The term “acute aortic syndrome” (AAS) has been used to describe a mixed group of thoracic aortic disorders that characteristically present with a typical combination of signs and symptoms.1,2,3 and 4 The most distinctive presenting symptom is aortic pain, which is often described as sharp, tearing, or ripping. Although there are several pathophysiologic entities that can present as AAS (Table 23.1) occasionally one process can precede another or occasionally they may coexist. Importantly though, all can be life-threatening and require immediate medical attention (often including a surgical intervention). Given the similarity in the clinical presentation and the need for urgent assessment, diagnosis, and treatment, it is useful to classify these syndromes into one group of disorders, similar to “acute coronary syndromes” or an “acute abdomen.”

AAS include the following:

Typically, patients with AAS present with an acute onset of chest pain with a long-standing history of hypertension or a known elastic tissue disorder (e.g., Marfan syndrome). The pain is classically described as abrupt in onset, intense, sharp, tearing, or ripping. Diseases that involve the ascending aorta typically produce pain that radiates to the neck or the jaw. Disease in the descending thoracic aorta often causes pain that radiates to the back or abdomen.5

A related process that will be discussed in this chapter as well is traumatic aortic rupture. Although aortic rupture is obviously a medical emergency that can present with symptoms of aortic pain similar to other AAS, patients present with a completely different scenario of onset of this process. For this reason, traumatic rupture is often not considered part of the classical AAS.

Aortic dissection is characterized by an intimal tear and separation of the intima or media from the surrounding adventitia. Typically, the separation occurs within the media such that the outer layer of the media forms the outside wall of the false lumen and the inner part of the media, along with the intima, forms the intimomedial flap. The thickness of the media that forms the external layer of the false lumen determines the stability of the false lumen wall and is an important determinant of the risk of free wall rupture. The dissection can propagate through the aortic wall both distally and proximally to the initial tear. This propagation can be the cause for many of the complications of aortic dissection (e.g., myocardial ischemia, renal failure). In many patients a reentrance tear can be found or multiple communications between the true and false lumens can be identified.

There are two widely accepted anatomic classifications of aortic dissection; the DeBakey and the Stanford classification (Figure 23.1). The DeBakey system divides aortic dissection to three subtypes: types I, II, and III. Type I DeBakey is a dissection that starts at the ascending aorta and continues at least up to or beyond the arch. Type II starts at the ascending aorta and is confined to the ascending aorta. Type III is a dissection that starts at the descending thoracic aorta and propagates either distally or less commonly proximally. The Stanford classification differentiates aortic dissection according to presence or absence of ascending aorta involvement, regardless of the initial site of origin; type A is a dissection involving the ascending aorta, and type B is a dissection that does not involve the ascending aorta. The Stanford classification is the one clinically used for treatment purposes; urgent surgical intervention versus medical stabilization. Because Stanford classification is the more commonly used system, we will use it throughout this chapter.

The incidence of aortic dissection is estimated to be 2.9 per 100,000 patient-years. The mean age of presentation is 65 years with approximately 60% predominance of men.5,6 and 7 Women with acute aortic dissection present at an older age than men and tend to present later in the course of the disease than men.8 Type A aortic dissection is more common than type B and accounts for 60% of cases of acute aortic dissection. Up to 30% of patients with acute type A dissection show involvement of the aortic arch as well.

Similar to acute ischemic syndromes, a circadian as well as seasonal variation in the frequency of acute aortic dissection
has been found.9 Acute aortic dissection is significantly more prevalent between 6 a.m. and 12 noon, and in particular between 8 a.m. and 9 a.m. A seasonal variation in acute aortic dissection presentation has also been found, with more frequent occurrence in the winter as compared to summer, with a peak incidence in January.

Acute aortic dissection presents slightly different in North American and European adults.10 North American patients tend to be older, demonstrate more ECG changes (significantly more nonspecific ST changes and a trend towards more ST elevations and acute myocardial infarcts), and have more atypical symptoms and less classic chest X-ray findings compared with European patients. Despite the differences in clinical presentation, there is no difference in the early outcome between North American patients and European patients.

