Watch the Ioniantastic online guitar lesson by Brad Carlton from Chord Studies: Modal Progressions Vol. 1
Our A Major scale is also called the Ionian mode. We use Quartal harmony on the 2nd, 3rd and 4th strings as we move up the neck. The natural 4th can be tricky in this pattern, especially in the first chord which is an AMaj7 but with the 4th. You just have to use your ears and musical discretion as to when and where this sound is appropriate.