The rhythm appears to be fascicular in origin because the QRS complex is different from supraventricular beats. Its origin is likely the left anterior fascicle because of the rightward and posterior terminal forces. Retrograde conduction block is observed with V-A dissociation and intermittent supraventricular capture beats.

The rhythm is due to digitalis toxicity which causes calcium overload in sarcoplasmic reticulum leading to abnormal release to the cell triggering arrhythmia by means of "delayed afterdepolarization" (DAD).

Most common arrhythmia in dig toxicity = PVCs. More specific, but not pathognomonic arrhythmias include AF with slow or regular ventricular rate, junctional tachycardia, AT with block, and bidirectional VT.

The bradyarrhythmias from digitalis toxocity is due to the main effect of digitalis itself that slows down the AV nodal conduction and increase vagal tone.