Which agent is used to terminate certain rapid heart rhythms by AV nodal suppression?

• A. Cimetidine
• B. Adenosine
• C. Vaccines
• D. Recombinant DNA

Answer: (B)

Adenosine is used to terminate certain rapid heart rhythms by AV nodal suppression. It works by briefly activating A1 receptors in the AV node, which causes a transient block of AV conduction. This interruption stops the reentrant circuit that depends on fast AV nodal transmission, allowing the heart to reset to a normal rhythm. The effect is very short-lived because adenosine is rapidly metabolized, so a rapid IV bolus can stop the tachycardia within seconds with minimal lasting effects. Other options do not affect AV nodal conduction—cimetidine is a gastric acid reducer, vaccines are immunizations, and recombinant DNA is a lab technique—so they aren’t used for terminating AV nodal–dependent tachyarrhythmias.