Which part of the heart does a first degree AV block primarily affect?

Which part of the heart does a first degree AV block primarily affect?

• A. The atria only
• B. The ventricles only
• C. The conduction between the atria and ventricles
• D. The SA node exclusively

Answer: (C)

A first degree AV block primarily affects the conduction between the atria and ventricles. This type of block occurs when there is a delay in the electrical conduction through the atrioventricular (AV) node, which is responsible for transmitting signals from the atria to the ventricles. In a first degree AV block, every atrial impulse successfully reaches the ventricles, but there is a prolonged interval between the atrial and ventricular contractions, which is represented as a prolonged PR interval on the EKG.

Since the characteristic of a first degree AV block is this delayed conduction specifically involving the AV node, it does not primarily involve the atria alone, ventricles alone, or the SA node exclusively. Instead, it highlights an issue in the communication pathway between these two parts of the heart, making the correct answer focus on the conduction between the atria and ventricles. Understanding this mechanism is crucial for interpreting EKGs and recognizing how different types of heart blocks can uniquely affect heart function.