Aneurysms: Descending Thoracic Aorta

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Dr. Morris: Welcome to an MUSC Health Podcast. Hi, I'm Dr. Pam Morris, and I'm here today with Dr. John Ikonomidis, and we're talking today about aneurysm of the ascending aorta. How common is this problem, Dr. Ikonomidis?

Dr. Ikonomidis: Ascending aortic aneurysms are not very common. There's a fair amount of population based studies performed on this, probably the most of which comes from Yale University, that shows that the incidence of ascending aortic aneurysms is probably six per hundred thousand patient years. In other words, it's a relatively uncommon condition, much more uncommon for example than aneurysms of the abdominal aorta, which you hear about a lot more.

Dr. Morris: Let's define for our listeners what an aneurysm is exactly.

Dr. Ikonomidis: So an aneurysm is a localized or diffused dilation of the aorta greater than one point five, one and a half times its normal diameter. And it involves all of the layers of the wall of the aorta.

Dr. Morris: And we're talking specifically about the aorta as it leaves the heart through the aortic valve?

Dr. Ikonomidis: Correct. In the chest the aorta is classified into three regions. First region is the so-called ascending aorta, which starts at the base of the heart, and travels up towards the head, and it stops at approximately at the top of the breastbone. And that section of the aorta is referred to as the ascending aorta. At that point it then arches backwards into the left, and gives off three blood vessels that supply the head and the arms, and that section of the aorta is referred to as the aortic arch. When the aorta begins to go beside the spine on the left hand side, down to the diaphragm, which is the muscular sheath which separates the lungs from the belly, that section of the aorta is referred to as the descending thorasic aorta. What we're talking about today is the first section of the aorta, the ascending aorta between the heart and the aortic arch.

Dr. Morris: What sorts of diseases would cause an aortic aneurysm?

Dr. Ikonomidis: The causes include degenerative causes, which have as risk factors hypertension, high blood pressure, smoking, high cholesterol. That forms a very large group. There are hereditary conditions which predispose to aneurysms, some of which involve so-called connective tissue diseases, so things like Marfan Syndrome, Aeler's Downler Syndrome are relatively rare, but real causes of ascending aortic aneurysms. There is a familial thoracic aortic aneurysm syndrome, in which patients do not have identifiable connective tissue disease. But clearly aortic aneurysms run in the family. There are certain other abnormalities which predispose to aortic aneurysms, the most common of which is something called a bicuspid aortic valve. And the aortic valve is one of the heart valves that is between the left ventricle, which is the main pumping chamber of the heart, and the ascending aorta, which the left ventricle pumps into. So the idea is that when the left ventricle empties blood into the aorta, it then relaxes again to fill up with blood. And to prevent the blood from leaking back into the ventricle, there's a valve there that closes. That valve is the aortic valve. In the majority of individuals that valve has three parts, or cusps, which open and close. But in about one percent of the population, two of those cusps are fused at birth, causing a so-called bicuspid aortic valve, as opposed to a tricuspid aortic valve. In those patients there is a predisposition towards aortic aneurysms, and we see that fairly commonly.

Dr. Morris: I would imagine that the degenerative diseases would tend to occur in older individuals, perhaps where the congenital, or genetic problems


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