Aortic Dissection

Podcast Transcript

Announcer:

Welcome to Cleveland Clinic Cardiac Consult, brought to you by the Sydell and Arnold Miller Family Heart, Vascular & Thoracic Institute at Cleveland Clinic.

Patrick Vargo, MD:

Hello, my name is Patrick Vargo. I'm one of the heart and aortic surgeons here at Cleveland Clinic and I'm going to be talking about aortic dissection. The things that we look for preoperatively to try and find people that are prone to have a dissection, they have an aneurysm. So they have a normal aortic valve, but the aorta is 5.5 centimeters. And actually in some more recent guidelines, even 5 centimeters, we know those folks are at an increased risk for having a tear, a dissection. Bicuspid valves are certainly prone to it, predominantly because they're prone to aortic aneurysms. So about a third to a half of people with bicuspid valve will have some amount of aortic dilation. Then certainly the connective tissue disorders. I think there are patients Marfan, Loeys-Dietz, Ehlers-Danlos. There's a host of other ones too, ACTA2, SMAD3. And we'll continue to learn more of the genetic mutations that are associated or correlated with dissections.

When you get to around 6 centimeters and the ascending aorta is 6 centimeters, that's where you have the big inflection risk where you go from the low single digits to almost a 30% risk of a dissection that year. So we've tried to head it off ahead of that and bring it to 5 to 5.5 range with elective surgery. Sometimes we'll compare the size of the aorta and the height of the person as well. It's a bad analogy, but sort of like shoe size. I mean if you're 6’4”, you're allowed to have bigger feet without it being unusual than if you're 5’4”. So we try to kind of size your aorta to your height. That being said, there is an absolute too big for any height. Just because you're 6’6” doesn't mean you can have a 6 centimeter ascending. But this is more used in folks who are shorter to some degree. An aorta that's not quite 5.5 is maybe very significant for you if you're 5’1”

This is sort of on the pre-op side here, our CIC before they go to surgery. Type A dissection is a very lethal event, so I've taken it for granted a little bit just saying type A. There's a couple classification systems for aortic dissection. Type A is a dissection that involves the ascending aorta. Type B dissection is a dissection in the aorta that does not involve the ascending aorta, so that's the arch and the descend. If you have any involvement of the ascending, it's a type A dissection. Similarly, there's another system called the DeBakey system. So you have DeBakey one, two, and three. One is a type A dissection, so it involves the ascending, but it goes the length of the aorta. A type two is just the ascending, so it's limited to the ascending aorta. And then type three is your classic descending type B dissection. So those are some of the nomenclature you may hear when people are talking about them.

The other one that goes along with them is you might hear IMH or intramural hematoma. It's on the spectrum of dissection. So a dissection is where you actually have an entry tear into the wall of the aorta and a flap gets created that causes two channels of blood flow. One where it's supposed to be in the lumen of the aorta and another one where they're created a false passage through the wall of it. And if you get a lot of blood flow through the false, through the wall of it, it can compromise blood flow or rupture. That's why it's so deadly. And IMH is where you have that blood entry into the wall of the aorta, but it's not free flowing. It's more of like a bruise. You have just a clot in the wall of the aorta and it's not a flowing channel. So it's on the spectrum of it, but we think of it as a little bit less severe than an outright dissection. Largely treated the same though because it's an emergency, it's an emergency. Sometimes you can watch it a little bit depending on the patient and how risky they are for surgery.

But anyway, when someone shows up to your emergency room with a type A dissection, there's a 1% mortality per hour without surgery. Basically at two days it's a 50/50 chance that they survive if they have not had surgery. So that's why we rush them off to the operating room if they're going to be a good candidate for surgery. I mentioned how a lot of the aortas dissect when they get bigger. They can dissect to normal size as well. It's definitely a distribution so I've seen aortas grow to 10 centimeters. We operated on one, it was not dissected. And then there's other ones they dissect at four centimeters, so it's definitely a range, but we know that inflection point is around five to six centimeters. So the causes of death is this: the inner layer is peeling away from the outer layer of the aortic wall. If it involves a valve, it can cause acute aortic insufficiency or leakiness, which can cause heart failure. If it affects these coronary arteries, it can cause a heart attack, malperfusion of coronary arteries.

