**Core Concept**
Atropine is an anticholinergic medication that blocks the action of acetylcholine at muscarinic receptors, leading to decreased parasympathetic tone. Norepinephrine is a catecholamine that primarily acts on alpha-1 and beta-1 adrenergic receptors, causing vasoconstriction and increased heart rate.

**Why the Correct Answer is Right**
When norepinephrine is administered to a patient already on atropine, the anticholinergic effects of atropine lead to a decrease in parasympathetic tone. This decrease in parasympathetic tone reduces the inhibition of the sympathetic nervous system, allowing the effects of norepinephrine to be more pronounced. As a result, the patient may experience a greater increase in heart rate and blood pressure due to the unopposed action of norepinephrine on alpha-1 and beta-1 adrenergic receptors.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the interaction between atropine and norepinephrine.
**Option B:** This option is incorrect because it implies a decrease in blood pressure, which is not a direct consequence of administering norepinephrine to a patient on atropine.
**Option C:** This option is incorrect because it suggests a decrease in heart rate, which is the opposite of what would be expected when norepinephrine is administered to a patient on atropine.

**Clinical Pearl / High-Yield Fact**
When administering catecholamines like norepinephrine to patients on anticholinergic medications, it is essential to monitor the patient's heart rate and blood pressure closely, as the unopposed action of the catecholamine can lead to significant increases in these parameters.

**Correct Answer:** B. Increased risk of arrhythmias, hypertension, and tachycardia.