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J Thorac Cardiovasc Surg 2001;122:1107-1124
© 2001 The American Association for Thoracic Surgery
Surgery for Acquired Cardiovascular Disease (ACD) |
From the Division of Cardiothoracic Surgery, Department of Surgery, Division of Biostatistics, New York University School of Medicine, New York, NY.
Supported in part by The Foundation for Research in Cardiac Surgery and Cardiovascular Biology.
Received for publication May 27, 1999. Revisions requested July 26, 1999; revisions received April 24, 2001. Accepted for publication April 25, 2001. Address for reprints: Eugene A. Grossi, MD, NYU Medical Center, Suite 9-V, 530 First Ave, New York, NY 10028 (E-mail: grossi{at}cv.med.nyu.edu).
Abstract
Objective: This study reviews the 223 consecutive mitral valve operations for ischemic mitral insufficiency performed at New York University Medical Center between January 1976 and January 1996. The results for mitral valve reconstruction are compared with those for prosthetic mitral valve replacement.
Methods: From January 1976 to January 1996, 223 patients with ischemic mitral insufficiency underwent mitral valve reconstruction (n = 152) or prosthetic mitral valve replacement (n = 71). Coronary artery bypass grafting was performed in 89% of cases of mitral reconstruction and 80% of cases of prosthetic replacement. In the group undergoing reconstruction, 77% had valvuloplasty with a ring annuloplasty and 23% had valvuloplasty with suture annuloplasty. In the group undergoing prosthetic replacement, 82% of patients received bioprostheses and 18% received mechanical prostheses.
Results: Follow-up was 93% complete (median 14.6 mo, range 0-219 mo). Thirty-day mortality was 10% for mitral reconstruction and 20% for prosthetic replacement. The short-term mortality was higher among patients in New York Heart Association functional class IV than among those in classes I to III (odds ratio 5.75, confidence interval 1.25-26.5) and was reduced among patients with angina relative to those without angina (odds ratio 0.26, confidence interval 0.05-1.2). The 30-day death or complication rate was similarly elevated among patients in functional class IV (odds ratio 5.53; confidence interval 1.23-25.04). Patients with mitral valve reconstruction had lower short-term complication or death rates than did patients with prosthetic valve replacement (odds ratio 0.43, confidence interval 0.20-0.90). Eighty-two percent of patients with mitral valve reconstruction had no insufficiency or only trace insufficiency during the long-term follow-up period. Five-year complication-free survivals were 64% (confidence interval 54%-74%) for patients undergoing mitral valve reconstruction and 47% (confidence interval 33%-60%) for patients undergoing prosthetic valve replacement. Results of a series of statistical analyses suggest that outcome was linked primarily to preoperative New York Heart Association functional class.
Conclusions: Initial mortalities were similar among patients undergoing prosthetic replacement and valve reconstruction. Poor outcome was primarily related to preexisting comorbidities. Patients undergoing valve reconstruction had fewer valve-related complications. Valve reconstruction resulted in excellent durability and freedom from complications. These findings suggest that mitral valve reconstruction should be considered for appropriate patients with ischemic mitral insufficiency.
See related editorial on page 1059.
Mitral insufficiency caused by coronary ischemia has various clinical presentations, ranging from cardiogenic shock related to acute papillary muscle rupture to chronic congestive heart failure related to ventricular dysfunction with annular dilation. Reported perioperative mortality for mitral reconstruction in these patients ranges widely, from 9%
1 to 18%, 2 although the variety of patient subtypes makes it difficult to analyze the impact of mitral valve reconstructive techniques in reports on small patient groups. Although mitral reconstruction demonstrably provides better preservation of ventricular function 3 than does mitral replacement without chordae-sparing procedures and produces superior freedom from valve-related complications 4 in patients with degenerative mitral insufficiency, similar advantages have not yet been definitely demonstrated for the subset of patients with ischemic mitral insufficiency. Kay and colleagues 5 demonstrated good results with mitral repair for patients with ischemic mitral insufficiency, but no analyses were performed to examine the impact of confounding variables. A study by Cohn and associates 6 reported that mitral reconstruction in patients with ischemic mitral insufficiency was associated with a 5-year mortality 5 times higher than that seen after replacement. Confounding variables, such as acuity of presentation, degree of global ventricular dysfunction, and the specific pathophysiologic characteristics of the ischemic mitral insufficiency, certainly influenced these outcomes. A large experience with long follow-up is required to resolve these issues and to provide a valid comparison between mitral valve reconstruction and valve replacement for patients with ischemic mitral insufficiency. This study reviews New York University Medical Center's 19-year experience with operations for ischemic mitral insufficiency.
