Registered Cardiovascular Invasive Specialist (RCIS) Practice Test

How does NTG work to decrease preload during an MI?

1. By dilating arteries

2. By dilating veins

3. By increasing heart rate

4. By reducing contractility

The correct answer is: By dilating veins

Nitrates, such as nitroglycerin (NTG), primarily decrease preload by dilating veins. In the context of a myocardial infarction (MI), reducing preload is crucial because it lowers the volume of blood returning to the heart. When NTG is administered, it relaxes the smooth muscle of the venous walls, which allows the veins to expand. This expansion increases the capacity of the venous system, resulting in less blood being returned to the heart during each contraction. The decrease in venous return reduces the volume of blood the heart must handle, which subsequently decreases the workload on the heart. This is particularly beneficial during an MI, as the heart's efficiency is compromised, and reducing the demand on the heart muscles can help alleviate symptoms and improve outcomes. Therefore, while there are other mechanisms at play in the cardiovascular system, the primary role of NTG in this scenario is its capacity to dilate veins and reduce preload.