Causes of Mitral Valve Regurgitation

Text Kathryn Statham, Genevieve Carbonatto

Mitral valve regurgitation is the most common valvular disease and a significant cause of morbidity and mortality in cardiovascular disease

Functionally the Mitral Valve apparatus consists of

  • the mitral annulus
  • the AMVL and PMVL
  • the chordae
  • the papillary muscles
  • the left ventricular myocardium underlying the papillary muscles

Anything that affects any of these components may lead to mitral regurgitation. Broadly speaking primary causes of MR affect the leaflet and chordae whilst secondary causes are due to left ventricular dilatation from ischaemic or myocardial processes leading to distortion of the left ventricle

Causes 

Of the primary causes, degenerative mitral valve disease and rheumatic valve disease are the most common causes of mitral regurgitation, however bacterial endocarditis causing tissue destruction and vegetations, along with CT diseases (ie Marfan’s), drug induced leaflet thickening (ie ergotamine), congenital mitral valve abnormalities and papillary muscle rupture are all causes of primary mitral valve regurgitation.
LV distortion due to coronary artery disease and cardiomyopathy is the most common cause of secondary MR, however, systolic anterior motion of the mitral valve 2 to a number of conditions affecting the left ventricle including HOCM and severe LVH and LA dilatation 2 to AF may also cause functional MR.
It is not uncommon to have 2 or more aetiologies at the same time causing MR such as annular dilation and degenerative mitral valve disease.

Primary – Leaflet and chordae abnormality

1.Degenerative Mitral valve disease

Degenerative valve disease makes up the bulk of primary mitral valve disease associated with mitral regurgitation.
This umbrella heading covers the entire MVP spectrum and nonspecific calcification and thickening of the leaflets associated with chronic renal disease, diabetes and hypertension

Below are 3  examples of degenerative mitral valve disease with varying amounts of mitral regurgitation from mild to more severe .
Looking at these clips, the mitral valves have similar amounts of thickening of the leaflets and calcification of the annulus but varying degrees of regurgitation from mild to severe. The degree of calcification or thickening doesn’t dictate the amount of regurgitation of the valve.

Trivial MR

Mild MR

Moderate MR

MV prolapse (MPV)

MVP is the most common type of primary mitral regurgitation.  The classic MVP is Barlow’s disease or floppy valve disease. Features of Barlow disease include

  • It affects  young patients. 2 -4% of the population
  • It is a myxomatous disease. Mucopolysaccharide deposits and water accumulation in the leaflets and the chordae cause them to become thick.
  • The leaflets are bulky and billowy.
  • There is usually multi segment prolapse
  • Chordal rupture is uncommon.
  • There is progressive displacement of the mitral leaflets into the LA during systole at least 2 mm from the annular ring in PLAX view

Symptoms include

  • Atypical chest pain
  • palpitations
  • SOB on exertion
  • reduced exercise tolerance
  • sudden death (due to endothelium disruption)
  • endocarditis  (due to endothelium disruption)

Diagnosis of prolapse should made from the PLAX not the 4CV as the MV is saddle shaped and may mimic prolapse in this view 

This patient presented to the emergency department with SOB on exertion and palpitations.
He demonstrates all the signs of Barlow’s disease.
The mitral valve is thickened and billowy. The chordae are thickened. There is prolapse of the mitral valve and the PMVL is flail
A flail leaflet can occur in 2 situations in Barlow’s disease when the leaflet tip everts on closing or if there is chordal rupture. In this case the leaflet tip is everted due to chordal rupture

 

MV prolapse due to fibroelastic deficiency has the following features

  • It affects patients > 60 years of age
  • It is associated with a connective tissue deficiency
  • The leaflets are thin
  • Prolapse is of one segment and there is no billowing of non prolapsing segments
  • Chordal rupture is uncommon

This is a patient with degenerative mitral valve disease and MVP. Here the posterior leaflet of the mitral valve is seen prolapsing below the anterior leaflet. The prolapse is causing an eccentric, anteriorly directed mitral regurgitant jet

 

