Chapter II Review of Literature
2.1 Abdominal Aortic Aneurysm (AAA)
2.1.1 Introduction of Abdominal Aortic Aneurysm
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Chapter II
Review of Literature
This is a service and innovation study in which conclusions are deduced from facts directly observed in daily medical practice or from comprehensive review of literatures. Related research works and literatures from both the medicine and the business study field were reviewed to formulate the theoretical bases of this service and innovation study.
We first briefly introduced the pathophysiology of abdominal aortic aneurysm and choices of treatment, focusing on the traditional open surgical repair and the innovative endovascular repair (2.1), followed by comparison of the two different treatment modalities concerning clinical results and cost-effectiveness (2.2). How patients make decision on treatment modality can be found from review of literatures on patients‘ decision-making process (2.3). In section 2.4 and 2.5, the innovation and dissemination process of endovascular repair are thoroughly discussed about.
2.1 Abdominal Aortic Aneurysm (AAA)
2.1.1 Introduction of Abdominal Aortic Aneurysm
Gloviczki, and Ricotta, (2011) wrote in Textbook of Vascular Surgery that the term aneurysm is derived from the Greek word aneurysma which means ―widening‖
and can be defined as a permanent and irreversible localized dilation of a blood vessel, having at least a 50% increase in diameter compared with the expected normal diameter. Ectasia is defined as a dilation less than 50% of the normal diameter.
Normal diameter of the aorta and the arteries depends on age, gender, body size, and
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other factors. In men, the infrarenal aorta is normally between 14 and 24 mm, and in women, it is between 12 and 21 mm. Therefore, an abdominal aortic aneurysm (AAA) is diagnosed if the diameter is 3 cm or larger in a man or 2.6 cm or larger in a woman.
The most frequent site of extracranial arterial aneurysms is the infrarenal aorta.
In one large autopsy series of patients with aortoiliac aneurysms, the most frequent location was the abdominal aorta alone (65%), followed by the thoracic aorta alone (19%), the abdominal aorta and iliac arteries (13%), the thoracoabdominal aorta (2%) and iliac arteries alone (1%). Peripheral arterial aneurysms are much less common.
Popliteal aneurysms account for about 70% of all peripheral aneurysms, femoral aneurysms are less frequent, and carotids constitute less than 4%. Visceral (splanchnic) and renal artery aneurysms have been considered rare, although their reported incidence due to frequent abdominal imaging has increased recently. Fig. 2.1 demonstrated the anatomy of AAA.
Figure 2.1 Illustration of abdominal aortic aneurysm. (source: “MedlinePlus‖)
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frequent and lethal complication of AAAs. In the United States, aneurysm rupture is the cause of death in 1.2% of men and 0.6% of women. About 15,000 deaths each year are caused by ruptured AAAs, making AAA the 13th leading cause of death in the United States. It is the 10th leading cause of death in men. In a study of 231 ruptured aneurysms, 71% of patients did not know before rupture that they had an aneurysm. Most ruptures occur into the retroperitoneal space, but free rupture of the anterior wall can result in herald bleeding into the abdominal cavity; rupture into the inferior vena cava or iliac vein causes aortocaval or aortoiliac arteriovenous fi stula, whereas rupture into the duodenum results in massive gastrointestinal bleeding due to a primary aortoduodenal fistula.After rupture of an AAA, only half of patients arrive at the hospital alive. In one study, 50% reached the hospital alive, 7% died before surgery, 17% died during the operation, and 37% died within 30 days of surgery for an overall mortality rate for open surgical repair of 45%. Although initial results of EVAR for ruptured AAA have been encouraging, about 25% to 30% of patients with a ruptured AAA will eventually survive. Occasionally, AAAs can lead to life- and limb-threatening conditions because of acute thromboembolism.
The larger the aneurysm diameter is, the greater the risk for rupture is. The annual risk for rupture of an AAA between 4 and 5.4 cm in size is about 0.5% to 1%.
For AAAs between 5.5 and 6 cm, the annual rupture risk is estimated between 5% and 10%. AAAs between 6 and 7 cm have an estimated yearly rate of rupture of 10% to 20%.
In 2003, a consensus statement was issued by the Society for Vascular Surgery regarding screening for AAAs. It recommended baseline ultrasound screening for AAA in men aged 60 to 85 years, women 60 to 85 years with cardiovascular risk
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factors, and men and women older than 50 years with a family history of AAA.
Subsequent ultrasound is recommended annually for AAAs 4.0 to 4.5 cm and every 6 months for AAAs larger than 4.5 cm. The United States approved the Screening Abdominal Aortic Aneurysms Very Efficiently (SAAAVE) Act to provide AAA screening at age 65, for male ever-smokers and men and women with a family
history of AAA, as recommended by the U.S. Preventive Services Task Force.
For patients with low-risk AAAs (small diameter without other risk factors for rupture) being followed with serial size measurements, attempts are made to reduce expansion rate and rupture risk. This can be accomplished with risk factor modifications, including smoking cessation, blood pressure control, and reduction of cholesterol, triglycerides, and lipoproteins.
The goal of elective AAA repair is to prevent rupture and prolong life. Careful assessment of factors that influence rupture risk, operative mortality, and life expectancy is essential, and patient preference receives increasing importance.