D-Dimer in Aortic Dissection Workup

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 A – Ascending 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

Discussion Questions / Future Exploration

• Can we develop decision rules similar to those developed for pulmonary embolus?
• Are there time limits related to D-dimer testing: when is it too soon or too late after symptoms onset for the test to be useful?
• Is there a better threshold level for D-dimer which might make it a more useful test?

References