https://eurointervention.pcronline.com/article/predicting-successful-guidewire-crossing-via-collateral-channel-at-retrograde-percutaneous-coronary-intervention-for-chronic-total-occlusion-the-j-channel-score-as-a-difficulty-estimating-tool-for-collateral-channel-guidewire-crossing-success-from-the-japanese-cto-pci-expert-registry