Dilation vs Hypertrophy

[NSV]

Hi,

I was wondering if someone could help clarify these two terms for me? Why does Mitral Stenosis cause Left Atrial dilation while Aortic Stenosis cause Left Ventricle hypertrophy?

Thank you

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[Instatewaiter]

Dilation is the enlargement of the chamber. Hypertrophy is the thickening of the walls caused by enlargement of the myocytes.

So for the left ventricle, things that cause volume overload or remodeling will cause dilation. So aortic regurgitation (volume overload) or non-ischemic cardiomyopathy (remodeling) cause LV dilation.

Left ventricular hypertrophy is caused by anything that increases afterload (or genetic conditions) like aortic stenosis or longstanding hypertension or hypertrophic cardiomyopathy. Note this should be differentiated from infiltrative conditions which do not induce myocyte hypertrophy but do induce LV thickening (Amyloidosis, Fabrys)

 

[iBS1972]

There will be some left atrial hypertrophy, which occurs before the left atrial dilation. Increased afterload will in general always result in hypertrophy of the wall, as a result of trying to provide more force/pressure to overcome the increased afterload. Years later, the left atrium will be more dilated than it is hypertrophied because it is not very muscular so it can only hypertrophy to a small degree. And when the limits have been reached, dilation occurs predominantly (though dilation occurs before this too). In response to increased afterload, the left ventricle predominantly hypertrophies to a greater degree because it is much much more muscular than the atrium. It too will eventually undergo a predominantly dilatory remodeling after years of prolonged increased afterload. Note, this dilation process is initially advantageous as it gives the heart greater force, (Frank-Starling curve: increased volume/stress leads to increased stroke volume) however it will eventually stretch to such a degree that this increased stroke volume no longer occurs and the heart is so dilated that it actually starts becoming less and less able to contract. At this point, it has reached a point what we call "heart failure" (arrow below).