Intravascular Ultrasound-Derived Calcium Score to Predict Stent Expansion in Severely Calcified Lesions

Background: Coronary calcification inhibits stent expansion. We sought to establish an intravascular ultrasound-derived calcium score to predict stent underexpansion. Methods: This is a retrospective observational study including de novo lesions that underwent intravascular ultrasound-guided stenting and had maximum superficial calcium angle >270 degrees. Lesions with angiographic calcium not treated with atherectomy or scoring/cutting balloon before stent implantation were randomly divided into derivation and validation cohorts. The end point was stent expansion (minimum stent area/average of reference lumen area) at the maximum calcium site, and stent expansion Results: The morphological characteristics associated with stent underexpansion in derivation cohort were (1) superficial calcium angle >270 degrees longer than 5 mm (regression coefficient, -13.0 [95% CI, -18.1 to -7.8], P<0.0001), (2) 360 degrees of superficial calcium (regression coefficient, -14.2 [95% CI, -22.8 to -5.5], P=0.001), (3) calcified nodule (regression coefficient, -8.3 [95% CI, -14.3 to -2.2], P=0.007), and (4) vessel diameter <3.5 mm (regression coefficient, -9.4 [95% CI, -16.0 to -2.7], P=0.006). The calcium score (0-4) was significantly correlated with poor stent expansion (regression coefficient, -8.1 [95% CI, -10.5 to -5.7], P<0.0001) in the validation cohort as well as in the atherectomy cohort (regression coefficient, -4.8 [95% CI, -7.2 to -2.5], P<0.0001) with significant interaction between validation and atherectomy cohorts (P-interaction=0.02). In lesions without angiographic calcium, all calcium severity parameters were less than in the validation cohort, and stent underexpansion was observed in only 1.5% (1/67) of lesions. Conclusions: This intravascular ultrasound calcium score provides the interventionalists with a reliable tool to identify calcified stenoses at risk for stent underexpansion and requiring adjunctive calcium modification before stent implantation.