Abdominal aortic aneurysms (AAA) are dilatations of the abdominal aorta that are greater than 3 cm. The abdominal aorta is a major blood vessel that connects the heart to the lower extremities. The prevalence of this illness increases with age. It is not common in persons who are younger than 50 years old. However, 5.2% of women and 12.5% of men between the ages of 74-84 have AAA. Each year, AAA accounts for approximately 11,000 deaths in the United States. The rate of mortality from ruptured AAA is approaching 90%.
Aneurysms arise when a major blood vessel has weakened walls. The risk factors for AAA are similar to other heart diseases. These risk factors include being male, age older than 65 years, a family history of AAA, and previous myocardial infarction or heart attack.
Beyond the risk of rupturing the aneurysm, patients with AAA are also at an increased risk for death, as well as other cardiovascular diseases. Aneurysms are “balloons” on the walls of major blood vessels. When these aneurysms rupture, extensive internal bleeding, or hemorrhage, occurs. Aneurysms occur most often in the aorta, which is the main blood vessel connecting the heart to the chest and the abdomen. The aorta carried blood from the heart to all other parts of the body, including the legs and the feet.
In most cases, AAA is not associated with a constellation of symptoms. Occasionally, patients may feel pain on their backs, abdomens, or sides. However, 75% of aneurysms are discovered when patients undergo routine diagnostic tests, such as x-rays, for other illnesses. In addition, individuals may also feel a tingling or numbness in their hands or feet, known as paresthesias, as well as coldness. Sometimes, patients may feel a pulsation in their abdomens. However, this is rare as aneurysms take years to develop. It is rare for aneurysms to cause symptoms before they rupture.
An aneurysm is a permanent widening of an artery to up to 1.5 times its normal diameter. The normal diameter of the aorta in men older than 50 years is 1.7 cm and in women, 1.5 cm. In contrast to this, an aorta outside of the kidneys that is at least 3 cm in diameter is considered to be aneurysmal.
The primary event in the development of an AAA is the degradation of collagen and elastin due to enzymes, in a process call proteolysis. Various enzymes participate in this event. They are all critical factors that cause degradation and the subsequent changes on the wall of the aorta.
Stress from free radicals, called oxidative stress, plays an important part in the development of AAA. There is also an autoimmune component to AAA. In particular, immunoglobulin G is deposited on the wall of the aorta, along with the infiltration of white blood cells and monocytes, which are specialized cells for immunity.
Smoking causes inflammation of the aortic wall. When the aortic wall experiences biomechanical stress, ruptures may develop.
The non-modifiable risk factors for AAA include male gender and increasing age. This has been validated in numerous studies. In 1-5% of patients, a family history of AAA was found to be associated with a current diagnosis of AAA. Ethnicity is another risk factors.
Evidence has shown that Northern Europeans are more prone to AAA compared to Africans or Asians.
Smoking is a significant risk factor for AAA. Continuously smoking is associated with the expansion of the AAA, increasing the risk of rupture and producing a worse outcome. However, there is some evidence to show that there is a small decline in risk if smoking is ceased. .The risk of AAA in the smoking population is 58/100,000 person a year.
High cholesterol levels are associated with an increased risk for AAA. Reducing cholesterol levels in patients at risk for AAA is desirable, although there is no evidence that this can reduce the chances of AAA development. Hypertension is weakly associated with AAA. In particular, arterial hypertension is associated with the disease. Studies have shown that using antihypertensive medications, such as amlodipine, can reduce the incidence of AAA from 49% to 0%. These studies show that there is an important link between the movement of blood in the body and aneurysm formation.
There are some connective tissue disorders that can increase a person’s chance of developing AAA. These include Marfan Syndrome and Ehlers-Danlos Syndrome.
Diabetes is another risk factor for AAA. The prevalence of this disease has increased in the last decades. However, the association between AAA and diabetes is not yet clear. Drugs used to treat diabetes predispose people to AAA.
The most serious complication arising from AAA is the risk of rupture. Once a rupture has occurred, surgery is much less likely to be successful. Thus, the goal of therapy is to treat the AAA before it ruptures.
Aneurysm repair is the primary treatment for aneurysms that are at high risk for rupturing of are symptomatic. However, repair itself is associated with complications. The risk of elective repair should be weighed against the risk of death from an aneurysm and from other complications. This decision requires an understanding of the natural course of the disease in patients with AAAs that have not ruptured.
The risk of rupture of small aneurysms, which are less than 4 cm in diameter, is much less compared to the rupture of larger aneurysms, which are defined as greater than 6 cm.
In addition to size, the risk of rupturing an AAA depends upon the rate at which the AAA is expanding. As an aneurysm becomes larger, the risk of death also increases. For small aneurysms, the risk of death is less than 0.5%. However, aneurysms greater than 8 cm in diameter carry a risk of death between 30-50%.
Other, lesser known complications of AAAs include fistulas, which are abnormal connections between a vein and the aorta, and thromboembolism, in which small blood clots from the AAA travel to other parts of the body. These blood clots can block blood flow in other areas, causing a stroke.
A cardiologist should be consulted when an AAA is suspected. The imaging tool of choice for diagnosis is an ultrasound. When performed by adequately trained radiologists, ultrasounds have a high sensitivity for detecting AAAs, up to 100%.
Screening is one of the ways through which AAAs are diagnosed. Screening benefits the patients who are most at risk- make, age older than 65 years, and smoking at least 100 cigarettes during their lifetime. This can be performed using an ultrasound.
Aside from these, the cardiologist will take a thorough medical, social, and family history in order to determine an asymptomatic person’s risk for AAA. If the patient is symptomatic, then a CT scan may be needed to determine the size and presence of the aorta.
If the AAA has already ruptured, the patient needs to be brought to the emergency operating room immediately to decrease the risk of death.
If an aneurysm is less than 4 cm in diameter, patients are often advised not to undergo surgery because the risks outweigh the benefits. However, they should get an ultrasound every 6 months to 3 years, depending on the diameter of an aneurysm.
On the other hand, patients with AAAs that are larger than 5.5 cm in diameter are advised to have repaired.
Drug interventions may also be used to treat AAAs. Typically, patients who have small aneurysms can be placed on medications. Their blood pressure needs to be carefully controlled. In addition to this, a beta-blocker, which is a type of drug used to treat hypertension, may be prescribed to slow the growth of an aneurysm. Increasing a person’s physical activity, such as through biking, walking, or running, can reduce the risk of rupture. However, patients should be advised to avoid strenuous activities, such as heavy lifting.
A surgical repair is also an option for larger aneurysms. Surgery may either be in the form of open surgery or through an endovascular stent graph.
The number one way to prevent aneurysms is to refrain from smoking. Smoking has been shown to increase a person’s risk of developing AAAs by as much as 200%. In addition, controlling blood pressure is another way to prevent AAAs. Taking anti-hypertensive medications as needed will prove to be beneficial. Eating a healthy diet low in fat and regular exercise can also prevent AAAs from developing.
The prognosis for patients with AAA depends upon the diameter of an aneurysm and how fast it is expanding. In general, aneurysms that are larger in diameter have a poorer prognosis and can lead to death. However, the prognosis for smaller aneurysms that are not quickly expanding is generally good. The person is able to live a normal life with minimal adjustments. Continuous monitoring and watchful waiting are keys to a better prognosis when it comes to AAAs. Prognosis may also depend on other co-morbid conditions that the patient may already have