Digoxin, or digitalis, is associated with several electrocardiographic changes and, in toxicity, can precipitate a myriad of tachydysrhythmias and bradydysrhythmias. Increased intracellular calcium increases automaticity, and atrioventricular blockade increase vagal tone. This combination can cause atrial tachycardia, junctional rhythms, premature ventricular contractions (most common), sinus bradycardia, and/or slow atrial fibrillation. Bidirectional ventricular tachycardia is near pathognomonic for digoxin toxicity. At therapeutic concentrations it causes scooping of the ST segment predominantly in the precordial leads with tall R waves (V5, V6).
Bidirectional Ventricular Tachycardia
1. Mattu A, Tabas J, Brady W. Electrocardiography in Emergency, Acute, and Critical Care. 2nd ed. Dallas, TX: The American College of Emergency Physicians; 2019.