Which of the following is a contraindication to nitroglycerin administration?

• A. Hypotension
• B. Hypertension
• C. Bradycardia
• D. Tachycardia

Answer: (D)

Nitroglycerin works mainly by dilating veins, which lowers preload and, to a lesser extent, afterload. This reduces wall stress and myocardial oxygen demand, making it helpful for chest pain from myocardial ischemia when blood pressure is solid enough to tolerate the drop.

When a patient is tachycardic, the heart is already beating rapidly, often as a compensatory response to stress or low perfusion. Giving nitroglycerin in this situation can drop blood pressure further because preload is reduced; with a fast heart rate and potentially diminished filling time, cardiac output can fall, leading to reduced coronary and cerebral perfusion. Additionally, nitroglycerin can cause reflex tachycardia, which raises myocardial oxygen demand just as you’re trying to relieve it, potentially worsening ischemia. For these reasons, tachycardia is a contraindication to nitroglycerin in many protocols, to avoid precipitating hypotension and worsening myocardial stress.