An AAA is a pathological focal dilatation of the abdominal stem artery. The AAA bears the risk of rupture. The rupture of the aneurysm is a traumatic emergency condition with a high risk of death. Immediate emergency surgery may reduce the risk of death (peri-operative mortality for emergency repair was described as between 40% and 60% {5}) but is often not available because of uncertainty about the time of rupture. The risk of rupture increases with the diameter of the dilatation {4}. The cut-off point for preventive surgery is 5.5 cm {27}. Elective repair is indicated for AAAs with a diameter of 4.0 to 5.4 cm {18}. A screening programme is indicated to identify AAA with a high risk of rupture. Identified individuals are offered preventive surgery to reduce their individual risk of the negative consequences of a spontaneous rupture.

In the ICD (International Classification of Diseases) 10 two branches are designed for AAA. Branch I71.3 “Abdominal aortic aneurysm, ruptured” defines a ruptured aneurysm, and branch I71.4 “Abdominal aortic aneurysm, without mention of rupture” defines the condition of AAA without rupture {8}.

The National Library of Medicine (where the medical literature catalogue PubMed is also located) defines the MeSH (medical subject headings) term used for AAA as “An abnormal balloon- or sac-like dilatation in the wall of the abdominal aorta which gives rise to the visceral, the parietal, and the terminal (iliac) branches below the aortic hiatus at the diaphragm” The definition was introduced in the year 1993 {9}.

There are several other definitions of AAA in the literature including "An aneurysm is a focal dilation of a blood vessel with respect to the original or adjacent artery. An abdominal aortic aneurysm is defined as an aortic diameter at least one and one-half times the diameter measured at the level of the renal arteries. The normal diameter of the abdominal aorta is approximately 2.0 cm (range 1.4 to 3.0 cm) in most individuals; a diameter greater than 3.0 cm is considered aneurysmal". {1}

A more pathophysiological definition of AAA is given by {3}: “the progressive loss in the capacity to resist high intraluminal pressure, related to the degradation of the arterial wall”.

Clarification: What is the current rate of screening adherence?

Age and sex are risk factors for AAA. The prevalence of AAAs increases with age. While they are uncommon in people below the age of 60 years, 1 person per 1000 develops an AAA in the 60-65 age group {4}. AAAs are four times more common in men than in women {4}. The following additional risk factors are discussed below:

• smoking
• cardiovascular disease
• family history of AAA
• hypertension (mentioned in some sources only —{HTA core model questionnaire})

In its natural course, an AAA is typically symptom free to begin with. The arterial dilatation takes place gradually over the years and is diagnosed as AAA when the arterial diameter reaches 3 cm (Different definitions are used for men and women because the vessels of women are on average smaller than those of men.). Over time the diameter usually increases at a rate that depends on the diameter. In small aneurysms it increases by about 2 mm per year, but in large aneurysms it grows by about 3.5 mm per year. In smokers the rate of increase can be higher. The rate of growth can vary, with phases of no growth and phases of rapid growth{Mohler, Natural ...}. AAAs can be symptomless during the whole life or until rupture. Alternatively symptoms may be present (see A0005).

The pathogenic roles of an inflammatory process (matrix metalloproteinase) and pathological coagulation (plasmin generation) have recently been described {3}. These processes damage the vessel wall, which becomes more vulnerable to the pulsating blood pressure leading to increased dilatation and finally to rupture.

Of the patients with a ruptured AAA, 50% reach hospital alive. Among those who reach hospital alive and have an operation, 50% survive the repair.

See CUR4

Unruptured AAAs are not usually symptomatic. However, symptoms of back pain or abdominal pain, or symptoms due to embolism to the leg can be present. During general clinical examination a pulsatlile abdominal mass may be present {4}. Hypotension may also be present. Other symptoms that are described in the literature may be symptoms from mass effects to adjacent structures (e.g. compression of the ureter or occlusion of a vertebral artery branch) {12}.

The risk of rupture is mainly associated with the diameter of the AAA. The annual risk according to the diameter has been described as follows {4}

Less than 4.0 cm in diameter = less than 0.5% chance of rupture

Between 4.0 to 4.9 cm in diameter = 0.5 to 5% chance of rupture

Between 5.0 to 5.9 cm in diameter = 3 to 15% chance of rupture

Between 6.0 to 6.9 cm in diameter = 10 to 20% chance of rupture

Between 7.0 to 7.9 cm in diameter = 20 to 40% chance of rupture

Greater than or equal to8.0 cm in diameter = 30 to 50% chance of rupture

The burden of AAA arises from the risk of AAA rupture and from harm that may arise from preventive actions against the risk of rupture. From a public health perspective the benefits and harms from organised preventive actions (and their consequences) must be compared with the benefits and harms from care that is not organised in the form of a public health programme (individual care, opportunistic screening).

The benefit and harm that may be introduced by a screening programme depend on the prevalence of the disease (prevalence of AAAs, ruptured AAAs and deaths from ruptured AAAs), and on the effectiveness of the screening and of the preventive interventions. Information about AAA prevalence is given in this result card, whereas information about screening programme characteristics (sensitivity, specificity) is given in the Description and technical characteristics of the technology (TEC) domain and information about the effectiveness of preventive interventions (e.g. surgery, behavioural change) is in the Effectiveness of the technology (EFF) domain.

