Step I Why does afterload decrease during acute mitral regurgitation?

[JJArms22]

I'm not very good at cardio physiology and I haven't been able to figure this out. What exactly causes the decreased afterload during acute MR? I know it eventually increases but I have no idea what the mechanism is for the acute stage.

 

[TBV]

Haven't reviewed cardio yet but less effective ejection from LV means less pressure in the aorta until you get compensation by abnormal filling pressures?

 

[zhopv10]

So after load is basically the pressure required for the LV to expel the blood or the pressure that the LV "see's" in systole if you will. Generally this is largely determined by the TPR. However in mitral regurg you have an open valve and the blood can exit out the open mitral valve thus creating an route of lesser resistance. So you have blood going out the mitral valve that is lower pressure and some blood going out the aorta at normal pressure so the Afterload that the LV effectively "see's" is lower than normal.


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[JJArms22]

So after load is basically the pressure required for the LV to expel the blood or the pressure that the LV "see's" in systole if you will. Generally this is largely determined by the TPR. However in mitral regurg you have an open valve and the blood can exit out the open mitral valve thus creating an route of lesser resistance. So you have blood going out the mitral valve that is lower pressure and some blood going out the aorta at normal pressure so the Afterload that the LV effectively "see's" is lower than normal.


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So basically the fact that you have less blood in the ventricle means less resistance to pump against?

 

[zhopv10]

More that there is a route of less resistance than going out the aortic valve. It is basically as if you lowered the pressure required to open and push blood out the aortic valve.


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[zhopv10]

So basically the fact that you have less blood in the ventricle means less resistance to pump against?

Also just to address this remember that actually there will be more blood in the left ventricle. Since you are sending blood back into the left atrium during systole (regurg) then that blood will drain back in during diastole so you actually get volume overloaded dilated left ventricle if I remember right.


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[Entadus]

In mitral regurgitation, the valve is incompetent (meaning the LV is pushing some of its blood back into LA instead of through the Aortic valve into Aorta)

So therefore there will be less blood in the Aorta at the end of systole, meaning the pressure across the aortic valve will be less.

From there just make the jump and realize that Lower systolic pressure = Lower afterload

Also just to address this remember that actually there will be more blood in the left ventricle. Since you are sending blood back into the left atrium during systole (regurg) then that blood will drain back in during diastole so you actually get volume overloaded dilated left ventricle if I remember right.


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Yes, it would not be a Hypertrophic (High pressure) situation but rather a Volume-overloaded (dilated) picture

The volume dilation would initially happen to LA (with the potential for a.fib). The backup would lead to Pulmonary hypertension with ensuing pulmonary edema