Screening for abdominal aortic aneurysms should reduce death rate

Although never cut out (!) to be a surgeon, I have fond memories of being a surgical intern. For three months I worked with Prof Greg Shanik, Mr Dermot Moore and their wonderful team at St James's Hospital.

They specialised in vascular surgery – essentially correcting abnormalities in the body’s arteries and veins. And whereas the stripping of varicose veins was one of the most boring operations, the same could not be said when it came to surgery on people with abdominal aortic aneurysms (AAA).

Risk of rupture
As some people get older, part of the aorta – the large blood vessel that carries blood from your heart to your body – can weaken and swell up like a balloon.

Most of these are small and not serious but larger ones carry a greater risk of rupture – a medical emergency that can be fatal in about 80 per cent of cases.

I remember we had some successes even with people who presented to the emergency department in a parlous state, but only after heroic feats of surgery lasting well into the night.

Even the planned surgical repairs of these aneurysms could provoke unwanted excitement. If one blew while the patient was on the operating table but before they had been repaired, pulses of bright red arterial blood would momentarily shoot towards the theatre roof before the judicious application of arterial clamps bought the surgeons some breathing space.

About 4,000 people in Ireland are diagnosed with these aneurysms each year. They occur about four times more frequently in men compared with women and are especially prevalent between the ages of 65 and 75. Ideally these are picked up and monitored while the ballooning is still small. Studies suggest that screening could reduce AAA-related deaths by up to a half by detecting aneurysms early so they can be repaired electively.

A 2011 Masters thesis by Maireád Brosnan of the Dublin Institute of Technology set out to answer the question: “Is there a benefit to screening for abdominal aortic aneurysm in an Irish male population between the ages of 55 to 75 years?”

She studied more than 900 men; of these 2 per cent had an undiagnosed AAA. Some 4.2 per cent of those screened were aged between 65 and 75, while the pick-up rate in the younger cohort was just 0.6 per cent.

Her conclusion was that an AAA screening programme for 65 to 75-year-old males in Ireland would be beneficial.

Screening using an abdominal ultrasound is completely non-invasive. Apart from identifying an aneurysm, the ultrasound aims to measure the diameter of the weak, ballooned part of the vessel.

Depending on its size, surgeons must assess whether the risk of rupture is greater than the risk of surgery.

Although cut-off points differ slightly from centre to centre, in general the risk is considered high enough to warrant surgery when the aneurysm is over 5.5cm for men and has grown 0.5cm in a year.

However, no screening system is perfect; about 20 per cent of aneurysms less than 5cm rupture.

In order to address the problem of some patients unnecessarily facing the risks of surgery while others are offered treatment too late, researchers at the University of Limerick have been looking at ways of improving the assessment process.

Writing recently in the journal Engineers Ireland, Siobhán O'Leary of the department of mechanical, aeronautical and biomedical engineering at the university described research aimed at identifying rupture prediction tools based on measurements of aortic wall strength and wall stress which she and her team hope will help surgeons further isolate high-risk aneurysms.

Using specialist software applied to CT scans, they are also looking at how measuring the intraluminal thrombus, a complex multilayered structure attached to the inner aneurysm wall, might offer patients a more accurate prognosis.

For an explanation of the treatments available for AAA, the website of the Western Vascular Institute in Galway (vascular.ie) is a useful resource.

mhouston@irishtimes.com
muirishouston.com