Chapter 30. Aortic Dissection

• Acute aortic dissection occurs more commonly than ruptured abdominal aortic aneurysm.
• The typical pain, poor peripheral perfusion, and evidence of aortic branch occlusion suggest the diagnosis.
• Early pharmacologic control of systolic blood pressure and the pulse wave (dP/dT) is imperative.
• Investigations must be undertaken urgently to confirm the diagnosis and direct definitive treatment.
• Emergency surgical repair is indicated for type A dissections.
• Control of hypertension is important to minimize complications and maximize survival both in the postoperative period and in the long term.
• Type B dissections may have a more ominous prognosis than previously thought and require very close long-term follow-up.

Aortic dissection is the most common catastrophe affecting the aorta, occurring two to three times more commonly than acute abdominal aortic aneurysm rupture.1 The reported incidence is approximately 10 to 20 per 1 million per year.2 Rarely is the outcome of a cardiovascular disease so dependent on the skills and cooperation of the emergency room physician, the cardiac surgeon, and the intensivist as it is with acute dissections of the aorta. Maximal survival depends on a high index of suspicion of the diagnosis despite a myriad of different presentations, early pharmacologic intervention for control of hypertension, rapid diagnosis with definitive imaging, and then appropriate relegation to medical or surgical management depending on the dissection type. Without treatment, the 3-month mortality is 85% to 90%, but with the appropriate treatment, survival rates of over 80% can be expected.

Previously, aortic dissections were referred to as dissecting aneurysms, as originally coined by Laënnec. This is a misnomer in that the pathology is a dissecting hematoma that separates the intima and inner layers of the media from the outer medial and adventitial layers (Fig. 30-1). The intima is therefore not aneurysmal, and is if anything, narrowed. Blood invades the media through a tear in the intima and proceeds ante- or retrogradely through the aortic wall, forming a false lumen. The hematoma spirals around the right and posterior aspects of the ascending aorta, supraposteriorly along the arch, and then down the left and posterior aspects of the descending aorta.3 The hematoma may then have several serious sequelae. It may rupture into the pericardial space causing tamponade, or into the pleural space with exsanguinating hemorrhage. This occurs less frequently than expected because the adventitial layer represents 66% of the overall strength of the aortic wall. It may also cause occlusion of aortic branch arteries or prolapse of one or more of the aortic valve cusps, resulting in acute aortic insufficiency.