Thoracic aortic dissections (TAD) are a bit of a nightmare. They are difficult to diagnose clinically, which is annoying as an Emergency Department (ED) clinician, but it gets even worse when you consider it from the patients perspective……
Half of all patients who dissect will die within 48 hours if its not diagnosed, compounded by misdiagnosis occurring in up to 30% of patients (Klompas 2002).
What is a TAD?
An acute aortic dissection can be defined as the rapid development of a false, blood filled channel within the tunica media of the aorta (Kumar et al 2005)
The classification of aortic dissection is based upon the anatomic involvement:
Stanford classification (link to this page for diagram http://circ.ahajournals.org/content/108/5/628/F1.expansion.html) :
- Type A – any dissection that involves the ascending aorta (proximal)
- Type B – any dissection involving the descending aorta (distal)
This is important, as the treatment of this condition will depend on the classification, type A requiring emergency surgical repair and type B being treated initially with medical therapy (Braverman 2010).
How can we spot them in the ED?
Classical presentation involves a patient presenting with a sudden onset of tearing chest pain which may, or may not, radiate to their back (Longmore et al (2004). Now this creates a bit of a problem, as we may see many patients every day who present with chest pain, but not every one will have a dissection. In fact its pretty rare, with only 3 cases per every 100,000 patients per year (Leitman et al 2013). In a recent study it was found that TAD represented 0.36% of 37,778 patients who presented to the ED with chest pain (Leitman et al 2013). This paper also threw us some really useful patient demographics to help us out:
- Mean age = 69 years
- Males (60%) vs females (40%)
- Previous diagnosis of hypertension in 71% of patients
- 35% of patients were smokers
It’s also useful to look at how these patients described their pain:
- Chest- 47%
- Abdominal – 24%
- Back – 24%
- Migrating – 35%
- Sharp – 18%
- No Pain – 28%
- Pressure/tight – 5%
- Heavy – 1%
- Increasing – 23%
- Sudden – 11%
- Constant – 37%
There have also been a number of clinical risk markers identified (Hiratzka et al 2011):
- Marfan syndrome
- Family history of aortic disease
- Known aortic valve disease
- Recent aortic manipulation
- Known thoracic aortic aneurysm
- Abrupt onset of pain
- Severe pain intensity
- Ripping or tearing pain
- Pulse deficit or systolic blood pressure difference in upper limbs (>20mmHg)
- Focal neurologic deficit (in conjunction with pain)
- Aortic murmur (in conjunction with pain)
- Hypotension or shock
It is also worth noting that there have been case reports of TAD in pregnancy and labour (Braverman 2010).
What is the diagnostic test of choice?
Well, helical thoracic CT scanning is the way to go if you want to catch everyone. Its got a reported diagnostic sensitivity of 100% and is 98% specific (Shiga et al 2006), which is pretty good!
But its not all good news, this type of CT exposes the patient to 7 mSv radiation, giving an additional lifetime cancer risk of 1 in 3500 (ish). Now this is fine if you’ve got a high pre-test probability of having TAD, because that carries a mortality of nearly 50%, but if you just scan everyone with chest pain, then you’re not going to find it in 99.6% of patients (if you refer back to the Leitman study), making this radiation exposure unnecessary and that’s not even considering the effects on cost and elective work.
What about chest x-rays?
These can help. The presence of a widened mediastinum was present in 52% of cases in the Leitman paper (2013), which reached a statistical significance. In comparison to the CT, a chest x-ray represents 0.1mSv radiation and an additional lifetime cancer risk of 1 in 260417…… so not a bad place to start in terms of tests.
Anything else we could use?
Well there might be, a study by Suzuki et al (2009) found that D-Dimer levels were markedly elevated in patients with acute aortic dissection. They found that for patients presenting within 24 hours of onset of pain, a D-Dimer level of <500ng/mL (the levels previously used to rule out venous thromboembolism) could reliably rule out aortic dissection. This paper only looked at 220 patients though…. So further research is probably warranted before you change your practice (plus, be sure your hospital uses the same assays as they do in the study).
What’s the take home message?
TAD is rare, but the best chance for your patient relies on you picking it up early. This means you need to be suspicious of all patients, but use the available evidence base to decide if they need that CT to confirm or refute your suspicions.
Rob qualified from the University of Nottingham in 2004 and has worked in a variety of emergency and critical care settings. He spent 8 years as a charge nurse in the emergency department prior to becoming a trainee Advanced Clinical Practitioner (tACP) last year.
He has also worked extensively in prehospital care since 2006 with both the West Midlands CARE team and West Midlands Ambulance Service MERIT team (until 2014), gaining his Diploma in Immediate Medical Care (DIMC) from the Royal College of Surgeons of Edinburgh last year.
He has a keen interest in both education and research, teaching regularly on a number of popular courses and is one of the lead authors of the work produced by the EXtrication In Trauma (EXIT) project.
For the “readers”
For the “listeners”
Intensive Care Network – http://intensivecarenetwork.com/aortic-catastrophes-rogers/
For the “watchers”
Braverman, A. C. (2010) Acute aortic dissection: clinician update. Circulation. Vol 122, pp 184-188. Available here: http://circ.ahajournals.org/content/122/2/184.full (last accessed 1/10/15)
Klompas, M. (2002) Does this patient have an acute thoracic aortic dissection? JAMA. Vol 287(17), pp 2262–2272.
Kumar, V., Abbas, A & Aster, J. (2005) Robbins & Cotran Pathologic Basis of Disease (9th edition). Elsevier. New York.
Leitman, I. M., Suzuki, K., Wengrofsky, A. J., et al. (2013) Early recognition of acute thoracic dissection and aneurysm. World Journal of Emergency Surgery. Volume 8 (47). Available here: http://www.wjes.org/content/8/1/47 (last accessed 1/10/15).
Longmore, M., Wilkinson, I. B & Rajagopalan, S. (2004) Oxford handbook of clinical medicine (6th Edition). Oxford University Press. Oxford.
Shiga, T., Wajima, Z., Apfel, C. C., et al. (2006) Diagnostic accuracy of transesophageal echocardiography, helical computed tomography, and magnetic resonance imaging for suspected thoracic aortic dissection: systematic review and meta-analysis. Archives of Internal Medicine. Volume 166(13), pp 1350–1356.
Suzuki, T., et al. (2009) Diagnosis of acute aortic dissection by D-Dimer: The International registry of acute aortic dissection substudy on biomarkers (IRAD-Bio) experience. Circulation. Volume 119, pp 2702-2707.