Importance of mitral regurgitation in ischaemic heart disease—more than just a bystander

Luísa M. Branco*

Department of Cardiology, Santa Marta SA Hospital, Rua de Santa Marta, 1169-024 Lisbon, Portugal

* Tel: +351 21 8465469; fax: +351 21 8465469. E-mail address: branco.online{at}mail.telepac.pt

This editorial refers to ‘Prognostic influence of mitral regurgitation prior to a first myocardial infarction’{dagger} by J. Zamorano et al., on page 343

Coronary artery disease (CAD) prognosis has been known for many years to depend on many factors, including the degree of left ventricular (LV) dysfunction as well as the presence of inducible ischaemia, viable dysfunctioning myocardium, and degree of coronary artery lesions. Mitral regurgitation (MR) is often a bystander and is a frequent finding after acute myocardial infarction (AMI) (in 15–64% of patients). It is an independent predictor of cardiovascular mortality,14 and results from many factors, such as papillary muscle dysfunction and/or mitral annulus dilatation, and LV remodelling with papillary muscle migration causing malcoaptation of the leaflets and excess valvular tenting with loss of systolic annular contraction.2 Myocardial viability in the infarct area reduces infarct expansion and ventricular remodelling, and prevents the development of MR. In the study by Golia et al.1 of 191 patients after uncomplicated AMI, MR was present in 58.6% of the patients and it was significant (>grade 1) in 26 patients (13.6%). It was associated with increased age, lower regional wall motion score index during dobutamine stress echocardiography, more severe CAD, and more frequent anterior/inferior infarctions. At multivariate analysis the extent of LV dysfunction and the presence of MR were significantly related to mortality.

Auscultation may not detect a murmur due to decreased turbulence, and echocardiography should be performed routinely on all patients for diagnosis. A regurgitant volume ≥30 mL, or an effective regurgitant orifice ≥2 mm2 defines a high-risk group.4,5

Many papers have focused on the importance of correcting MR during coronary artery bypass grafting (CABG) for a better long-term prognosis, even when there is no definite major organic cause (such as papillary muscle rupture, which needs quick correction to improve immediate survival, and acute haemodynamic deterioration). Nevertheless some series have shown a significant operative risk of the combined surgery6,7 (15–19.5% mortality).

In conditions such as dilated cardiomyopathy, the importance of correcting significant MR in order to decrease symptoms and eventually enhance outcome has been demonstrated.8 Besides, not only the presence but also the degree of significant MR is fundamental in these patients, when submitted to resynchronization therapy.9 Much of its success might result from the fact that a more homogeneous systolic performance might cause a decrease of chamber size (remodelling) and decrease MR.

In this issue of the Journal the paper by Zamorano et al.10 reports the prognostic importance of the presence of organic non-ischaemic MR prior to a first AMI.

Trivial MR is frequent in the normal population and tends to increase with age, not only in prevalence but also in degree, very often due to degenerative mitral valve disease, annular calcification, and mitral valve prolapse, or even rupture of cordae, becoming the most common valvular heart disease in developed countries. More than trivial MR is also common4 and affects the patient's long-term prognosis. So the presence of even mild MR was an independent predictor of long-term mortality in the study by Pellizon et al.3 in 1976 post-AMI patients.

In the study reported in the present issue,10 almost 62% of the population had degenerative MR prior to the AMI. Of course, if the patient had had MR, there were more clinical reasons to have been previously submitted to echocardiography, as were the criteria to include patients in this study. Only patients with degenerative MR were evaluated, as other causes of previous MR were excluded. This population was elderly with a mean age of over 75 years. Atrial fibrillation (AF) was only present in the MR group (in 21%). As it is usually accompanied by an enlarged left atrium, a larger left atrium should have been expected in this group, but it was of equal size in both groups.

