Table 1.

Modified ASITN collateral grading scale.

Grade	Angiographic assessment
0	No visible collaterals to the ischemic site
1	Slow collaterals to the periphery of the ischemic site with persistence of some defect
2−	Rapid collaterals to the periphery of the ischemic site with collateral filling in <50% of the territory
2+	Rapid collaterals to the periphery of the ischemic site with collateral filling >50% of the territory
3	Collaterals with slow but complete angiographic blood flow of the ischemic bed by the venous phase
4	Complete and rapid collateral blood flow to the vascular bed in the entire ischemic territory by retrograde perfusion