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Ann Thorac Surg 2005;79:462-470
© 2005 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio
b Department of Biostatistics and Epidemiology, The Cleveland Clinic Foundation, Cleveland, Ohio
Accepted for publication July 14, 2004.
* Address reprint requests to Dr Gillinov, Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, 9500 Euclid Ave, Desk F25, Cleveland, OH 44195 (E-mail: gillinom{at}ccf.org).
Presented at the Fortieth Annual Meeting of The Society of Thoracic Surgeons, San Antonio, TX, Jan 26–28, 2004.
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Abstract |
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 Top Abstract IntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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METHODS: From 1980 to 2000, 467 patients with moderate ischemic mitral regurgitation underwent CABG alone. The course of unrepaired mitral regurgitation was estimated by a longitudinal analysis of 267 follow-up echocardiograms from 156 patients. The survival impact of moderate ischemic mitral regurgitation was determined among propensity-matched patients with and without ischemic mitral regurgitation.
RESULTS: Mitral regurgitation was dynamic early postoperatively. Immediately postoperatively, it was absent or mild in 73% and severe in 6%; by 6 weeks, these figures were 40% and 22%, respectively. The course of postoperative mitral regurgitation was not associated with the preoperative extent of coronary artery disease or left ventricular dysfunction. Five-year survival of matched bypass patients without ischemic mitral regurgitation was 85% compared with 73% for patients with moderate ischemic mitral regurgitation (p = 0.003).
CONCLUSIONS: Moderate ischemic mitral regurgitation does not reliably resolve with CABG surgery alone and is associated with reduced survival. Therefore, a mitral valve procedure may be warranted for such patients presenting for CABG. A randomized trial comparing strategies of revascularization with mitral valve repair and revascularization alone is required to determine optimal treatment.
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Introduction |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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| Dr McCarthy discloses that he has a financial relationship with Edwards Lifesciences.
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There is general agreement that patients with severe (3+ or 4+) ischemic mitral regurgitation (IMR) should undergo mitral valve surgery at the time of coronary artery bypass grafting (CABG) [1, 2]. However, the importance of moderate (2+) IMR in such patients is controversial [3–5]. Clinical studies conflict regarding the time course of mitral regurgitation (MR) after CABG alone [4–9]. Objectives of this study were to track the course of unrepaired moderate IMR after CABG alone, identify factors associated with worsening postoperative IMR, and assess the impact of unrepaired moderate IMR on survival.
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Patients and Methods |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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The group included 316 men (68%), and mean age was 66 ±10 years (range 32 to 89). Cardiac and noncardiac comorbidities are summarized in Table 1. Some degree of left ventricular dysfunction was observed in 77% of patients, and three-vessel coronary artery disease was present in 77%.
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Ischemic Mitral Regurgitation
DEFINITION
IMR was defined as mitral valve regurgitation caused by coronary artery disease [1]. All IMR patients had a previous myocardial infarction 30 days or more before hospital admission for CABG and exhibited functional IMR. Patients with papillary muscle infarction causing papillary muscle rupture or elongation were excluded, as were those with angiographic or echocardiographic findings that demonstrated rheumatic, infectious, or degenerative (myxomatous) mitral disease.
PREOPERATIVE MITRAL REGURGITATION GRADING
The severity of IMR was assessed by preoperative contrast left ventriculography alone in 30% of patients, transthoracic echocardiography (TTE) alone in 20%, and both in 51%. By ventriculography, the estimation of the MR grade was based on the volume of regurgitant contrast material entering the left atrium during systole (none = 0, mild = 1+, moderate = 2+, moderately severe = 3+, severe = 4+). By TTE, estimation of the MR grade was based on the size and geometry of the regurgitant jet (0 = none, 1+ = mild, 2+ = moderate, 3+ = moderately severe, 4+ = severe) [10]. The highest grade of MR observed preoperatively was used to classify patients.
