Which arrhythmias are never seen in digitoxicity?
Mobitz Type II second degree AV block does not occur in digitoxicity. Mobitz type II block is due to conduction problem below the bundle of His, in the bundle branches, where digoxin has no effect. Hence Mobitz type II block cannot occur with digoxin toxicity.
Sinus tachycardia and atrial fibrillation with fast ventricular rate are not seen in digitoxicity. Digoxin suppresses the sinus node, mainly due to increased vagal activity. So only sinus bradycardia can occur, not tachycardia. For the same reason AV nodal conduction is also slowed which causes ventricular rate to be slow in atrial fibrillation.