Abdominal Aortic Aneurysm (AAA) Prognosis Calculator

How does the abdominal aortic aneurysm prognosis calculator work?

This is a health tool that addresses AAA rupture risk and aortic dilatation size and determines the predicted average annual expansion rate, absolute lifetime risk of rupture and clinical recommendation in the case of aneurysms of sizes from 3 cm to 7 cm and above in incrementals of 0.10 cm.

The user of the abdominal aortic aneurysm prognosis calculator needs to select the size in the tool and then will be given information about the gradual development, associated risks and a clinical recommendation.

For example, in the case of an aneurysm of 5 cm, the following data will be provided:

■ Predicted Average Annual Expansion Rate: 3 to 5 mm;

■ Absolute Lifetime Risk of Rupture: 20%;

■ Clinical Recommendation: Ultrasonography or Computed Tomography every 6 to 12 months plus considering surgical consultation.

AAAs medical guidelines

An AAA is defined as the enlargement of the abdominal aorta to 3 centimeters or more caused usually by the degeneration of the media portion in the arterial wall, by atherosclerosis hardening or other causes, including natural wear and tear with age.

The dilatation is continuous and gradual.

The most at risk of developing AAAs are men older than 65 years of age and suffering from peripheral atherosclerotic vascular disease.

One of the reasons why most aortic aneurysms are diagnosed when they have already reached high levels of rupture risks is because of the lack of symptoms until vast expansion or rupture.

Expanding abdominal aneurysms are usually palpable during physical exams and are characterized by sudden, severe low back pain, pain in flank or groin. Other symptoms due to the local compression might include nausea, vomiting, venous thrombosis or fever.

Ruptured aneurysm patients are cyanotic, tachycardic, hypotensive and with altered mental status although this is not absolutely necessary as there are cases in which vital signs are still in norms due to the retroperitoneal containment of hematoma.

Diagnostic of abdominal aortic aneurysms is done through imagistic means such as:

■ Ultrasonography;

■ Computed tomography (CT);

■ Magnetic resonance imaging (MRI);

■ Angiography;

■ Plain radiography.

The main repair method is surgery, whether elective or in emergency. Either open surgery with transperitoneal or retroperitoneal approach or endovascular repair with access from the femoral vessels and the placement of a graft in the AAA lumen.

In some cases aneurysm treatment medication, beta blockers might be recommended in small aneurysms associated with high blood pressure and statins for high cholesterol.

Abdominal aortic aneurysm prognosis

Outcome in AAAs depends on factors like size, location and individual patient data.

Aneurysm rupture risk is determined by the size, specifically the diameter, size which expands at a rate of about 10% per year. There are different rates of rupture risk increasing with diameter size.

Clinical determinations, such as the finite element method (FEM) which can determine exactly the diameter of the aneurysm and correlate it with the risk of rupture. The mechanism of rupture depends on the moment when artery wall stress exceeds wall strength.

There are other determinations such as the rupture potential index (RPI) and the finite element analysis rupture index (FEARI) or the analysis of geometrical parameters during CT.

The major risk is aneurysm rupture which usually results in a deadly hemorrhage in 80% of cases and urgent surgery has a rate of 50% success.

Survival rates are lower than 45% in the case of ruptured AAAs, with most patients not surviving to reach the ER units and dying of sudden cardiovascular collapse. Survival rates are said to drop further with about 1% per minute, therefore intervention needs to be very rapid.

Elective surgery complications depend on location and type but are relatively low compared to other cardiac surgery and to the overall risk if the aneurysm is left uncorrected.

Long term prognosis on the other hand is correlated with associated comorbidities such as chronic heart failure or COPD, otherwise repairing surgery tends to be very durable and with small risk of graft infection.

Prevention methods to avoid or delay the enlargement of a prospective or existent aneurysm include a balanced diet, especially avoiding cholesterol rich foods, exercise and giving up smoking.

References

1) Hirsch AT et al. (2006) ACC/AHA 2005 guidelines for the management of patients with peripheral arterial disease. J Am Coll Cardiol; 47(6):1239-312.

2) Lederle FA, Kane RL, MacDonald R, Wilt TJ. (2007) Systematic review: repair of unruptured abdominal aortic aneurysm. Ann Intern Med; 146(10):735-41.

3) Bower TC, Cherry KJ Jr, Pairolero PC. (1989) Unusual manifestations of abdominal aortic aneurysms. Surg Clin North Am; 69(4):745-54.

4) Gadowski GR, Pilcher DB, Ricci MA. (1994) Abdominal aortic aneurysm expansion rate: effect of size and beta-adrenergic blockade. J Vasc Surg; 19(4):727-31.

5) Vasconcelos J et al. (2013) Unruptured symptomatic abdominal aortic aneurysms. Rev Port Cir Cardiotorac Vasc; 20(3):153-6.