• Therapeutic Window of Digoxin
• ECG and Digoxin
• Digoxin Toxicity
• ECG and Digoxin Toxicity

Therapeutic Window of Digoxin

• Digoxin is used for:
• Controlling heart rate in atrial fibrillation
• Treating heart failure
  
  
• Digoxin has a narrow therapeutic window
• The therapeutic plasma level is 0.5 - 1.5ng/ml
• A level of < 0.5ng/ml is ineffective
• A level of > 2ng/ml is toxic and poses a risk of cardiac arrhythmias

Digoxin and Atrial Fibrillation

• Atrial Fibrillation
• The heart rate is irregularly irregular
• No P waves are visible
• Downsloping ST depression (II, III, aVF, V5, V6)
• The patient is not digoxin-intoxicated
• Flat to negative T waves (in all leads)

ECG and Digoxin Toxicity

• Digoxin toxicity does not have a single characteristic ECG pattern
• Most commonly, supraventricular arrhythmias and AV block
  
  
• Most common arrhythmias in digoxin toxicity:
• Ventricular extrasystoles (Bigeminy, Trigeminy)
• AV blocks of various degrees
• Supraventricular arrhythmias with slow ventricular response
• Accelerated junctional rhythm
• Atrial fibrillation
• Atrial flutter
  
  
• Controlled atrial fibrillation (has regular ventricular response - QRS complexes)
• In AV block III degree, an escape rhythm (junctional or ventricular) is activated
• This escape rhythm is regular
• Patient has atrial fibrillation and regular frequency of QRS complexes
• Because supraventricular impulses are blocked due to AV block III degree
  
  
• In severe toxicity,
• Polymorphic ventricular tachycardia
• Bidirectional ventricular tachycardia

Digoxin Toxicity, Focal Atrial Tachycardia, and Second-Degree AV Block (2:1)

• Focal atrial tachycardia
• Heart rate P waves approximately 150/min.
• Every second P wave is within the T wave (see lead II)
• Second-degree AV block (2:1)
• Every second P wave is conducted to the ventricles
• Ventricular rate (QRS) approximately 75/min.
• This is a supraventricular arrhythmia with slow ventricular response
• The patient was digoxin toxic

Digoxin Toxicity and Controlled Atrial Fibrillation

• Frequency of atria approximately 400/min.
• This is coarse atrial fibrillation with an amplitude > 0.5mm, resembling atrial flutter
• Regular QRS complex frequency 75/min.
• Atrial fibrillation almost always has an irregular ventricular response
• Third-degree AV block
• Atria and ventricles are electrically isolated from each other
• An escape junctional rhythm with a frequency of 75/min. is activated
• The patient was digoxin toxic
• Controlled atrial fibrillation is characteristic of digoxin toxicity

Digoxin Toxicity and Atrial Flutter

• Frequency of F waves: 300/min.
• F waves have the characteristic "sawtooth" appearance
• Atrial flutter always has an F wave frequency of approximately 300/min.
• Conduction to the ventricles: 5:1, indicating slow conduction to the ventricles
• Every 5th F wave is followed by a QRS complex
• The patient was digoxin toxic

Digoxin Toxicity and Bidirectional Ventricular Tachycardia

• Frequency: 150/min.
• Wide QRS complexes (> 0.12s)
• Heart axis changes by approximately 180° (most clearly seen in lead II)
• AV dissociation
• P waves (stars in V1) are independent of QRS complexes
• AV dissociation is a key sign of ventricular tachycardia
• The patient was digoxin toxic
• In bidirectional ventricular tachycardia, always consider digoxin toxicity