Functional MR is a term used , when it occurs due to defective LV function, ie LV dysfunction. This happens in spite of normal mitral leaflets and intrinsically normal mitral valve apparatus. The above statement can be instantly disputed because LV muscle is also a part of the apparatus. Then realistically, functional MR occurs due to dysfunctional LV and infact becomes a part of primary. Then, logically we need to replace the term functional MR to dysfunctional MR .A classical double oxymoron isn’t.
Image source : Barbara Brzezińska and Krystyna Łoboz-Grudzień from the Book : Structural Insufficiency Anomalies in Cardiac Valves Mechanism of functional mitral regurgitation. (A) Balance of closing and tethering forces acting on mitral leaflets during systole. (B) Disrupted balance of closing and tethering forces due to local LV remodeling (dark shading). LA: left atrium; LV: left ventricle; PM: papillary muscle; Ao: aorta; ME: mitral regurgitation.
Why fight with nomenclature ?
Classification and nomeclature are the foundation for any medical entity .Since, we build our knowledge over it, If it goes wrong, everything grows out of it is problamatic. This is exactly, is the reason we are blinking at the diagonally opposite results with COAPT & MITRA-FR trials. Ofcourse , it is not a pleasnt job to shake the foundation often as well,as it has its own side effects.
It is expected in cardiology academic forums, we use the term secondary MR. While secondary MR is preferable, I guess myocardial MR may be a more apt term. We know secondary MR is further subdivided into ischemic and non-ischemic.
Need for a combined New entity : Combined Primary and Secondary (cps-MR)
This occurs in two situations
MR begets MR: If primary MR is severe, it invokes LV dilatation and dysfunction of LV . Then it becomes cps-MR by default.
Ischemic MR causing structural damage to chordae: If Ischemic MR ends up in chordal disruption or severe destruction of papillary muscle , it doubles up as combined primary & secondary MR
Final message
What is “functional” in functional MR ?
Nothing. Everything is dysfunctional. The only good thing is that the leaflets are structurally normal. (Please note, any of the other 5 components of MV may still be abnormal) Semantics and nomenclature should not bother us, as long as we understand the mechanism of MR and the principles of its management. Understanding the concept of cps-MR could throw more light on why the intermediate and long term outcome of MVR can be as unpredictable as a tropical storm in nay given case of secondary MR.
Postamble : If LV is part of mitral valve apparatus, then, let us realise the same thing will apply for RV as well. This would imply, right ventricle is a component of tricuspid valve apparatus .(at least to a lesser extent) This fact, is rarely taught to cardiology fellows.There is evidence for progresssive RV dysfunction, to worsen the TR, inspite of the reduced contractlity .The fact,TR begets TR, is less popular among us for no obvious reasom (Rana BS et al Echo Res Pract. 2019 )
Reference
Dr.S.Venkatesan MD 