Single-lead electrocardiogram showing atrial flutter

The atrial rate in this tracing of atrial waves is 300 beats per minute, and the flutter waves, which are "saw toothed," are uniform in morphology, amplitude, and cycle length. Impulse conduction to the ventricles is dependent upon the electrophysiologic characteristics of the atrioventricular node. Most commonly, every other atrial impulse is conducted and there is 2:1 block. However, when conduction through the atrioventricular node is impaired as a result of underlying disease, drugs, or increased vagal tone, there may be higher degrees of block, which may be variable, resulting in a regularly irregular ventricular rate.

Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright.