What Causes Atrial Flutter?

The 2-3 minor peaks in between the large ventricle beats
are a signature of atrial flutter.

Atrial Flutter has many causes. It is when a rogue section of the atrial wall that starts sending out its own electrical signals; generally much faster than the SA or AV nodes.

Atrial flutter has several supposed causes, but the following list seems pretty random to me:
ischemia (decreases blood flow to the heart),
high blood pressure,
heart disease, bad heart valves, disfunction of the sinus node, hypertropy (enlarged heart), overactive thyroid, blood clots in the lungs, other lung diseases, alcohol, and stimulants from cocaine to caffeine.

Despite the huge number of potential causes, one third of atrial flutter cases have no assigned cause.

This site discusses magnesium deficiency as a reason for atrial flutter. Essentially Magnesium clogs the ion channels and regulates the intake of Calcium.