POSTOPERATIVE IMR
To characterize patterns of postoperative IMR over time, data recorded for 267 follow-up TTE reports from 156 patients (33% of the total group) were extracted from The Cleveland Clinic Foundation's echocardiogram database or abstracted from reports solicited from patients' cardiologists. The decision to obtain follow-up echocardiograms was made by patients' referring cardiologists; there was no systematic schedule. Median time to post-CABG TTE was 2 months (range 1 day to 14 years). Although sporadic, these data were sufficient to determine the course of MR over time. Patients who had postoperative echocardiograms were similar to those who did not, including similar degree of left ventricular dysfunction and extent of coronary artery disease, indicating that they were representative of the entire group (Appendix Table 1).
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COURSE OF POSTOPERATIVE IMR AND ITS PREDICTORS
The course of postoperative IMR was analyzed using repeated measurements of MR grade and longitudinal mixed-modeling techniques for ordinal data [11, 12], as previously described [13] (See Appendix 1).
COMPARATIVE SURVIVAL
To assess the effect of unrepaired moderate IMR on survival, a cohort of 2097 patients known to be without IMR (no-IMR group) undergoing CABG from 1997 to 2000 were used to propensity match moderate IMR patients operated on in the same time frame. This generated 210 matched pairs for comparison of survival (Appendix Table 2).
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Presentation
Mortality and survival estimates are accompanied by asymmetric 68% confidence limits (CL), comparable to ± 1 standard error.
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Results |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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Comment |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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We sought to address these limitations by selecting a relatively homogeneous group of patients with moderate IMR identified by using currently accepted definitions [1, 2], by clarifying the clinical course of IMR after CABG, and by comparing survival of these patients with that of a propensity-matched group of patients without IMR undergoing CABG.
Key findings are that (1) IMR of moderate (2+) or greater severity is present in 60% of patients by postoperative week 6 after CABG alone, (2) return of IMR is not predicted by cardiac function or extent of coronary artery disease, and (3) early survival of patients with unrepaired moderate IMR is reduced compared with similar patients without IMR.
Course of IMR after CABG
Our findings parallel those of Aklog and colleagues, who observed that treating moderate IMR by CABG alone left 40% of patients with moderate or severe residual IMR at 6 weeks [4]. In another study of patients with moderate IMR undergoing CABG, Ryden and colleagues reported that 37% had moderate or severe IMR at follow-up [6]. The latter data were gathered from only 40 patients in a nonsystematic fashion over a 3-year span. Although these studies and our own demonstrate that IMR persists in a substantial percentage of patients after CABG alone, Tolis and colleagues found that CABG resulted in a reduced MR grade in patients with ischemic cardiomyopathy and mild-to-moderate IMR [7]. The reduction in MR grade was accompanied by improved left ventricular function, suggesting that revascularization of ischemic or hibernating myocardium may contribute to improved mitral valve function.
Risk Factors for Postoperative IMR Severity
Recognizing that MR grade decreases in some patients after CABG alone, we sought to identify factors that were associated with the severity of postoperative MR. We had anticipated that more extensive ischemic disease and a greater degree of left ventricular dysfunction might be associated with the more rapid return of IMR and with increased severity; they were not. Instead, we found that smaller patients, women, and patients with single internal thoracic artery grafting were more likely to experience the return of IMR, findings that seem unrelated to the known pathophysiology of regurgitation. Because echocardiographic data are opportunistic, these may represent a greater clinical sensitivity of smaller patients and women to MR, with corresponding over-representation of echocardiograms.
Impact of Preoperative Moderate IMR on Survival
One of our key findings is that patients with unrepaired moderate IMR undergoing CABG have a greater early postoperative risk of death than otherwise similar patients undergoing the same procedure. This higher early hazard separates the survival curves almost immediately after CABG, and this difference persists until the late hazard phase. Patients undergoing CABG with and without IMR were well matched, as demonstrated in Appendix Table 2. This analysis confirms the presence of moderate IMR as an independent risk factor for early mortality after CABG.
