Hi!
Left atrial enlargement is of course not good, and is something that is considered, but does not seem a key factor. End of diastolic LV diameter is also something to take into account, but seems not as important as the "end of systolic diameter". The logic behind this, i beleive, is that even if LV has enlarged, if it contracts well (that is, your "end of systolic" diameter is small), then the LV systolic function is preserved. In what respect to the regurgitation estimation (none, trivial, mild, moderate, severe), in some cases (as mine), the regurgitant jet is very eccentric, so i was told that many formulas commonly used do not give reliable results. So, the degree is somewhat estimated by the specialist performing the echo.
On the other hand, there are some recent studies suggesting that, for SEVERE mitral regurgitation, early surgical repair may be a better option than a watchfull waiting. By "early" i mean that none of the triggers i mentionned are present. However, at least in my country and according to my own experience, cardiologists seems to prefer a more conservative approach.
Good luck to all!