Methods
Variable definitions
Ischemic mitral insufficiency was considered to be the presence of severe mitral incompetence (according to either echocardiographic or angiographic criteria) arising from an ischemic process confirmed by the intra-operative pathologic evaluation of the valve. Patients with other causes for the mitral insufficiency (degenerative, rheumatic, infective, or congenital) were excluded from this analysis. Mitral insufficiency was considered acute if the onset of symptoms was less than 1 month before the operation or was associated with an acute myocardial infarction during the same hospitalization.
A modification of the pathophysiologic classifications proposed by Rankin and colleagues, 7 Carpentier, 8 and Cohn and associates 6 was used. The mitral insufficiency cases were classified into three largely exclusive categories. Annular dilation was characterized as intact leaflets, chordae, and papillary muscles in association with a dilated anulus (type 1). Structural mitral insufficiency was characterized by the presence of ruptured or elongated papillary muscles (type 2). Ventricular-papillary dysfunction consisted of ischemic or infarcted nonruptured papillary muscles in association with normal chordae and intact anulus and leaflets (type 3).
Patient population
From January 1976 through January 1996, a total of 223 consecutive patients at our institution underwent isolated mitral valve surgery for severe mitral insufficiency of ischemic origin. Mitral insufficiency was measured by either preoperative ventriculography or echocardiography; in the latter half of this series intraoperative transesophageal echocardiography was routinely used. The mitral operations included 152 reconstructions (77% Carpentier technique 4 with ring annuloplasty and 23% suture annuloplasty) and 71 mitral valve replacements (82% with bioprostheses and 18% with mechanical prostheses). Moderate systemic hypothermia and cold blood cardioplegia were used throughout the series, with retrograde cardioplegic delivery used extensively in the last decade. The patients undergoing mitral replacement had preservation of the posterior leaflet whenever possible. Mitral replacement was preferred for patients with significant disruption or necrosis of the papillary muscle and with ventricular-papillary muscle dysfunction. Annular dilation was preferentially treated with mitral reconstruction.
The mean age for all the patients in the study was 67.9 ± 8.8 years, and 86% of the patients underwent concomitant coronary artery bypass grafting. Those patients who did not undergo concomitant coronary artery bypass grafting typically had either acute papillary muscle rupture in association with a completed transmural infarction or chronic mitral insufficiency with coronary disease that could not be ameliorated by coronary artery bypass grafting. Indices of preoperative risk included preoperative use of an intra-aortic balloon pump in 7% of the cases, preoperative intubation in 13%, and cardiogenic shock in 5%. Ventricular function was impaired in most patients (54%).
After the operation all patients received coumadin for the first 3 months if tolerated. After that, patients with a mechanical valve, chronic atrial fibrillation, or history of thromboembolic events continued to receive coumadin indefinitely.
Operative information and patient demographic characteristics for mitral valve patients are routinely collected at our institution and are maintained in a database. The standard terminology for reporting valvular surgery outcomes, such as hospital mortality, was used throughout. 9 Patients were followed up for complications and deaths from all causes. Deaths from all causes are reported here, but late death (death from any cause of a patient who survived 
30 days after surgery) was also examined. Late cardiac death (including valve-related deaths, sudden unexplained deaths and deaths due to congestive heart failure, acute myocardial infarction, and documented fatal arrhythmias) was the cause of all but one of these late deaths. All patients who underwent mitral valve reconstruction were requested to undergo echocardiographic assessment of the mitral valve at 6 months and at 1 year after the operation and then once a year after the first year. The results of the most recent echocardiographic assessment were obtained at follow-up contact. For the follow-up study, clinical research nurses contacted the patients, their families, or their physicians once each year. Follow-up was obtained in 97% of cases; searches made with the social security numbers of those patients who were unavailable for follow-up suggested that they were still alive, although they could not be contacted. A total of 550 patient-years of follow-up was reviewed in this report (mean 30.8 months, median 14.6 months, range 0-219 months).Figure 1 shows the distribution of follow-up times according to type of surgery.
