Hi Sandra - welcome to the forum. I have some similarities to you though not quite the same.
I had aortic valve replacement in January 2014 when I was 60. I too had a 19mm bovine valve, and my average gradient post surgery was 18, peak 36. Three years later in 2017 at my annual echo my average gradient had suddenly jumped to 32, peak to 58, effective orifice area was 0.76. I was immediately referred to a cardiac surgeon for a surgical reassessment.
I had TOE (TEE) and further echos. There was nothing wrong with my valve - the surgeon explained that I had “moderate patient prosthesis mismatch” - my valve is effectively too small for my body size - I’m slim, I’m 5ft 4ins (162cm) and 46 kilos. My pressure gradients on annual echos have remained in the 30’s average and 50’s peak, always the effective orifice area is at 0.76. I have a very loud murmur which sounds like the murmur of aortic stenosis but it isn’t. I have no symptoms. I’ve learned that pressure gradients on echo and orifice areas do not appear to have the same significance or meaning as with a native valve on echo. For example, the real orifice area of the 19mm valve is clearly not just 0.76 but that is the "effective area”, and with me it’s due to the mismatch between my body size and the valve. The cardiac surgeon would not have been able to put in a larger valve because the size implanted is due to the size of the annulus which is accurately measured during surgery. The annulus is very fibrous and tough and cannot take a larger valve than it’s measured size (I believe a valve can be implanted supra-annularly which means a bigger valve can be put in).
The surgeon I saw in 2017 said he would recommend a mechanical valve when I need the valve replacing…I would not want that due to the ticking noise and warfarin. The surgeon wouldn’t do a redo back then as he said my mortality risk was "too high” - well I think that gets higher with age but once the valve is degenerated then that over rides the risk. When my valve goes wrong then I will go for a tissue valve again..
You wrote that one of your leaflets is severely calcified - would that be the cause of your increased pressure gradients ?
I take vitamin K2, been taking it since 2008, I started taking it after reading on a cardiologist’s blog about it and also because it helps with osteoporosis. I had some calcification on my native bicuspid valve…though I don’t think the calcification on it was too bad, it was only “moderate” when I had the valve replaced. I begin to question whether I should have had surgery originally when I did as I had felt very fit and well then…but the original surgeon said I could have “sudden death” - I wonder about that, but can’t go back in time LOL
All the very best to you, do let us know how things go.