I read this last week, and I emailed my cardiologist at Stanford and this was the reply
It has been proposed that (based on the syndromes' underlying biology) Losartan may be beneficial for patients with aortic aneurysm due to Marfan Syndrome or Loeys-Dietz Syndrome.
Unfortunately, there is only a tiny bit of trial data supporting even this conclusion. Some large trials to look at this question are in progress, but none have yet reported results. Also (and somewhat of concern) they did not stop the biggest trial on Marfan and losartan early, as they surely would have if an obvious and clear benefit had been seen. We participated in that trial, and are still waiting for them to publish the results.
There is no trial data at all yet available for people with bicuspid valve (your condition), and we are not putting people on losartan at this time. A small trial with only 25 people was recruiting in Michigan... again not enough to make a decision with.
You will hear Hal Dietz (of Johns Hopkins) encourage everyone with aortic aneurysm to take losartan, but he is rather a crusader in this area, and he is operating on very limited clinical information. Basically, he's guessing.
For the time being we are sticking with beta blockers (like metoprolol), the standard and best known medicine to slow enlargement of any and all aortic aneurysms. I would not consider changing until more data become available.
Hope that's clear!