Does mitral regurgitation (MR) cause a heart murmur?

From the Guidelines

Mitral regurgitation (MR) typically causes a heart murmur, which is usually holosystolic and best heard at the apex of the heart, although the murmur may not always be appreciated, especially in acute severe cases. This murmur occurs due to the abnormal backward flow of blood from the left ventricle into the left atrium during systole because of incomplete closure of the mitral valve 1. The intensity of the murmur generally correlates with the severity of the regurgitation, though this relationship isn't always perfect.

Clinical Presentation and Diagnosis

When examining a patient with suspected MR, physicians typically have the patient lie in the left lateral decubitus position and use the bell of the stethoscope to better appreciate the murmur. The murmur may be accompanied by other findings such as a displaced point of maximal impulse in chronic cases or an S3 gallop in severe regurgitation. Understanding this characteristic murmur is crucial for clinical diagnosis, though definitive assessment of MR severity requires echocardiography, particularly color Doppler-echocardiography, which is the best method to assess the presence and severity of mitral regurgitation 1.

Key Points to Consider

• The murmur of mitral regurgitation can be soft or even absent in cases of acute severe MR, especially when it presents with pulmonary edema and/or shock 1.
• The mechanisms of acute mitral regurgitation include mitral valve annulus dilatation, papillary muscle dysfunction, and papillary muscle rupture, with the latter typically presenting as a sudden hemodynamic deterioration 1.
• Management of MR, especially in the context of acute myocardial infarction, may involve urgent surgery, medical therapy, and the use of intra-aortic balloon pump, with the goal of improving survival and ventricular function 1.

From the Research

Mitral Regurgitation and Heart Murmurs

• Mitral regurgitation (MR) is a condition where the mitral valve does not close properly, causing blood to flow backward into the left atrium 2.
• A study published in the European Heart Journal found that 15 out of 186 patients with acute myocardial infarction had a systolic murmur due to mitral regurgitation, with a prevalence of 8% 2.
• The severity of MR was graded semi-quantitatively, with 12 patients having moderate MR and 3 having mild, moderate to severe, or severe MR 2.

Diagnosis and Clinical Impact

• A study published in the Journal of Cardiovascular Development and Disease found that ACE inhibitors and angiotensin receptor blockers (ACE-I/ARB) can improve clinical outcomes in patients with moderate to severe MR and preserved to mildly reduced left-ventricular ejection fraction 3.
• Another study published in ESC Heart Failure found that the administration of β-blocker after surgical aortic valve replacement was not associated with lower risk of major adverse cardiovascular and cerebrovascular events, but was potentially beneficial for improving functional mitral regurgitation 4.
• A systematic review published in The Journal of Heart Valve Disease found that ACE inhibitors and ARBs can reduce the regurgitant fraction, regurgitant volume, and left ventricular size in chronic primary MR 5.

Etiology and Diagnosis of Systolic Murmurs

• A study published in The American Journal of Medicine found that echocardiography can provide insights into the origin of systolic murmurs, and that physical examination has limitations but also unappreciated value in diagnosing systolic murmurs 6.
• The study found that four echocardiographic variables can predict the presence of systolic murmurs: peak aortic velocity, mitral regurgitation severity, mitral valve E-point velocity, and absence of pericardial effusion 6.
• The study also found that the distribution of the murmur on the chest wall can help distinguish between different types of murmurs, with the "broad apical" murmur pattern suggesting significant mitral regurgitation 6.