Intravascular Ultrasound (IVUS)
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].
