Certified Rhythm Analysis Technician (CRAT) Practice Exam 2025 – All-in-One Study Guide for Exam Success!

A first-degree AV block is characterized by a prolonged PR interval on the electrocardiogram (ECG). The PR interval represents the time taken for electrical impulses to travel from the atria to the ventricles. In a first-degree AV block, this conduction time is extended, leading to a PR interval that exceeds 0.20 seconds (200 milliseconds). This is a key identifying feature of the condition, indicating that there is a delay in the electrical conduction through the AV node, but every atrial impulse still leads to a ventricular contraction.

The other options do not accurately represent the distinguishing characteristics of a first-degree AV block. For instance, a prolonged QRS duration typically suggests issues with ventricular conduction rather than atrial-ventricular conduction. Consistently irregular R-R intervals are indicative of other types of arrhythmias, such as atrial fibrillation, rather than a first-degree AV block, which features regular ventricular responses. Absent P waves point towards atrial activity being disrupted, which is not a characteristic of first-degree AV block as P waves are present, with each having a corresponding QRS complex albeit with a longer PR interval.