Which of the following is contraindicated in a patient with bradycardia?

In cases of bradycardia, it is crucial to understand the effects of different medications on heart rate. Calcium channel blockers are contraindicated because they can further depress heart rate and negatively affect cardiac conduction, exacerbating bradycardia. These medications work by blocking calcium channels in the heart, which can lead to decreased heart contractility and slower heart rates.

In contrast, beta blockers are also used cautiously in bradycardic patients, but they may be prescribed when there's a need to control heart rate or in certain arrhythmias, as they can sometimes help in managing the overall cardiac workload. Diuretics and anticoagulants do not have a direct impact on heart rate, making them less concerning in the context of bradycardia. Therefore, the critical point here is the specific action of calcium channel blockers and their potential to worsen bradycardia, making them inappropriate for patients experiencing this condition.