IMR is associated with reduced survival in other settings as well. In a study that used quantitative echocardiography in nonsurgical patients, Grigioni and colleagues demonstrated that IMR was associated with excess mortality independent of the degree of left ventricular dysfunction [14]. Mortality risk was directly related to the degree of IMR; those with more severe MR had the greatest reduction in survival. Trichon and colleagues examined large cohorts of patients with ischemic and nonischemic cardiomyopathies and also demonstrated a graded effect of MR on survival [15]. Recently, Ellis and colleagues noted similar decreased survival in patients with IMR early after percutaneous coronary intervention [16]. This effect was particularly pronounced in patients with an ejection fraction of less than 40%.
Similarly, studies of large numbers of patients have demonstrated that IMR is associated with reduced survival after CABG [6, 17, 18]. However, patients with IMR who present for CABG tend to be older and more gravely ill, with reduced left ventricular function and greater comorbidity [6, 17, 18]. This raises the question, is IMR simply a marker of high-risk patients or is it a true risk factor for mortality? Paparella and colleagues suggested that it is a marker rather than an independent predictor of long-term mortality. However, using statistical methodology that enabled us to study the different hazard phases for mortality, we identified moderate IMR as an independent risk factor in the early hazard phase, which extends to about 9 months after CABG.
Limitations and Future Directions
COURSE OF IMR AFTER CABG
There are little published data documenting the course of IMR after CABG alone; the data reported here represent the largest series and the longest echocardiographic follow-up. However, an important limitation is nonsystematic echocardiographic follow-up with imaging studies obtained sporadically at the discretion of treating cardiologists. Nevertheless, we gathered sufficient data to chart the course of IMR and to create a model for identifying predictors of postoperative IMR severity. Patients who had postoperative echocardiograms were similar to those who did not have such studies, suggesting that they may be representative of the entire group. It must be acknowledged that some of these echocardiograms may have been "clinically driven" by patient symptoms (heart failure) or physical examination (murmur); this would tend to cause over-representation of patients with more severe MR. A systematic study with echocardiograms performed in all patients at predetermined intervals would clarify this issue.
IMPACT OF PREOPERATIVE MODERATE IMR ON SURVIVAL
This study was not designed to answer the question, "Does repair of moderate IMR confer a survival benefit?" Although compelling data from multiple studies demonstrate that IMR is an independent risk factor for mortality, the impact of mitral valve repair on the survival of patients undergoing CABG has not been defined. During the period of this study, our general policy was not to repair the mitral valve in the setting of moderate MR; therefore, we had an insufficient number of patients to assess the impact of repair in such patients.
Although the current study was not randomized, propensity matching in the survival analysis helped adjust for important differences between patient groups. Because measured left ventricular function is affected by the presence of MR, it is possible that patients were not perfectly matched for the extent of left ventricular dysfunction, and other, unrecorded variables may have influenced the results.
Summary
For patients with moderate IMR undergoing CABG alone, early postoperative improvements in MR did not persist; recurrent MR was observed in 60% within 6 weeks of operation and was not associated with either the preoperative extent of ischemic disease or left ventricular dysfunction. Moderate IMR patients experienced decreased survival compared with similar patients with no IMR, largely because of an early (6 to 9 months) high risk of death, which coincided with the period of rapid change in MR.
Clinical Inferences
A randomized prospective trial is necessary to clarify the role of mitral valve repair in patients with moderate IMR undergoing CABG. Our data suggest that moderate IMR usually does not resolve with isolated revascularization and jeopardizes survival. Therefore, until such a trial is performed, we suggest a low threshold for mitral valve repair in such patients.
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Appendix 1 |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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For risk analysis (see Appendix 2 for variables analyzed), grades 3+ and 4+ MR were collapsed into a single ordinal category because of the low frequency of grade 4+ and to meet proportional odds assumptions. Variable selection used backwards elimination such that the final models contained variables with p of 0.1 or less.
COMPARATIVE SURVIVAL AND PROPENSITY MATCHING.
Because of expected differences between the IMR and no-IMR groups (Appendix Table 2), a fair comparison of survival required taking these differences into account. We did this using propensity score adjustment and matching [19, 20]. First, using known preoperative variables and multivariable logistic regression, we established a model that contained factors associated with IMR compared with no-IMR, irrespective of the level of significance. The c statistic was 0.76. A propensity score was then calculated for each patient by solving the logistic equation and was used in the multivariable survival analysis for risk adjustment. In addition, it was used to match IMR patients with no-IMR patients, yielding 210 well-matched patient pairs for survival comparison.
