DALLAS, Oct 7 -- A chemical version of a "balloon-popper" has been identified that may help explain why some aortic aneurysms rupture and others do not. The report appears in today's American Heart Association journal Circulation.
Aortic aneurysm occurs when the outer wall of the aorta, the main artery feeding the heart, weakens and a balloon-like structure is formed at the weak spot of the aorta. People with an aortic aneurysm sometimes say that their heart feels as if it has dropped down into their abdomen. But often the first symptom may be a sudden heart attack, which occurs when the aneurysm ruptures, spilling out blood.
Why some aneurysms rupture and others do not is a medical mystery that is a little closer to being solved, say the study authors, William Pearce, M.D., professor of surgery at Northwestern University Medical School in Chicago and William McMillan, M.D., fellow of vascular surgery. Researchers have known that aneurysms that grow larger than five centimeters (about three inches) in diameter are prone to rupture, but the fate of smaller ones is less predictable.
Pearce and his colleagues studied 19 patients whose aneurysms were being repaired. The researchers measured levels of "metalloproteinase" (MMP), a protein that dismantles collagen, cellular scaffolding found in the aorta wall.
Individuals whose aneurysms were 5-6.9 cm. had four times the amount of MMP than those with aneurysms 3-4.9 cm.
Having too much MMP may be the reason some aneurysms expand and others do not.
"Present relationships between aneurysm size and expression of particular MMPs could be exploited by therapies designed to slow aneurysm expansion and prevent rupture, thus avoiding the need for surgery," says Dr. Pearce.
Each year about 40,000 individuals undergo operations to repair aortic aneurysms in which the aneurysm is replaced with a plastic tube.
Contact: Dr. Pearce can be reached at (312) 908-8064