Mitral regurgitation is one of the most common lesion of rheumatic heart disease .Mechanism of MR in acute rheumatic fever is different from chronic rheumatic heart disease.
Acute Rheumatic fever
The following mechanisms contribute to MR of acute rheumatic fever
- Edema of leaflets (Carey Coombs murmur )
- Valvulitis
- Small verrucous vegetations (See Image )
- Acute LV dilatation in fulminant cardiac failure.
* Note : Acute rheumatic fever in its first episode can never cause stenosis however fulminant the fever may be .There is no acute mitral stenosis .But , during recurrence and reactivation some amount of stenotic process may occur. Still , recurrence and reactivation are more often related to significant MR rather than MS. ( Isolated mitral stenotic lesions rarely give h/o recurrent rheumatic fever )
Chronic rheumatic heart disease
As the mitral valve gets progressively damaged any combination of MS or MR occur .The following mechanism are involved in the genesis of MR. (Pathology of Mitral stenosis is not discussed here)
- Chordal shortening, tethering , pulling , prevent proper co-optation
- Chordal lengthening
- Chordal disruption (Minor > Major )
- Prolapse of either AML or PML (Not both ,unlike myxamatous MVPS)
- Infective endocardits of leaflet
- Perforations of leaflet
- Annular dilatation
- Fibrosis of posteromedial/Antero-lateral pap muscle(Rare )
- Left atrial pathology
* The direction and the width of MR jet is related to the mechanism of MR.
If there is chordal shortening due to fibrosis of mitral valve co -optation plane is altered . The degree of chordal shortening , pap muscle fibrosis (rare) symmetry of chordal involvement determine the MR.
Rheumatic mitral valve prolapse
- This could be more common than we realise.
- It can be true or pseudo.
- True prolapse occur due to chordal weakening or lengthening .
- In chordal disruption the leaflet tips usually become flail
Since rheumatic process fixes the PML first , the AML appear to overshoot the plane of PML and appear as prolapse.(Pseudo )
The sail like AML commonly directs the jet posteriorly and laterally .(Murmur conducted to axilla and back )
It is rare for PML to prolapse in RHD , if it does occur , it directs the jet anteriorly (murmur conducted to aortic area mimic AS !)
It is rare to see a perfect central jet in RHD . presence of Central jet is a good sign to consider mitral valve repair.
Myocardial involvement in RHD.
Even though rheumatic fever is a classical example for pan-carditis , it is surprising to note (Of course fortunately !) how myocardium escapes in the chronic process of RHD.
Is it really true , myocardium do not get involved in chronic RHD ?
Clinical cardiologists rarely discuss this issue. Pathogists indeed have documented significant lesions within myocardium . Involvement of left atrial myocardium and rarely ventricular myocardium in the sub mitral zone can influence the degree of MR
* Even in acute rheumatic fever with fulminant carditis , myocardial involvement is disputed by many ! . My belief is , there will definitely a subset in both acute and chronic forms of RHD , in which myocardium gets involved . In our institute LV dysfunction associated with RHD occur in up to 5 % of RHD population .
Importance of knowing the mechanism of MR
Two aspects appear important
1. Is there a potentially reversible component in pathology so that we can wait before intervention ?
I have seen children referred for mitral valve replacement due to severe MR . In due course MR regress by the time they reach the tertiary center (waiting period included ) At least one child i remember, the MV surgery was canceled due to spontaneous regression MR.
It was later found the MR was more of valve inflammation than degeneration .
* Always think about the possibility of reversible rheumatic MR in every severe isolated MR in children (Do not apply this rule in adults or in combined MS or MR ) Do a ESR, ASO and start an intensive anti inflammatory therapy , aspirin with strict penicillin prophylaxis .With this one can definitely postpone the surgery in few cases and may avoid it altogether !
2. Surgical implication
If we could delineate the exact pathology of MR it will facilitate the repair . Annular reduction and neo chordae etc . Of course ,the surgery could be very difficult in scarred mitral valves , Dr Sampath kumar *of AIIMS New delhi , India would feel other wise !
*A pioneer in mitral valve repair in chronic RHD (See reference 2 )
Questions that need answers
How is balloon/Surgery related injury different from rheumatic process ?
Why is rheumatic mitral vale prone for bacterial infection ?
What is the relationship between extent of aortic valve involvement and degree of mitral valve involvement in RHD ?
Reference
1.http://circ.ahajournals.org/content/94/1/73.full?sid=10599470-3563-4c38-b688-c5fc8c032f96
2. http://icvts.ctsnetjournals.org/cgi/reprint/5/4/356
Books
There two popular books exclusively for cardiac pathology
1.Silver
2. Renu Virmani
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Dr.S.Venkatesan MD 