© Borgis - Postępy Nauk Medycznych 8/2012, s. 668-676
*Włodzimierz Hendiger, Zbigniew Kwietniak, Adam Lewszuk, Walerian Staszkiewicz
Możliwości i ograniczenia w endowaskularnym zaopatrzeniu tętniaka aorty brzusznej
Possibilities and limitations in the endovascular repair of abdominal aortic aneurysm
Department of Vascular Surgery and Angiology of the Medical Centre for Postgraduate Education, The Jerzy Popiełuszko Memorial Bielański Hospital
Head of Department: prof. Walerian Staszkiewicz, MD, PhD
Tętniak aorty brzusznej (TAB) jest przyczyną od 1 do 3% zgonów wśród mężczyzn pomiędzy 65 i 85 rokiem życia. Rejestruje się w ciągu ostatnich dwudziestu lat wzrost zachorowań na tętniak co może być związane ze starzeniem się społeczeństwa, wzrostem liczby palaczy ale także z wprowadzeniem programów przesiewowych i stałym unowocześnieniem metod diagnostycznych. Pacjenci z bezobjawowymi tętniakami o średnicy od 55 mm kwalifikowani są do elektywnego zabiegu wyłączenia tętniaka celem zmniejszenia ryzyka pęknięcia. Dostępne są dwie metody zabiegowe: metodą otwartej laparatomii oraz metodą wszczepienia wewnętrznej protezy (tak zwanego stentgraftu) od strony tętnic udowych bez otwierania jamy brzusznej. Wszczepienie stentgraftu przeprowadzane jest wewnątrznaczyniowo (EVAR). Celem pracy jest wybór metody postępowania, kwalifikacja do metody otwartej lub wewnątrznaczyniowej leczenia tętniaków aorty brzusznej. Planowy zabieg wewnątrznaczyniowy 2-3 krotnie zmniejsza 30 dniową śmiertelność pooperacyjną w stosunku do operacji klasycznej. EVAR w stosunku do klasycznej operacji jest procedurą małoinwazyjną polegającą na wewnątrznaczyniowy wprowadzeniu specjalnej protezy (stentgraftu) do jamy tętniaka z dostępu przez tętnice udowe. Nawet jeżeli EVAR łączy się z większym odsetkiem reinterwencji późnych to jest leczeniem chętniej akceptowanym przez pacjentów. Wewnątrznaczyniowa metoda zaopatrzenia tętniaka staje się metodą z wyboru.
The abdominal aortic aneurysm (AAA) is the cause of 1 to 3% of deaths among males in the age between 65 and 85 years. Within the last twenty years, increased incidence of aneurysms was recorded, which may be associated with population aging, and increasing number of smokers, but also with introduction of screening programs and constant modernization of diagnostic methods. Patients with asymptomatic AAA measuring at least 55 mm in diameter are classified to elective surgery in order to reduce the risk of aneurysm rupture. Two treatment methods are available: an open laparotomy and implantation of an internal prosthesis (so-called stent graft) through the femoral artery approach without opening the abdominal cavity. Stent graft is implanted with the endovascular method (EVAR). Purpose of this study is to select treatment methods, and qualification for the open laparotomy or endovascular treatment of the abdominal aortic aneurysms. Comparing to standard surgery, there is two- to three-fold reduction of 30-day postoperative mortality in the elective endovascular treatment. EVAR, comparing to the classic surgery, is a minimally invasive procedure involving the introduction of a special endovascular prosthesis (stent graft) into the aneurysm cavity through the femoral artery approach. Even if EVAR is associated with higher rates of late repeated interventions, it is more willingly accepted by the patients. Endovascular aortic repair becomes the method of choice.