It is not quite clear from this paper how MR prior to AMI might have influenced prognosis, as the two populations studied (with and without prior MR) seemed to be very similar, except in the outcome after the acute event. The quality of treatment of the two populations in terms of reperfusion therapy, LV infarction size, and timing of treatment seemed equivalent. The presence of MR might have caused an additional burden to a ventricle already stressed by ischaemia, and it might have influenced LV function calculation in terms of ejection fraction. In both groups there was an increase in MR after AMI, but more (not significantly) in group 2. The fact that both groups had similar previous ejection fraction makes one wonder if contractility was not more affected in group 1, as MR tends to increase the calculated EF, which is very dependent on after-load. MR may increase wall stress and oxygen consumption and cause anatomical changes in the myocardium with fibrosis which may predispose to arrhythmias. This may also be the reason why defibrillator therapy seems to be important for the long-term results of ventricular resynchronization in ischaemic and non-ischaemic dilated cardiomyopathies. In fact, the group with MR had larger ventricles after AMI. It is however very strange that having different degrees of MR, the previous LV end-diastolic diameter was similar in both groups, and was within normal range. Having developed larger ventricles after MI, there seems to be no reason why, having the same location and size of infarctions, MR did not increase more in group 1. Another reason for the different evolution might result from different severity of the coronary artery lesions, and/or more proximal stenosis in the group with degenerative MR. It is not clear from the text whether they had similar CAD in terms of these characteristics, and in complexity of coronary lesions.

There was a worsening of short-(2 weeks) and long-term prognosis (40.5 vs. 11.5% cardiovascular mortality!), in spite of similar incidence of heart failure, and AMI—most patients died suddenly! There was a 28.6% incidence of sudden death (33% of the long-term survivors) in the group with previous MR during a follow-up of 490 days. Cardiac surgery was performed only (though not significantly more) in the group without previous MR. Nothing is said about ischaemia detection and it might also have influenced the mortality, acting as a trigger for arrhythmias and death.

Strangely, the presence of diabetes mellitus, previous AF, ejection fraction, and the number of significant CAD lesions did not influence prognosis in this elderly population. Neither did age, although there was a trend for its effect on outcome. There was a trend to have more diabetes and hypertension in group 1 as well as more therapy with ACE-inhibitors, or diuretics, and less with beta-blockers, and thrombolysis (P=0.1). As the population is small, all of these factors might have influenced the results and not only the presence of previous MR. One of the limitations of this study is the small size of the population studied, with about one-fourth of the population with AMI admitted to the hospital in the period of study. As AF was only present in the group with MR and it is not specified whether they were submitted to oral anticoagulation, this might also account for embolic phenomena, and different outcomes. On the other hand Ascione11 found an association between significant MR after a first AMI, and the prevalence of LV thrombus.

Almost 70% of patients in the present study were submitted to reperfusion therapy, equally distributed between angioplasty and thrombolysis. Only 43% had previous MR degree ≥II. However, its presence conferred an almost four-fold increase in the probability of death, more than the usually two-fold increase in mortality referred in other studies of MR after AMI. The presence of MR after AMI is influenced by the size of the infarction (higher in larger AMI), and its location (being more common in inferior infarctions than in anterior infarctions of similar size).

In conclusion let us say that one should always look carefully at the findings of a routine echocardiogram, and take the presence of significant organic mitral valve disease into special consideration. In this study, MR was usually evaluated in a semi-quantitative way and no ventricular volumes were analysed, but merely the LV end-diastolic and end-systolic diameters. What one might wonder after reading this interesting paper is whether, when stratifying patients after AMI, more importance should be given to the presence of previous MR. These patients should probably be more completely studied in terms of prevention of sudden death. A prospective study of patients with degenerative MR should also be carried out in order to evaluate how often they develop AMI and if the importance of its presence per se would also be a significant independent predictor of mortality, as it was in this study. If so, one would have to follow these patients more carefully, and more aggressively, during the acute event, and in the long term thereafter.

Footnotes

{dagger} doi:10.1093/eurheartj/ehi065 Back

References

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  3. Pellizzon GG, Grines CL, Cox DA et al. Importance of mitral regugitation in patients undergoing percutaneous coronary intervention for acute myocardial infarction: the Controlled Abciximab and Device Investigation to Lower Late Angioplasty Complications (CADILLAC) trial. J Am Coll Cardiol 2004;43:1368–1374.[CrossRef][ISI][Medline]
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Related articles in EHJ:

Prognostic influence of mitral regurgitation prior to a first myocardial infarction
José Zamorano, Leopoldo Perez de Isla, Lucía Oliveros, Carlos Almería, José Luis Rodrigo, Adalía Aubele, José Banchs, and Carlos Macaya
EHJ 2005 26: 343-349. [Abstract] [Full Text]  




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