Ischemic mitral regurgitation

Associate Editors-In-Chief: Varun Kumar, M.B.B.S ; Lakshmi Gopalakrishnan, M.B.B.S

Overview
Ischemic mitral regurgitation can be defined as mitral regurgitation that occurs as a consequence of myocardial infarction or acute myocardial ischemia with resultant alteration in left ventricular geometry or function. Echocardiography should demonstrate that annular dilation or restriction of leaflet motion in systole (Carpentier type IIIb ) is the cause of regurgitation.

If mitral regurgitation occurs as a complication of MI it is permanent while if it occurs as a result of ischemia, it is transient and resolves with resolution of ischemia.

Pathophysiology
Papillary muscle normally exert a perpendicular force on mitral valve leaflets thereby achieving optimal coaptation. With distortion of left ventricular geometry and displacement of papillary muscle secondary to myocardial ischemia/infarction, the tethering forces are exerted at an oblique angle resulting in insufficient coaptation there by causing regurgitation of blood through mitral valve.



Ischemic Mitral Regurgitation can be due to :
 * 1) Papillary muscle rupture secondary to acute myocardial infarction.
 * 2) Dilatation of mitral annulus secondary to left ventricular dysfunction/enlargement causes incomplete mitral valve coaptation with normal leaflet motion.
 * 3) Most often Ischemic Mitral Regurgitation is functional and due to papillary muscle displacement involving a left ventricular-wall motion abnormality as well as alteration in left ventricular geometry . In absence of global left ventricular dysfunction and dilatation, mitral regurgitation resulting from localized left ventricular remodelling with wall motion abnormalities usually occur secondary to myocardial infarction in inferobasal and mid ventricular regions of heart . This can cause displacement of papillary muscles causing suboptimal coaptation of leaflets. A recent study demonstrated that alteration in ventricular geometry secondary to myocardial infarction in anterioapical region with inferoapical extension can also cause significant mitral regurgitation despite normal ventricular contraction in basal inferior and mid ventricular region . This correlates with increased tethering length from the papillary muscle tip to the annulus, and reduced systolic tethering length because of papillary muscle retraction toward the apex.

Epidemiology
A study which evaluated 482 patients with ischemic mitral regurgitation concluded that 76 percent had mitral regurgitation was functional rather than structural.

In another community based study, 773 patients with STEMI or NSTEMI were evaluated within 30 days of the event using echocardiography and it was found that mitral regurgitation was present in 50% with mild regurgitation in 38% and moderate or severe in 12%

A higher incidence is observed in elderly and women and is associated with anterior wall infarction, persistently occluded infarct artery, larger end-systolic and end-diastolic ventricular volumes, and severe heart failure.

Symptoms
The clinical presentation of Ischemic mitral regurgitation reflects the state of LV dysfunction more than the state of mitral valve.
 * Asymptomatic detected by Echocardiography or Angiography
 * Weakness, fatigue
 * Exercise Intolerance

Signs

 * Approximately one half have holosystolic murmur
 * Decreased cardiac output
 * Exercise produces severe regurgitation in patients with mild ischemic mitral regurgitation.
 * Severe cases present with pulmonary edema

Exercise Echocardiography

 * Effective regurgitant orifice (ERO) area increase with exercise is associated with increased risk for acute pulmonary edema
 * Exercise induced ERO ≥13 mm2 is an independent predictor of cardiac death.


 * 3D ECHO can be helpful in differentiating ischemic mitral regurgitation from functional MR secondary to ventricular dilatation. The valvular abnormality is asymmetric in ischemic mitral regurgitation and symmetric in functional MR.

 DOPPLER ECHOCARDIOGRAPHY


 * Echocardiogram showing incomplete closure of posterior mitral leaflet due to tethering from MI

Treatment
Treatment varies depending on the severity of ischemic mitral regurgitation with reperfusion in acute MI or heart transplantation.


 * Ischemic mitral regurgitation associated with reduced left ventricular ejection fraction (LVEF) should be treated by reducing the after load with angiotensin converting enzyme inhibitors and/or angiotensin II receptor blockers, and beta blockers.


 * Ischemic mitral regurgitation with normal mitral leaflets but abnormal left ventricular function and geometry can be treated by percutaneous revascularization which decreases ventricular remodeling & hence prevents MR.


 * Acute ischemic mitral regurgitation is managed with intra-aortic balloon pump & medical therapy.


 * Revascularization is less rewarding in chronic ischemic mitral regurgitation.


 * Ischemic mitral regurgitation due to papillary muscle rupture : Emergent mitral valve repair (which can be done only when there is no papillary muscle necrosis) despite a high operative mortality (20-25%).


 * Surgical approach for ischemic mitral regurgitation : The decision for valve surgery should be made prior to CABG as it increases the likelihood of air embolism, prolongs cardiopulmonary bypass time and thereby increasing operative mortality.
 * Standard Surgical ring annuloplasty
 * Restrictive annuloplasty
 * Edge-to-edge leaflet repair
 * Chordal manipulation eliminates tethering and restores normal leaflet coaptation.
 * Modifying papillary muscle geometry
 * Segmental ventricular constraints
 * Biventricular pacing decreases tardiness of the posterior papillary muscle bearing segment & hence reduces tethering.

In ring annuloplasty antero-posterior annular dimension is reduced to restore coaptation. However, if the annular size alone is reduced, it persistently leaves the tethering to the displaced left ventricular wall and thereby causing recurrent MR.

Currently for ischemic mitral valve repair double orifice technique (edge-to-edge repair) along with ring annuloplasty is used to facilitate leaflet coaptation.

There is a mixed opinion regarding the outcome of mitral valve repair versus mitral valve replacement in patients with ischemic mitral valve with some investigators reporting mitral valve repair to be associated with better outcome.

Transvenous catheter-delivered annuloplasty device is an investigational alternative.

Posterior suture annuloplasty for Ischemic mitral regurgitation : 


 * Cardiac Transplantation is an option in patient with severe ischemic mitral regurgitation and left ventricular dysfunction due to improved prognosis in comparison with valvular surgery but is contraindicated in elderly.

Prognosis
Ischemic mitral regurgitation is associated with a poor prognosis, however there is no sufficient evidence that the regurgitation is the cause for the poor outcomes and surgical correction of regurgitation at the time of CABG, has little impact on survival with limitation in functional class.

Acute ischemic mitral regurgitation is often associated with anterior wall infarction and wall motion abnormality leading to increased left ventricular volumes and subsequent heart failure.

Ischemic mitral regurgitation in patients with non-ST elevation acute coronary syndrome, mitral regurgitation was found to be the independent predictor of long term outcome and the presence and degree of mitral regurgitation confer a worse long-term prognosis to patients after the first event. Thus, the assessment of presence of mitral regurgitation in every patient after a non-ST elevation acute coronary syndrome is warranted.

Independent of left ventricular function, MR is associated with higher mortality.