UltraSound of Silence Abdominal Aortic Aneurysm

– A Milestone Evidence in Japanese Hypertensive Elderly Has Come Out –

Abdominal aortic aneurysm (AAA) is known as a “silent killer” because it potentially grows year by year and its outcome becomes more lethal once it has grown larger in size.¹ The clinical definition of AAA is commonly that the maximum short-axis diameter at infrarenal measurement (taken below the renal artery branches) exceeds 30 mm.² Another definition of AAA is also in use, whereby AAA is defined as at least a 50% increase in diameter compared with the expected normal diameter of the aorta.³ Patients with aneurysms >55 mm in diameter are generally considered for elective surgical repair,^2,3 because mortality significantly drops once the AAA is >55 mm.^1,2 The only consensus for radical intervention is surgical repair, but recently, endovascular aneurysm repair (EVAR) gives surgeons an alternative and less invasive therapeutic option.⁴ Patients with aneurysmal diameters ≤55 mm (termed smaller AAA [smAAA]) are managed with aneurysm surveillance because previous evidence revealed that immediate surgical intervention for smAAA had no advantage compared with surveillance (UKSAT and ADAM trials).^5–7

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Likewise, regarding the advantage of EVAR for smAAA, clinical trials (CAESAR and PIVOTAL) found no advantage of EVAR for smAAA when compared with surveillance.⁸ Thus, an unsolved concern is how physicians should manage the preoperative smAAA because currently there is little high-quality evidence or guidelines worldwide.^3,5

It seems a more urgent issue to be solved in our region is that the clinical characteristics of AAA remain uncertain, particularly in Asians, including Japanese. In this issue of the Journal, Fukuda et al⁹ report milestone evidence in elderly Japanese patients with hypertension regarding the uncertain milieu of the asymptomatic AAA. This “AAA Japan study” was designed as a multicenter prospective observational study for assessment of the incidence of occult AAA in elderly hypertensive patients using the “pocket echo” (Figure). The total number registered reached 1,731 patients with hypertension aged >60 years, and the prevalence of AAA was 4.1%.³ Prior to measurement by pocket echo, the protocol required abdominal palpation. Readers will recall the importance of physical examination as an important basis for cardiologists to diagnose silent AAA. However, this study urged caution regarding AAA screening by palpation because the diagnostic sensitivity by abdominal palpation was found to be low (52%). It is noteworthy that if the size of the AAA was large enough (>40 mm), the sensitivity rose up to 75%.

Figure.

Variety of pocket-sized portable echo equipment (illustrations from the merchandise brochures published by the corresponding manufacturers). (A) Vscan1.2 (GE Healthcare Inc) used in the present study; (B) SONIMAGE P3 (Konica-Minolta Healthcare Inc); (C) ACUSON P10 (Nihon-Koden Inc and Simens Japan Inc), showing typical image when operating the portable echo (D).

The diameter of the aorta measured by ultrasound is known to vary from the original size. One of the causes is coexisting kinking, as well as anatomical variations of the aorta, which leads to overestimation.¹⁰ It would have been beneficial if comparable CT assessment had been performed in the present study (but of course, that was impractical). To overcome this potential weakness, in the present study the reproducibility of the ultrasound measurements in terms of the interobserver variability in 15 subjects was carefully assessed by 2 independent blinded observers who were one of the trial investigators (H.W.) and an independent participant (K.S.). Furthermore, intraobserver variability was analyzed in another group of 15 subjects by the same observer (K.S.) at 2 different time points. The results found excellent correlation with the interobserver (r=0.98) and intraobserver (r=0.99) measurements. Collectively, the AAA Japan study demonstrated that AAA is not rare in the Japanese population with atherosclerotic risks, such as aging, hypertension, and familial history.

Clinical evidence regarding AAA is more concrete and extensive in Western countries. The Cochrane annual report anticipates that there will be an increasing number of AAA cases if more patients are screened.³ More concrete numbers and details are displayed in Table. Aneurysms >55 mm (50 mm in the Japanese guideline) in the maximum short-axis diameter carry a high risk of rupture, and rupture carries a high risk of death.

Table. Prevalence of AAA According to Previous Clinical Studies

	AAA-Japan9	Meta-analysis13	UK14	USA7	Sweden15
Age (years)	>60	65–79	>65	50–79	65
Prevalence of AAA % (AAA/total patients)	4.1% (69/1,731)	5–10%	1.5–4.6% (2,412/50,130)	2.1% (1,031/73,451)	2.2% (480/22,304)
Measurement	Ultrasound (pocket echo)	Ultrasound and CT	Ultrasound	Ultrasound	Ultrasound
Comments	All patients had comorbid hypertension In patients >80 years old, AAA prevalence was higher (9.7% for males, 5.7% for females)9	4.1–14.2% in men and 0.35– 6.2% in women	5% in men and ≈one-third of this in women14	ADAM trial	Only males and limited to 65 years of age

AAA, abdominal aortic aneurysm.

The original meaning of the song “The Sound of Silence” by Simon and Garfunkel was the inability of people to communicate with each other. To break the “silence”, some positive action is essential. The present study suggests the essential role of positive survey of the overlooked/silent AAA by palpation and ultrasound in the patient population at risk of atherosclerosis. An advanced and nationwide strategy has already begun in England. The national screening program for AAA (The NHS Screening Programmes) is organized as a part of Public Health England and an executive agency of the Department of Health also supports the UK National Screening Committee.^11,12 This type of approach might be considered inorder to establish a higher quality clinical database regarding AAA in Japan and Asia more widely.

References

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