A virtual histology intravascular ultrasound analysis of coronary chronic total occlusions

OBJECTIVES: We used virtual histology intravascular ultrasound (VH-IVUS) to investigate plaque composition of chronic total occlusions (CTO). BACKGROUND: There are limited data on the composition of CTOs, especially in vivo. METHODS: VH-IVUS was performed in 50 CTO lesions (49 patients) after guidewire crossing or pre-dilation using a 1.5-2 mm balloon. Plaque composition in the proximal reference, distal reference, and CTO segment (subsequently divided into proximal, middle, and distal subsegments) was analyzed and reported as median and interquartile range. VH-IVUS phenotype was also assessed. The definition of a fibroatheroma was >10% confluent necrotic core (NC) in more than three consecutive frames. RESULTS: Overall, the maximum NC within the CTO [35.5% (28.7, 44.3%)] was similar to the proximal reference [35.6% (24.1, 42.1%)] and greater than the distal reference [31.5% (22.6, 35.2%), P < 0.01]. There was no difference in maximum NC observed among proximal [31.4% (25.2, 10.4%)], middle [31.0% (23.3, 38.3%)], and distal CTO subsegments [30.4% (22.0, 39.5%)]. Overall, 42/50 CTOs contained a VH-fibroathroma; and 8/50 did not. CTOs containing a VH-fibroatheroma had more NC and dense calcium while CTOs not containing a fibroatheroma had more fibrotic and fibrofatty plaque. Importantly, 60.5% of VH-fibroatheroma-containing CTOs had a thin-cap fibroatheroma (NC abutted to the lumen) in the proximal reference. CONCLUSIONS: Using VH-IVUS, CTO morphology can be divided into two patterns: (1) CTO with VH-fibroatheroma or (2) CTO without VH-fibroatheroma. This suggests two mechanisms of CTO formation-the majority evolving from acute coronary syndrome and thrombosis and the minority from atherosclerosis progression.