Single-lead electrocardiogram (ECG) showing atrial fibrillation (AF) with junctional escape beats suggesting digoxin toxicity

The 4 electrocardiograms in this sequence demonstrate increasing severity of digoxin toxicity in a patient with atrial fibrillation.
This ECG shows atrial fibrillation with an irregularly irregular ventricular response. However, the longest recurring R-R intervals are constant, suggesting junctional escape beats due to AV nodal block. The escape interval of 680 msec indicates an accelerated automatic pacemaker with a rate of 88 beats/min.

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.