Why are we checking that d-dimer?

An interesting question was posed at the VA: when is a d-dimer helpful. The question of venous thromboembolic disease aside, the lab test can also be helpful when consider aortic dissection in your differential. Take a look at the review below,

Introduction

  • Aortic Dissection is a cleavage of the aortic media layer created by a dissecting column of blood. This is different pathologically than an aortic aneurysm but the two terms are frequently interchanged incorrectly
  • Uncommon => 2-4 per 100,000 person-years (Acute Coronary Syndromes is about 100-200 times more common)
  • About 1 of every 2,000 ED patients presenting with any symptom associated with thoracic aortic dissection (TAD) will have TAD
  • Life-threatening – mortality rate of 1.2% per hour in the first 48hr

Recap / Basics

  • Three variants
    • Intimal Flap tear  – ~70-80% of cases
    • Intramural hematoma (believed to start from rupture of the vasa vasorum) – ~10-15%
    • Penetrating atherosclerotic ulcer – ~10-15%
  • Risk Factors
    • Hypertension – 72%
    • Collagen disorders – Marfan’s, Ehlers-Danlos
    • Inflammatory vasculitis disorders – Giant cell arteritis, Takayasu arteritis, rheumatoid arthritis
    • Instrumentation or structural abnormalities – cardiac cath / CABG, bicuspid valve, aortic coarctation, valve replacement
  • Classification
    • Stanford
      • Type AAscending and Arch
        • Higher Mortality
        • Surgical Management
      • Type  B – descending; Below the left subclavian
        • Lower Mortality
        • Often medical management
    • DeBakey
      • I – Ascending, arch and possible descending
      • II – Ascending only
      • III – Descending aorta
  • Pain is common >90%
    • Abrupt ~85%,  excruciating (“worst ever”) ~90% and most severe at onset
    • Chest or Back
    • Sharp, tearing, ripping but may be pressure or crushing
    • Migration suggests dissection but occurs only ~ 30% of cases
  • Physical exam, ECG, and chest x-ray are insufficiently sensitive to help with diagnosis
  • Other advanced imaging needed
    • Contrast CT Chest – sensitivity ~100%, specificity ~98%
    • MRI – sensitivity ~98%, specificity ~98%
    • Transesophageal Echocardiography (TEE) – sensitivity ~98%, specificity ~95%
  • Treatment
    • ED treatment is to reduce blood pressure to target systolic BP = 100-120
      • β-blockers – Esmolol or labetalol
      • Sodium nitroprusside
    • Surgery generally performed for Type A and complicated Type B dissections and possibly other Type Bs
    • Medication management for uncomplicated Type B

What’s New

  • Can the D-dimer help to include or exclude patients who might need advanced imaging?
  • The D-dimer is a fibrin degradation product indicating recent or ongoing coagulation
  • The D-dimer is very sensitive for picking up most dissections. Data from several different pooled studies show sensitivity 94-97%, specificity 34-100%
  • This has led several authors to suggest the D-dimer seems to have value as a screening tool for “ruling out” acute aortic dissection; i.e. if the D-dimer result is below a threshold level (generally below 400 – 500 ng/mL), then TAD is unlikely
  • However, false negatives (D-dimer levels below the threshold in patient with documented TAD) have been reported in several papers and one paper (Paparella) reported a surprising high false negative rate of 18% (11/61) with time of symptom onset to diagnosis ranging from 2 – 72 hours
  • Other authors have suggested the D-dimer should be part of the work-up if TAD is suspected. However using the D-dimer alone would lead to an unacceptably high number of false positives and follow-up advanced imaging
  • Higher d-dimer levels correlate with more segments of the aorta involved, with false lumen type dissections, and with higher mortality rates
  • D-dimers seem to be lower in patients with intramural hematomas

Bottom Line / Pearls & Pitfalls

  • A negative D-dimer (< 400 ng/mL) makes TAD unlikely but it is not 100% and false negatives occur
  • A positive D-dimer occurs in a very high percent of patients with TAD but also occurs in many other conditions
  • What is needed is a well-tested clinical decision rule to help select patients for further testing; that is when should we order, or not order, a D-dimer and/or when should we order, or not order, advanced imaging

Copyright Tim Schaefer, at emdocs.net

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