Certified Rhythm Analysis Technician (CRAT) 2025 – 400 Free Practice Questions to Pass the Exam

The correct choice is the PR interval, which is crucial for diagnosing first degree AV block. This condition is characterized by a delay in the conduction through the atrioventricular (AV) node, which results in a prolonged PR interval on an electrocardiogram (ECG).

The PR interval measures the time taken for electrical impulses to travel from the atria to the ventricles, represented from the beginning of the P wave to the beginning of the QRS complex. In first degree AV block, this interval is longer than normal (greater than 200 milliseconds) but remains consistent throughout the ECG.

In contrast, the QT interval measures the time from the start of the Q wave to the end of the T wave, reflecting ventricular depolarization and repolarization, but is not involved in the diagnosis of AV blocks. The ST segment is crucial for assessing ischemia and repolarization, while the QRS segment represents ventricular depolarization. Although important for various cardiac assessments, neither the QT interval, ST segment, nor the QRS segment is used to gauge AV conduction specifically. Thus, understanding the role of the PR interval is essential for identifying first degree AV block effectively.