Table 1.

Types of presteal waveforms in vertebral artery

Type	Flow pattern	Degree of stenosis(%)
Type 1	Two systolic peaks with flow velocity at the nadir of the notch greater than the flow velocity at the end diastole	43
Type 2	Two systolic peaks with flow velocity at the nadir of the notch equal to or less than the flow velocity at the end diastole	53
Type 3	Two systolic peaks with flow velocity at the nadir reaches the baseline	72
Type 4	Two systolic peaks with flow velocity at the nadir below the baseline	80