Histopathologic Validation of the Intravascular Ultrasound Diagnosis of Calcified Coronary Artery Nodules

A calcified nodule is a type of potentially vulnerable plaque accounting for approximately 2% to 7% of coronary events. Because its intravascular ultrasound (IVUS) features have never been validated, the aim of this study was to assess the IVUS characteristics of calcified nodules in comparison to histopathology. IVUS was performed in 856 pathologic slices in 29 coronary arteries (11 left anterior descending, 5 left circumflex, and 13 right coronary arteries) in 18 autopsy hearts. Pathologic sections were analyzed every 2 mm; qualitative and quantitative findings of matched IVUS were analyzed. IVUS detected calcification in 285 frames; 17 (6.0%) were calcified nodules, and 268 (94.0%) were non-nodular calcium by histopathology. Two calcified nodules (11.8%) were solitary, and 15 (88.2%) were adjacent to non-nodular calcium. IVUS characteristics of calcified nodules were (1) a convex shape of the luminal surface (94.1% in calcified nodules vs 9.7% in non-nodular calcium, p <0.001), (2) a convex shape of the luminal side of calcium (100% vs 16.0%, p <0.001), (3) an irregular luminal surface (64.7% vs 11.6%, p <0.001), and (4) an irregular leading edge of calcium (88.2% vs 19.0%, p <0.001). Luminal area at the calcified nodule site was larger (6.2 ± 2.4 vs 4.3 ± 1.6 mm2, p <0.001) and plaque burden less (57 ± 6% vs 68 ± 5%, p <0.001) than at the minimum luminal area site. In conclusion, calcified nodules have distinct IVUS features (irregular and convex luminal surface) permitting their prospective identification in vivo.