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Characteristics were compared at baseline (time of surgery) for patients who underwent valve replacement and valve repair procedures. To screen for baseline differences between the two groups of patients, distributions of characteristics at surgery were compared with 2-sided t tests for the continuous variables such as age and with 
2 tests or Fisher exact tests for the categorical variables. Because the P values were used only as a screening tool, no adjustments for multiplicity were made.
Differences between the operative groups at the time of surgery were then examined with methods of linear discriminant analysis and multiple logistic regression. Variables selected for inclusion in these analyses included the variables judged from the univariate analyses to be potentially different between the two groups and also included other variables that may play an important role in the choice of procedure to be performed. All subjects with complete data on all candidate variables were included in the models. Model diagnostics and goodness of fit tests (Hosmer-Lemeshow C statistics for the logistic models and The Hotelling T square for the linear discriminant models) were performed.
Thirty-day mortalities in the repair and replacement groups were also compared with multiple logistic regression models. Models were selected with procedures similar to those described previously to compare the two groups of patients at the time of surgery.
Time-to-failure curves were compared with log-rank tests for (1) total mortality (death) and (2) first complication or death across the entire follow-up period. Cox proportional hazard models were also developed to compare the patients in the two groups with adjustments for variables that were (1) selected from the analyses of the baseline characteristics as sources of possible differences between the repair and replacement groups, and (2) considered a priori to be important in the choice of surgery or prognosis. Model diagnostics and likelihood ratio tests for goodness of fit were performed. Hazard ratios and 95% confidence intervals (CIs) were estimated from these models. Time-to-failure models were also developed for the repair and replacement groups separately to explore the effects of patient selection on the results of the comparisons between the two groups of patients.
To assess the potential impact on model development of the use of cases with complete data, Kaplan-Meier survival curves were compared for patients with and without complete data in the repair and replacement groups separately.
Supplementary analyses with propensity score methods 10 were also applied to aid in the understanding of the impact of covariates on outcome in these two selected groups of patients. All analyses were carried out with SAS V.8.0 (SAS Institute, Inc, Cary, NC) and S Plus 2000 software packages.
Results
Baseline characteristics and outcomes
Baseline characteristics
Two hundred twenty-three consecutive patients underwent surgery with either mitral valve repair (n = 152) or replacement (n = 71) at New York University Medical Center between 1976 and 1996.Table 1A provides a summary of the characteristics of these patients at the time of operation. The average age of these patients was 68 years. Although the groups were comparable in many respects, the proportion of the patients in New York Heart Association (NYHA) functional class IV was greater among the patients undergoing replacement (79%) than among those undergoing repair (59%). Ninety-two percent of patients in the repair group had angina, and 96% of the patients in the replacement group had congestive heart failure. The distributions of time of surgery (year) were also markedly different in the two groups of patients(Figure 1
). In fact, few repairs were conducted in patients with ischemic mitral insufficiency before 1988. We therefore examined this cohort effect (before 1988 vs 1988 or later) by separately performing all the multivariable analyses reported here on patients operated on in the latter half of our series;Table 1B provides a comparison of the two groups after 1988. Table 2 provides a summary of the mortality and complication outcomes according to type that are included in the subsequent analyses of mortality and complication-free survival.