The underlying pathology in many cases of aortic dissection is cystic medial necrosis causing degeneration of the aortic media. Of note, this is in fact a misnomer as pathology specimens do not demonstrate either cysts or necrotic material. However, it is a commonly used term that describes the generative process of the aortic media that involves degeneration of the elastic tissue. There are several predisposing factors that have been identified as risk factors for aortic dissection. The commonest risk factor that has been recognized is systemic hypertension. Up to 72% of patients who present with acute aortic dissection have a history of systemic hypertension.7 History of atherosclerosis is also common; it is found in up to 32% of patients presenting with acute aortic dissection. These risk factors are particularly noteworthy in patients above 40 years of age who present with acute aortic dissection.

Acute aortic dissection has also been found to be associated with collagen/elastic tissue diseases such as Marfan syndrome and Ehlers Danlos syndrome. Of all patients with acute aortic dissection, 4.9% have a history of Marfan syndrome.5,7,11 However, among patients younger than 40 years of age who present with acute aortic dissection, 50% have Marfan syndrome.11

Several other predisposing risk factors have been identified in patients presenting with acute aortic dissection5,7,11:

The hallmark of the clinical presentation of acute aortic dissection is “aortic pain.” This is frequently described as an abrupt onset of severe, sharp, tearing, or ripping chest pain. Radiation to the jaw or the neck is more common with type A dissection, whereas radiation to the back is seen more commonly with type B or abdominal aortic dissection. However, painless dissection has also been described, in up to 6.4% of patients presenting acute aortic dissection.15 Patients who present with painless dissection are older than those with painful dissection, have a higher prevalence of type A dissection, and present more commonly with syncope, congestive heart failure, and stroke. The mortality rate in this group is also higher as compared to those who present with acute aortic pain, in particular in the group with painless type B dissection (who have a significantly elevated risk of aortic rupture).

Patients with acute aortic dissection can also present with syncope; this has been described as the presenting manifestation in 13% of patients and was found to be associated with significantly increased in-hospital mortality.16 In multivariate analysis, syncope has been found to be associated with presence of cardiac tamponade, stroke, and proximal aorta involvement. The increased mortality risk associated with syncope persisted after controlling for patients’ demographic characteristics but not after adjusting for the comorbid conditions (stroke, tamponade, and proximal dissection).

Pulse deficit (absence of carotid, brachial, or femoral pulse owing to intimal flap involving major branch vessels or compressing hematoma) has been described in up to 15% of patients, more commonly in type A dissection versus type B (19% vs. 9%, respectively). Pulse deficit has been associated with increased in-hospital complications (such as renal failure, coma, hypotension, and limb ischemia) as well as an independent predictor of 5-day in-hospital mortality.17

Patients with acute dissection can present with hypertension, normotension, hypotension, or shock.5 Overall, 50% of patients present with hypertension. It is significantly more common for type B dissection to present with hypertension (70% of patients) as compared with type A dissection (36%). Hypotension or shock on presentation is significantly more common in type A dissection as compared with type B (25% and 5%, respectively).

Proximal dissection, involving the ascending aorta can result in one or more of the following clinical characteristics (Table 23.2):

Descending thoracic aorta involvement can give rise to several distinct clinical characteristics including sudden onset of chest and back pain (86% of patients), abdominal pain, spinal cord ischemia (3% of patients), ischemic peripheral neuropathy (2% of patients), renal failure, shock, and lower extremity ischemia.5,21

Age and gender play a role in the clinical presentation of acute aortic dissection.8,22 Atherosclerosis, hypertension, and iatrogenic dissection are significantly more common in the older patient population, whereas Marfan syndrome-associated dissection is seen solely in the younger age group. Typical symptoms and signs of acute dissection (e.g., sudden onset of “aortic pain,” presence of aortic regurgitation murmur) are less common in the older (≥70 years) as compared with the younger (<70 years) patient population. Outcome and treatment of acute aortic dissection also differ between the age groups.

Women with acute aortic dissection are generally older and present later in the course of the disease.8 Pericardial or pleural effusion, tamponade, periaortic hematoma, altered mental status or coma, and hypotension are more frequent in women
and result in higher prevalence of in-hospital complications and mortality rate.