A 69-year-old woman suffering from episodes of very rapid irregular palpitation for several months, lasting a few hours is presenting to the Electrophysiology Clinic on the referral of the family doctor who suspected episodes of paroxysmal atrial fibrillation and started her on digoxin. This ECG is recorded shortly before the consultant’s visit:

• Junctional tachycardia,129/min

Conditions that cause an increased rate of impulse formation in the AV node (e.g. digitalis toxicity, ischemia) may result in an accelerated junctional rhythm (rate 70-130/min). When the junctional rate is >100/min the term “junctional tachycardia” is commonly used. The ventricles are activated from the AV junction and the QRS duration is normal, unless there is bundle branch block or aberrant ventricular conduction. The atria may be activated retrogradely from the AV node or have its own independent rhythm (AV dissociation). If an accelerated junctional rhythm occurs in a patient on digoxin the possibility of digitalis toxicity should always be considered. In the case of this patient the serum digoxin level was in the low therapeutic range.