Digoxin [Antiarrhythmic (Class III)] competes with Potassium for binding to cellular Na+/K+ ATPase pumps. Hypokalemia predisposes the patient to Digoxin toxicity. Most common arrhythmia associated with Digoxin toxicity is paroxysmal atrial tachycardia with 2:1 block. However, Bradycardia can occur and presence of a bidirectional ventricular tachycardia is practically pathognomonic for Digoxin toxicity!
HOW?? When potassium levels are low, it allows increased Digoxin binding to ATPase pumps to exert its inhibitory effects.
NOTE: Digoxin toxicity can cause Hyperkalemia (Digoxin inhibits Na+/K+ ATPase, so K+ remains in the plasma). In theory, if you give IV Calcium it can cause an influx of Calcium into the cardiac myocytes resulting in a non-contractile state (the so called “Stone Heart“).
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