Atrial flutter results from the development of a reentry circuit within the atria generating a loop that discharges impulses at a flutter rate of 250-350 / minute. Most often the AV junction passes every second (rate = 150, called a 2:1 response) or every fourth impulse(rate = 75, called a 4:1 response) through to the ventricles. Atrial flutter is readily identified by the sawtooth baseline.