The mechanism of MR in ischemic /Functional is complex. Technically, pure ischemic MR should have a structurally normal leaflet and the subvalvular mechanism dominates But,the combination of the two is also prevalent. In fact, a degenerative component is added to this in many elderly patients.
Mechanism of Ischemic mitral regurgitation
Any of the following may contribute either alone or in in different combinations.
- Global LV dilatation with or without annular dilatation
- Spherical left ventricle
- Altered inter papillary muscle distance (Degree and direction of posterior vs apical displacement of pap muscle)
- Chordal shortening /Lengthening/Abnormal tethering
- Leaflet tenting distance and volume
- Basal LV dysfunction and Local LV (Sub-mitral) remodeling
We have come a long way , since the days of Carpentier and Duran who did pioneering work .It involved partial or complete mitral annular stabilization with surgical ring technology that helped us to change the shape of the annulus. Advanced imaging, with 3 D printing will enable us to procure perfectly matched designer valve rings and (may be leaflets also) in the near future. Percutaneous mitral valve Interventions, with clips , valve, are going to dominate the mitral valve therapeutics.
Still, we are largely ignorant about Individual contribution from various components in the genesis of ischemic /functional MR. This becomes important because the preservation of native valve is better on any day than replacing. One thing is very clear, even though left ventricle forms part of mitral valve apparatus, the degree of LV dysfunction has no linear correlation with the severity of MR . Its a well-known fact, even severe LV dysfunction (Say < 25 % )may enjoy the company of a perfectly competent mitral valve. It’s interesting to note uniform global LV dysfunction cause more of central MR , while dispropotinate basalLV dysfunction especially the posteroinferior pap muscle cause eccentric jet. One more curiosity is mitral regurgitation improving with worsening disease as contractile force weakens.(Functional MR depends on LV function you know !)
We have witnessed at least two patients who had a significant MR following an inferior posterior MI which was managed medically, showed dramatic regression in the degree of MR when he had anterior MI later*.The pleasant irony was apparently due balanced dysfunction of anterolateral pap muscle that happened in countering the original postero-medial pap muscle dysfunction.(*Allowing second MI to happen is of course a treatment failure !)
Image source -Christos G. Mihos Journal of Thoracic disease Vol 8, No 1 (January 2016)
Mitral valve is essentially avascular structure, Still, ischemia affects this valve not by valve necrosis but by other sub valvular mechanisms .Note the MR here is due to poor motion of PML due to ischemic LV dysfunction.
Ischemic MR in early hours following STEMI (also NSTEMI) is still a nightmare. We realized in a harsh way, it’s rarely corrected fully even with a successful IRA plasty. (Especially LCX and posteromedial pap muscle that is in extreme distress) In fact , many of the mechanical complications that lead to flash pulmonary edema would need emergency CABG rather than primary PCI. (What to do for Ischemic MR ? An excellent review article( Elsayed Elmistekawy Curr Opin Cardiol 2013, 28:661–665)
Mitral valve, though looks like an obedient, innocuous structure that silently does its job , only in special times, it makes us realize, its the most critical part in the entire heart.(Guarding the lung against flooding when the left ventricle experiences turbulent ischemic times during ACS.) Note -Acute MR often kills , not the ACS as such.
The mechanism of MR in various pathologies is comparable to the behavior of a cow grazing in an arc tethered to a poll. Normally its expected to follow a set pattern. If it behaves wayward, one may need to tighten the rope(Chordae), or loosen it, strengthen or move the poll(Pap muscle) . . . still more options like whipping (clipping ) the cow(Leaflet) may be tried. Of course ,ultimately one may need to replace the cow (MVR). EP guys do have an electrical solution to tame this cow , called CRT to regress Ischemic MR .
Reference
2.Mitral valve repair over five decades Ann Cardiothorac Surg. 2015 Jul; 4(4): 322–334
