External aortic wall diameter in screening is preferred, CX delegates believe

In the first debate of Sunday’s CX, the majority of delegates (71%) agreed with the motion that “we prefer external aortic wall diameters in screening”

Naghmana Riazuddin, Wycombe, UK, who was speaking for the motion, said that the inner wall of the aorta was difficult to see and that the external wall was “much clearer”.

To support her arguments, Riazuddin outlined the findings of the UK Small Aneurysm Trial, which showed that the “outer to outer” method of measuring aortic diameter (in abdominal aortic aneurysms) could be used without any problems. She added that there is approximately 3mm of difference between inner-to-inner measurements and outer-to-outer measurements.

She said, therefore, if a patient was found with an aortic diameter of 2.9cm, by using the inner-to-inner method, they could actually have a diameter of 3.2cm. Riazuddin explained that this could have implications for treatment. She said: “A 4.7cm aorta via an inner-to-inner method would not be referred for vascular surgery, but it would be 5cm via an outer-to-outer method.” The threshold for intervention is 5cm. Concluding, she said that the outer-to-outer method was traditionally used and most of the trial data was based on this method. She explained that in a poll of 41 centres across Europe, 32 said that they used the outer-to-outer method. She added: “Aortas scanned by others outside of the [UK National] screening programme are still using outer-to-outer, so will we have different actual measurements for the 5.5cm threshold?” 

Arguing against the motion was Tim Hartshorne (Leicester, UK). He outlined the benefits of the inner-to-inner method. He said a study, of which he was the lead author, found that (as Riazuddin argued) there was the expected difference between the inner-to-inner method and the outer-to-outer method in terms of diameter, but it also showed that there was better accuracy and reliability with the inner-to-inner method.

He said: “This is important in the context of National Screening Programmes to assure consistency between technicians and surveillance visits.” Countering Riazuddin’s argument that the outer-to-outer method should be used because the 5cm threshold is based on trials that used that method, he said: “The inner-to-inner method should be used given that that there is evidence of better reproducibility but it would be possible to adjust referral thresholds if it was found that there was an increased rupture rate in men under surveillance, for instance from 5.5cm to 5.2cm (inner-to-inner method).”

He added: “Screening programmes including the NHS abdominal Aortic Aneurysm Screening Programme will gather large amounts of data on the natural history of aortic aneurysms, providing information and evidence that may lead to modification and improvement of the present schedules.”

After the debate, Roger Greenhalgh, Imperial College, London, CX programme chairman, and chair of the first aortic session, also posed the question: “Is it crazy that we ever adopted a variety of ultrasound borders for determining aortic diameter for infrarenal aortic abdominal aneurysms? The delegates overwhelmingly voted “yes” , with only 17% saying “no”.