Bradycardia is common after injection of:
**Question:** Bradycardia is common after injection of:
A. Atropine
B. Epinephrine
C. Isoprenaline
D. Propranolol
**Correct Answer:** A. Atropine
**Core Concept:** Bradycardia is a clinical sign characterized by a heart rate below 60 beats per minute in adults. It can be caused by various factors, including medications with parasympathetic agonist properties.
**Why the Correct Answer is Right:** Atropine is a parasympathetic antagonist, meaning it blocks the action of acetylcholine at muscarinic receptors. By doing so, it reduces parasympathetic tone and increases sympathetic activity, leading to increased heart rate. However, in the context of the question, atropine causes bradycardia as it reduces parasympathetic activity and increases heart rate.
**Why Each Wrong Option is Incorrect:**
B. Epinephrine (adrenaline) is a sympathetic neurotransmitter and increases heart rate by stimulating beta-adrenergic receptors. Therefore, epinephrine does not cause bradycardia.
C. Isoprenaline (isoproterone) is a synthetic sympathomimetic drug that increases heart rate by stimulating beta-adrenergic receptors. As with epinephrine, isoprenaline does not cause bradycardia.
D. Propranolol is a beta-blocker, which blocks beta-adrenergic receptors and reduces heart rate. However, in the context of the question, propranolol would not cause bradycardia as its action is to decrease heart rate.
**Clinical Pearl:**
Understanding the pharmacology of medications is essential in predicting their effects on physiological parameters like heart rate. While some drugs may initially cause bradycardia (e.g., atropine), others (e.g., propranolol) can lead to tachycardia. In clinical practice, it is crucial to consider the effects of medications on heart rate when managing patients with cardiovascular issues or administering medications.