Intravascular Ultrasound (IVUS)

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Clinical outcomes of patients with left main coronary artery disease as determined by IVUS[1]

Equations:

  • CSA = cross-sectional area
  • EEM = external elastic membrane
  • Lumen Area Stenosis = 100 x [(Reference Lumen CSA - Minimal Lumen CSA) / Reference Lumen CSA ]
  • Lumen Eccentricity = 1 - (Minimum Lumen Diameter / Maximum Lumen Diameter)
  • Lesion Atheroma Area = EEM CSA - Lumen CSA
  • Atheroma (Plaque) Burden = 100 x (Lesion Atheroma Area / Lesion EEM Area)
  • Atheroma Volume = Σ (EEM CSA - Lumen CSA)
  • Remodeling Index = Lesion EEM CSA / Reference EEM CSA
    • Normal: 0.95-1.05
    • Positive: > 1.05
    • Negative: < 0.95

Cut-off Thresholds

  • Must separate left main from non-left main lesions.
  • Data comparing non-left main coronary IVUS measurements to fractional flow reserve (FFR) show cut-off threshold ranging from 2.1-4.4 mm2[2].
  • Minimum lumen diameter of 3.0 mm2 is the most common value used [2].
  • Sensitivity > 80% but specificity < 50%[2].
  • Due to low specificity, FFR and not IVUS should be used to assess the haemodynamic significance of non-left main coronary artery lesions.
  • For left main coronary artery lesions FFR of 0.75 correlates with minimal lumen area of 5.9mm2[3] i.e. if the left main coronary artery CSA is less 6 mm2 it is likely to be haemodynamically significant.
  • Distribution of left main luminal area (study performed in Minnesota, USA)[4]:
    • Mean = 16.25 mm2
    • Standard deviation = 4.30 mm2
    • Mean - (2 x standard deviations) = 7.65 mm2
  • Left main minimal lumen area < 7.5 mm2 left untreated is associated with long-term major adverse cardiovascular events[4].

References

  1. JACC 2014;64:207
  2. 2.0 2.1 2.2 JACC 2014;64:207
  3. Circ 2004;110:2831
  4. 4.0 4.1 JACC 2005;45:204