European Heart Journal Advance Access originally published online on October 2, 2006
European Heart Journal 2006 27(22):2655-2660; doi:10.1093/eurheartj/ehl287
Prognostic significance of functional mitral regurgitation after a first non-ST-segment elevation acute coronary syndrome
Instituto Cardiovascular, Echocardiographic Laboratory, Hospital Clínico San Carlos, Plaza Cristo Rey, 28040 Madrid, Spain
Received 11 May 2006; revised 1 September 2006; accepted 14 September 2006; online publish-ahead-of-print 2 October 2006.
* Corresponding author. Tel: +34 913303290; fax: +34 913303290. E-mail address: jlzamorano{at}vodafone.es
See page 2615 for the editorial comment on this article (doi:10.1093/eurheartj/ehl320)
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Abstract |
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Aims The development of mitral regurgitation (MR) after an acute myocardial infarction (AMI) is a recognized and frequent complication and its negative impact on survival has been observed. However, few data exist regarding MR after non-ST-segment elevation acute coronary syndrome (NSTSEACS). Our aim was to investigate the incidence, clinical predictors, and prognostic implications of MR in the setting of NSTSEACS.
Methods and results We studied 300 consecutive patients (71.7% men, mean age 66.9±13 years) admitted to our coronary care unit for an NSTSEACS. Every patient underwent an echocardiographic study during the first week after the index NSTSEACS and was clinically followed up. MR was detected in 42% (126 patients; 88 men, mean age 71.3±11 years). Mean follow-up was 425.6±194.8 days. Only age and left ventricular (LV) ejection fraction (EF) were found as independent markers of the development of MR; no variable was found as an independent predictor of in-hospital mortality and only MR was found as an independent predictor of long-term outcome.
Conclusion MR is frequent after an NSTSEACS. Age and a low LV EF are factors associated to its development. The presence and degree of MR confer a worse long-term prognosis to patients after a first NSTSEACS. Thus, the presence of MR should be specifically assessed in every patient after an NSTSEACS.
Key Words: Myocardial infarction • Mitral regurgitation • Prognosis • Non-ST-segment elevation acute coronary syndrome
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Introduction |
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Mitral regurgitation (MR) is a frequent complication during and after the acute phase of a myocardial infarction, with reported incidences ranging from 3.4 to 35%.1–5 It has been proved to be a predictor of the long-term cardiovascular mortality after an acute myocardial infarction (AMI).1–6 Furthermore, its prognostic implication after a non-Q-wave AMI7 and the role of the existence of MR previous to an AMI8 have been already shown. Nevertheless, until now, the prognostic importance of functional MR after a non-ST-segment elevation acute coronary syndrome (NSTSEACS) has been poorly addressed. Thus, the incidence, risk factors, and prognosis of functional MR after NSTSEACS remain a controversial area of study.
Our aim was to assess the incidence, associated factors, and prognostic significance of functional MR in the short- and long-term prognosis after a first NSTSEACS.
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Methods |
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Study population
We studied 300 consecutive patients who were admitted to the Coronary Care Unit of the Cardiovascular Institute of San Carlos Clinic Hospital for a first NSTSEACS between December 2003 and August 2005. All patients eligible for the study were included. Every patient with a stablished diagnosis of NSTSEACS completed all the procedures of this study. The diagnosis of NSTSEACS was based on the European Society of Cardiology criteria.9 Medical history, laboratory findings, and in-hospital course were collected for each patient.
