Aortic Aneurysms

What is an abdominal aortic aneurysm (AAA)?

The aorta is the main artery from the heart and carries blood to the organs and limbs. An aortic aneurysm is an enlargement of the aorta.

In the abdominal aorta an aneurysm is defined as an enlargement of the aorta of at least 1.5 times its normal diameter, or greater than 3 cm diameter in total.

Causes

Most are caused be atherosclerosis ("furring/hardening of the arteries"). Rarely the artery wall is weakend by hereditary conditions

The main risk factors for AAA include smoking, high blood pressure, increasing age and a family history of aneurysms.

What is the incidence of aortic aneurysm in the UK

Around 4% of men aged between 65 and 74 in England have an AAA (approx. 80,000 men) this results in approximately 6000 deaths per year in England and Wales.

Deaths from AAA account for around 2% of all deaths in men aged 65 and over

Women are much less likely to develop abdominal aortic aneurysms. They are about three times more common in men than in women.

How do I know if I have an abdominal aortic aneurysm?

Most aneurysms do not produce any symptoms.  Occasionally they can cause abdominal or back pain, or even a pulsating sensation in the abdomen. However, pain in a patient with a known aneurysm can be a sign of impending rupture and urgent medical attention should be sought.

Most aneurysms are found incidentally (by chance) when tests are carried out for other reasons or are picked up by screening.

Screening;  

Some centres are already screening for asymptomatic abdominal aneurysms. There is a national screening programme for AAA which is under way. The first centres have started screening in March 2009. The remaining centres will be managed in a phased roll-out over the next 5 years. All men over 65 years old will be invited to attend unless they have already been scanned or treated for AAA. The screening involves having an ultrasound scan. This is painless and takes only a few minutes.  You will be told the results immediately after the scan and also by a letter in the post shortly afterwards.

Risks with aneurysms

The most serious risk is that the aneurysmal blood vessel can eventually enlarge until it bursts. This bleeding is usually life threatening and urgent surgery is needed. 80% of patients with a ruptured AAA will not survive. Unfortunately, even with emergency surgery, only about half survive beyond 30 days. Rupture can be avoided if the aneurysm is repaired before this occurs.

The risk of rupture increases with the size of the aneurysm. An aneurysm of 6 cm in diameter has an annual risk of rupture of 25%. Symptoms of rupture can include; Sudden severe abdominal or back pain. This may be accompanied by signs of shock (collapse, light headedness/dizziness, rapid heart beat, fainting, nausea and vomiting, excessive thirst, sweating). Immediate medical attention must be sought.

Treatment options and risks

Your doctor may recommend surveillance (watch and wait) or Surgical Repair.   The decision will depend on the size and type of aneurysm, the short and long term benefits/risks of surgical repair; and your physical fitness.   The main surgical options are:

1. Conventional open surgery
2. Laparoscopic (key hole) surgery
3. Endovascular repair 

Surveillance

Current guidelines from the Vascular Society and the National Screening Committee recommend that patients with symptomatic aneurysms of less than 4.5 cm in diameter should be followed up with ultrasonography every 6 months, and aneurysms of 4.5–5.5 cm in diameter should be followed up every 3 or 6 months. (reference)

Elective surgery is generally recommended for patients with aneurysms larger than 5.5 cm in diameter and with aneurysms larger than 4.5 cm in diameter that have increased by more than 0.5 cm in the past 6 months.

At a diameter of less than 5.5 cm it has been generally accepted that the risk of rupture is lower than the risk of open surgery. The risk of surgery however varies with the method of repair chosen and from individual to individual.

Open surgery

Traditionally abdominal aortic aneurysms have been repaired surgically. This is major abdominal surgery. 

• A large incision is made in the abdomen and the aorta is clamped to stop the blood flow through it (and consequently the organs it supplies). 
• This allows the surgeon to cut into the aneurysm and a synthetic tube (graft) is sewn onto the aorta to replace the abnormal blood vessel. 
• The clamp is then removed and blood flow is restored. 
• The operation is almost always carried out under general anaesthsia with the patient asleep. 
• As this is major surgery, patients usually have to spend some time in the intensive care unit after the operation to recover.

Risks of open surgery

• Most patients will recover from the operation and go home without any significant problems.
• However, as with all surgery there is a risk of serious complications. The main complications are bleeding (this can be severe especially in an emergency repair); complications related to the clamping of the aorta and subsequent lack of blood to the tissues (called ischaemia) such as kidney failure, risk to the legs, bowel and spinal ischaemia with a very small risk of paralysis.

Keyhole surgery

Laparoscopic ("key hole") surgery or hand assisted laparoscopic surgery can be performed uses a smaller incision than in open repair. A graft is sewn in and the aneurysm is repaired in a similar way to open repair. This technique is not performed in many centres.

Endovascular aortic aneurysm repair (EVAR)

• Relatively new technique (approx 10 yrs) but is now widely accepted as an alternative to open surgery. It is carried out in most large centres.
• It is minimally invasive surgery and usually only involves a small incision in each groin.
• The graft that has been pre-packed into a thin catheter/tube and is introduced through the artery in the groin.
• It is advanced under x-ray guidance into the aneurysm and then it is then deployed where it expands to fit into the inside of the aorta.
• Unlike open surgery where the aorta is effectively replaced by the graft, in EVAR the graft re-lines the inside of the vessel.

Advantages and disadvantages of EVAR

Advantages of EVAR are:

The 30 day post operative mortality following aneurysm repair is significantly lower with EVAR compared with open surgery (two thirds lower in the EVAR 1 trial).

• Reduced time under anaesthesia
• Less pain after surgery
• Less blood loss and immediate complications
• Shorter stay in hospital with faster recovery

Disadvantages are:

The EVAR graft may not form a complete seal in the aorta and blood will then continue to flow into the aneurysm. This is called an endoleak.

• Most endoleaks do not require any specific treatment except monitoring to ensure the aneurysm does not expand further.
• Some endoleaks will require further procedures to correct and occasionally open surgery is needed.
• Because some endoleaks can develop later on, patients who have had EVAR need continued follow up scans and clinic visits. This may be for years.
• Open surgical repair does not usually require any special follow up.

Links

National Institute for Heath and Clinical Excellence www.nice.org.uk   

Society of Interventional Radiology  www.sirweb.org     

NHS Abdominal Aortic Aneurysm Screening Programme http://aaa.screening.nhs.uk/

National Institute of Health and Clinical Excellence (NICE) guidance

The decision on whether endovascular aneurysm repair is preferred over open surgical repair should be made jointly by the patient and their clinician after assessment of a number of factors including:

• aneurysm size and morphology

• patient age, general life expectancy and fitness for open surgery

• the short- and long-term benefits and risks of the procedures including aneurysm-related mortality and operative mortality.

  Endovascular aneurysm repair should only be performed in specialist centres by clinical teams experienced in the management of abdominal aortic aneurysms  

Endovascular aortic stent–grafts are not recommended for patients with ruptured aneurysms except in the context of research.

Elective surgery is generally recommended for patients with aneurysms larger than 5.5 cm in diameter and with aneurysms larger than 4.5 cm in diameter that have increased by more than 0.5 cm in the past 6 months.NICE has recommended as a treatment option for patients where sugical repair is to be considered.