The public health burden of AAA is increasing in developed countries because of its increasing prevalence in many populations {10}. This increase in prevalence can be explained, in part, by the increase in the number of people in the age groups at higher risk of developing AAA. In European countries {Table} the number of people aged 60-79 has increased from 14% in 1990 to 17% in 2010.

Mortality in different age groups

The mortality due to ruptured AAAs varies in different age groups as follows {5}:

Prevalence in high risk groups

The following table shows AAA prevalence in high risk age groups among five British populations (with definitions of AAA by diameter around 3 cm):

Overall, the prevalence of AAA in these ‘high risk’ age groups is around 4%-8 %.{5}

Incidence is poorly defined (and the usual approach is to use cases that have already been incident), these figures may only give a broad and vague picture.

Ruptured AAAs have a high risk of death (see CUR6). If the patient survives the emergency surgery, they still have a higher mortality risk.

By entering the screening programme the following clinical and economic outcomes may change:

• mortality (overall/disease specific)
• life expectancy
• progression to ruptured AAA
• complications of surgery including distal embolus, haemorrhage and graft failure, coronary and cerebrovascular events and renal complications
• subjective measures including quality of life scores and ability to work
• use of resources including hospital stay and use of intensive care facilities

{19}

In many organised screening programmes the target population (those who are invited) is around 65-80 years and males. In some screening programmes additional risk factors must be present to be included to screening.

In European countries the percentage of men in the high risk age group varies across countries and has tended to increase over the last 20 years. In 2010 Germany and France had the highest percentage (20%) of men aged 60-79. The lowest percentages reported were in Iceland and Ireland (13%). The average percentage of men aged 60-79 (among all men) has risen in 31 European countries* from 14% in 1990 to 17% in 2010. With the exception of Norway (1990:16%, 2010:16%), all the countries show trends towards an increasing percentage in this age group.

In 31 European countries there are ~43 millions of men aged 60-79.

A nationwide population-based screening programme is performed only in the UK ({3} citing {20}).

The EUnetHTA survey reported that Sweden also invites men for AAA screening.

In many countries possible implementation of a screening programme is being discussed.

The highest attendance rates can be expected from decentralised screening {21}, followed by hospital based screening {21}. The lowest rates are likely for general practice based screening {5}.

The VIBORG study {21} presents attendance rates for a hospital based mass screening for AAA showing the effect of various factors:

It has also been reported that while hospital based screening has an attendance rate of around 80%, the uptake in a general practice based screening is likely to be between 50% and 70% {5}

Population-based screening programmes may be implemented nationwide or regionally. The AAA screening described in the literature is either hospital based screening or general practice based screening, for which different attendance rates are described. No statements about the quality of the screening programme (patient information, safety, characteristics of the screening instrument and the preventive intervention   strategy) could be identified in the literature on the types of screening.

In the literature, variations in attendance rates in different screening programmes were the only variations identified. (see CUR23)

Screening programmes vary in the intended target groups, in the location of screening and the number of screenings during a lifetime.

In the UK National Health Service (NHS) AAA screening programme men who turn 65 are automatically invited to the programme. Men who are older and have not been screened previously can opt in through self-referral {UKNSP2010#Health...}.

No information was identified, about how different screening programmes vary in the preventive strategies used (e.g. surgery, behavioural change).

In the survey questions about “other technical devices beside the gold standard” five countries listed the following techniques:

• Denmark: computed tomography (CT) scan
• Lithuania: Ultrasound  and computed tomography, magnetic resonance tomography
• Latvia: MR angiography
• Sweden: If ultrasound does not provide adequate images, CT is performed. This is very infrequent
• Croatia: There is no AAA screening programme in Croatia. But, for example, digital subtraction angiography (DSA) could serve as a diagnostic technology. MR could also serve for diagnosis, because AAA could be an incidental finding during examination for other abdominal illness or during colour-Doppler examination of peripheral arteries.

There are several guidelines giving recommendations on AAA screening.

These recommendations vary in the age groups for whom screening is recommended, in the question of whether women should generally be included or not, and in whether inclusion should be limited by individual risk factors such as smoking.

The results from the EUnetHTA survey list open surgery and endovascular surgery for treating high risk AAAs as follows:

• Austria: open surgery with aortic grafts or abdominal stent
• Croatia: open surgery or EVAR
• Finland: open or endovascular surgery
• Latvia: open surgery (common) or endovascular surgery (for patients participating in clinical trial)
• Lithuania: open or endovascular surgery
• Slovakia: open surgery or stent graft
• Spain: open surgery or EVAR
• Sweden: open or endovascular surgery

Intervention depends on the diameter of the AAA. For smaller aneurysms (3.0 –3.9 cm) with a lower risk of rupture, medical therapy and watchful waiting is recommended (see CUR14). For medium sized aneurysm (4.0 – 5.4 cm) elective surgery is indicated (see CUR14). AAAs that are 5.5 cm or more in diameter the cut-off point of repair is reached {27}. Whether to use endovascular or an open surgical approach should be decided on an individual base. Open surgery is indicated for patients with a low preoperative risk (younger patients). Endovascular surgery is indicated in patients with favourable anatomy and who are at high surgical risk {Baum#Endovascular repair}.

Alternatives to screening based on research (a study design with a control group) could not be identified.

This question seems not to be applicable for AAA screening.

To be identified.