the Cleveland Clinic, particularly because Dr David pointed out that a lot of your patients are in the current era of valve repair, what percentage of patients with anterior leaflet prolapse actually undergo repair?
Second, is there an age cutoff for repair? At 80 years or 85 years do you go in and basically replace the valve?
Third, in patients who have depressed left ventricular function, are you today more likely to go straight to valve replacement?
Dr Faber. I have numbers here, but I am going to start with the last one. No, we tried to repair these valves. And especially in patients who have good left ventricular function, we are going to at least attempt to repair those valves. There is no age cutoff to choose between repair and replacement, and we tried to show that in our experience if a patient has good left ventricular function and is 70 years of age, for example, the mitral valve repair is going to be attempted, and we always try to do that.
Concerning how many patients had anterior mitral prolapse, 20% of the total patients had anterior leaflet only prolapse: with mitral valve replacement, it was 21%; with mitral valve repair, it was 19%. Twenty-three percent of the whole group had bileaflet prolapse, and of course, as I showed, those are the patients who are more prone to have their valves replaced in the beginning of our experience.
Dr Adams. And what about poor ventricular function? If a patient today comes to the operating room with an ejection fraction of 20%, are you trying to do repair or replacement or what?
Dr Faber. I particularly think that we still need to try to repair those valves if it is a simple repair, but we showed in our data that those are the patients who are not going to benefit from the repair. Therefore it is fair to say that if you replace those valves, you are going to be back there.
Dr O. Wayne Isom (New York, NY). I have a question, because if you look at some of the Cleveland Clinic brochures that we all get, by my calculations, this would be 26 years and 700 patients. That is about 27 patients a year. That is about one patient who needs a mitral valve repair or replacement and a coronary bypass every other week. What about the numbers in there, the later years or the earlier years? You have got to be doing more than one every other week.
Dr Faber. We extracted those 700 patients from a total of 1500 patients. That was the total number of patients we had in this period with just pure degenerative mitral valve disease. We came up with about 700 patients.
Dr Isom. How did you decide it was degenerative?
Dr Faber. We looked at echocardiography, we looked at pathology, and we looked at the operative note and the surgeon's description of the valve. Those were the 3 ways that we looked at that. And we tried to exclude them and come up with the cleanest data. Therefore we checked on the patients who had ischemic mitral regurgitation in our Cardiovascular Information Registry, and we excluded those patients and also patients with endocarditis and any other pathologies.
Dr Isom. Let me just ask a question. I have admired Dr Blackstone for years, but many times after I read the article I cannot tell whether he is for it or against it. Today, if a patient comes into the Cleveland Clinic with a 30% ejection fraction, fairly extensive triple-vessel disease, and needs 4 or 5 bypasses and has a ruptured chordae posteriorly but anterior leaflet prolapse is quite a bit, and therefore you are going to have to do something to that, what are you going to start out doing on the mitral valve? Are you going to repair it, or are you going to replace it or do it after you do the coronary bypasses before? How do you approach that?
Dr Faber. I think that is a very fair question. The way we look into that, it is based on our data. You would be okay if you just replace those valves because those are the subset of patients who did not do that well with the repair. But it depends on the experience of the surgeon. If you have more experienced surgeons, they are going to try to do a quick repair if they can, but if you just replace those valves, that would be a fair attitude.
Dr Endre Bodnar (Northwood, United Kingdom). I have a comment. I missed a lot of the ejection fractions of the 2 groups. Nowadays that is the first data one would look at before deciding for repair or replacement, and it is a great pity that in such a huge patient material this important information was missing. My question is that the frequency of repair over the years from the late 1970s to mid-1990s quadrupled. Now, why was that, because your patient material has changed so repair was a more likely procedure or because the surgeon's attitude has changed, in which case, are you justified to lump all these patients into one basket?
Dr Faber. Thank you for your question. I think that all surgical procedures and all surgeons go through a learning curve. As you do more and you get better results, you keep doing more, and those would account for this increase in our repair throughout the years, and that I think would be the biggest effect on this. I think once you pass through the learning curve, you are going to be more comfortable and you are going to be able to do better repairs on most degenerated valves than when you start your experience with that.
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Acknowledgments |
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Footnotes |
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*For additional details, see http://www.clevelandclinic.org/heartcenter/hazard.
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TopAbstractIntroductionPatients and methodsResultsDiscussionAppendix 1Appendix 2Appendix: DiscussionReferences |
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