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Why mitral valve replacement carries poorer outcome than aortic valve replacement ?

Posted Jul 06 2009 6:18pm 1 Comment

The valve replacement surgery is one of the great innovations in cardiac surgery. The common disorders that require mitral and aortic valve replacement are

  • Degenerative , calcific  aortic stenosis and regurgitation.
  • Rheumatic mitral, aortic valve disease.
  • Ischemic heart disease -Ischemic MR
  • Some cardiomyopathies

The mortality in valve replacement surgeries vary  between AVR, MVR, and DVR.

AVR – 2-5%

MVR 4-12%

DVR  6-15%

Source CTS.net

Determinants of outcome

General factors applicable for both valves

Elective vs Emergency

LV function

Associated CAD /CABG

Co morbid conditions

The following observations  can be  made  in valve replacement surgery

  • Mitral valve function is closely linked to LV function while Aortic valve  is not .
  • AVR  patients always do well than MVR in  the  immediate post operative period
  • Aortic stenosis patients do well than aortic regurgitation .
  • Mitral stenosis patient do well than mitral regurgitation
  • In   DVR  the excess mortality is due to  the addition of MV , not by  AVR .

Aortic valve replacement has better post operative outcome when compared to mitral valve replacement ,Why ?

Aortic valve has only two components namely a  annulus  and leaflets. The prosthetic  aortic valve  replaces both these natural components . Mitral valve has 6 components , prosthetic mitral valve has only two components . Hence  , any prosthetic mitral valve is far inferior to natural mitral valve . The  pap muscle, chordae, and LV muscle fail to assist the artificial  mitral valve.  So , between AVR and MVR   AVR is far perfect  prosthetic surgery and  the hemodynamics   mimic as closely to the natural valve.

Why aortic stenosis patients do better than aortic regurgitation ?

Aortic stenosis  results in severe  LV outflow obstruction .The LV struggles to pump across the obstruction.So , once it is relieved by a prosthetic valve , there is great relief for LV .We know the the aortic valve orifice becomes <1cm2 in critical AS . (Like a pin hole !) .Prosthetic aortic valve at least doubles or triples this orifice and the LV enjoys this sudden relief  and  becomes active or even hyperactive in immediate post operative phase , later  it    settles to a near normal LV function. It has been observed even very severe LV dysfunction associated with aortic stenosis recovers well .

What happens  in AVR done for  dominant or isolated  aortic regurgitation ?

Here the situation  is dramatically opposite.The purpose of  prosthetic aortic valve is  reduce the  aortic valve orifice .

In AR ,  the  left ventricle  is  used to eject blood  merrily  across LVOT   without  much  resistance  ,  only to find part of the blood returning  back into the chamber again . In  the next beat it does the same and  the cycle   continues for ever .This in due course , dilates the LV  and increases  wall stress and afterload.  LV dysfunction follows .This  takes long time to set in.That’s why chronic asymptomatic AR patients  do so well and they do not require surgery until after the onset of LV dysfunction .(End systolic LV >55mm)

After the aortic valve replacement , the LV suddenly finds  the newly introduced prosthetic valve  a hindrance !. As all artificial  valves  have  less than the natural orifice. LV   takes some time to adapt to the new environment . The EF initially may slightly fall and recovers later.

If pre- operative LV dysfunction was significant the immediate post operative period can be critical.As even a slight fall in EF can result in prolonged hypotension.Many of these   pateint may  require  prolonged inotropic  support.

What are the differences between MVR done for mitral stenosis and MVR done for mitral regurgitation ?

Here again ,  the same principles apply.The Mitral stenosis patients do well following MVR than MR patients.This is because of two reasons .  MR patients  have dilated LV  and may also have associated impaired LV function .A chronic MR is  some   what  a stress reliever  for the LV  ,  as  with every contraction it can decompress a little   bit  . It is an important hemodynamic  fact  ie  ,  presence of   even a  trivial  MR helps the LV to tackle the  it,s  afterload  easily by increasing the dp/dt and also the EF.

So when we introduce a a fully competent prosthetic mitral valve all of a sudden the LV again struggles for some time.

Final message

MVR  patients has less favorable  clinical outcome than AVR .

Coming  soon

How  different is the anticoagulation  protocol difference between AVR  and  MVR ?

Comments (1)
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Patients with a biological valve may need of 10-15 years. Mechanical valves may also fail, so patients should inform their doctor if they have symptoms of valve insufficiency. Patients with mechanical valves must take blood-thinning medication at the end of their lives. Because these medicines increase the risk of bleeding in the body, you should always be used in medical notification bracelet and the doctor or dentist that you are taking anticoagulant medicine. Even if you take anticoagulant medication, you should always inform your doctor and dentist to have had valve surgery. If you have any surgery or dentistry, you should take antibiotics before the procedure. The bacteria can enter the bloodstream during these procedures. If bacteria enter the repair or artificial heart valves, can lead to a serious condition called bacterial endocarditis. Antibiotics can prevent bacterial endocarditis.

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