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Posts Tagged ‘papillary muscle dysfunction’

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.ischemic mitral regurgitation functional carpentier drsvenkatesan venkatesan madras medcial college 002It looks to me ,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

1.Yiu S.F.,Enriquez-Sarano M.,Tribouilloy C.,Seward J.B.,Tajik A.J.Determinants of the degree of functional mitral regurgitation in patients with systolic left ventricular dysfunction: a quantitative clinical study. Circulation 2000;102:14001406

2.Mitral valve repair over five decades  Ann Cardiothorac Surg. 2015 Jul; 4(4): 322–334 

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Ischemic MR is a critical entity in determining the long-term survival in post MI patients as well as dilated cardiomyopathy. (Originally described  by J. H. Philips Ann Intern Med. 1963;59(4):508-520)

The mechanism of MR  can really be complex .We know mitral apparatus consists of  six components.The sub valvular apparatus plays a key role. LV  free wall especially the inferior and lateral segments which subtends the two papillary muscle has a critical role in maintaining the mitral valve competency .

There seems to me a complex mechano -anatomical behavior of subvalvular structures in progressive LV dysfunction especially so in ischemic cardiomyopathy. The LV size, shape eccentricity in attachment of leaflets to papillary muscle is (Simply called altered geometry ) .The intraventricular desynchrony ,disproportionate  LV dysfunction also make MR more likely .

Beware of a striking  physiological irony in ischemic MR.

While infero basal free wall dysfunction occurs commonly with  LCX/RCA Infarct and  is commonly associated with Ischemic of MR .There is something unique happens . . . when the infarct is larger and involves the head of the papillary muscle .Yes, it attenuates the severity of MR.(Friendly Infarct extension!) The mechanism is , papillary muscle dysfunction  tends to prevent apical tensor effect leading to   improved tethering of leaflets .This may appear a blessing in terms of  prevention of acute pulmonary edema. This also explains why some patients are as cool as cucumbers and lie flat comfortably with silent lungs in spite of severe LV dysfunction .The LV is too weak it doesn’t  have contractile energy to generate acute  severe MR.

Here is an illustration  from circulation .Note: The Infarct extends to pap muscle head, the MR is arrested.

Image courtesy : Emmanuel Messas J. Luis Guerrero, Mark D. Handschumacher, et all  Paradoxic Decrease in Ischemic Mitral Regurgitation With Papillary Muscle Dysfunction Insights From Three-Dimensional and Contrast Echocardiography With Strain Rate Measurement Circulation. 2001; 104: 1952-1957

Further debates 

Papillary muscle dysfunction may be protective against progressive MR.Still ,sudden papillary muscle rupture result in flash pulmonary edema and death is imminent . How ? Complete rupture  causes flail free-floating leaflet that prolapse into LA and result in free MR.While simple dysfunction without flail leaflet is less likely to cause MR . The key determinant seems to be the net force that keeps the alignment of mitral,leaflet at annular level.

In this context , we also realise the impact of primary PCI on the  regression of  Ischemic MR is not uniformly positive.Reasons not clear.

Final message

Ischemic MR  due to LV free wall infarct is a near knockout punch , that may determine the ultimate ACS  outcome. However , a simultaneous lesser punch ( by a friendly devil ! ) on the adjacent head of papillary muscle neutralises the effect of Initial Injury. While such non academic scripts are enjoyable , we are still a long way away to understand this anatomical ,hemodynamic conundrum.

Reference

1.

mechanism of ischemic mitral regurgitation papillary muscle dysfunction

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