Serial Assessment of Tissue Precursors and Progression of Coronary Calcification Analyzed by Fusion of IVUS and OCT: 5-Year Follow-Up of Scaffolded and Nonscaffolded Arteries

Objectives The aim of this study was to assess calcium growth with fused grayscale intravascular ultrasound (IVUS), IVUS–virtual histology, and optical coherence tomography (OCT) from baseline to 5-year follow-up in patients treated with bioresorbable vascular scaffolds. Background IVUS and OCT have individual strengths in assessing plaque composition and volume. Fusion of images obtained using these methods could potentially aid in coronary plaque assessment. Methods Anatomic landmarks and endoluminal radiopaque markers were used to fuse OCT and IVUS images and match baseline and follow-up. Results Seventy-two IVUS–virtual histology and OCT paired matched cross-sectional in- and out-scaffold segments were fused at baseline and follow-up. In total, 46 calcified plaques at follow-up were detected using the fusion method (33 in-scaffold, 13 out-scaffold), showing either calcium progression (52.2%) or de novo calcifications (47.8%). On OCT, calcification volume increased from baseline to follow-up by 2.3 ± 2.4 mm³ (p = 0.001). The baseline virtual histologic tissue precursors of dense calcium at follow-up were necrotic core in 73.9% and fibrous or fibrofatty plaque in 10.9%. In 15.2%, calcium was already present at baseline. Precursors on OCT were lipid pool in 71.2%, fibrous plaque in 4.3%, and fibrocalcific plaque in 23.9%. Conclusions The use of OCT and IVUS fusion imaging shows similar calcium growth in- and out-scaffold segments. Necrotic core is the most frequent precursor of calcification. The scaffold resorption process creates a tissue layer that re-caps the calcified plaques.