The abdominal aortic aneurysm (AAA) is the cause of 1 to 3% of deaths among males in the age between 65 and 85 years. Usually, the aneurysm is asymptomatic, unless its rupture occurs, which in 65-80% of case results in death (1). The abdominal aortic aneurysms are usually detected by accident during ultrasound evaluation of the abdominal cavity due to general surgical diseases or urological diseases. Within the last twenty years, increased incidence of aneurysms was recorded, which may be associated with population aging, and increasing number of smokers, but also with introduction of screening programs and constant modernization of diagnostic methods. Significance of the ultrasound screening methods in order to diagnose AAA is emphasized (2). This evaluation is performed by trained personnel (technicians, nurses) using ultrasound machine. The study focuses on the abdominal segment of the aorta. Longitudinal and transverse imaging of the aorta should be performed (3). The aneurysm is diagnosed if the diameter of the abdominal aorta exceeds 30 mm. Measurement is performed outside of the aorta. If the measurement is performed within the lumen of the aorta, then actual size is larger by thickness of the wall, i.e. by 2-5 mm, provided that there is no clot in the lumen. Studies demonstrate that the most beneficial screening in form of decreased percentage of recorded ruptured aneurysms is achieved if the screening is conducted in male patients in the age between 65 and 85 years, especially in smokers as well as persons with congenital burden (4). In case of stable and asymptomatic aneurysms, their treatment method mainly depends on their size. Aneurysms measuring over 55 mm are qualified for the elective surgery. Studies on small aneurysms revealed no benefits from conducted surgical treatment in case of aneurysms measuring less than 55 mm in diameter (5). In case of aneurysms below this size, the risk of surgery exceeds the risk of the aneurysm rupture. The patients with asymptomatic aneurysms measuring at least 55 mm in diameter are qualified for the elective surgery of the aneurysm elimination in order to reduce the risk of rupture. Currently, two surgical methods are available: an open laparotomy and implantation of an internal prosthesis (so-called stent graft) from the femoral artery approach without opening the abdominal cavity. Stent graft is implanted with the endovascular method (EVAR). This method is used if performing classic laparotomy would overburden the patient. Performing classic laparotomy may not be possible due to difficult anatomy of the aneurysm, or it may be associated with the risk of complications such as leakages, thrombosis in the prosthesis, movement of the prosthesis or its damaging.
Purpose of this study is selection of treatment methods, and qualification for the open laparotomy or endovascular treatment of the abdominal aortic aneurysms.
The expression “aneurysm” (aneurysma) comes from Greek word ανευρυσμα.
It means dilation of the artery lumen. The first description of the aneurysm comes from the 2nd century B.C. from Roman physicians, Antyllos and Galen. They described pulsating tumors occurring after the vessel injury.
The abdominal aortic aneurysm is formed by saccular or fusiform dilation of the aorta lumen by 50% in its abdominal segment comparing to diameter of normal vessel located above (6, 7). Currently, after analysis of data provided by CT-scan (fig. 1), it is assumed that diameter of normal aorta in the abdominal segment, below the renal artery, in adult male is 19.9 mm ± 2.2 mm (ranging from 15 to 24 mm) (8), and in females it is smaller by 2-3 mm. The diameter depends on age, gender and body weight (9). Therefore, the abdominal aortic aneurysm means dilation of the aorta, which is exceeding 30mm in diameter (10-12).
Fig. 1. Image of 3D reconstruction of the abdominal aortic aneurysm in the computerized tomography angiogram.
95% of aneurysms of the abdominal segment of the aorta is located below the renal arteries. It should be remembered that in 12% of the patients, the abdominal aortic aneurysm is also accompanied by aneurysms in other locations (13): e.g. iliac, popliteal. For this reason, it is important during diagnostics to pay attention at other segments of the arteries, not only at the abdominal segment.
Image of the abdominal aortic aneurysm in CT-scan is presented in figure 1.
Extended life expectancy in population, and first of all, dynamic technological progress and availability of the minimally invasive ultrasound diagnostics, computerized tomography and magnetic resonance imaging, resulted in increase in detection of the abdominal aortic aneurysms (14-17). It is believed that sensitivity of the magnetic resonance imaging in detection of the abdominal aortic aneurysms is 100% (18). Within the period from 1951 to 1980, there was nearly seven-fold increase in number of the patients treated due to the aneurysm in Mayo Clinic, which clearly indicates significance of this fact (19).
