Natural History

Natural history of acute aortic syndrome is best outlined prognostically by differentiating patients into those with involvement of the ascending aorta (type A) versus individuals with acute pathology confined to the distal arch and the descending aorta (type B). This distinction is notable for the differing risk factors for development of dissection and also for the critical proximal branch vessels and anatomic details affecting patient outcomes acutely and chronically by virtue of malperfusion syndrome, syncope, tamponade, or shock8'13'48'66'67.

TYPE A (PROXIMAL) DISSECTION

Acute aortic dissection of the ascending aorta is highly lethal, with mortality ranging between 1-2% per hour early after symptom onset3,49. Symptoms such as instantaneous onset of severe chest (85%) or back (46%) pain are characteristic presenting symptoms, however; abdominal pain (22%), syncope (13%), and stroke (6%) are common3,11-13,66,67 but not always present. Some patients may have lost consciousness or are severely hypotensive from shock, making a reliable history impossible. Contained rupture into the pericardium (pericardial tamponade), involvement of one or more coronary arteries causing acute myocardial ischemia/infarction, or dissection compromising cerebral perfusion carries a particularly high risk48,51,53. Additionally, aortic valve disruption leading to acute congestive heart failure, extensive aortic involvement as manifested by multiple pulse deficits and/or renal failure, and advanced age also correlate with increased risk8,11,13,66,68 (Figures 2.3A, 2.3B). Other less appreciated risk scenarios for type A dissection include prior cardiac and valvular surgery (15%)3,18,34 and iatrogenic dissection occurring during cardiac surgery or cardiac catheterization (5%). Iatrogenic aortic dissection carries a mortality of 35%, which is even higher than noniatrogenic (24%)19.

Acute type A dissection is always a surgical emergency. Medical management alone is associated with a mortality of nearly 20% by 24 hours, 30% by 48 hours after presentation, 40% by day 7, and 50% by one month. Even with surgical repair, mortality rates are 10% by 24 hours, 13% by 7 days, and nearly 20% by 30 days, as recently documented in the largest registry of aortic dissection (Figure 2.4). Aortic rupture, stroke, visceral ischemia, and cardiac tamponade or circulatory failure are the most common causes of death8,13,66,69.

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