Echocardiography
All patients underwent a complete echocardiographic study before hospital discharge, which included a specific evaluation of the mitral valve anatomy and function, during the first week after the NSTSEACS. The echocardiography was performed with a Philips Sonos 5500 (Phillips, Andoven, MA, USA) with 2.5 or 3.5 MHz transducers. Standard parasternal M-mode register was employed to measure left atrial and left ventricular (LV) diameters. Global EF was calculated on bidimensional echocardiography from two- and four-chamber apical views by the modified Simpson's method and systolic thickening evaluated in the 16 segments defined by the American Society of Echocardiography.10 The presence and degree of MR were evaluated using the PISA method and a validated nomogram for semi-quantitative estimation.11,12 This validated and simplified semi-quantitative method, based on proximal isovelocity surface area, has a good correlation with the angiographic degree of MR. Taking into account only the radius of proximal isovelocity surface area and the velocity of aliasing used, a nomogram is used to allow a fast semi-quantitative estimation of the degree of MR.12 Thus, MR was classified according to these criteria in four degrees of severity (I: mild; II: mild to moderate; III: moderate; IV: severe). Patients with trace MR were included in the group without MR. The systolic pressure of the pulmonary artery was calculated using tricuspid regurgitation and inferior cava vein diameters.13 Patients with structural disease of the mitral valve and/or subvalvular apparatus were excluded from the cohort of study, in order to study only those with a functional cause of MR.
Cardiac catheterization
Cardiac catheterization was performed according to the treating physician's preferences. Coronary angiography was performed using standard techniques. Significant coronary artery disease (CAD) was defined as 
70% diameter stenosis of an epicardial coronary artery. The extent of CAD was characterized by the traditional one-, two-, or three-vessel disease classification.14 Percutaneous revascularization was performed according to the physician's criteria.
Follow-up
During hospitalization and follow-up, cardiovascular death was considered the endpoint. After discharge, all patients were followed in the outpatient clinic. Planed timings of follow-up in the outpatient clinic were: immediately after the hospital discharge, one month later and for less than 6 months of intervals afterwards. If a patient did not show up at outpatient clinic, medical records and phone interview were used.
Statistical analysis
Baseline characteristics are expressed as mean±standard deviation for continuous variables and absolute number (proportions) for categorical variables. Comparisons between groups were made with Pearson's 
2 test for categorical variables and the t-test for continuous variables. In the analysis, MR was used as a categorical variable. Long-term follow-up survival curves for various groups were constructed using the Kaplan–Meier method, and comparisons were made using the log-rank test. Logistic regression and Cox's proportional hazards regression univariate analysis were used to select the variables associated with in-hospital and long-term events, respectively. Multivariable logistic regression analysis and Cox's proportional hazards regression were used to adjust for differences in demographic and clinical variables in order to asses the independent effect of MR on in-hospital and long-term survival, respectively. Linearity assumption was assessed using the residual analysis. This assumption was satisfied by every continuous variable. For the Cox regression analysis, the proportional hazards assumption was assessed using stratified analysis and it was satisfied by every continuous variable. Those variables with a P<0.1 in the univariate analysis as well as MR were included in the multivariable analysis. The endpoint considered was cardiac mortality. Comparisons were considered significant in the presence of a P-value of <0.05.
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Results |
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Incidence and baseline characteristics
Mean age was 66.87±13 years. Two hundred and fifteen patients (71.7%) were men. The incidence of MR was 42% (126 patients; 88 men, mean age 71.3±11 years). The distribution of the severity of MR was: 79 patients degree I (62.7%), 25 patients degree II (19.8%), 18 patient degree III (14.3%), and four patients degree IV (3.2%). Baseline characteristics are shown in Table 1. Mean age (63.9±14 vs. 71.3±11), the incidence of diabetes mellitus (24.1 vs. 38.9%), renal failure (7 vs. 18.3%), the number of coronary vessels with significant disease (1.6±1 vs. 2.1±1), and the involvement of left anterior descendent coronary artery (LAD) coronary artery (48.3 vs. 61.9%) were significantly higher in the group with MR when compared with the group without MR. Eleven patients were excluded because of the lack of an adequate acoustic window able to provide an MR assessment. Seven patients underwent transeophageal echocardiogram to accurately assess the severity of the MR.
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Predictors of MR development
In the univariate logistic regression analysis, age, diabetes mellitus, renal failure, LV ejection fraction (EF), LV end-diastolic diameter, left-atrial diameter, and the presence of LV segmentary contraction defects were found as factors related to the development of MR. The location of the contractility alteration was not related to the development of MR. Nevertheless, in the multivariable logistic regression analysis, only age and LVEF were found as independent markers of the presence of MR (Table 2).