Multicenter studies conducted on large groups of patients allow estimating incidence of the aneurysms in populations and risk factors favorable for their development. The prospective study Honolulu Hart, which was the program lasting over 20 years, and conducted on the group of 7682 males showed the following: the aortic aneurysm was diagnosed in 151 persons, and in 138 cases it was located in the abdominal segment. Risk factors in this group of the patients included increased blood pressure, increased cholesterol level in serum and smoking (20). The next program conducted in 1992-1995, Aneurysm Detection and Management (ADAM), included 15 centers (Veterans Affairs Medical Administration). In total, 73 451 subjects in the age of 50-79 years were studied. The aortic aneurysm was diagnosed in 1.4% of cases. Risk factors included hypercholesterolemia, hypertension, smoking to a large extent, and age as well as occurrence of this disease in a family history (21). The screening was also conducted in elderly male patients in multicenter study MASS (The Multicenter Aneurysm Screening Study). The group included 67 800 males in the age between 65 and 74 years. After randomization, ultrasound evaluation was performed in 33 839 subjects. Among persons, who underwent ultrasound evaluation, the abdominal aortic aneurysm was diagnosed in 1333 patients, which is 3.9% of subjects qualified for ultrasound evaluation and 1.9% of all males enrolled into the study. This study also demonstrated that 65 patients died due to rupture of the aneurysm (22). The Cardiovascular Heath Study including 4 populations living in the United States, studied 4734 males and females in the age of 65 years, and the abdominal aortic aneurysm was diagnosed in 8.8% of subjects, and it was more common in elderly males burdened with smoking, heart diseases, and hyperlipidemia. This study also revealed interrelation between occurrence of the abdominal aortic aneurysm and increased thickness of the wall of the carotid artery.
Aforementioned data shows how important is diagnostics and search for early factors of development of the aortic diseases in order to start treatment as early as possible.
Pathophysiology of the aneurysm development
The main cause for the abdominal aortic aneurysm development is functional and structural loss of the elastin in the aortic wall. This process has not been fully explained. Below, some processes will be discussed, which may lead to the aneurysm development.
Influence of the paramural clot
The paramural clot develops within the lumen of the aneurysm. It is associated with disturbed, irregular, turbulent flow in the dilated vessel. Usually, the clot has layered structure as a result of its gradual accumulation. The clot itself does not decrease pressure acting on the aortic wall, but only creates more even distribution of forces acting in the aneurysm. Computer analysis reveals that in case of presence of the clot, the highest tension occurs at its edges (23). It does not reduce the risk of the aneurysm rupture. The clot leads to ischemia of the aortic wall by impaired diffusion of the nutritional facts and to accumulation of the inflammatory cells within the space near the wall of the aneurysm (24-26). The inflammatory cells lead to activation of metalloproteinases. These processes lead to decrease in thickness of the aneurysm wall under the clot, which is favorable for its rupture (27). There are some publications, which suggest increasing risk of the aneurysm rupture near dynamically developing clot (28). However, there are no explicit evidence, which would justify change in management due to established presence of the clot.
Risk factors for the aneurysm occurrence
Analysis of risk factors for the aneurysm development is important especially in case of qualifying the patient for conservative treatment in case of small aneurysm. Limitation of risk factors may slow down the rate of dilation of the aorta.
Hypertension. It is the basic factor for incidence and rupture of the aneurysm (29). The aneurysm is diagnosed in 11.9% of patients with hypertension comparing to 6.5% of persons with normal blood pressure (30). Mechanism of occurrence of the abdominal aortic aneurysm in case of hypertension is not clearly explained, but it may be related to increased transmural pressure and overlapping the pulse wave reflected from the iliac arteries.
Smoking. Chronic smoking of cigarettes is possibly one of the most important environmental risk factors for occurrence of the abdominal aortic aneurysm (31). There is four-fold increase in risk of aneurysm occurrence in smoking persons comparing to non-smokers (32-34). The aortic aneurysm is diagnosed 7.6 times more frequently in current smokers and 3 times more frequently in former smokers than it is in non-smokers35. In reference to other locations of the vascular system diseases, smoking is associated with three-fold higher risk of occurrence of the abdominal aortic aneurysm comparing to occurrence of the coronary heart disease, and five-fold higher risk of this disease comparing to vascular disease of the central nervous system (36). Also the aneurysm growth rate in smokers is higher than it is in non-smokers, i.e. 2.83 mm/year and 2.53 mm/year, respectively (37). Products from the tobacco coming into the blood stream probably activate alpha 1-antitrypsin by melatonin oxidation, which leads to enzymatic damage of the aortic wall.
