Aortic Valve Insufficiency in Aortic Dissection

This is Dr. Cal Shipley with a review of aortic valve insufficiency during aortic dissection.

Acute aortic valve insufficiency occurs in one half to two-thirds of aortic dissection involving the ascending aorta. It is important for clinicians to be on the lookout for this potentially very serious complication.

Aortic Valve Anatomy

Let’s start with a review of aortic valve anatomy and function. Here is a side view of the aorta and the left ventricle of the heart seen in cross-section, with the aortic valve located at the junction between the two. The aortic valve’s primary function is to facilitate blood flow from the left ventricle into the aorta during systole, when the ventricle contracts and the valve is open.

During the phase of the cardiac cycle known as diastole, the left ventricle relaxes and refills with blood coming from the left atrium. The aortic valve closes during diastole to prevent backflow of blood from the aorta into the left ventricle.

Here’s a closer look at the aortic valve viewing it from inside the left ventricle. During systole the valve is open, and during diastole it is closed. The action of the valve therefore ensures that blood flow is one-way only from the left ventricle into the aorta. This view of the valve also shows that it is composed of three separate leaflets, all of which are attached to the aortic annulus located at the root of the aorta. It’s important to note that aortic insufficiency occurs only in dissections which have involved the ascending aorta.

Mechanisms of Aortic Valve Insufficiency in Aortic Dissection

There are three basic mechanisms by which aortic insufficiency may occur during aortic dissection.

Leaflet Detachment

Let’s start by looking at leaflet detachment. If the process of dissection moves down the ascending aorta, it may involve the aortic roote, causing one of the leaflets to detach from the annulus.

Looking at the aortic valve from inside the left ventricle, the area of dissection within the aortic root progresses until the leaflet has become detached. As a result of the leaflet detachment, blood can now flow backwards from the aorta into the left ventricle during diastole. This is known as aortic insufficiency or regurgitation. Contrast a normally functioning aortic valve, which permits one-way flow blood from the left ventricle into the aorta, with the leaflet detached valve, which allows backflow of blood from the aorta into the left ventricle during diastole. In the side view in cross-section, we see how the normal one-way flow blood becomes a two-way flow in aortic insufficiency due to leaflet detachment.

Loss of Coaptation

The second form of aortic insufficiency associated with aortic dissection that we’re going to look at his loss of aortic valve leaflet coaptation.

Coaptation refers to the normal physical closure of the aortic valve leaflets with the edges of each leaflet butting up against the edges of the leaflets on either side during valve closure. When the process of aortic dissection involves the aortic root, it may spread along the length of the aorta or longitudinally as seen here. It may also spread around the aorta or circumferentially. Circumferential dissection of the aortic root may cause the aortic root to expand, pulling the attach leaflets away from each other and preventing proper coaptation from occurring.

Loss of proper valve leaflet coaptation results in aortic insufficiency with regurgitation of blood across the aortic valve.

Intimal Flap Prolapse

The third mechanism by which aortic insufficiency may occur in aortic dissection is with prolapse of the intimal flap. The vast majority of aortic dissections begin with a tear in the intimal layer of the inner aortic wall. Depending on the extent of the tear, an intimal flap may form as shown here. If the intimal flap is located in the area of the aortic root near the aortic valve, the changing pressures generated during the contraction and expansion of the left ventricle may cause the intimal flap to become trapped between the leaflets of the valve. This process is known as prolapse of the intimal flap. The presence of the prolapsed intimal flap among the valve leaflets leads to loss of leaflet coaptation and aortic insufficiency with regurgitation.

Acute Aortic Insufficiency

Finally, a word on the significance of aortic insufficiency. Rapid onset of aortic insufficiency, also known as acute aortic insufficiency, as may occur in aortic dissection, can lead to congestive heart failure and pulmonary edema, a condition which if not rapidly, corrected may lead to cardiorespiratory failure and death.

For more information on congestive heart failure and pulmonary edema, please see the cardiovascular and pulmonary libraries.

Cal Shipley, M.D. copyright 2020