**Question:** Most characteristic arrhythmia seen with Digoxin toxicity is

A. Ventricular tachycardia
B. Atrial fibrillation
C. Bradycardia
D. Sinus bradycardia

**Correct Answer:** .

**Core Concept:** Digoxin is a cardiac glycoside used in the management of congestive heart failure and atrial fibrillation. It works by increasing the heart's contractility and reducing the force of contraction, thereby decreasing the heart rate. However, digoxin toxicity can occur if the drug level becomes excessively elevated, leading to its arrhythmogenic effects.

**Why the Correct Answer is Right:** Digoxin toxicity causes a decrease in the sodium-potassium ATPase pump activity, leading to an increase in intracellular sodium levels. This results in the activation of the l-type calcium channels, which causes an increased influx of calcium ions into the cardiac myocytes. This leads to the development of various arrhythmias, including ventricular tachycardia, due to the increased influx of calcium ions causing a higher demand for oxygen in the heart muscle.

**Why Each Wrong Option is Incorrect:**

- **Option A (Ventricular tachycardia):** While ventricular tachycardia can occur in digoxin toxicity, it is not the most characteristic arrhythmia. The most common arrhythmia seen with digoxin toxicity is atrial fibrillation (Option B).
- **Option C (Bradycardia):** Digoxin toxicity leads to bradycardia (slow heart rate) due to the inhibition of the vagal tone, which is mediated by the acetylcholine receptors (M2 subtype). However, the most characteristic arrhythmia seen with digoxin toxicity is atrial fibrillation (Option B) and not bradycardia.
- **Option D (Sinus bradycardia):** While sinus bradycardia can occur with digoxin toxicity, it is not the most characteristic arrhythmia. As mentioned earlier, the most common arrhythmia seen with digoxin toxicity is atrial fibrillation (Option B).

**Clinical Pearl:** The most characteristic arrhythmia seen with digoxin toxicity is atrial fibrillation due to the inhibition of the vagal tone and the subsequent decrease in sinus node sensitivity. This results in impaired sinus node function and atrial rate control, leading to atrial fibrillation.

In summary, digoxin toxicity primarily affects the sinus node, leading to sinus bradycardia or atrioventricular block. However, the most characteristic arrhythmia seen with digoxin toxicity is atrial fibrillation due to the inhibition of the vagal tone and the subsequent decrease in sinus node sensitivity. This results in impaired sinus node function and atrial rate control, leading to atrial fibrillation.