Can mitral valve act as a safety valve in patients with dilated cardiomyopathy ?
Posted Jan 25 2009 5:00pm
Competence of mitral valve is vital for proper hemodynamics of heart .A trivial mitral regurgitation ,is observed in nearly 10-20% of normal population detected by doppler echocardiograpgy .This is other wise clinically insignificant. In fact , it is expected , the sonographers do not report this, as it might increase the patient anxiety.
Can a mildly incompetent mitral valve be a hemodynamic advantage ?
Left ventricle , physiologically can have only one exit, namely LVOT and aortic valve.If there is normal impedance , at this level (LV after load ) it is refered to as physiological .In disease states , as in cardiac failure there is raised after load or LV wall stress.this makes the LV struggle to pump blood into aorta.The more the dilatation the more the wall stress (Laplace law). more the wall stress more the after load.
The main principle of management of cardiac failure for decades has been promoting LV inotropism .Now we have realised this is fundamentally a wrong concept, (Except in acute heart failure). Hence the main option available now is to reduce the after load , ACEI do that most effectively and proven to improve survival.
What is the effect of trivial or mild MR on LV after load ?
It is a hemodynamic fact for MR to increase LV contractility and Dp/Dt due to a relative reduction of after load.
In patients with cardiac failure , even a mild improvement in LV contractility can give a symptomatic improvement .
Can mitral valve act as controlled safety valve allowing only a trivial or mild MR ?
This may be difficult . But it happens naturally in many of our patents in cardiac failure .
Probably , these are same patients who come under the 20% incidence of physiological doppler MR.Other group could form the functional MR*
We have found, patients with DCM with mild mitral regurgitation tolerate excercise better than patients who have very competent and rigid mitral valve.It is presumed a mitral valve which gives in a little bit , decompresses the LV with a symptomatic benefit.But if the MR , is occurs in an eccentric path or it results in significant volume burden the potential advantage becomes a liability.
*Functional mitral regurgitation. Functional MR is said to occur , when patients with cardiac failure, and resultant dilatation of mitral annular ring, and lack of opposition of leaflets
While milder forms of MR are well tolerarted , when it occurs acutely ( even if it is mild) , it can be dangerous and result in sudden pulmonary edema .This usually happens in acute MIor infective endocarditis etc.
Minimal or mild mitral regurgitation without any significant volume overlading in some of the patients with dilated cardiomyopathy could bring a hemodynamic advantage .
So one may not unduly worry about , a mild MR (central jet) in patients with DCM.It could be after all a safety exit for overstrained LV
We will report the results of the ongoing study about the impact of presence /absence of mild MR on the 6 minute walk test in patients with dilated cardiomyopathy.