Is accurate intravascular ultrasound evaluation of the left circumflex ostium from a left anterior descending to left main pullback possible?

Treatment of left main coronary artery bifurcation lesions might depend on the ostial left circumflex (LC) or ostial left anterior descending (LAD) disease severity. We sought to evaluate whether intravascular ultrasound assessment of the side branch ostium requires direct imaging or is accurate from the main vessel. Our retrospective analysis included 126 patients with left main coronary artery bifurcation disease (plaque burden > or =40% by intravascular ultrasound scanning). We analyzed pullbacks from the LAD and the LC. First, during the main vessel pullback (ie, from the LAD), we evaluated the side branch ostium (ie, of the LC). Second, we compared this oblique view with the direct ostial measurements during LC pullback. Finally, we repeated this process, imaging the ostial LAD from the LC. From the LAD, the oblique LC ostial lumen diameter was 3.0 +/- 0.8 mm compared to the directly measured lumen diameter of 2.9 +/- 0.6 mm. From the LC, the oblique LAD ostial lumen diameter was 2.9 +/- 1.1 mm compared to the directly measured lumen diameter of 2.8 +/- 0.5 mm. However, Bland-Altman plots showed significant variation in the oblique versus direct comparisons. The 95% limits of agreement ranged from -1.84 to 1.14 mm (mean difference -0.35, SD 0.75) for the LAD and -1.69 to 1.22 mm (mean difference -0.23, SD 0.73) for the LC. The "oblique view" detection of any plaque in the side branch predicted 40% or 70% plaque burden with good sensitivity but poor specificity. In conclusion, intravascular ultrasound evaluation of a side branch ostium from the main vessel is only moderately reliable, especially for distal left main coronary artery lesions. For an accurate assessment of the side branch ostium, direct imaging is necessary.