If the Purkinje fibers, situated distal to the A-V junction, become the pacemaker of the hea, what is the expected hea rate?
**Core Concept**
The Purkinje fibers are specialized cardiac conduction fibers that transmit electrical impulses from the atrioventricular (A-V) node to the ventricles. Normally, the A-V node acts as the heart's pacemaker, regulating the heart rate.
**Why the Correct Answer is Right**
When the Purkinje fibers become the pacemaker, the heart rate increases due to their faster rate of depolarization compared to the A-V node. The Purkinje fibers have a discharge rate of approximately 20-40 impulses per minute, which is faster than the A-V node's rate of 40-60 beats per minute. As a result, the expected heart rate would be closer to the Purkinje fibers' discharge rate.
**Why Each Wrong Option is Incorrect**
* **Option A:** This would be too low, as the Purkinje fibers' discharge rate is faster than the A-V node's.
* **Option B:** This is the normal heart rate, which occurs when the A-V node is the pacemaker.
* **Option D:** This would be too high, but not as high as the expected rate when the Purkinje fibers become the pacemaker.
**Clinical Pearl / High-Yield Fact**
The Purkinje fibers' faster discharge rate can lead to an increased heart rate, which may be beneficial in certain situations, such as during exercise or in response to stress. However, it can also lead to arrhythmias, such as ventricular tachycardia, if the Purkinje fibers' electrical activity becomes abnormal.
**Correct Answer: C. 40-60 beats per minute.**