Chapter 59: Aortic Dissection and Related Aortic Syndromes

INTRODUCTION AND EPIDEMIOLOGY

Acute aortic syndromes encompass a number of life-threatening aortic emergencies. These include aortic dissection, penetrating atherosclerotic ulcer, intramural hematoma, and aortic aneurysmal leakage or ruptured abdominal aortic aneurysm (see chapter 60, Aneurysmal Disease).

Acute aortic syndromes are uncommon but frequently fatal. The incidence ranges from 2.9 to 4.7 cases per 100,000 people per year.^1,2,3,4 The 1-year, 5-year, and 10-year actuarial survival rates are 92%, 77%, and 57%, respectively, for operative patients.⁴ Twenty-two percent of cases are undiagnosed prior to death.⁵ The most common cardiovascular complication of Marfan's syndrome is aortic root disease and type A dissection (ascending aorta). The identification of gene mutations associated with Marfan's syndrome, such as TGFBR2 and FBN1, combined with regular follow-up can reduce fatal outcomes.⁶

PATHOPHYSIOLOGY

Acute aortic syndromes occur in the setting of chronic hypertension and other factors that lead to degeneration of the media of the aortic wall. Bicuspid aortic valve, Marfan's syndrome, Ehlers-Danlos syndrome, and familial history of aortic dissection all predispose to aortic syndromes. Chronic cocaine or amphetamine use accelerates atherosclerosis, increasing the risk for dissection.⁷ Prior cardiac surgery is another risk factor for aortic dissection. All mechanisms involve weakening of the medial layer and intimal wall stress. Response to stress may include aortic dilation, aneurysm formation, development of a penetrating ulcer, intramural hemorrhage, aortic dissection, and aortic rupture.

Aortic dissection occurs after a violation of the intima allows blood to enter the media and dissect between the intimal and adventitial layers. The dissecting column of blood forms a false lumen and may extend proximally, distally, or in both directions. Blood may dissect and reenter the intima, and this may clinically suggest a spontaneous cure. Alternatively, the blood may dissect through the adventitia, which nearly always proves rapidly fatal.

Aortic dissection has a bimodal age distribution.⁴ The first peak involves younger patients with specific predisposing conditions such as connective tissue disorders. The second peak includes those aged >50 years with chronic hypertension. Other atherosclerotic risk factors appear to be only minor contributors to pathogenesis of acute aortic syndromes.

Aortic dissections are classified using two separate systems, the Stanford and DeBakey systems. The Stanford classification considers any involvement of the ascending aorta a type A dissection. Stanford type B dissections are restricted to only the descending aorta. DeBakey type 1 dissections simultaneously involve the ascending aorta, the arch, and the descending aorta. DeBakey type 2 dissections involve only the ascending aorta, and type 3 involve only the descending aorta.

An aortic intramural hematoma results from infarction of the aortic media, usually from injury to the vasa vasorum.⁸ An intramural hematoma may resolve spontaneously or may lead to dissection.⁹ Penetrating atherosclerotic ulcer can lead to intramural hematoma, aortic dissection, or perforation of the aorta.^8...