Single-lead electrocardiogram (ECG) showing atrial tachycardia with 2:1 atrioventricular (AV) block

Atrial tachycardia with 2:1 atrioventricular (AV) block. The atrial rate is about 160 beats/min while the ventricular rate is about 80 beats/min. The nonconducted P waves (arrows) are superimposed on the ST-T segments. The P waves have a similar morphology to normal P waves suggesting that the ectopic site is near or even in the sinoatrial node. This arrhythmia may be an important sign of digoxin toxicity, but can also occur in other settings.

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.