Final answer:
Beta blockers are contraindicated in patients with second degree AV block, type 2, and third degree AV block, but they are not necessarily contraindicated in first degree AV block.
Step-by-step explanation:
Beta blockers are a type of sympatholytic drug commonly used to treat cardiovascular diseases. They work by blocking the β-receptors that are associated with vasoconstriction and cardioacceleration, which can help to improve cardiac function in patients with conditions such as congestive heart failure or a history of heart attacks. Beta blockers like metoprolol and propranolol have different affinities for these receptors, with metoprolol specifically blocking the β1-receptor and propranolol nonspecifically blocking β-receptors.
Regarding the question, "Beta blockers are contraindicated in patients with which of the following except:" beta blockers are typically contraindicated in patients with second degree AV block, type 2, and third degree AV block due to the risk of exacerbating the blockages. However, they may not be contraindicated in first degree AV block, where there is only a delay in the conduction between the SA and AV nodes without missed beats, as there may be some room for the therapeutic effect without significant risk of complete heart block.