Digitalis toxicity, commonly caused by digoxin overdose, manifests with distinct electrocardiographic (EKG/ECG) changes. Recognizing these findings is crucial for early diagnosis and management. This article provides a detailed review of the EKG manifestations of digitalis toxicity, along with its pathophysiology, risk factors, and treatment considerations.
Mechanism of Digitalis Toxicity
Digoxin, a cardiac glycoside, exerts its effects by inhibiting the Na⁺/K⁺ ATPase pump, leading to increased intracellular calcium and enhanced myocardial contractility. However, in toxic doses, this mechanism contributes to abnormal automaticity, conduction disturbances, and arrhythmias.
Key EKG Findings in Digitalis Toxicity
1. Classic “Scooped” ST Segment Depression (Digitalis Effect)
- Downsloping ST depression with a characteristic “scooped” appearance.
- Not indicative of toxicity but rather therapeutic digoxin levels.
2. Atrial and Ventricular Arrhythmias
- Atrial tachycardia with AV block (hallmark of toxicity)
- Frequent premature ventricular contractions (PVCs)
- Bidirectional ventricular tachycardia (specific but rare)
3. Bradyarrhythmias and AV Blocks
- Sinus bradycardia due to increased vagal tone.
- First-degree AV block (prolonged PR interval).
- Second-degree AV block (Mobitz Type I or Type II).
- Complete heart block in severe cases.
4. Hyperkalemia-Associated Changes
- Peaked T waves (due to digoxin-induced hyperkalemia).
- Widened QRS complex in severe toxicity.
Differentiating Digitalis Effect from Toxicity
| Feature | Digitalis Effect | Digitalis Toxicity |
|---|---|---|
| ST Changes | Scooped ST Depression | Scooped ST + Other Arrhythmias |
| Arrhythmias | None | Atrial Tachycardia, AV Block, PVCs |
| Potassium | Normal | Hyperkalemia |
Risk Factors for Digitalis Toxicity
- Renal insufficiency (impaired digoxin clearance)
- Electrolyte imbalances (hypokalemia, hypercalcemia, hypomagnesemia)
- Drug interactions (amiodarone, verapamil, quinidine)
- Elderly patients (decreased drug metabolism)
Management of Digitalis Toxicity
1. Immediate Discontinuation of Digoxin
- Stop digoxin to prevent further toxicity.
2. Correcting Electrolyte Abnormalities
- Potassium: Normalize levels to 4.0–4.5 mEq/L.
- Magnesium: Administer magnesium if deficient.
3. Antiarrhythmic Therapy
- Atropine: For symptomatic bradycardia or AV block.
- Lidocaine or Phenytoin: For ventricular arrhythmias.
- Avoid Amiodarone (increases digoxin levels).
4. Digoxin-Specific Antibody (Digibind) Therapy
- Indicated in life-threatening arrhythmias, hyperkalemia (>5.5 mEq/L), or severe toxicity.
5. Supportive Care
- IV fluids, oxygen therapy, and hemodynamic support as needed.