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Echocardiographic parameters
LV end-systolic diameters were higher in the patients with MR, reaching statistical significance (29.4±9 vs. 33.9±8.6 mm), LV performance was diminished in the group with MR (LVEF 58.6±17 vs. 51±16% in the groups without and with MR), the prevalence of LV wall motion abnormalities in the echocardiographic study was higher in the group with MR (46.6 vs. 61.1%), and the left-atrium diameter was larger in the group with MR (38±9.7 vs. 42.5±8.5 mm). These results are depicted in Table 3.
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Coronary anatomy
Two hundred and sixty patients (87.6%) underwent coronary angiography during hospitalization. The mean number of vessels with significant lesions was 1.6±1 in the group without MR and 2.1±1 in the group with MR (P<0.001). The number of vessels with significant lesions for each patient is described in Table 1. One hundred and sixty patients underwent revascularization procedures (55.3% of patients; 98 patients in the group without MR and 68 patients in the group with MR). Forty-eight patients (69.6%) in the group without MR and 41 patients (65.1%) in the group with MR were submitted to percutaneous coronary intervention of more than one coronary lesion. By-pass graft surgery was performed in 22 patients without MR (12.6%) and in 20 patients with MR (15.9%). Percutaneous revascularization was performed in 85 patients in the group without MR (48.9%) and in 52 patients in the group with MR (41.3%). The number of patients revascularized in each group did not reach a significant difference. No patient in our series underwent mitral valve repair combined with coronary artery by-pass graft.
In-hospital outcomes
In-hospital outcomes are shown in Table 4. Regarding the incidence of in-hospital cardiac death, it was significantly higher in the group with MR. Furthermore, the higher the severity of the MR, the higher the incidence of in-hospital cardiac death. Logistic regression univariate analysis showed that age, left-atrium diameter, systolic pressure in the pulmonary artery, and the presence and degree of MR were predictors of in-hospital outcome (Table 5). Nevertheless, the logistic regression multivariable analysis did not find any independent predictor of in-hospital mortality.
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Long-term follow-up
Patients were followed for a median time of 431 days (interquartile range: 309–572). Survival curves showed that the long-term outcome depends on the MR severity (Figure 1). Thus, survival was greater in patients without MR. Cox regression univariate analysis showed age, left-atrium diameter, renal failure, the systolic pressure in the pulmonary artery, and the presence and degree of MR as variables related to the long-term prognosis. Nevertheless, only MR was found as an independent predictor in the multivariable Cox regression analysis (Table 6).
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Discussion |
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This work is, to our knowledge, the first one to consider the prognostic implications of the development of MR after a first NSTSEACS. In the present study, the incidence of MR after a first NSTSEACS is higher than what has been observed in Q-wave AMI.4,5 It could be due to the older mean age of the population enrolled in our series.
Functional MR occurs with a structurally normal valve as a result of an altered force balance on the mitral leaflets.15 The causal mechanisms of ischaemic MR have been studied both in the acute and chronic stage after myocardial infarction. They include ischaemia or scar at the level of the papillary muscles, annulus dilatation, change in the ventricular geometry causing tethering of the mitral leaflets, and papillary muscle rupture. Annular dilatation and systolic dysfunction have been considered additional factors that aggravate MR caused by the restricted movement of the leaflets.5–21 Nevertheless, all the factors involved in the development of MR after AMI are still not well described and understood.
Larger LV systolic diameters, as well as lower LVEFs, were more common in patients with MR after NSTSEACS. We postulate that hibernated or stunned myocardium produces LV remodelling in hearts with no transmural necrosis and that the progressive change in LV size and shape leads to the development of MR.7
Regional wall-motion abnormalities were more frequent in patients with MR. No relation was found between the location of the contractility alteration and the development of MR. This is in contrast with the previous findings in transmural MI, where involvement of the posterior papillary muscle generates MR with mild or moderate dilatation.18 We believe that segmental dysfunction, LV dilatation, and MR are consequences of severe CAD in our patients and probably it is the factor most related to the development of MR after an NSTSEACS. Furthermore, the effect of MR on the long-term outcome despite the limited infarct transmurality is relatively new. In this study, patients with MR were older, had a higher incidence of renal failure, were more frequently diabetic, and showed a more advanced CAD. Thus, probably the finding of a more dilated and dysfunctional LV is only the reflection of a more advanced chronic ischaemic cardiomyopathy and MR is a marker of severe ischaemic cardiomyopathy in our population.
