Aortic Dissection

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The true incidence of acute aortic dissection is difficult to determine, as many cases may go undiagnosed, but its documented incidence is approximately 2.9 per 100,000 per year, with at least 7,000 cases per year in the United States15. A healthy aorta with an intact medial layer rarely dissects. Alternatively, those in whom the integrity of the media is compromised are at risk for aortic dissection. Therefore, any disease process or condition that damages the elastic or muscular components of the media predisposes the aorta to dissection. Indeed, cystic medial degeneration, as discussed above, is a major predisposing factor in aortic dissection.

The peak incidence of aortic dissection is in the sixth and seventh decades of life, with a mean age of 62 years among more than a thousand subjects in the International Registry of Acute Aortic Dissection (IRAD)16. Overall, men are affected twice as often as women (68% vs. 32%) and are affected at younger ages as well, with male patients having a mean age of 60 years and female patients a mean age of 67. However, as shown in Figure 1.2 the male predominance is most striking at young ages, with males outnumbering females 4:1

Figure 1.2. Proportion of males vs. females per age group in IRAD; * p < 0.001. Adapted with permission from reference 16.

at ages less than 50. With increasing age, however, the difference lessens, and among those older than 75, males and females are equally represented.

Table 1.1 summarizes the contribution of recognized risk factors on the incidence of aortic dissection among the IRAD population. About three-quarters of patients had a history of hypertension. Only 14% had a known thoracic aortic aneurysm. Many more patients likely had a preexisting aneurysm that had simply gone undetected prior to the aorta's dissection. Bicuspid aortic accounted for 3.4% of aortic dissection cases, which was not much less than the 5% attributable to Marfan syndrome. As is the case with ascending thoracic aortic aneurysms, the risk of aortic dissection appears to be independent of the severity of the bicuspid valve stenosis. Much less commonly, aorta dissection results from other congenital cardiovascular abnormalities, including coarctation of the aorta and Turner syndrome.

The risk factors for and presentation of aortic dissection differ between younger and older patient populations. In IRAD, 7% of patients were younger than 40 years old. The differences between the two age groups are summarized in Table 1.2. Not surprisingly, Marfan syndrome was the major risk factor among younger patients, accounting for 50% of cases17. Conversely, this can be reframed to highlight the fact that 50% of young patients did not have underlying Marfan syndrome as a predisposing risk factor for aortic dissection.

Table 1.1. Known risk factors for aortic dissection from IRAD

Advanced age (mean)

62 years

Male gender

68%

History of hypertension

72%

Prior aortic dissection

5%

Known aortic aneurysm

14%

Marfan syndrome

5%

Bicuspid aortic valve

3%

Peripartum period of pregnancy

0.2%

Cocaine

0.5%

Cardiac catheterization/surgery

5%

Prior cardiac surgery

22%

Table 1.2. Comparison of younger vs. older patients with aortic dissection

Feature

Age < 40 (%)

Age > 40 (%)

Marfan syndrome

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Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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