Epidemiological characteristics and risk factors Abdominal aorta often undergoes limited dilatation, and when the diameter is greater than 1.5 times of normal, it is called abdominal aortic aneurysm (AAA). The natural tendency of abdominal aortic aneurysm is to gradually increase in size, and then rupture and hemorrhage occurs, which leads to the rapid death of the patient. Although the improvement of medical standards has reduced the mortality rate of early abdominal aortic aneurysm surgery to less than 3%, the clinical outcome of ruptured abdominal aortic aneurysm (RAAA) is still quite unsatisfactory, and the mortality rate of surgery for those who are still alive at the time of diagnosis is as high as about 50%, and the total mortality rate of AAA can be as high as 50 %, if we add in the number of people who died before arriving at the hospital. If the number of deaths before arrival at the hospital is added, the total mortality rate of ruptured AAA can be as high as 80%~90%. Therefore, rupture is the most common and serious complication of AAA, so early diagnosis, correct resuscitation, and emergency surgery are the keys to successful treatment. The incidence rate of abdominal aortic aneurysm in western countries is about 3~117 people/100,000 population, in Europe and America, the incidence rate of abdominal aortic aneurysm in 60~74 years old males is about 3%~6%, and the incidence rate in old males suffering from hypertension is 12%; the incidence rate of abdominal aortic aneurysm in brothers is as high as 20%~29%, and the ratio of the incidence rate of male to female is about 4:1.The incidence of AAA has been increasing year by year, and Swedish data reported that AAA in 30 years had a mortality rate of 80%~90%. The incidence of AAA has been increasing year by year, and Swedish data reported that the incidence of AAA has increased 7 times in 30 years, and there is no epidemiological investigation data of AAA in our population, and the incidence rate is relatively low, but in clinical practice and relevant literature, it also shows that the incidence rate is increasing.The rupture of AAA usually occurs in the winter months, and the most common age is 76 years old in men, and 81 years old in women. Deaths from abdominal aortic aneurysms occur predominantly in men at younger ages, with a male-to-female ratio of 11:1, but the male-to-female ratio decreases to 3:1 in patients over the age of 80 years.Smoking is the strongest environmental risk factor for AAA formation and death.Smoking is more likely than coronary artery disease to result in the formation of an AAA, with the prevalence of AAA in smokers 25 times higher than that of nonsmokers, and deaths from rupture of an AAA from smoking are four times more common than those from nonsmoking. Important risk factors for AAA rupture are large aneurysm diameter, hypertension and chronic obstructive pulmonary disease (COPD). The shape of the aneurysm is also associated with rupture, with eccentrically shaped sacs tending to rupture more often than concentrically shaped homogenous ones. Hypertension (mainly hypercalcemia) is an important determinant of AAA dissection and rupture, and more than 40% of patients with AAA have comorbid hypertension. Trauma (e.g., abdominal surgery, etc.) can cause increased elastase activity in the aortic wall and is another important risk factor for AAA rupture. Atherosclerotic plaques have a nonspecific association with AAA formation, stripping and rupture. Etiology and pathogenesis The etiology of AAA is still unclear, and it is the result of the interplay of genetic, environmental and biochemical factors. The vast majority of AAA is caused by arterial sclerosis, while other rare causes include aortic dysplasia, syphilis, trauma, aortitis, Marfan syndrome, infection, Bechet syndrome, etc. In the formation of AAA, there are pathological changes such as apoptosis of intima-media smooth muscle cells and degradation of elastin, which cause the intima-media to become progressively thinner, and ultimately, collagen becomes the main component of tensile strength, which, with the action of various factors, becomes the main component of tensile strength. Under the action of various factors, with the increase of pressure load and collagen depletion, the tumor ruptures. Once an aneurysm is formed, no matter why it is formed, due to the hemodynamic characteristics of the aneurysm will continue to increase in size. According to Laplace’s law, the larger the aneurysm diameter, the greater the pressure on the aneurysm body, and the greater the risk of rupture, such as the aneurysm will rupture when the shear stress on the aneurysm wall exceeds its maximum expansion capacity, so the aneurysm diameter is a reliable indicator for predicting the rupture of the aneurysm. AAA diameter <4cm, the rupture rate is 0% per year; AAA diameter 4~5cm, the rupture rate is 0.5%~5%/1 year AAA diameter 5-6 cm, rupture rate of 3-15%/1 year; AAA diameter 6-7 cm, rupture rate of 10%-20%/1 year; AAA diameter 7-8 cm, rupture rate of 20-40%/1 year; AAA diameter >8 cm, rupture rate of 30-50%/1 year. Another data showed that the rupture rate of untreated AAA within 5 years: 10%-15% for tumors with a diameter of 4cm or less, 20% for tumors with a diameter of 5cm or less, 33% for tumors with a diameter of 6cm, and 75%-95% for tumors with a diameter of 7cm or more. Based on the rupture rate of AAA in relation to the curve of aneurysm diameter, those with a diameter of 6 cm or more are called dangerous aneurysms. Although the diameter of the aneurysm is an important risk factor for rupture, studies have shown that small AAA also has a fairly high rupture rate, especially when the atheromatous plaque is large, resulting in uneven force or asymmetric aneurysm, and the risk of rupture is increased by closing the localized vesicle-like protrusions. Gronenwett et al. found that the risk of AAA rupture was significantly increased in patients with obstructive pulmonary disease and systolic hypertension.