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and1B. Note that 17% of the patients in the repair group had acute regurgitation, compared with 29% of those in the replacement group, and 67% of the patients in the repair group had isolated annular dilation, compared with only 34% in the replacement group. Linear discriminant analysis and multiple logistic regression analyses were carried out to explore the differences between the two operative groups. The following variables were included in the various exploratory analyses: surgery before or after 1988, acuity of mitral insufficiency, annular dilation, structural failure such as ruptured papillary muscle, ventricular papillary muscle dysfunction, congestive heart failure, NYHA functional class, gender, concomitant coronary artery bypass grafting, previous cardiac surgery, emergency operation, angina, diabetes, and age. The most important variable found from these models was the year of surgery (1988 or later vs before 1988).Tables 3A and3B summarize the results of the models resulting from each of these two approaches. Only NYHA functional class and the presence of annular dilation were significant in the multivariable analyses. Furthermore, in all the exploratory models the predicted classification was poor (<20% correct). Goodness of fit was assessed with the Hosmer-Lemeshow C statistics for the logistic models and the Hotelling T square for the linear discriminant models.
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2 (8 df) = 18.33, P = .0189). When the choice of operative procedure is confounded with respect to disease characteristics, it is not unexpected that no balance can be achieved through the use of propensity scores. 10-12 Propensity scores were therefore not used to carry out adjustments in the subsequent analyses reported here. Table 4 illustrates the nature of the confounding among NYHA functional classification and the presence or absence of angina and choice of repair or replacement procedure. Thirty-six percent of the patients in the repair group were in NYHA functional classes I through III with angina, compared with 18% of those in the replacement group. Only 2% of the patients in the repair group were in functional class IV without angina, compared with 20% of those in the replacement group.
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, suggest that the odds of death within 30 days after surgery for all patients and for patients operated on in 1988 or later were markedly elevated for patients in NYHA functional class IV relative to patients in classes I through III (9.6 times greater and 5.8 times greater, respectively). Results were similar for death or complication within 30 days of surgery. No other variable, including type of operative procedure, contributed significantly to the prediction of the odds of death within 30 days.
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provides the results of these analyses, which suggest that the odds of death within 30 days after surgery or complication or death within 30 days after surgery were significantly lower for patients with repair than for patients with replacement. This result supports the observation that the selection of patients for type of surgery is confounded with NYHA functional class and the presence of angina, and the lowered risk for patients in the repair group may have been due to the selection criteria for the surgery rather than to the surgical procedure.
Outcome: Survival and complication-free survival
Survival for all patients in the cohort is shown inFigure 2, A; survival for patients operated on in 1988 or later is shown inFigure 2, B. The risk of death for the repair group relative to the replacement group was 0.75 (95% CI 0.463-1.202) for all patients and was 0.66 (95% CI 0.338-1.302) for patients entered in 1988 or later. Appendix Tables 1A and 2A provide survival rates for 5 years from surgery for all patients and for patients entered in 1988 or later.
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The risk of death in the hospital for repair relative to replacement was 0.98 (95% CI 0.5-1.97), and the risk of complication or death was 0.81 (95% CI 0.43-1.56). For patients entered in 1988 or later, the risk of death and the risk of complication or death were 0.72 (95% CI 0.32-1.6) and 0.63 (95% CI 0.29-1.35).
Outcomes according to characteristics at time of surgery (patients entered in 1988 or later)
Table 7 shows the hazard ratios for death and for complication or death for patients who received mitral repairs relative to those who received valve replacements in 1988 or later within subgroups defined by levels of baseline variables. Although the numbers of patients in each subgroup were small, the results suggest that within most of these subgroups patients with repair had a lower risk of death or complication or death than did patients with replacement (although most of the CIs on the hazard ratios included unity). Patients older than 70 years had markedly lower risks with repair, as did patients without concomitant coronary artery bypass grafting, patients with emergency surgery, and patients with isolated annular dilation.
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Tables 8A and8B present the results of the model for the comparison of repair and replacement groups. InTable 8A all variables are included for model selection in addition to the type of surgery. The variables included in the final models are provided, along with the associated adjusted hazard ratios and 95% CIs and the test of model fit. Patients in NYHA functional class IV had a markedly increased adjusted risk or complication in all the patient subsets. Other characteristics of patients at the time of surgery also contributed to modification of the risks, although the particular characteristics varied with the patient subset. In no instance did the type of surgery emerge as an additional independent variable that contributed to outcome.
