Kris,
Glad you developed the chutzpah to make yourself known. Your concerns and fears just mean that you are facing open heart surgery, not that you are weak.
You are not likely to be having any heart symptoms at this point. Your valve issues are mild, and you have not shown enlargement of the heart. Symptoms in most people show up after those items show change.
It is, as you say, very difficult to tell, once your judgement is clouded by knowing what to expect. We've all had that question run through our minds. Was that my heart or my brain? It goes the other way, too. Some people have to wonder whether they are truly symptomless, or somehow in denial or oblivious to their own symptoms.
Ten years was only a guess on the part of your physician. It was probably just to answer teh question that he assumed would come next. He knows it's coming, because the process has begun. The symbols of that are the rise in your mean and peak gradients, and the fact that your estimated valve opening size is getting smaller. However, the speed at which this happens is different for each person.
Your body has reacted to a chemical signature on the valve leaflets that indicates your valve has been damaged, and it is coating the valve to try to protect it. The opening size is being reduced due to that calcification forming on the valve leaflets and cusps. Once this coating and depositing process starts, it may take time to complete, but it doesn't stop.
The effective circumference of your valve opening gets smaller as calcification continues, and as time passes, it takes less and less further calcification to narrow the valve further. This is like frosting the inside hole of a bundt cake. The hole starts to fill, and it takes less frosting each layer to make the hole much smaller. The axiom is "The worse it gets, the faster it gets worse."
The pressure gradients fit into this like a thumb on a garden hose. If you run water through a hose slowly, it trickles to the ground. If you place your thumb over the end of the hose, and make the hole smaller, the water builds up pressure and spurts through the smaller opening in a stream. The smaller the hole, the farther the stream shoots out, and the more pressure you have to put on your thumb to keep it in place on the hose's end.
The pressure of the water going through that smaller hole is like the pressure of your blood passing through the smaller aortic opening. As the heart is trying to push the same amount of blood through each beat, the smaller the aortic valve hole, the faster the blood passes through, and the greater the pressure required to do it - pressure that your heart muscle has to provide.
Surprisingly, descriptions of a "normal" valve opening vary. The usual range given for a normal aortic valve opening size is between 1.5cm and 3.5cm, with most people in the 2cm-3cm range. However, normal varies for the size of the person and the size of the heart. In any case, at about 1.5cm (give or take some echo variation), you are now leaving the normal range.
Although you're not really ready to address this fully yet, you should get full copies of your echo reports, including the prior ones. One reason is to establish your heart's own norms, as well as you can.
Cardiologists often don't consider a heart enlarged until its size is greater than a standard. However, your own heart may enlarge quite a bit before it reaches that standard. As such, it may be important for you to bring up how much your heart chamber sizes have enlarged from your own norm, rather than whether they have exceeded a general standard. This would be the case if the doctors get to a point where you have strong symptoms and they seem to be dragging their feet.
Keeping your heart records can only help you, especially if you need leverage. Having it now means you can produce it instantly, vs. trying to get the records from various doctors in a hurry later, when you may not see time as your friend.
I absolutely agree with Gemma and many others above, who said that now is certainly not the time to stop living and wait for this to happen. Now is the time to get really good at the things you will want to continue to do after your surgery.
I would definitely take on that next horse...
Best wishes,