AORTIC DISSECTIONAsheesh Kumar, MD, and Rae M. Allain, MDCH

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1. Define aortic dissection.An aortic dissection is a tearing of the layers within the aortic wall, classically associated withsudden-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 hemodynamicinstability and, often, a rapid death. Prompt diagnosis and appropriate treatment are critical tomaximize the possibility of survival. Significant dissections are often fatal and rarely surviveto clinical attention; the majority of dissections seen in the critical care environment are eithersubacute, 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 thenpropagates into themedia creating a false channel forblood to flow and hematoma to form. The dissection process may alternatively originate withhemorrhage in the media that secondarily causes disruption of the intima. In approximately 70% ofpatients, the intimal tear, which is the beginning of the dissection, occurs in the ascending aorta. In20% of patients it occurs in the descending thoracic aorta, and in 10% of patients it occurs in theaortic 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 systemsmost commonly used both have anatomic as well as managementimplications.

The DeBakey classification describes three types of dissection (Fig. 30-1):n Type I: extends from aortic root to beyond the ascending aortan Type II: involves only the ascending aortan Type III: begins distal to the takeoff of the left subclavian artery and has two subtypes

□ Type IIIA: limited to the thoracic aorta□ Type IIIB: extends below the diaphragmThe Stanford classification has two types of dissection (Fig. 30-2):

n Type A: involves the ascending aortan Type B: involves the descending aorta, distal to the left subclavian artery

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 30cases per million people per year. Population-based studies suggest that the incidence ofacute dissection ranges from 2 to 3.5 cases per 100,000 person-years, which correlates with6000 to 10,000 cases annually in the United States. It may be that two to three times as manypatients die of dissections as of ruptured aortic aneurysms; approximately 75% of patients withruptured aortic aneurysm will reach an emergency department alive, whereas for aorticdissection 40% die immediately. Furthermore, only 50% to 70%will be alive 5 years after surgerydepending on age and underlying cause.

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

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