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. In these models patients in the repair group had 45% to 61% the adjusted risk of death of those in the replacement group and 55% to 61% the adjusted risk of complication or death in the presence of the covariates included. These results confirm the selection process associated with the choice of surgery for these patients. Because of the patient selection inherent in the choice of surgical procedure and the confounding of baseline characteristics at time of surgery with the choice of procedure, we also developed Cox models for each of the two surgical cohorts separately.Table 9 provides the results of the Cox models for each of the groups. Among all patients in the repair group the relative risk of death or any event was 3 times greater for patients in NYHA functional class IV than for those in classes I through III. For patients with replacement, those with mitral structural failure had a third the risk of complication or death of those without structural failure. For patients operated on in the latter half of our series, the risks for patients in NYHA functional class IV were even greater; risks were also increased for patients with emergency surgery or previous cardiac surgery.
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Repair group: Outcome according to type of mitral reconstruction
In our series of patients who had repair operations performed in 1988 or later and survived for at least 30 days, the unadjusted risk of death after 30 days was 0.29 (95% CI 0.1-0.83) for repair with a ring annuloplasty relative to simple suture repair, and the unadjusted risk of complication or death was 0.32 (95% CI 0.11-0.91) for ring annuloplasty repair relative to suture annuloplasty repair. Appendix Table 3 provides the Cox models and adjusted hazard ratios.
Discussion
The central questions pertinent to the treatment of ischemic mitral insufficiency by reconstructive techniques include effectiveness, appropriateness, and long-term benefits. Although none of these questions can be answered directly from the data in this 2-decade nonrandomized experience, several conclusions can be drawn.
Is mitral reconstruction an effective treatment option?
Although the different exploratory statistical approaches do not permit us to conclude that there is an independent impact (positive or negative) of operative procedure, the immediate postoperative outcomes were most predicated on the covariates of NYHA functional class, emergency surgery, and previous cardiac surgery. In almost every patient baseline subgroup the comparison of reconstruction with replacement demonstrated a hazard ratio of less than unity for the risk of death or complication within 30 days. This result suggests evidence of improved immediate outcomes among patients selected for mitral valve reconstruction. In fact, the 1-year survival for patients who underwent reconstruction in 1988 or later was 78%, and the relative risk of death during the follow-up period for patients who were in NYHA functional classes I through III was a third that of patients in NYHA functional class IV.
For which patients is repair appropriate?
Although the applicability of reconstruction is easily appreciated in the subset of patients with chronic ischemia and annular dilation, it is noteworthy that 17% of the repairs in our series were done in cases of acute ischemic mitral insufficiency. These cases are challenging to the surgeon because evaluation of the damage to the subvalvular apparatus may be difficult. Not only does structural damage (ruptured chordae or papillary muscle) need to be readily discerned, but subtle, ongoing pathologic processes of the subvalvular apparatus must also be accurately appraised. The few patients with valve reconstruction who required reoperation did so within a short period after the original operation. These reoperations were mainly because of further disruption of the subvalvular apparatus when the extent of damage to the subvalvular apparatus had not been fully appreciated initially. Although there was a trend toward further reintervention in the patients with valve repair, this difference can be attributed mainly to the learning curve associated with recognizing the extent of reconstruction in acute infarction. It is important to note that in our series there were no late valve-related deaths among patients undergoing further mitral valve surgery.
What are the long-term benefits?
The 5-year survival among the patients with mitral reconstruction in this series compares favorably with those reported by others, 5,6,13 which have ranged from approximately 64% to 75%. Strikingly, the various subsets of patients undergoing valve reconstruction had similar survivals regardless of the pathophysiologic mechanism of the regurgitation. The overall results are in sharp contrast to the study by Cohn and coinvestigators, 6 which reported a 5-fold greater mortality among patients with ischemic mitral regurgitation undergoing valve reconstruction (56% freedom from death for repairs at 5 years compared with 91% for replacement). Cohn and coinvestigators 6 suggested that it was not the mitral reconstruction itself that jeopardized patient survival; rather, annular dilation was a surrogate variable for the poor ventricular function that decreased late survival (5-year survival for reconstruction of annular dilation 43%). Cosgrove similarly reported a 3-year survival of only 48% among the patients who underwent mitral reconstruction for ischemic annular dilation. In contrast, in this study patients undergoing valve reconstruction for annular dilation had a 5-year survival of 71% (95% CI 61%-82%; AppendixTable 4).