2.MV prolapse : Rheumatic fever

Rheumatic heart disease is characterised by

  • chordal thickening in 56 – 100% of patients due to chordal shortening, chordal fusion, leaflet thickening, calcification, or commissural fusion
  • restricted leaflet motion
  • excessive leaflet tip motion during systole.  Excessive leaflet tip motion is defined as displacement of the tip or edge of the involved leaflet towards the left atrium, resulting in abnormal coaptation and regurgitation.
  • mitral stenosis or mitral regurgitation
  • doming of the AMVL
  • calcification of the subvalvular apparatus

Normal MV  leaflets coapt in the midline and do not prolapse below the annular plane in systole. In rheumatic heart disease if there is excessive leaflet tip motion abnormal coaptation occurs causing mitral regurgitation. The echocardiographic criteria of mitral valve prolapse  is defined as > 2mm billowing of the leaflet into the left atrium in systole.

Characteristic features of rheumatic fever, chordal thickening, excessive leaflet tip motion, restricted leaflet motion and doming of the AMVL.

3. Bacterial endocarditis

MV regurgitation can be caused by bacterial endocarditis. The vegetations of bacterial endocarditis are a mass of fibrin, platelets  and infective organisms held together by agglutinating antibodies produced by bacteria. This causes leaflet thickening. Regurgitations if often from several points in the valve due to leaflet perforation and leaflet destruction.

Features include

  • leaflet thickening
  • vegetations (sessile and pedunculated)
  • leaflet perforation
  • destruction of leaflet (may cause rupture)
  • abscesses
  • myscotic aneurysms

Below the clip shows a large vegetation attached to the anterior mitral leaflet causing severe mitral regurgitation  with multiple jets due to valve perforation

Secondary/Functional

1.LV dilatation

A  common cause of MR is due to ischaemia or dilated cardiomyopathy which causes remodelling of the LV. In this case, the valves are normal but there is either ischaemic distortion of the LV underlying the papillary muscles or dilatation of the LV underlying the papillary muscles. This causes lateral displacement of the papillary muscles and tethering of the chordae leading to abnormal coaptation of the MV and therefore MR. This can be further exacerbated by mitral annular dilatation

2.Systolic anterior motion of the MV

Another  cause of mitral regurgitation is SAM or systolic anterior motion of the mitral valve. This is a functional cause of MR. SAM describes the dynamic movement of the mitral valve during systole anteriorly towards the LVOT.
This causes obstruction to flow of blood from the LVOT through to the aorta in systole. Subsequently there is poor coaptation of the mitral valve in systole and functional MR.
In the past only hypertrophic cardiomyopathy was thought to cause SAM, but now it is recognised that anything that alters the anatomy of the LV may cause SAM such as structural abnormalities, geometric factors and kinetic factors.

 

References

  1. Nat Rev Cardiol. Author manuscript; available in PMC 2017 Jul 24.Published in final edited form as:Nat Rev Cardiol. 2012 Feb 28; 9(5): 297–309.Published online 2012 Feb 28. doi: 10.1038/nrcardio.2012.7PMCID: PMC5523449 NIHMSID: NIHMS862529 PMID: 22371105
    World Heart Federation criteria for echocardiographic diagnosis of rheumatic heart disease—an evidence-based guideline
    Bo Reményi, Nigel Wilson, Andrew Steer, Beatriz Ferreira, Joseph Kado, Krishna Kumar, John Lawrenson, Graeme Maguire, Eloi Marijon, Mariana Mirabel, Ana Olga Mocumbi, Cleonice Mota, John Paar, Anita Saxena, Janet Scheel, John Stirling, Satupaitea Viali, Vijayalakshmi I. Balekundri, Gavin Wheaton, Liesl Zühlke, and Jonathan Carapetis
  2. European Journal of Cardio-Thoracic surgery Volume 41, Issue 6 June2012, Pages 1260 – 127
  3. The practice o clinical echocardiography : Catherine Otto Elseiver
  4. A sonographer’s guide to the assessment of heart disease : Bonita Anderson

 

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