Atrioventricular block (AV block) can be caused by all of the following drugs EXCEPT:

UP NHM CHO 7 Sept 2022(shift-1st)

Pharmacology

Hard

Appeared in: UP NHM CHO 7 Sept 2022(shift-1st)

Explanation

Atropine is an anticholinergic (muscarinic antagonist) drug.
It works by blocking the parasympathetic (vagal) nerve impulses to the heart, which normally slow the heart rate.
By blocking this slowing effect, Atropine increases the sinus rate and enhances electrical conduction through the atrioventricular (AV) node.
Due to this mechanism, it is used as a primary treatment for symptomatic bradycardia and certain types of AV block, not as a cause.

Option B: Digitalis (a cardiac glycoside) slows conduction through the AV node by increasing vagal tone and through a direct inhibitory action. It is a well-known cause of all degrees of AV block, especially in cases of toxicity.
Option C: Non-dihydropyridine calcium channel blockers, such as verapamil and diltiazem, directly depress AV nodal conduction by blocking the influx of calcium ions, which are necessary for the electrical impulse to pass through the node. This makes them a common iatrogenic cause of AV block.
Option D: Beta blockers antagonize the effects of the sympathetic nervous system on the heart's beta-1 receptors. This action decreases heart rate, myocardial contractility, and, importantly, slows conduction velocity through the AV node, which can lead to or worsen AV block.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacological causes of atrioventricular (AV) block as background academic context rather than a clinical decision trigger.
Nurses must carefully monitor the ECG and heart rate of patients taking Digitalis, Calcium channel blockers, or Beta blockers, as these medications place them at risk for developing bradycardia and AV block. A PR interval longer than 0.20 seconds is an early warning sign.
Recognizing that Atropine is a treatment for symptomatic bradycardia and AV block is a critical competency, especially in emergency and critical care settings. It is a first-line drug in the ACLS (Advanced Cardiac Life Support) algorithm.
Patient education should include the signs and symptoms of bradycardia (e.g., dizziness, fatigue, syncope) for individuals starting on AV node-blocking agents.

How to Approach the Question

First, recognize that this is a negative question using the keyword 'EXCEPT'. This means you are looking for the one option that does not fit the described category.
The category is 'drugs that can cause Atrioventricular block'. Therefore, you need to find the drug that does not cause AV block.
Think about the primary action of each drug on the heart's conduction system.
Recall or deduce that Digitalis, Calcium channel blockers, and Beta blockers all have mechanisms that slow down the heart rate and/or conduction through the AV node.
Recall or deduce that Atropine is an anticholinergic, which has the opposite effect: it blocks the 'braking' action of the vagus nerve, thereby increasing heart rate and AV conduction.
Conclude that Atropine is the exception because it treats AV block rather than causing it.

Concept Tested & Keywords

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E6 Pharmacology KD Tripathi Essentials 9e Part 2 p. 213-215