Ascending aortic dissection secondary to Marfan’s syndrome. The history is classic for an aortic dissection. Additionally, the history and physical exam suggest the patient has suffered complications secondary to the aortic dissection including acute aortic insufficiency (early diastolic murmur and increased pulse pressure) and pericardial effusion (muffled heart sounds). It is also suggestive from the presentation that this patient has Marfan’s syndrome. Patients with Marfan’s syndrome are typically tall, thin, and can have cardiac, skeletal (pectus excavatum, arachnodactyly, hyperflexible joints), and/or ocular (ectopic lentis: displacement of the crystalline lens) abnormalities. It is important to rapidly establish the diagnosis of aortic dissection and to determine the dissection type (A or B), as the management of a dissection is dramatically different from other diagnoses and the management of type A and B also greatly differs (discussed further below).

The risk factors for aortic dissection are hypertension, connective tissue disease (e.g., Marfan’s, Ehlers-Danlos), advanced age, atherosclerosis, pregnancy, cocaine use, aortic injury (e.g., trauma, cardiac catheterization), bicuspid aortic valve), and aortic coarctation.

Uneven pulses suggest that the blood supply to one of those extremities is adversely affected and therefore provides a clue as to the location of the dissection. An upper extremity pulse discrepancy is consistent with a dissection involving the aortic arch, whereas a lower extremity pulse discrepancy suggests involvement of the descending aorta all the way down to the iliac arteries.

Patients with aortic insufficiency will present with a widened pulse pressure (as in this patient). Diastolic pressure decreases due to regurgitation, while systolic pressure increases secondary to the increased stroke volume as a result of the backflow of blood from the aorta (increased preload).

An aortic dissection is a progressive separation of the aortic wall that results from a tear in the intima that progresses into the media, essentially splitting the aorta into an inner layer of intima and inner media and an outer layer of outer media and adventitia. This produces two lumens: a true lumen and a false lumen. The true lumen is where the blood usually flows, while the false lumen is the blind sac that is formed between the intimal flap and the outer media. As blood flows into the false lumen, the tear propagates and the false lumen enlarges. Eventually secondary tears may develop, which allow the blood to reenter the true lumen. The tear is a direct consequence of aortic wall shear stress and most often happens in areas exposed to high mechanical forces (such as the aortic arch and proximal descending aorta just distal to the left subclavian artery).

Marfan’s is a connective tissue disease that has an autosomal dominant mode of transmission. Its primary defect involves the misfolding of fibrillin proteins, which can result in cystic medial necrosis of large vessels such as the aorta. The subsequently weakened medial wall is left susceptible to dissection.

No. An aneurysm is dilation (mostly fusiform) of all three layers of an artery that progressively enlarges. Patients with Marfan’s are at risk for both aneurysm (mainly in the aortic root) and dissection. Confusion arises in that dissection weakens the arterial wall, such that the lumens (both true and false) dilate over time.

Two traditional classification schemes exist (DeBakey and Stanford), both of which describe dissections based on the segments of the aorta involved (Fig. 7.2). A Stanford type A dissection involves the ascending aorta/aortic arch, whereas a type B does not. A Stanford type B dissection begins in the descending aorta, distal to the takeoff of the left subclavian artery. The main disadvantage of the Stanford classification is that it does not distinguish between patients with isolated ascending aorta/aortic arch dissection and patients with dissection involving the entire aorta. However, since the most important determinant of therapy is whether the ascending aorta/aortic arch is (Stanford A) or is not (Stanford B) involved, the Stanford classification is more commonly used.