A 48-year-old man was admitted to the coronary unit with an acute myocardialinfarction. He had been suffering from a left bundle branch block which now changed into a Mobiz 1 AV block. His heart rate decreased from 70 BPM to 48 BPM. Which of thefollowing drugs would be appropriate to manage the patient’s bradycardia?

Atropine

Answer: E When complicating an inferior myocardial infarction, AV block often results from an increased parasympathetic tone and usually respond to atropine. Sometimes the block resolve spontaneously, but in the present case the block must be treated since the heart rate is too low for a sufficient cardiac output. A) Epinephrine can increase the heart rate but is usually contraindicated in myocardial infarction, since it increases the heart workload and oxygen consumption. Moreover in this case bradycardia is due to acetylcholine. Epinephrine is a physiologic antagonist of acetylcholine whereas atropine is a pharmacological antagonist. As a general rule, pharmacological antagonism is much better than physiologic antagonism, in most cases. B, D, E) These drugs are actually contraindicated because they decrease, not increase, the heart rate.