An Observational Cohort Study of People Attending the ED With Symptoms of Acute Aortic Syndrome (AAS)

AAS is a life-threatening emergency condition which presents to the ED. Around 4,000 people suffer per year in the UK [1], many not receiving timely diagnosis and treatment. 25% of patients are not diagnosed until 24 hours after arriving in the ED due to the varied nature of presentation [2]. Chest pain is the most common presenting symptom of AAS (80%) although back pain (40%) and abdominal pain are not uncommon [1]. These symptoms account for over 2 million ED attendances per year in England [National Health Service; NHS Digital A&E 2021] and are overwhelmingly due to causes other than AAS. The estimated incidence of AAS is 1 in every 980 ED attendances with atraumatic chest pain [3], thus creating a substantial diagnostic challenge.

Prognosis is best when patients are treated early, and mortality increases 2% per hour of delay. [4] The misdiagnosis rate during the initial ED visit for AAS is estimated to be between 1 in 3 to 1 in 7 AASs [5], leading to worse outcomes [6,7] whilst CTA over testing leads to diagnostic yields as low as 2-3%. [2,8]. CTA scanning of the aorta has high sensitivity and specificity for diagnosing AAS, but an unrestricted CT strategy will incur significant costs, has ionising radiation risks, resource implications, CT delays for non-AAS patients and the burden of 'incidentalomas'.

Clinicians therefore need to use CTA selectively but there is no validated scoring system to help this decision. Several have been proposed [1, 9-14] including the ADD-RS score, the Canadian clinical practice guideline Clinical Decision Aid [13], the AORTAs score [14] and the Sheffield score [unpublished]. D-Dimer has been suggested as a rule-out biomarker in low pre-test probability patients (95-98% sensitivity) [15,16] and has been incorporated into the Aortic Dissection Detection-Risk Stratification (ADD-RS) score to reduce CTA rate in low pre-test probability patients. None have been studied in truly undifferentiated ED populations, or in the UK where CTA threshold is different compared to North America. It is currently unclear whether any have sufficient sensitivity to be acceptable to clinicians, which is the most accurate, and whether they are likely to lead to CTA and D-Dimer over testing. Assessment of CTA rate and CT positivity has also not previously been studied. The Royal College of Emergency Medicine has recently released a national guideline advocating any patient with an ADD-RS score of >=1 (no D-dimer incorporated) should have a CT aorta performed (unless other cause for symptoms identified and evidenced). The recommendation is not based on UK-validated clinical evidence, however, and clinical impacts of the recommendation are yet to be seen.

In view of these diagnostic challenges, the investigators aim in our programme of work to ultimately to assess which of the four aforementioned clinical decision tools is most effective, assess external validity, and assess clinical impact. This study (Phase 1; DAShED) will involve prospective data collection on all characteristics of four different risk scores, in addition to evaluation of patient characteristics, potential CT aorta rates with different strategies, and enrolment rates at participating sites. This will inform Phase 2, which will involve full interventional external validation study of the decision aid(s) selected in Phase 1 (including biomarker collection); the main objective being to select the score to subject to assessment of clinical impact (intervention step-wedge trial) in Phase 3.

This is an observational cohort study of all people attending the ED with symptoms of possible AAS, including new-onset chest, back or abdominal pain, syncope or symptoms related to malperfusion.