I am not a doctor, but my understanding is: (1) the rate of aortic dissections for aneurysms of less than 50 mm is very low (I believe around 1% or less) provided there are no other risk factors, like Marfans or a genetic issue; and (2) the physics involved with stenting the ascending aorta are simply very challenging (short distance, blood vessels branching off, etc.) compared to the abdominal aorta - when I asked my doctor (in the US) about it, his view was that stenting the ascending arch was likely at least five years away from being a viable and reliable option.