How does atropine affect heart rate and its clinical use?

How does atropine affect heart rate and its clinical use?

• A. Anticholinergic increases heart rate by blocking vagal tone; used to treat bradycardia or during anesthesia
• B. It decreases heart rate
• C. It stabilizes heart rate during atrial fibrillation
• D. It reduces cardiac output by vasodilation

Answer: (A)

Blocking parasympathetic input to the heart with an antimuscarinic raises heart rate by removing the vagal brake. Acetylcholine from the vagus normally slows the SA node and slows AV conduction; atropine blocks those muscarinic receptors, letting the heart fire faster. Clinically, this makes atropine useful for treating symptomatic bradycardia and to prevent vagal reflex bradycardia during anesthesia or procedures that stimulate the vagus. It does not decrease heart rate, and it isn’t used to stabilize rate in atrial fibrillation. It also doesn’t reduce cardiac output through vasodilation—the main effect is an increased heart rate, with possible tachycardia as a side effect.

Blocking parasympathetic input to the heart with an antimuscarinic raises heart rate by removing the vagal brake. Acetylcholine from the vagus normally slows the SA node and slows AV conduction; atropine blocks those muscarinic receptors, letting the heart fire faster. Clinically, this makes atropine useful for treating symptomatic bradycardia and to prevent vagal reflex bradycardia during anesthesia or procedures that stimulate the vagus. It does not decrease heart rate, and it isn’t used to stabilize rate in atrial fibrillation. It also doesn’t reduce cardiac output through vasodilation—the main effect is an increased heart rate, with possible tachycardia as a side effect.