Thoracic Aortic Dissection
Robert D McBane, MD: I'm Rob McBane, director of the vascular medicine program at Mayo Clinic in Rochester, Minnesota. Today we will be discussing the very important topic of acute and chronic type B thoracic aortic dissection for theheart.org|Medscape Cardiology.
I am joined today by my colleagues Dr Tom Bower, the chair of vascular surgery at Mayo Clinic Rochester, Dr Alberto Pochettino, from cardiovascular surgery, and Dr Randy De Martino from the section of vascular surgery at Mayo Clinic Rochester.
Tom, why should our audience care about thoracic aortic dissection? What is the big deal with this topic?
Thomas C Bower, MD: Although it is rare, with an incidence of approximately three per 100,000 patients, for us as surgeons or interventionists, it's exceedingly challenging and one of the most vexing acute aortic syndromes that we deal with. It's important to first define the difference in classification of aortic dissection.
The DeBakey and Stanford classifications, which are pushing 4 years in age, are probably outdated, but it is very clear that dissections involving the ascending aorta and arch become much more of an emergency than many of the type B dissections. In fact, type B dissection occurs less frequently than type A dissection. Mortality risk is much higher in the emergency setting in type A dissections.
There has been a real change in the management of type B dissections, in which the intimal flap begins somewhere at or distal to the left subclavian artery. Much of the change has been prompted by the advent of endovascular therapy.
One of the greatest advances in vascular and cardiovascular surgery in recent years has been the use of stent grafts to treat infrarenal abdominal aortic aneurysms and thoracic aortic aneurysms. This technique is superior to open repair at many centers, and now it is being introduced and has been used often to treat complicated type B dissections.
Stratifying Dissections
Dr Bower: If we want to set the stage for this discussion, the first thing we need to do is define the difference between acute, subacute, and chronic conditions. Acute dissection is less than 2 weeks in duration, subacute is between 2 weeks and 3 months, and chronic dissection is beyond 3 months.
We have to decide whether patients are complicated or uncomplicated. Complicated by definition would mean rupture of the aorta or a malperfusion syndrome to one of the major organ beds, either by static or dynamic branch-vessel occlusion. Patients who present with ischemia to the brain, the spinal cord, the extremity, the gut, or the kidneys would be considered complicated.
The uncomplicated dissection (although there are some people, including Chris Nienaber and others,[1] who argue that every dissection is complicated) would be in a patient who comes in with pain and elevation of blood pressure. The blood pressure becomes easily manageable. The pain goes away with medical management. A scan is done. There is no aneurysmal dilatation or malperfusion syndrome. Currently, that is where the controversy exists.
If we walk through this, as I see the challenges now, the first is to come up with a better scheme for classification of these dissections, which will help the clinician manage them, and then the question is who should be treated, how should they be treated, and when they should be treated?
Who Requires Intervention?
Dr McBane: Albert, we now we have some classification schemes—acute, chronic, complicated, and uncomplicated. Help us to discern which of these patients in the acute setting needs intervention.
Alberto Pochettino, MD: Some of that goes back to how we got involved in managing dissection and focusing on type B dissection that is beyond the subclavian. The history goes back to having to intervene when a patient is clearly dying. A dying event is what we now call complicated dissection—a rupture or malperfusion that is significant enough that the patient has an organ in jeopardy that compromises his or her survival.
Early on, the only option was open surgery, and open surgery (we are talking about 1960s and 1970s) involved resecting some of the thoracic aorta to reestablish true lumen flow. Very early on it became clear that that operating on all-comers with complicated type B dissection was very morbid and associated with a high mortality. When you had nothing else to offer to somebody who is in trouble, that was the treatment.
The advance of endovascular treatment has allowed us to provide something that succeeds in increasing true lumen flow, which is for most malperfusion the goal, or to stop the leakage if it is ruptured without having to open the chest and replace the thoracic aorta. And the treatment of endovascular therapy for complicated type B dissection over the past decade or so has become so good that using open technique has pretty much disappeared. The morbidity and mortality profile of endovascular treatment of complicated dissection is far superior to anything else. The patient who is dying, either from rupture or from organ malperfusion, should be treated. End of story. Endovascular treatment is the preferred route.
The next issue is the management of patients who have a non–life-threatening dissection, who traditionally were treated medically. The issue to some degree is why treat someone who is going to do fine in the short term? If you look at International Registry of Acute Aortic Dissection (IRAD) data,[2] uncomplicated type B dissection has an acute mortality of less than 10%. Within the first few months, the mortality of an uncomplicated type B dissection is 5% to 10%. However, if you look at the same data 5 years out,[3] almost half of those patients will die of typical complications of their dissection. That is the driving force of doing something without hurting the patient. You have to start from that 10% mortality up front, and yet get this patient to survive much longer than 5 or 10 years, and that is the benefit of endovascular treatment in patients who are not dying but who are not going to do well long term if left alone.
Aortic Dissection in the Acute Setting
Dr McBane: The patient comes into the emergency room. The diagnosis is made. The patient is treated in the hospital, and discharged, and it is now 2 weeks later, and the patient is into the subacute, maybe even chronic, setting. The patient comes to the vascular or cardiac clinic. If we are going to intervene, when would we want to intervene on this patient? What is the timing? How long should we wait? Should we extend the time or should we offer a rather prompt repair of the dissection?
