Final answer:
The classic ECG finding in atrial flutter is a sawtooth pattern of atrial activity.
Step-by-step explanation:
The classic ECG finding in atrial flutter is a sawtooth pattern of atrial activity. This is characterized by a series of rapid, regular atrial depolarizations that resemble the teeth of a saw on the ECG tracing. The sawtooth pattern is caused by the rapid firing of multiple atrial ectopic foci, resulting in a rapid atrial rate of 250-350 beats per minute.