Watch the Example 9 online guitar lesson by Brad Carlton from Guitar Lab: Boogie-Woogie
This is a five voice passage out of A mixolydian. The chords are A7, D/A. Em/A (A9no3rd) and back to D/A. The 5th voice (the lowest voice) pedals the the root. All of the other voices ascend and descend step-wise through A mixolydian. I suggest you play each voice separately, then build the passage voice by voice. Use this technique on all examples in this entire lesson so that you will think linearly as you play the chords.