Running at Altitude

What is the impact on the heart and blood when running at a higher altitiude (up to 9,000 feet), and how much more stress would it put on an aortic aneurysm(1 cm bulge)?  What steps could be taken to minimize any negative impact on the heart?  This would be in an ultra race with total ascent around 15K feet and descent 20K.  Currently a beta blocker is taken to keep the heart rate below 155.

[CCFCardio MD1]

This is a complex question as there are many factors that lead to risk of complications from an aneurysm (size and location of the aneurysm, underlying causes, other medical conditions, rate of growth of the aneurysm, etc).  Anything that increases heart rate and blood pressure will increase the stress inside the heart and vasculature which in turn may have negative effects on an aneurysm.  A beta-blocker is used to reduce the stress inside the heart.  Exercise at elevation produces complex changes in the body, most of which are dependent on how acclimated a person is to that altitude.  In general, however, blood pressure and heart rate are elevated.