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

OBJECTIVES

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.

CONCLUSION

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.