Aortic Dissection

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Chapter 30 Aortic Dissection

Asheesh Kumar, MD , Rae M. Allain, MD

1 Define aortic dissection

An aortic dissection is a tearing of the layers within the aortic wall, classically associated with sudden-onset chest or back pain, a pulse deficit, and mediastinal widening on a chest radiograph. Depending on size and degree of aortic involvement, it may result in marked hemodynamic instability and, often, a rapid death. Prompt diagnosis and appropriate treatment are critical to maximize the possibility of survival. Significant dissections are often fatal and rarely survive to clinical attention; the majority of dissections seen in the critical care environment are either subacute, contained, or sparing the major aortic vessels.

2 What is the anatomy of injury in aortic dissection?

The tear usually originates in the intima. It then propagates into the media creating a false channel for blood to flow and hematoma to form. The dissection process may alternatively originate with hemorrhage in the media that secondarily causes disruption of the intima. In approximately 70% of patients, the intimal tear, which is the beginning of the dissection, occurs in the ascending aorta. In 20% of patients it occurs in the descending thoracic aorta, and in 10% of patients it occurs in the aortic arch. Only rarely is an intimal tear identified in the abdominal aorta.

3 Describe the DeBakey and Stanford classifications of aortic dissection

The two classification systems most commonly used both have anatomic as well as management implications.

The DeBakey classification describes three types of dissection (Fig. 30-1):

image Type I: extends from aortic root to beyond the ascending aorta

image Type II: involves only the ascending aorta

image Type III: begins distal to the takeoff of the left subclavian artery and has two subtypes

image Type IIIA: limited to the thoracic aorta
image Type IIIB: extends below the diaphragm
image

Figure 30-1 DeBakey classification.

Illustration by Samuel Rodriguez, MD.

The Stanford classification has two types of dissection (Fig. 30-2):

image Type A: involves the ascending aorta

image Type B: involves the descending aorta, distal to the left subclavian artery

image

Figure 30-2 Stanford classification.

Illustration by Samuel Rodriguez, MD.

4 What is the epidemiology of dissection, including mortality?

Aortic dissection is a relatively rare but a highly lethal disease. The estimated incidence is 5 to 30 cases per million people per year. Population-based studies suggest that the incidence of acute dissection ranges from 2 to 3.5 cases per 100,000 person-years, which correlates with 6000 to 10,000 cases annually in the United States. It may be that two to three times as many patients die of dissections as of ruptured aortic aneurysms; approximately 75% of patients with ruptured aortic aneurysm will reach an emergency department alive, whereas for aortic dissection 40% die immediately. Furthermore, only 50% to 70% will be alive 5 years after surgery depending on age and underlying cause.

For untreated acute dissection of the ascending aorta the mortality rate is 1% to 2% per hour after onset. For type A dissections treated medically it is approximately 20% within the first 24 hours and 50% by 1 month after presentation. Even with surgical intervention, the mortality rate for type A dissection may be as high as 10% after 24 hours and nearly 20% 1 month after repair.

Although type B dissection is less dangerous than type A, it is still associated with an extremely high mortality. The 30-day mortality rate for an uncomplicated type B dissection approaches 10%. However, patients with type B dissection who have complications such as limb ischemia, renal failure, or visceral ischemia have a 2-day mortality upwards of 20% and may prompt the need for surgical intervention.

5 What are the risk factors and associated conditions for dissection?

The prevalence of aortic dissection appears to be increasing, independent of the aging population, as noted by Olsson and colleagues, who found that the incidence of dissection among Swedish men has increased to 16 per 100,000 yearly. Risk factors include the following:

image Hypertension: Present in 70% to 90% of patients with acute dissection.

image Advanced age: Mean of 63 years in the International Registry of Acute Aortic Dissection (IRAD).

image Male sex: Represented by 65% of patients in the IRAD.

image Family history: Recently recognized is a genetic, nonsyndromic familial form of thoracic aortic dissection. Studies of patients referred for repair of thoracic aortic dissections and aneurysms who did not have a known genetic mutation have indicated that between 11% and 19% of these patients have a first-degree relative with thoracic aortic disease.

image Trauma (deceleration/torsional injury)

image Congenital and inflammatory disorders: present as Marfan syndrome in almost 5% of total patients in the IRAD and half of those patients under age 40 years. Other associated congenital disorders include Ehlers-Danlos syndrome, Loeys-Dietz syndrome, bicuspid aortic valve, aortic coarctation, Turner syndrome, Takayasu and giant-cell aortitis, relapsing polychondritis (Behçet disease, spondyloarthropathies), or confirmed genetic mutations known to predispose to dissections (TGFBR1, TGFBR2, FBN1, ACTA2, or MYH11).

image Pregnancy: Associated with 50% of dissections in women under age 40 and most frequently occurring in the third trimester. This might be attributable to elevations in cardiac output during pregnancy that cause increased wall stress.

image Circadian and seasonal variations: Producing a higher frequency of dissection in the morning hours and in the winter months.

image Iatrogenic: Occurring as a consequence of invasive procedures or surgery, especially when the aorta has been entered or its main branches have been cannulated, such as for cardiopulmonary bypass.

6 Describe the common clinical signs and symptoms of aortic dissection

image Pain: The most common presenting symptom is chest pain, occurring in up to 90% of patients with acute dissection. Classically, for type A dissections, sudden onset of severe anterior chest pain with extension to the back occurs that is described as ripping or tearing in nature. However, in the IRAD, pain was more often described as sharp rather than ripping or tearing. The pain is usually of maximal intensity from its inception and is frequently unremitting. It may migrate along the path of the dissection. The pain of aortic dissection may mimic that of myocardial ischemia. Patients with type B dissections are more likely to be seen with back pain (64%) alone.

image Syncope: Syncope is a well-recognized clinical feature of dissection, occurring in up to 13% of cases. Impairments of cerebral blood flow can be due to acute hypovolemia, low cardiac output, or dissection-involvement of the cerebral vessels. Patients with a presenting syncope were significantly more likely to die than were those without syncope (34% vs. 23%), likely because of the frequent correlation with associated cardiac tamponade, stroke, decreased consciousness, and spinal cord ischemia.

7 Describe the common clinical findings associated with aortic dissection

A systems-based approach can be used to describe the wide range of clinical findings that can be associated with aortic dissection.

image Neurologic symptoms.

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