• Digitalis inactivates the Na-K-ATPase pump to increase intracellular calcium and extracellular potassium, causing + inoptropy, hence usage in CHF patients
• Dig also increases vagal tone and decreases conduction through the AV node, hence usage in atrial fibrillation. In toxic doses, this is what leads to bradydysrhythmias

Toxicity can either be Acute or Chronic:

ECG Pearls:

• PVCs are the most common ECG finding
• Bidirectional VT is fairly specific for dig toxicity
• If you see "Slow Atrial fibrillation," think dig toxity
• In acute toxicity, tend to see more bradycardia and blocks (SVT with AV block)
• In chronic toxicity, ventricular dysrhythmias are more common

Additional Pearls:

• Serum dig levels may not correlate with symptoms!
• Treating hyperkalemia in the normal manner with IV calcium is NOT dangerous
• Replete low K in chronic toxicity!
• When a patient (in real life or hypothetical on an exam) is complaining of seeing "yellow halos around lights," think dig toxicity!

Indications for Digoxin-Specific Antibodies:

• Ventricular dysrhythmias
• Bradycardia unresponsive to therapy
• K > 5.0 mEq/dL in acute ingestion
• Potentially massive OD

References:

Blok, et al. First Aid for the Emergnecy Medicine Boards, 2nd Edition. McGraw Hill Education. 2012.

Ma, et. al. Emergency Medicaine: Just the Facts, 2nd Edition. MCGraw Hill Education. 2004.