STS E Book - Type A Aortic Dissection, Ascending Aneurysm

Question 1

What makes up the aortic root complex?

Answer 1

ventriculo-aortic junction, aortic valve leaflets, aortic sinuses of Valsalva, sinotubular junction

Question 2

What are the three sinuses of Valsalva, and how are they designated?

Answer 2

left, right, and noncoronary; designated according to the respective coronary artery

Question 3

In relation to the aortic sinuses, where is the cardiac conduction system? What portion of the tricuspid is this conduction system close to?

Answer 3

The interleaflet triangle between the right and noncoronary sinus segments is anatomically in close relation to the cardiac conduction system that courses within the membranous septum and in close proximity to the septal leaflet of the tricuspid valve.

Question 4

What are the 3 layers of the aortic wall?

Answer 4

The layers are constant throughout the arterial tree, consisting of the smooth inner intimal layer, the medial layer, and the outer adventitial layer consisting of connective tissue.
The intima is formed by a single layer of endothelium that is supported by the underlying basal lamina.
The media layer consists of smooth muscle cells, elastin sheets, and collagen, as well as the extracellular matrix.
The outer layer of connective tissue defines the adventitia, and this also is comprised of the vasa vasorum and neural tissue (strength layer d/t collagen).

Question 5

What is the strongest layer of the aorta?

Answer 5

The outer layer of connective tissue defines the adventitia, and this also is comprised of the vasa vasorum and neural tissue. This is the strongest layer of the aorta.

Question 6

What is principal biologic cause of aneurysm formation in the ascending aorta?

Answer 6

cystic degenerative processes in the elastic media (figure); atherosclerotic changes are primarily responsible for aneurysm formation of the descending thoracic and abdominal aorta

Question 7

What is the pathological process in cystic medial degeneration?

Answer 7

When matrix metalloproteinase and cathepsin activity become excessive, disintegration of the extracellular matrix within the media layer occurs as a result. As the elastic layer fragments and smooth muscle cells lose their function, a cystic mucoid material forms in the media layer.
Aneurysm formation occurs as this medial degeneration translates to weakness in the arterial wall.

Question 8

Other than excessive enzyme processes, what else contributes to medial degeneration and the aneurysm process of the ascending aorta?

Answer 8

To a lesser extent, mild degeneration of the aortic wall occurs with age and explains the gradual dilation of the ascending aorta in elderly patients. Smoking has been shown to accelerate the medial degeneration process.

Question 9

What is intramural hematoma as it relates to aortic dissection?

Answer 9

In intramural hematoma, bleeding emanates from the vasa vasorum and extends to the media layer (figure - Hemorrhage occurs due to rupture of the vasa vasorum with weakening of the aortic wall media. Subsequent dilation of the aortic diameter occurs, and the intima layer remains intact in intramural hematoma). This leads to an area of increased stress in the aortic wall, and intimal disruption may ensue.

Question 10

What are some risk factors associated with ascending aortic dissection?

Answer 10

Conditions that increase direct mechanical forces on the aortic wall, such as hypertension and hypervolemia, as well as connective tissue disorders predispose to aortic dissection. Hypertension is seen in the majority of patients who present with aortic dissection.
Iatrogenic causes include cardiac catheterization procedures, aortic cross-clamping and cannulation, surgical procedures on the aorta (aortic valve replacement and coronary bypass grafting), and intra-aortic balloon pump placement.

Question 11

Describe the intimal disruption in ascending aortic dissection? What is the dissection flap comprised of?

Answer 11

Intimal disruption is generally greater than 50% of the circumference of the aorta. After the cleavage plane has formed within the media layer, the dissection flap is comprised of intima and partial-thickness media.

Question 12

Where is the typical entry site in a type A dissection, and how does it traverse through the distal aorta?

Answer 12

The entry site in type A dissection typically occurs on the right anterior side of the ascending aorta and often corkscrews through the arch and into the thoracoabdominal aorta posteriorly and to the left.

Question 13

What complication can occur if a type A aortic dissection extends retrograde?

Answer 13

Extension into the aortic root may occur as well, leading to coronary malperfusion. Can also cause pericardial effusion and tamponade.

Question 14

What are the predominant causes for death in acute type A dissection?

Answer 14

myocardial infarction or acute aortic rupture into the pericardium with tamponade; in the downstream aorta, aortic side branch perfusion may be jeopardized, leading to malperfusion and end-organ ischemia

Question 15

Describe how branch vessel compromise occurs in aortic dissection?

Answer 15

True lumen compression by the false lumen is the most common mechanism.

Question 16

What are some of the issues caused by downstream fenestrations that can arise in aortic dissection?

Answer 16

Often there are downstream fenestrations that arise, leading to multiple sites for communication between false and true lumens. The compromised outer wall of the aorta will dilate over time, especially in the absence of close blood pressure management.