For which type of heart block is atropine not indicated?

Atropine is a medication that is often used to increase heart rate by inhibiting the vagus nerve. It is typically effective in cases where there is a complete block of conduction within the atrioventricular (AV) node, particularly in 1st and 2nd degree heart blocks where the conduction pathway is still partially functioning. In these cases, atropine can help restore heart rate and improve circulation.

However, in third-degree heart block (complete heart block), the atria and ventricles are completely dissociated. The electrical signals are blocked entirely at the level of the atrioventricular node, meaning that atropine would not have a significant effect because there is no conduction through the node to facilitate a faster heart rate. The ventricles may rely on intrinsic pacemaker activity, which is usually slower and not influenced by atropine's action. Therefore, the use of atropine is not indicated in this circumstance, as it would not address the underlying complete block of conduction occurring in this type of heart block.

In summary, the inefficacy of atropine in complete heart block due to the absence of any electrical activity through the AV node supports the conclusion that this type of heart block is where atropine is not recommended.