Cardiac Medicine Certification (CMC) Practice Exam

Which condition is indicated by a first-degree AV block?

1. Conduction delay between the SA node and the atria

2. Conduction delay between the SA node and the ventricles

3. Complete blockage in the conduction system

4. Asynchronous contraction of the atria and ventricles

The correct answer is: Conduction delay between the SA node and the ventricles

A first-degree AV block is characterized by a prolonged PR interval on an electrocardiogram (ECG), which signifies a delay in the conduction from the atria to the ventricles through the atrioventricular (AV) node. In this context, the correct answer reflects that there is noticeable conduction delay occurring specifically between the SA node and the ventricles. This means that while the electrical impulses from the SA node are still reaching the ventricles, the time taken for this conduction is longer than normal, resulting in a significant but not complete interruption of the conduction pathway. The other conditions described do not accurately represent a first-degree AV block. For instance, a complete blockage would imply a more severe interruption of the conduction system than what is seen in a first-degree block, and asynchronous contraction refers to a lack of coordination between the atria and ventricles, which is not a characteristic of this type of block. Also, there is no direct conduction delay between the SA node and the atria in the context of a first-degree AV block, as the primary issue centers on the slowing of conduction from the AV node to the ventricles.