What Happens During an Aortic Dissection?
An aortic dissection is a tear in the wall of the aorta that allows blood to flow within the layers of the aorta. Early diagnosis and treatment of this illness is critical for survival. Certain types (Type A) of dissections, if left untreated, kill 33% of patients within the first 24 hours, 50% of patients within 48 hours, and 75% of patients within 2 weeks.
The aorta is the main vessel that sends blood away from the heart to the rest of the body. It is shaped like a candy cane and is about as wide as a garden hose (2.5-3.5 cm). When blood is pumped by the heart, it first travels through the aorta. Similar to a plumbing system, blood is then delivered through connecting vessels to the rest of the body.
Figure 1: the Aorta
The wall of the aorta consists of 3 layers: the intima, media, and adventitia. The intima is the innermost layer; the media, the middle layer; the adventitia, the outer later. These layers are shown in Figure 2.
Figure 2: LAYERS OF THE AORTIC Wall
A dissection occurs when a tear of the intima (the inner lining) allows blood to leak into the media (middle layer). This creates two passages for blood: a true lumen, which is the normal passageway of blood, and a false lumen, the newly created passageway. A normal aorta and a dissected aorta are shown in Figure 3.
Figure 3: Normal Aorta and Dissected Aorta
What problems do dissections cause?
As blood flows into the false lumen, the false lumen may enlarge and block blood flow into the true lumen. The false lumen may also divert blood flow away from the true lumen. In addition, after an initial tear causes a dissection, the dissection may spread and involve branching vessels, valves, or even the sac surrounding the heart. Multiple tears may even form as a result of the initial tear.
The end result of an aortic dissection is that the amount of oxygen and nutrients available for organs of the body is decreased. As can be seen in Figure 4, the aorta is in close proximity to many organs. The brain, kidneys, intestines, heart, and even the arms and legs may be affected by an aortic dissection.
For example, the following organs can be involved:
- Brain: if the common carotid arteries are involved
- Kidneys: if the renal arteries are involved
Figure 4: Major vessels from the aorta
Approximately 2000 new cases are reported every year in the United States. It is a rare but serious condition that mostly occurs in men aged 60 to 80. However, the male-to-female ratio is 3:1 and aortic dissections do occur in young people, especially those with risk factors.
The following risk factors have been associated with aortic dissections. Please see the Glossary for more information about many of the conditions listed below.
- Hypertension - the most important predisposing risk factor. In research published by IRAD, hypertension has been associated in over 70% of patients.
- Preexisting aortic aneurysm - more common cause in patients under age 40
- Connective Tissue Disorders
- Marfan syndrome
- Ehlers-Danlos syndrome
- Inflammatory diseases that cause a vasculitis (disease that causes damage to blood vessels)
- Giant cell arteritis
- Takayasu arteritis
- Rheumatoid arthritis
- Syphilitic aortitis
- Bicuspid aortic valve - a congenital anatomic abnormality
- Turner syndrome
- Coronary Artery Bypass Graft surgery - dissection is a rare complication of this surgery
- Cardiac catheterization - a rare complication of this procedure
- High-intensity weight lifting - during significant weight training a patient's blood pressure may increase significantly. Especially in patients with risk factors or family history of aneurysms, strenuous weight lifting can be extremely dangerous.
- Family history - first degree relatives with history of aneurysms or dissections
- Crack cocaine - average time between last cocaine use and dissection was 12 hours
Physicians divide the aorta into 3 sections: the ascending aorta, the descending aorta, and the abdominal aorta. These divisions are shown in Figure 5. A dissection may occur anywhere along this path.
Figure 5: Divisions of the aorta
Aortic dissections are classified by physicians based on where the tear in the inner lining occurred. The 2 most common classification systems are the DeBakey and Stanford classification system. Depending on where in the aorta a dissection occurs, the treatment may range from medications to surgery.
- DeBakey Classification:
- Type I - originated in ascending aorta
- Type II - originated in and is confined to ascending aorta
- Type III - originated in descending aorta
- Stanford Classification system
- A - Originated and involves ascending aorta.
- B - Originated and involves descending aorta
Figure 6: Type A and Type B Dissections
- Aortic Dissections are caused by a tear in the intimal layer, allowing blood to leak into the middle medial layer.
- Depending on where the tear occurs and how far it spreads, the brain, kidneys, heart, arms, or legs could be affected.
- Most dissections are associated with hypertension or connective tissue disorders.
- Dissections are classified by where the tear originated.