Abdominal Aortic Aneurysms


Abdominal aortic aneurysm diameter (cm)

Risk of rupture in 12 months (%)

<4.0

0

4–4.9

0.5–5

5–5.9

1–13

6–6.9

10–20

7–7.9

20–40

>8

30–50


Adapted from: “Aggarwal S, Qamar A, Sharma V, Sharma A. Abdominal aortic aneurysm: A comprehensive review. Exp Clin Cardiol. 2011;16(1):11–5.” and “Belardi P, Lucertini G, De Caro G. Type I aneurysmosis: complementary index for diagnosis. Vascular. 2005;13(1):11–5.” and “Zankl AR, Schumacher H, Krumsdorf U, Katus HA, Jahn L, Tiefenbacher CP. Pathology, natural history and treatment of abdominal aortic aneurysms. Clin Res Cardiol. 2007;96(3):140–51”



The second factor is the growth rate of the transverse aortic diameter. An increase of 1 cm or more in 12 months is a marker for aneurysm rupture, regardless of the previous diameter [1, 4, 17].

The third factor is the shape of the aneurysm. Saccular aneurysms have a more erratic and unpredictable behavior, with rupture not associated to its diameter. Therefore, if clinical conditions are favorable, it is an indication for intervention [1, 4, 17].

The fourth and last risk factor for rupture is the presence of symptoms. As seen above, recent onset of abdominal or lumbar pain is probably due to acute wall expansion or rupture [1, 4, 17].

Some small aneurysm rupture and some large don’t. These first three “risk factors,” diameter, growth rate, and morphology, are simply clinical surrogate markers for some as of yet unknown process, likely a defect of some sort in extracellular matrix or connective tissue. This fact is still poorly understood.



Image Exams



Abdominal Ultrasonography


Once physical exam has low accuracy, an image test should be indicated to confirm the presence of the abdominal aortic aneurysm. Abdominal ultrasound is cheaper, most commonly used for surveillance, well accepted by patients, does not have radiation, and is relatively accurate over serial measurements. It is also very suitable to follow up aortic diameters of initially nonsurgical patients overtime [18].

In emergency department is frequently a test of choice. An association of free abdominal fluid and large aortic diameter reveals ruptured aneurysm in many cases.

It is also useful as screening method for patients with risk factors for abdominal aortic aneurysm (see below). However, if the patient has a surgical indication for the abdominal aortic aneurysm (see below), other imaging tests should be used for a precise preoperative planning [18, 19].


Angiotomography


Angiotomography is more expensive than ultrasound and its use involves radiation exposure and intravenous hyperosmolar contrast medium injection that can lead to allergic reactions and nefrotoxicity. However, this method offers more accurate measurements possibilities. Thus, it is the method of choice in preoperative planning for abdominal aortic aneurysms repair [19].


Magnetic Resonance Imaging


This method is distinguished by the absence of ionizing radiation. However, the high cost, the difficulty of analyzing calcified plaques, the low resolution when compared to angiotomography , the complexity of standardization, and intolerance in claustrophobic patients are limiting factors. Magnetic resonance imaging has its use established in patients allergic to iodine medium contrast.

Historically, the use of this technique in patients with chronic renal failure and contraindication to use of iodine contrast medium has been observed. However, recent studies have shown an increased risk of fatal nephrogenic sclerosing fibrosis in patients with chronic renal failure after intravenous injection of gadolinium. It is a second-line method in the preoperative planning for abdominal aortic aneurysms surgical repair [19].


Screening Program


As previously seen, abdominal aortic aneurysms are mostly asymptomatic. However, its first symptom can be rupture. The mortality rate after abdominal aortic aneurysm rupture may be greater than 90 %. Once the mortality rate for the elective repair is around 5 %, it is advisable to actively screen for patients with asymptomatic abdominal aortic aneurysm in order to avoid death [20, 21]. Screening with abdominal ultrasound an asymptomatic and selected group of patients was able to reduce the overall mortality and aneurysm-related mortality in several studies. The recommendations of the U.S. Preventive Services Task Force are summarized below:



  • 65–75 years old smoker men—Screening with ultrasonography


  • 65–75 years old non-smoker men—Selectively screening rather than routinely screening all men in this group


  • 65–75 years old smoker women—Current evidence is insufficient to assess the balance of benefits and harms of screening


  • 65–75 year old non-smoker women—Recommends against routine screening [20, 21]


Treatment


The treatment approach for abdominal aortic aneurysms is based on the natural history of the disease, balancing the risk of rupture and the risk of the intervention and the patient’s life expectancy [1, 4, 17].

