PR interval is reduced in ?
**Core Concept**
The PR interval, also known as the P-R interval, is the time from the onset of the P wave to the start of the QRS complex in an electrocardiogram (ECG). It represents the time taken for the electrical impulse to travel from the atria to the ventricles through the atrioventricular (AV) node.
**Why the Correct Answer is Right**
A reduced PR interval indicates that the electrical impulse is reaching the ventricles more quickly than normal. This is often due to an abnormality in the AV node, such as an accessory electrical pathway (e.g., Wolff-Parkinson-White syndrome) or a condition that causes the AV node to fire more quickly (e.g., AV nodal reentrant tachycardia). The AV node is responsible for delaying the electrical impulse to allow the atria to fully contract before the ventricles contract. A reduced PR interval suggests that this delay is being bypassed or shortened.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, so we cannot address it.
* **Option B:** There is no specific condition or mechanism that would cause a prolonged PR interval to be reduced.
* **Option C:** A prolonged PR interval is often seen in conditions such as first-degree atrioventricular block, where the electrical impulse is delayed in reaching the ventricles.
**Clinical Pearl / High-Yield Fact**
Remember that a reduced PR interval can be a sign of an accessory electrical pathway, which can increase the risk of arrhythmias. This is a key concept to remember when interpreting ECGs.
**Correct Answer:** C. A prolonged PR interval is often seen in conditions such as first-degree atrioventricular block, where the electrical impulse is delayed in reaching the ventricles.