D-Dimer for Dissection
August 8th, 2008 at 12:47 am by NickThere’s a certain symmetry to starting the first journal club of the year studying d-dimer for dissection (last time around, we looked at the PERC rule and d-dimer for PE). This month, Bing examined a paper by Ohlmann and others, called “Diagnostic and prognostic value of circulating D-Dimers in patients with acute aortic dissection” (Crit Care Med. 2006 May;34(5):1358-64. PMID: 16557157). For background, we also read “D-dimer in ruling out acute aortic dissection: a systematic review and prospective cohort study” (Eur Heart J. 2007 Dec;28(24):3067-75. PMID: 17986466) and got some perspective on D-dimer the with Klompas addition to the JAMA rational clinical exam series: “Does This Patient Have an Acute Thoracic Aortic Dissection?” (JAMA 2002;287(17):2262-2272. PMID: 11980527).
The clinical background was useful in delineating the scope of the problem: acute aortic dissection (AAD) is rare — in some rigorous European surveys, incidence is 3-4 / 100,000 and in EDs, 2-3 of 1000 chest pain patients have AAD (so if you see about 1000 chest pain patients in the course of your residency…). We miss it a lot — Klompas said 39% of patients have a delay in diagnosis of more than 24 hours, 10% of autopsies for show missed dissections, and we only suspect AAD properly less than half the time (as low as 15% of the time).
There are a few key features of dissection that should set off alarm bells for AAD — pulse deficits and blood pressure cuff differences > 20 mmHg (positive likelihood ratio 5.7), focal neuro deficits (LR+ 6-33), and a description of “tearing pain” (LR+ 10.8). But many other signs are sensitive but not that specific, or not even that sensitive (and ‘tearing pain’ is only reported 39% of the time, with focal neuro deficits found just 17% of the time). Chest Xrays have a LR+ of around 2, and are only 60-80% sensitive (though a completely normal CXR — normal width mediastinum and normal aortic knob, have a LR- 0f 0.3).
What’s really needed to diagnose AAD is not-so-standard imaging, like CT, TEE, or MRI (all 98% sensitive or greater, with specificies in the high 90’s as well). So there’s an opportunity for a lab test to step in and help us guide decisionmaking. And d-dimer, a substance released by fibrinolytic activity unleashed when the extrinsic pathway is activated in dissection, in theory could work well as a marker.
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