Which medication class is contraindicated in patients with a history of heart block?

Beta-blockers are contraindicated in patients with a history of heart block due to their pharmacological action of slowing down the heart rate and decreasing conduction through the atrioventricular (AV) node. In patients who already have an impaired conduction system (such as those with heart block), the use of beta-blockers can exacerbate the condition, leading to further complications such as a complete heart block.

While the other medication classes may have specific contraindications or precautions, they do not have the same direct impact on heart conduction as beta-blockers. For instance, ACE inhibitors can be used cautiously unless there are other contraindications, and diuretics generally do not affect heart conduction. Calcium channel blockers can be used, but specific subtypes (like non-dihydropyridines) may require caution due to their effects on heart rate and conduction. Overall, beta-blockers' ability to significantly dampen electrical impulses in the heart makes them particularly dangerous for patients with pre-existing conduction abnormalities.