Plaque composition and morphologic characteristics in significant left main bifurcation disease; virtual histology intravascular ultrasound study.

Objective: Although the left main coronary artery (LMCA) is clinically the most important site, little is known about the longitudinal plaque distribution and composition in the significant LMCA disease.

Methods: Preprocedure virtual histology intravascular ultrasound data were analyzed in 120 patients with significant LMCA bifurcation lesions (angiographic diameter stenosis>50%) requiring revascularization. Plaque burden and percentage of necrotic core (%NC) at the minimal lumen area site and maximal %NC site were measured in four segments: proximal LMCA, distal LMCA, left anterior descending (LAD) ostium, and proximal LAD.

Results: Angiographically, a significant LMCA and ostial LAD stenosis were observed in 89.2 and 81.7% of patients, respectively. At the minimal lumen area site, the proximal LAD segment showed the smallest lumen [3.5 mm (2.5-4.7), P<0.001] and the greatest plaque burden [73.2% (63.0-79.3), P<0.001] compared with the other segments. Also, there was a significant downward trend in the number of IVUS-defined lesions toward the proximal LMCA (P=0.001). At the maximal %NC site, the proximal LAD segment carried the largest necrotic core [32.7% (25.7-40.1), P<0.001] and the most frequent virtual histology thin-cap fibroatheroma (67.6%, P<0.001) among the segments, followed by the proximal LMCA [30.3% (22.3-40.0) and 32.9%, respectively]. Most of the plaques carried, at least, one slice of fibroatheroma in every segment; thus, fibroatheroma distributed in a continuous pattern from the proximal LAD to the proximal LMCA.

Conclusions: In the significant LMCA bifurcation disease, the proximal LAD segment was found to have the smallest lumen, the largest plaque burden, the highest virtual histology thin-cap fibroatheroma rate, and thus presented the most vulnerable characteristics by virtual histology intravascular ultrasound.