Which medication is most closely associated with tachycardia: (a) fentanyl, (b) succinylcholine, (c) morphine, or (d) pancuronium?

Pancuronium is the Medication Most Closely Associated with Tachycardia

Among the options provided, pancuronium (d) is the medication most strongly associated with tachycardia as its main side effect. This is due to its significant vagolytic effects through blockade of cardiac muscarinic receptors 1.

Pharmacological Mechanisms Behind Tachycardia

Pancuronium causes tachycardia through the following mechanisms:

• Direct blockade of cardiac muscarinic receptors 1
• Vagolytic effects that reduce parasympathetic tone to the heart
• This autonomic effect is independent of its neuromuscular blocking action

Comparison with Other Listed Medications

Succinylcholine (b)

• Produces variable cardiovascular effects depending on age and dosing
• In adults, may cause initial tachycardia but more commonly associated with bradycardia after a single dose 2
• In children, primarily causes bradycardia rather than tachycardia 3
• Its cardiovascular effects are inconsistent and not considered its main side effect 4

Fentanyl (a)

• Actually produces bradycardia rather than tachycardia
• Studies show fentanyl prolongs RR intervals by 26-45% and increases AV node conduction time 5
• When combined with pancuronium, the bradycardic effects of fentanyl are partially reversed by pancuronium's tachycardic effects 5

Morphine (c)

• Not primarily associated with tachycardia
• More commonly causes bradycardia, hypotension, and respiratory depression
• No evidence in the provided literature suggests tachycardia as its main side effect

Clinical Implications

Understanding these cardiovascular effects is important for:

• Selecting appropriate neuromuscular blocking agents in patients with cardiovascular disease
• Anticipating and managing hemodynamic changes during anesthesia induction
• Avoiding potentially dangerous drug combinations in patients with pre-existing cardiac conditions

Common Pitfalls in Clinical Practice

1. Assuming all neuromuscular blocking agents have similar cardiovascular effects
2. Failing to recognize that pancuronium's tachycardic effect may be beneficial in some situations (e.g., bradycardic patients) but harmful in others (e.g., patients with coronary artery disease or aortic stenosis)
3. Not accounting for the interaction between pancuronium and other medications that affect heart rate

In conclusion, when considering the cardiovascular side effect profiles of these medications, pancuronium stands out as the agent most consistently associated with tachycardia as its main side effect.