The relationship between calcium thickness and stent expansion by optical coherence tomography for concentric or eccentric calcified lesion after intravascular lithotripsy

Background Coronary calcification is one of predictor for suboptimal stent expansion. Shockwave intravascular lithotripsy (IVL) is a useful device that modifies calcified lesions. Purpose We investigated that efficacy of IVL to concentric and eccentric calcifications by optical coherence tomography (OCT). The aim of this study was whether relationship between calcium fractures after IVL and stent expansion by OCT assessment. Methods A total of 80 patients who underwent OCT-guided IVL and coronary stenting were included. Cross-sectional OCT images at 1-mm intervals in pre-IVL (2,398), post-IVL (2,380), and post-stenting (2,728) time points were analyzed. All lesions were divided into 2 groups with median calcium arc 180ﾟin each segments. Concentric group had 53 lesions with over 180ﾟ calcifications, eccentric calcium group had 27 lesions with less than 180ﾟ calcifications. Baseline maximum calcium thickness was similar between 2 groups. Final stent expansion index (SEI) was also similar between 2 groups. Results Calcium fractures after IVL were more frequent in concentric group compared with eccentric group (32.0% vs. 23.3%, p=0.03). Stent under-expansion (SEI < 0.85) was associated with maximum calcium thickness in concentric group (p=0.03), but not in eccentric group (p=0.56). In concentric group, receiver operation characteristic curve analysis identified maximum calcium thickness 1,225μm as the best cutoff to predict SEI < 0.85. Percentage of fractured segment after IVL was positively correlated with SEI (r=0.337, p=0.01). Fracture width after IVL was also correlated with SEI (r=0.377, p< 0.01). Conclusions Calcium fractures after IVL were more frequent in concentric calcification compared with eccentric calcification. Percentage of fractures and large fracture width after IVL are associated with higher stent SEI. Our study suggests that calcium thickness over 1,225μm is predicted for stent under-expansion in concentric calcified lesions.