The rate of in-hospital deaths was relatively low. Aggressive management of these high-risk syndromes could be a reason for these findings. Furthermore, it is of note that the development of MR is associated with a worse long-term outcome, but it is not associated to a worse in-hospital outcome in our series. This finding could be due to the fact that the deleterious action of post-NSTSEACS MR is based on a progressive LV remodelling and it takes time to develop. The results of the present study contrast with the results of a previous work7 in which the presence of MR did not add any independent prognostic significance in the setting of non-Q-wave AMI. Nevertheless, it is of note that the population in that study consisted in only one-third of the population of the present study and the definition used for inclusion was the old definition of non-Q-wave AMI instead of the new definition of NSTSEACS. Thus, the design and the results of the present work are more reliable.
It has been described that LV dysfunction resulting from viable hibernating but recoverable myocardium has a better prognosis when revascularization is performed and that an improvement of myocardial performance and reversal of dilatation decreases MR after surgical revascularization.22,23 Probably, severe ischaemia played an important role in our results. Improvement of systolic function and reversal of dilatation may have decreased both MR and ischaemic events after percutaneous revascularization. Nevertheless, it is of note that the non-transmurality of necrosis makes the expansion of the scar unlikely, even in the cases in which revascularization was not performed. Thus, it is improbable that MR appeared or progressed in subsequent months.
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Limitations |
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We cannot make sure that in the patients enrolled in our study, any degree of MR was not present before the index NSTSEACS. Thus, we cannot distinguish between pre-existing MR and new-onset MR. Pre-AMI MR is a recently described prognostic factor.8 It is very difficult to obtain echocardiographic data of patients before the index myocardial infarction. Nevertheless, in the studies analysing prognosis after a Q-wave myocardial infarction, the presence of pre-AMI MR is not analysed. Thus, we think that this limitation is only a minor one if we keep in mind the previously published works. It is of note the high prevalence of MR. Probably there is a large list of factors involved in its development, but it would be very difficult to obtain any definitive conclusion regarding which are these factors because it would be necessary a group of patients with Q-wave AMI to compare in order to obtain more solid conclusion.
Not every patient in our series had coronary arteriography but it is of note that this study is not an intervention study. Thus, the management of these patients was the standard management at that time in our institution and it depended on the physician's preferences. So, in this way, our results reflect more closely the daily clinical practice.
The morphology of the mitral valve was not specifically assessed or quantified in the present work. Thus, the diagnosis of ischaemic or functional MR was performed excluding those patients with structural alterations at the level of the mitral leaflets or mitral subvalvular apparatus, following the methods used in the previous reference papers.6 In this sense, our work does not differ from other works regarding MR after AMI. Furthermore, the present study provides no information to confirm the mechanism of MR. Patients with ischaemic MR after an NSTSEACS have one fundamental mechanism (restricted leaflet closure caused by dilatation of the annulus, deformation of the ventricle, etc.). Nevertheless, to our knowledge, no work has been published evaluating this specific subject in the setting of NSTSEACS. Thus, these authors do not know whether, in the case of MR after NSTSEACS, the mechanism is one or more than one. Further evaluation is needed in order to understand the mechanisms of MR after this specific type of acute coronary syndrome.
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Conclusions |
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MR is a frequent complication after an NSTSEACS. Age and a low LVEF are factor associated to its development. The presence of MR after a first NSTSECAS adds prognostic significance to other known negative factors. The presence and degree of MR confer a worse long-term prognosis to patients after a first NSTSEACS. Thus, the presence of MR should be specifically assessed in every patient after an NSTSEACS.
Conflict of interest: none declared.
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References |
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