When I have downtime and I’m riding my bike or indeed tending to my Dads “prize winning” broad beans on the allotment; my mind unfortunately often wanders to recent cases in the ED that have gone bad.
I start to reflect on things I could have done better, or wonder if I could have affected patient outcomes for the better….
It’s the curse of the Emergency Physician.
This last week I have been pondering the dissecting thoracic aortic aneurysm (really type A dissections). Perhaps I’m practicing an area of unknown high incidence but I have come across 2 cases in recent months (normal incidence – by the way – 3/100,000) that have ended badly. Now, we all know that it’s a diagnosis that we find scary – the time bomb of doom – 1-2% of patients will die for each hour after onset of symptoms untreated. We know that symptoms aren’t reliable and you’ve gotta have a high index of suspicion (it is the “most undiagnosed serious condition” with up to 30% of diagnosis made at autopsy!).
I don’t claim to be a normal person, but I am always wary of patients (not intentionally, but, their “truths” can vary, they hide things, they’re never classic….) and my index of suspicion is always high….
BUT when you need some diagnostic imaging for your crazy, paranoid hypotheses – it not always that easy to get a timely solution from our friendly radiologists.
What are the conventional options?
The Chest x-ray whilst much loved is awful as a rule-in or rule-out for dissecting thoracic aneurysm. It will be completely normal in 20% of your patients and if your looking for mediastinal widening then you’ll only see that in 15%….as for the other myriad of “classic” signs we might as well get our euro millions lottery ticket.
The contrast CT, 79-100% sensitive, 87-99% specific – great, but not as “readily available” at the district hospital (where most EP’s) work as we might hope. The radiologist will argue that there is a high dose of radiation and no-one ever likes to use contrast. Meanwhile as we are debating and waiting for a slot in the scanner the time bomb is ticking.
And, Yes, there are also MR scan, transoesophageal echo and retrograde angiography, but I’m not convinced these diagnostics are available in many centres.
SO… what do I want in an ideal world? I would like bedside diagnostics that I can perform to help me expedite treatment rapidly…..So my big idea has been to use the ED ultrasound to perform Transthoracic echo (TTE) and measure the aortic root and get views of the arch to look for intimal flaps combined with standard descending aorta views. The question is – How confident can I be to use my ultrasound as a rule-out or rule-in for dissecting type A aneurysm?
Allow me to look over the literature:
The European Society of Cardiology have recommendations for aortic disease. They say that “TTE is an excellent modality for imaging aortic root dilatation…..not the ideal tool for visualizing all aortic segments”. In a related article from the Society they quote the “Literature of the past” i.e .1980’s and 1990’s, suggesting that for type A dissection TTE has a sensitivity of 78-100%, but as low as 57% in some series! They do point out that there have been no recent studies…. and certainly they would not use TTE as a rule-out. All very opinion based………
Luckily, to the rescue of evidence based practitioners, comes a diagnostic study published this year by an Italian team headed by Moreno Cecconi. They have asked a question similar to my own – “what is the current diagnostic value and the possible role of TTE in the management of patients with suspected aortic arch syndrome?”
270 patients (retrospectively collected data!?! And selection criteria not explained) all assessed by TTE as first line investigation and subsequently imaged by either CT/MR or transoesophageal echo…..Quoting: Sensitivity 87%, Specificity 91%, PPV 75%, NPV 95%.
In all honesty there are lots of problems with the methodology, and it’s from a dedicated cardiac centre – not really generalisable for the average EP ultrasound operator – but it’s the only data we have using the latest generation of ultrasound technology. The authors are confident with their results and even go as far to say bedside TTE is “useful in establishing or excluding the differential diagnosis in the acutely unwell patient, particularly in the absence of aortic root dilatation”.
What conclusions can I draw from the limited evidence? Well, as with FAST and FASH etc, bedside TTE is another diagnostic modality in our armoury…. Its highly operator dependent but its quick and safe and can definitely guide your management. Would I rely on it to completely exclude a diagnosis of type A aortic dissection? Probably not… But I would measure the aortic root diameter and think hard about my next move…
Rare conditions with serious outcomes – its like being a goalkeeper facing a penalty in soccer – make a save and you’re a hero, drop the ball and you feel like a villian with the weight of the world on your shoulders… but the odds were always stacked against you. The magic wand of ultrasound – when used wisely – can be a significant arrow in your quiver of imaging diagnostics, but when the incidence is low and the risks are high, think hard before using TTE as a lone rule-out investigation…Its not an ideal world in the world of diagnostics…….
And that is what I think about when I’m tending broad beans.