As shown above, the risk of rupture is related to aortic diameter in fusiform aneurysms, the presence of saccular aneurysm , increase of aneurysm diameter >1 cm in 12 months, or the presence of recent symptoms, particularly abdominal or lumbar pain [1, 4, 17].

On the other hand, the risk of the intervention is associated with the presence of comorbidities such as symptomatic coronary artery disease , heart failure, renal failure, chronic obstructive pulmonary disease, and old age [1, 4, 17].

The method of interventional treatment also is related to postoperative mortality. Open repair for abdominal aortic aneurysm is performed under general anesthesia and through a large midline or retroperitoneal incision. After clamping the infrarenal aorta and iliac arteries to achieve hemostasis, the surgeon opens the aneurysm sac, removing thrombus and debris from within the aorta, suturing a graft into the aorta proximally and distally at the iliac or femoral vessels, whichever is deemed appropriate. Short-term mortality for elective series ranges from 1 to 5 % [22]. Perioperative complications related to the procedure include lower extremity ischemia, bowel ischemia, pelvic ischemia, renal dysfunction, and late complications include incisional hernia, anastomotic aneurysm, graft infection, and aortoenteric fistulae. Late complications were indentified in 9.5 % of patients [23].

Endovascular surgery is performed by inserting graft components folded and compressed within a delivery sheath through the lumen of an access vessel, usually the common femoral artery. Upon deployment, the endograft expands, attaching to the aorta wall and excluding the aneurysm. Endovascular repair is associated with lower perioperative morbidity and mortality compared with open surgical repair. The short-term mortality is 1.6 %. Endograft-related complications are common and occur in 11–30 % of the cases [24]. Technical complications include vascular injury, endoleak, breakdown, fracture, or endograft collapse. Endoleak is defined as persistent flow blood into the aneurysm sac after the device placement and indicates failure to completely exclude the aneurysm. This complication is the most prevalent, occurring with all device types in an incidence of 10–45 % [25] (Table 8.2).


Table 8.2
Comparative early mortality in EVAR versus open abdominal aortic repair [24, 26, 27]























 
EVAR (%)

Open repair (%)

EVAR trial

1.8

4.3

DREAM trial

1.2

4.6

OVER trial

0.5

3.0


Adapted from: “Prinssen M, Verhoeven EL, Buth J, Cuypers PW, van Sambeek MR, Balm R, et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. N Engl J Med. 2004;351(16):1607–18.” and “Greenhalgh RM, Brown LC, Powell JT, Thompson SG, Epstein D, Sculpher MJ. Endovascular versus open repair of abdominal aortic aneurysm. N Engl J Med. 2010;362(20):1863–71.” and “Lederle FA, Freischlag JA, Kyriakides TC, Padberg FT, Jr., Matsumura JS, Kohler TR, et al. Outcomes following endovascular vs open repair of abdominal aortic aneurysm: a randomized trial. JAMA. 2009;302(14):1535–42”

Therefore, intervention should be indicated when the risk of rupture is higher than the risk of the intervention and that the patient has a life expectation >1 year [28]. Indications for surgical abdominal aortic aneurysms repair are summarized in Table 8.3.


Table 8.3
Indications for abdominal aortic aneurysms surgical approach [1, 4, 17, 28]















Transverse diameter greater than 5.0–5.5 cm for fusiform abdominal aortic aneurysm

Greater aortic expansion rate (>1 cm/year) for fusiform abdominal aortic aneurysm

Transverse diameter greater than 4.5 cm for saccular abdominal aortic aneurysms

Characteristic abdominal pain or rupture signs in any diameter

Distal embolization (mural thrombus)

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Sep 30, 2017 | Posted by in CARDIOLOGY | Comments Off on Abdominal Aortic Aneurysms
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