Randall R De Martino, MD: In the acute setting without complications, you have to intervene right away. Once we realize that a patient has an uncomplicated dissection, the question is, when is the optimal time to intervene? Historically, we have waited for something bad to happen—an aneurysm could form, or aortic rupture or other aortic complication could occur. The question is whether we can prevent those from happening, because 30% to 50% of patients will have something happen to their aorta long term if left untreated.
There are many people in whom we would like to be able to intervene sooner. The question is when the right time is to do that, and there is a balance. If you intervene very early in the acute setting, intervention with endografts has a higher rate of retrograde dissection. The intimal flap is very thin. It would be very easy to propagate that in a retrograde fashion, leading to a second aortic emergency. By delaying the operation by some time, you can reduce that risk, but if you delay too long, the dissection membrane starts to stiffen over time. Your ability to expand the true lumen will start to diminish, or it won't be as beneficial.
Right now, we don't know the exact timing. It is likely that sometime after the acute setting, but before several months' time, is the optimal time to do something. Encouraging data from randomized trials show that this could alter long-term survival or the occurrence of long-term aortic-related events.[4] It is an area of ongoing study to try to define the optimal time. It is certainly not going to be right away, but by waiting too long, you may miss your window.
Mortality in Aortic Dissection
Dr McBane: The relationship of survival to optimal medical management or an intervention, such as thoracic endovascular aortic repair [TEVAR] with endograft is nuanced. Can you speak to that, Alberto? We have the acute survival. We have the long-term survival. What is the difference? How does TEVAR help our survival for these patients with type B dissection?
Dr Pochettino: If we go back to the definition of complicated and uncomplicated dissections, in the complicated scenario, untreated patients don't do well. Most of them die. Treated with traditional open surgery, the mortality can be 30% to 50%. Treated with endograft, the mortality has been, in most series, <10%. So clearly, that is the way to go.
With uncomplicated dissection, the early mortality is low, and you want to keep it low when you intervene. The issue that was raised in terms of timing is that we want to keep that mortality well below 10%. We want to, however, improve the long-term survival, and these patients develop aneurysm in the long term. Aneurysm repair of the type that these patients develop, between 6 months and 5 years out, is a very complex operation, and some patients may be elderly and not able to withstand that kind of surgery. You want to be able to prevent that altogether. We don't have a number, but untreated, more than half of these patients at 10 years will not be there to have the option of an open repair or other treatment. That is why it is important to intervene earlier.
Role of Open Surgery
Dr McBane: We have talked about open repair and about the benefits of an endograft. Is there a role for open surgery in these patients? When would you see open repair being played out here?
Dr Bower: Open surgery in the acute setting is to be avoided if at all possible because the mortality and morbidity are so exceedingly high. There are very clear data now around the world suggesting that stent graft repair when possible is the better alternative.
Once you get beyond the 2-week to 3-month mark and patients develop an enlarging aneurysm, for example, or some other complication, then there is a role for open surgery. We would treat patients with connective-tissue disorders, and younger patients who have extent type II and III thoracoabdominal aneurysms associated with chronic dissection, and then selectively treat higher-risk patients, because complex fenestrated endovascular repair in patients with chronic dissection is not a freebie, either.
That is where I see the biggest role for open surgeries—young patients, especially those with connective-tissue disorders who have dissecting aneurysms or aneurysms that are degenerated.
How Much Should You Fix?
Dr McBane: Randy, the patient presents to you and his entire aorta is dissected from the subclavian all the way to his femoral arteries. The entire aorta is diseased now. How much should you fix?
Dr De Martino: It is an important question that must be considered when treating. If you have made the decision to treat the patient, the primary goal is to cover the primary entry tear, usually located just distal to the left subclavian. Beyond that, most people advocate covering most of the thoracic aorta down toward the celiac artery. Although that hasn't always been done in the past, that is the feeling of most people doing the procedure now. The idea is to cover that section of thoracic aorta and try to promote false lumen thrombosis. When that occurs, the aorta can then remodel around the stent graft.
The risk is that the more coverage you perform, the higher the risk of paraplegia. By covering a limited segment of the aorta just in the chest, you can try to minimize that, but these patients are still at risk for paraplegia even with that amount of coverage. Treating the primary entry tear and most of the thoracic aorta is the mainstay right now, and doing anything more than that elevates the risks associated with the intervention, particularly paraplegia.
Management Options Are Critical
Dr McBane: Any final comments? Future directions?
Dr Pochettino: Endovascular therapy has changed our lives and, of greatest importance, has improved the survival for a lot of these patients. The technology is progressing, and we are going to be able to use this technology better, with smarter devices to benefit more patients, and the role of open surgery will decline.
It is important to have all options available so that when a patient comes in we don't just have one tool, but we have multiple tools. Having open surgery as a backup is always important. To have the ability to manage the patient in any way that is necessary is going to be important for success.
Dr Bower: A key issue for future clinical research is to identify factors, whether anatomic or physiologic, that will predict which patients will have an uncomplicated dissection and the timing of the intervention with a stent graft to allow for this remodeling.
The second key issue is that at any institution that handles aortic emergencies of any sort, it's very important to have emergency-room and care pathways and protocols in place and to standardize practice as much as we can.
Dr McBane: Thank you, all. And thank you to our viewers. We appreciate your time. We hope that you will continue to follow our roundtable review series at theheart.org on Medscape.
© 2015
Mayo Clinic
Cite this: Type B Thoracic Aortic Dissection: When to Intervene - Medscape - Mar 02, 2015.
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