What are the causes of acute mitral regurgitation?

Causes of Acute Mitral Regurgitation

Acute mitral regurgitation most commonly results from functional (secondary) MR due to left ventricular dysfunction following acute myocardial infarction, followed by papillary muscle rupture (particularly the posteromedial muscle), spontaneous chordal rupture in degenerative valve disease, and infective endocarditis. 1

Primary Etiologies by Mechanism

Ischemic Causes (Post-MI)

The most frequent cause of acute MR in the acute cardiovascular setting is functional MR secondary to LV dysfunction without structural valve abnormalities, resulting from increased leaflet tethering and decreased mitral closing forces 1. This occurs most commonly after acute myocardial infarction or during transient myocardial ischemia involving the posterior and lateral LV wall 1.

Papillary muscle rupture is the catastrophic ischemic complication:

• The posteromedial papillary muscle ruptures far more commonly than the anterolateral muscle because it has a single coronary artery blood supply (right or circumflex artery distribution) 2
• Can be complete or partial rupture 1
• Typically presents with sudden hemodynamic deterioration, pulmonary edema, and/or cardiogenic shock 2, 3
• The murmur is often soft or absent due to rapid equalization of LA and LV pressures 2

Non-Ischemic Structural Causes

Spontaneous chordal rupture is now the most common etiology of acute severe MR in contemporary practice 4:

• Occurs in degenerative/myxomatous valve disease (floppy mitral valve/mitral valve prolapse) 1, 5
• Can also occur in rheumatic mitral valve disease 1
• Presents with flail leaflet on echocardiography 1

Infective endocarditis causes acute MR through multiple mechanisms 1:

• Leaflet perforation
• Chordal rupture
• Papillary muscle rupture
• Prosthetic valve ring dehiscence
• When new MR occurs with acute symptoms, maintain high suspicion for IE 1

Other Important Causes

• Acute heart failure (systolic or diastolic) 1
• Trauma (blunt chest trauma) 1, 6
• Mitral prosthetic dysfunction (dehiscence, structural failure) 1
• Iatrogenic injury during transcatheter procedures 6, 7
• Stress-induced (Takotsubo) cardiomyopathy 7, 5

Critical Diagnostic Considerations

Echocardiography is mandatory when acute MR is suspected 1. Key distinguishing features from chronic MR include:

• Normal or only mildly increased LV and LA dimensions in acute severe MR (the chambers haven't had time to dilate) 1
• Short deceleration time on aortic flow velocity curve 6
• Early mitral valve closure 6
• Pressure half-time <300 ms indicates rapid equilibration of aortic and LV diastolic pressures 6

Common Pitfalls

1. Underestimating severity: Even mild MR in the acute MI setting carries worse prognosis 1
2. Missing the murmur: In acute severe MR with rapid LA pressure rise, the systolic murmur may be soft or absent 2
3. Dynamic nature: Secondary MR severity is frequently dynamic and reduced with positive pressure ventilation 1
4. Color Doppler limitations: May underestimate severity in very severe regurgitation, and eccentric jets are difficult to assess quantitatively 1

Transthoracic echocardiography should be performed immediately when acute MR is suspected, with transesophageal echocardiography reserved for diagnostic uncertainty or surgical planning 1. In papillary muscle rupture with cardiogenic shock, emergency surgery is indicated while temporizing with intra-aortic balloon pump and medical therapy 2, 3.