Survival estimates were obtained using the Kaplan-Meier nonparametric method. A parametric model was also used to resolve a number of phases of instantaneous risk of death (hazard function) and to estimate shaping variables [12]. Survival was compared between propensity-matched pairs by using the log-rank test.
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Appendix 2 |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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Symptoms: New York Heart Association functional class (I–IV), emergency operation.
Ventricular dysfunction: Previous myocardial infarction, degree of left ventricular dysfunction (1 = none, 2 = mild, 3 = moderate, 4 = severe).
Coronary anatomy: Left main trunk disease (% stenosis), left anterior descending coronary artery system disease (maximum % stenosis), right coronary artery system disease (maximum % stenosis), left circumflex coronary artery system disease (maximum % stenosis).
Other cardiac comorbidity: Family history of ischemic heart disease, hypertension.
Noncardiac comorbidity: diabetes mellitus (insulin-treated, noninsulin-treated, and treated), history of peripheral vascular disease, history of smoking, carotid disease, chronic obstructive pulmonary disease, renal disease, creatinine (mg/dL), blood urea nitrogen (mg/dL), bilirubin (mg/dL), hematocrit (%).
Experience: Date of operation (years since 1/1/1980)
INTRAOPERATIVE
Procedure: Internal thoracic artery graft used.
Support: Aortic clamp time (minutes), cardiopulmonary bypass time (minutes).
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DISCUSSION |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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Most would agree that 3 to 4+ ischemic MR is associated with worse long-term prognosis and is best treated with a concomitant mitral valve procedure. This paper addresses the vexing problem on what to do with the patient with coronary artery disease and only 2+ ischemic MR. This provocative paper provides the type of sophisticated outcome analysis that few institutions outside The Cleveland Clinic and Dr Blackstone can achieve. I congratulate them on their ability to get the most useful information and inferences as possible from a retrospective data analysis. I have five questions.
The first. Though you demonstrate that there is a decreased early survival in patients with 2+ ischemic MR and coronary artery disease compared with a propensity-matched control group with coronary artery disease alone, 40% of your patients showed a significant decline in mitral insufficiency, to 0 or 1+. What was the survival in these 40% of patients where the MR actually improved?
Secondly, one could hypothesize that 2+ ischemic MR is only a marker for a sicker ventricle or a sicker patient. Its elimination would not affect survival. Do you have survival data on patients with 2+ ischemic MR that were surgically repaired and their MR thus eliminated, and if not, would a randomized study be indicated?
Thirdly, one limitation of this study was that echoes were done in only approximately one-third of your 467 patients and without set criteria. Do you think that this might overestimate the true incidence of recurrent MR, since presumably patients with symptoms would be more likely to get echoes than asymptomatic patients?
The fourth question. Given the fact that 40% of the patients had significant improvement in their degree of MR, do you think that replacing a ring in all patients with 2+ MR is justified?
And finally, you surprisingly found no correlation between recurrent MR and coronary artery bypass alone and degree of ischemic burden or LV dysfunction. How do you propose then we decide on who to repair and who not?
Again, I want to thank Dr. Lam and his colleagues from The Cleveland Clinic for this very important presentation and paper.
DR ROBERT GUYTON (Atlanta, GA): I enjoyed the presentation. I do have great difficulty with the inclusion of some of your patients. In particular, 60% of your patients were functional class III or IV. Normally, in most institutions, patients who have functional class III or IV symptoms would undergo mitral repair or even replacement. Why did you not focus primarily on patients who were functional class I or II? These are the real patients that we are concerned about. In other words, it is the patients with incidental MR that we have the problem with. It is not the patients that come to the OR in congestive failure. I think everybody would agree today that people that are functional class III or IV should have a mitral operation. By inclusion of 60% of patients with that symptom complex in your series, your conclusions are difficult to apply to the treatment of mildly symptomatic MR at the time of CABG.