You can imagine if all the layers aren't there, the wall is weakened, so you can actually get a rupture that you can tamponade. If this same sort of flap is happening up by the head vessels, the ones that go to your brain, then you can end up with stroke. People present with stroke sometimes. And then similarly, if it happens and causes more blood flow in the false lumen, it compresses that true lumen as it goes to your rest of your body. You can get ischemia or malperfusion to your viscera, so your intestines, your kidneys, and even your limbs. So you feel like a cold limb to present with their leg.

The risk factors, connective tissues, aneurysms. The things that we can kind of control a little more, or at least think we can control are things like high blood pressure, diabetes. Smoking is certainly something we can control as a modifiable risk. We see these with trauma sometimes, so you can have a bad car accident that can cause an aortic dissection. Things that increase your blood pressure like cocaine and methamphetamines can cause dissection.

Heavy weight lifting drives blood pressure way high. So there was a study that you hear about sometimes done way back where they put invasive A-lines in athletes, have them lift really heavy things and while they're lifting up these really heavy weights, their blood pressure goes 200, 300. It shoots way up. So that's why we caution people with aneurysms not to lift heavy things. And then there's other things like inflammation of the aorta, so aortitis, things like Giant Cell. There's also I think salmonella and some other things, syphilis, that cause aortitis, so and that's more inflammation.

So here's some cross-sections of the aorta. Here's an outright aortic dissection, so you have an entry tear and it causes a channel of free-flowing blood. An intramural hematoma is where it may or may not still be there, but basically this isn't free flowing. This sort of forms like a clot, a bruise, a hematoma on the aortic wall.

And then penetrating an atherosclerotic ulceration, this is an example of that where it's a focal area. It's the inner layers of the aortic wall are ulcerated and you get some bruising in that spot, but it doesn't track up and down the aortic wall. They're all spectrums really of the same thing. So you get a tear and you get blood into the wall of the aorta and you get a separation of the media from the adventitia. So there's three layers of the aortic wall, the intima, the media, and the adventitia. Basically the media starts to split, pull away. The word dissection comes from that wall being dissected apart, so you can kind of think of about it as like a hydro dissection. So you get pressurized liquid blood in this case into the wall of the aorta, and then it just dissects the layers apart along the length of the aorta. That's why they call it a dissection, and it can go backwards towards the heart or forward towards your feet depending on where it starts.

During type a dissection, most of them are primary entry tear where the site of injury happens is the arch and the ascending. You have some that we see that will start in the descending and go backwards 6%, or some where we can't even find the tear. It's probably something along the line of a either very small in the CAT scan or it's something that opens and closes and just heals. Generally, most of the dissections happen in the beginning. They usually go antegrade as a heart pumps blood into the wall and it pushes along the length of it. Very often it spirals. We'll see an ascending on the right anterior side of the aorta and it'll curve around the great side and then kind of descend and spiral down.

What's variable is re-entry tear. So there's multiple communications along the length of the flap generally. Usually where it's shearing off the origin of branches, so you have a bunch of arteries that go to your spine and your lungs. They're called bronchioles, intercostals. They're really small along the length of the aorta. You also have the blood vessels that go to your kidneys, intestines, and all these. So as that flap pulls away from those openings, you get communications where blood can go back and forth from the true and the false. A lot of times that's what actually maintains not having malperfusion say in a type B dissection or in a type A that's been repaired the in front, but you have residual dissection. You get some free flowing between the two flaps. So even though you may have flow in the false lumen, it communicates back and forth with the true and doesn't collapse the true. Those are in situations where it doesn't malperfuse. On the other hand, if you get those entry tears where it goes into the false and presses the flap to close the true, that's where you get a lot of malperfusion and parts of the body basically start to die from ischemia.

Well, thanks for having me. It was great talking to you. If you have any questions, don't hesitant to reach out.

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