What is a contraindication for the use of adenosine?

Adenosine is a medication primarily used to treat certain types of supraventricular tachycardias by slowing down conduction through the AV node. A contraindication for its use is AV block, particularly second-degree or third-degree AV block, because adenosine can further exacerbate conduction delays and may worsen the heart's ability to effectively conduct electrical impulses. In patients with AV block, the use of adenosine could lead to significant bradycardia or asystole, which can be life-threatening.

In contrast, while adenosine may be used cautiously in stable ventricular tachycardia, in patients with asthma, the risk is more about potential bronchoconstriction rather than a complete contraindication, and rapid atrial fibrillation may not be an ideal indication, but it is not intrinsically contraindicated. Therefore, the presence of AV block distinctly identifies a scenario where adenosine should not be used.