Our experience with valve reconstruction for ischemic insufficiency included both simple suture annuloplasty and ring annuloplasty. Czer and coworkers 2 reported less postoperative mitral insufficiency after ring annuloplasty than after suture annuloplasty for patients with pure annular dilation. In this study both improved survival and improved complication-free survival were associated with remodeling ring annuloplasty.
This report provides additional evidence that the well-described benefits of valve reconstruction, such as superior freedom from the valve-related complications of embolism and endocarditis and from anticoagulant-related complications, also apply to patients with ischemic disease.
Limitations of the study
The term ischemic mitral insufficiency includes multiple pathologic disease processes with the final result of mitral insufficiency. Our analysis, which began before the availability of routine echocardiography, used a classification system similar to that proposed by Rankin and colleagues 7 in the 1980s. Recently, with the advent of transesophageal echocardiography and detailed leaflet analysis, a more functional analysis has been developed with subgrouping of either structural insufficiency or functional insufficiency. Structural insufficiency includes those patients with ruptured or elongated chordae or papillary muscle defects (type 2). Functional insufficiency includes those patients with restricted leaflet motion (type 3b) and those with annular dilation (type 1). The classification system that we used can be roughly translated into structural and functional categories. As more detailed studies of patients with ischemic mitral insufficiency are performed, the functional analysis will become the standard.
This patient series encompassed a 2-decade surgical experience. This was a retrospective study without randomization, and the relatively small numbers in each group of patients with this fairly rare disease made case matching impractical. When the assignment of patients to treatments is not random but is the result of some selection process that may be biased, the attribution of causality becomes difficult. In our series the choice of type of surgery was related to characteristics of the patient at presentation as well as to other unknown selection biases on the part of the surgeons. In addition, in our series the 20-year span encompassed changing technology and surgical techniques. Although cold blood cardioplegia was used throughout the series, the most significant change in our surgical practice occurred in the middle portion of this experience with the introduction of retrograde cardioplegia. The improved distribution of cardioplegia with this method allowed us to more aggressively pursue mitral reconstruction after this point in time, thus changing surgical practice. In addition, the repair operation was infrequent before 1988. Our focus on patients with surgery in 1988 or later allowed us to minimize the effects of these changes on our results.
Conclusions
These analyses suggest that the type of surgery has little influence on prognosis after adjustment for NYHA functional class and presence of angina at time of surgery. After exclusion of these two confounding variables, the risk of death and the risk of complication or death within 30 days of surgery were markedly reduced for patients who underwent repair relative to patients who underwent replacement. Similar results were obtained for total mortality and risk of complication or death. When we examined the repair group separately, the risk for death or complication was 3 times greater for patients in NYHA functional class IV at surgery than for those who were NYHA functional classes I through III. From the models developed for each cohort separately, we have discerned the factors associated with increased risks for patients selected for repair and for patients selected for replacement that can provide guidance to the surgeon with respect to selection of patients for these procedures.
We make the following recommendations. Aside from catastrophic, acute structural mitral valve failure, mitral valve reconstructive techniques are applicable in cases of both acute and chronic ischemic mitral insufficiency. Those patients with leaflet prolapse related to limited rupture of chordae or papillary muscle tips should undergo repair with the appropriate technique. Caution should be applied in the case of patients with acute insufficiency related to ischemic or infarcted papillary muscles; rather than relying on jeopardized tissue for reconstruction, mitral replacement should be performed in these cases. Likewise, patients with severe ventricular-papillary dysfunction often have more reliable correction with valve replacement. Finally, patients with chronic annular dilation have excellent results with mitral valve reconstruction and ring annuloplasty. For these patients valve repair provides superior freedom from valve-related complications with equivalent survival and therefore is preferred. In summary, in the case of ischemic mitral valve disease, it is up to the operating surgeon to appropriately choose valve repair or replacement, depending on the acuity of the presentation and the pathophysiologic mechanism involved.
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