Age. Incidence of the abdominal aortic aneurysm increases with age. Prevalence of the aneurysm in the age of 65-69 years is 4.8%, and in the age of 80-83 years it is 10.8% (38). Together with aging, contamination of elastin with protein fractions increases, which results in calcification and defragmentation of its fibers. Weakening, i.e. loss of elasticity of the aortic wall during ageing process, is related to disintegration of the elastin fibers. Also phenomenon of apoptosis of the smooth muscle cells in the aortic wall is important in the aneurysm development, because it leads to reduction of their number, which results in intensification of the disintegration processes in the aortic wall (39).
Atherosclerosis. as the risk factor of the aneurysm. It is believed that atherosclerosis and hyperlipidemia (40) increase the risk of the aneurysm occurrence, but its mechanism is not known. Probably, the atherosclerotic deposits lead to weakening of the aortic wall, and in case of their regression, favorable conditions occur for the aneurysm development. Experimental animal studies demonstrated that treatment of hypercholesterolemia increases risk of the aneurysm occurrence (41). This phenomenon has not been confirmed in humans. Some studies do not show relationship or show insignificant relationship between decreasing rate of the aneurysm growth and administration of statins (42). In humans, the atherosclerotic plaques probably impair nutrition supply to the aortic wall provided by diffusion, which may weaken the tunica media. However, coexisting atherosclerosis and the aneurysm is probably caused by different causes and they are independent from each other.
Gender. Prevalence of the aneurysms increases in males after the age of 55 and in females after the age of 70 (43).
Chronic obstructive pulmonary disease (44). It may favor development of the aneurysm in mechanism of deficit of alpha 1-antitrypsin, which is present in both diseases. However, there is still no explicit evidence of faster development of the aneurysm in persons with COPD (45).
Risk factors for the aneurysm rupture
The aneurysm size is independent and the most important risk factor for the aneurysm rupture (46, 47).
There are the following factors, which are favorable for the aneurysm rupture: smoking, female gender, hypertension (48).
Some studies indicate five-fold higher risk of the aneurysm rupture in females than it is in males (49), which suggests use of the surgical treatment in case of smaller aneurysm’s size than 55 mm.
Relationship between the aneurysm size and risk of its rupture within the year is presented in table 1.
Table 1. Relationship between the aneurysm size and risk of ruplture.
|Aneurysm size (mm)||Rupture risk (%)|
Depending on the aneurysm size, the patient is qualified for conservative treatment and observation or for surgical treatment. Scheme of qualification is presented in figure 2.
Fig. 2. AAA – scheme of procedure.
Indication for surgical treatment results from obtaining such size of the aneurysm that the risk of rupture exceeds the risk of surgery. UKSAT study, after analyzing 1090 cases with small aneurysm measuring 40-55 mm in diameter, showed no difference in 5-year mortality in the patients undergoing classic surgery comparing to the patients under observation (50). Risk of rupture was 1%, and mortality in case of surgical procedure was 5.6%. In ADAM study, these values were 0.6% and 2.7%, respectively. The males are qualified for the surgery if diameter of the aneurysm is at least 55 mm, and females, due to higher risk of rupture, are qualified for the surgery if diameter of the aneurysm is at least 52 mm (51).
Indications for urgent aneurysm repair are as follows:
1. Growth of the aneurysm diameter by 10 mm per year or 5 mm over 6 months.
2. Symptomatic aneurysm.
3. Ruptured aneurysm.
The following symptoms of the aneurysm advance decision on surgery:
1. Peripheral embolism (e.g. blue toe syndrome)
2. Acute thrombus formation
3. Back pain
4. Non-specific abdominal pain
Limitations of the classic laparotomy method
According to UKSAT study, perioperative mortality is 5.6%, and according to ADAM study, 2.7%.
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