Aims: To characterise plaque phenotypes in the left main stem (LMS) and the proximal left anterior descending (LAD) coronary artery using virtual histology assisted intravascular ultrasound (VH-IVUS).
Methods and results: Patients with IVUS pullbacks including no less than the proximal 30 mm of the LAD and through the ostium of the left main were identified from a global IVUS registry. Plaque composition and phenotype frequency in the LMS and five consecutive non-overlapping 6 mm segments in the LAD were studied, resulting in six analysed segments per patient. There were 74 patients (72% male, mean age 65 years). The median LMS length was 5.4 mm (IQR 2.8-8.7 mm). The percent of fibrofatty plaque was greater in the LMS compared to the proximal LAD segments (27.9% [20.0-39.2] vs. 17.3% [12.2-23.1], p<0.001). Dense calcium and necrotic core content was less prevalent in the LMS compared to the LAD segments (2.5% [0.9-4.7] vs. 7.9% [4.1-12.3], p<0.001; and 8.0% [3.7-11.8] vs. 14% [9.2-17.9], p<0.001). The frequency of thin cap fibroatheroma (TCFA) was higher in the LAD compared with LMS (0% vs. 16.9% [4.9-34.5], p<0.001). Within the LAD, TCFA was most frequently observed in the second 6 mm segment, 12 mm from the ostium.
Conclusions: TCFA was present more frequently in the proximal LAD than LMS, supporting the notion that plaque rupture occurs in non-uniform locations throughout the coronary tree and preferentially spares the LMS.