Secondly, the fact that only one-third of your patients had postoperative echoes and only two-thirds of those had two echoes makes it very difficult to really generalize your findings. You have generalized it to all patients with 2+ MR having coronary bypass alone. If the patients who come back for postop echoes are seen primarily because of clinical indications, then it is a real problem for me to say you can generalize results in that subgroup to all patients.
And finally, I must say that there may be difficulty with the propensity matching in this case. I presume that ejection fraction was utilized as one of your criteria for propensity matching. You cannot say that a patient with 2+ MR and a 40% ejection fraction is the same as a patient with no MR and a 40% ejection fraction. The patient with MR is likely to have a considerably worse ventricle, even though the ejection fraction is the same, because of the unloading with the MR.
DR HORMOZ AZAR (Norfolk, VA): First of all I would like to echo Dr. Guyton's comments, and congratulate the authors on a very nice study. My question relates to initial increase mortality but subsequent parallel course of the curves, without showing progressive decline in survival of patients with mitral regurgitation. Do you have any comments related to this observation? Thank you.
DR DAVID SABORIO (Brooklyn, NY): This was a very interesting paper that deals with an important clinical issue. I would like to have seen a comparison in the survival curves of the patients with coronary artery disease and moderate mitral insufficiency who had CABG only with those Cleveland Clinic patients who had CABG with mitral valve procedures. I think this is one of the reasons most surgeons would be a little reluctant to perform a mitral valve operation along with CABG in a patient who has only 2+ MR, because it is well known that CABG/mitral valve replacement or repair has a higher incidence of mortality and complications compared with CABG alone.
DR LAM: First of all, I would like to thank Dr Acker and Dr Guyton for their very insightful comments and for their questions.
To start off, we did not look specifically at the 40% or so of patients that had an improvement in their mitral regurgitation postoperatively, but that is definitely an issue that needs to be addressed in order to maybe decipher what possible predictors may differentiate this population from the ones that did not have an improvement in their MR.
Second of all, to address the question of the echo sampling, yes, only about 156 of our patients had postoperative echocardiograms. We did perform an intergroup comparison between those who did have an echo and those who did not have an echo, and we did not come up with any significant predictors in terms of differentiating the two groups that might ultimately affect the return of the MR long-term.
As to the question regarding the predictors of worsening mitral regurgitation, well, we agree with you that we are very surprised as to those predictors showing up, and we are expecting to have more of the usual cardiac variables, such as age, extent of coronary disease and so on. It is an unpredictable group, and we haven't yet been able to exactly tease out what specific predictors can actually identify the group of patients that in whom the MR comes back.
With regards to the question of repairing 2+ mitral regurgitation, well, this data certainly has lowered the threshold at The Cleveland Clinic for some surgeons in terms of repairing a mitral valve in patients with 2+ MR when it is feasible.
To address the question by Dr Guyton with regards to the propensity matching, although it is a statistical method that tries to mimic a prospective randomized trial, it has its limitations in terms of what it can control and cannot control. Therefore, the variables that are answered in the analysis are the only variables that we have to work with. So there are ultimately variables or factors out there that we cannot control through the propensity match. So with regards to that, yes, I think that a randomized trial with this entity would likely answer a lot of these questions.
To answer the question from the first discussant with regards to mitral regurgitation and long-term survival, yes, the curves do parallel each other, and we have not been able to identify mitral regurgitation as an independent predictor of late survival.
And finally, with regards to repair versus nonrepair, this study is somewhat historic in that it spans 20 years, and I think the general consensus during that practice was that 2+ mitral regurgitation was really repaired. Therefore, I do not think that comparing the patients that we have repaired, on occasion 2+ on, with patients with 3 or 4+ mitral regurgitation who underwent repair is an adequate approach to the problem, not only because of the different grades of MR but also because of the very small number of patients that we would have in terms of 2+ MR who were repaired.
Thank you.
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References |
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TopAbstractIntroductionPatients and MethodsResultsCommentAppendix 1Appendix 2DISCUSSIONReferences |
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