Watch the Diatonic Triad Approach #2 online guitar lesson by Brad Carlton from Guitar Lab: The Imaj7 VIIm7 Progression

Heptatonic arpeggios are simply modes with the notes aligned in intervals of thirds instead of seconds. I will demonstrate how the Dmaj13#11 arpeggio (which is a D Lydian heptatonic arpeggio) can be viewed as the interlocking of the triads out of the key of A major. Likewise, the C#m13 arpeggio (which is a C# Dorian heptatonic arpeggio) can be viewed as the interlocking triads out of the key of B major.