Cardiac Medicine Certification (CMC) Practice Exam

What does Atrial Fibrillation cause in terms of ventricular contractions?

1. Regular rhythm with consistent PR interval

2. Irregular rhythm with no PR interval

3. Consistent QRS morphology

4. Uniform firing from the AV node

The correct answer is: Irregular rhythm with no PR interval

Atrial fibrillation (AFib) is characterized by chaotic electrical activity in the atria, leading to disorganized and rapid atrial contractions. This results in a highly variable and irregular rhythm of the ventricular contractions. In terms of its impact on the heart's conduction system, the atrial impulses do not lead to a regular pattern of ventricular depolarization. Instead, the impulses reach the AV node in an unpredictable manner due to the lack of a coordinated atrial contraction. This unpredictability means that there is no consistent PR interval because each time the atrial rhythm triggers a ventricular contraction, it may do so at different intervals. This irregularity is a hallmark of atrial fibrillation, where the absence of a discernible pattern means the rhythm is classified as irregular, accompanied by a distinct absence of a fixed PR interval, which is typically present in more organized rhythms. Regarding the other potential answers, a regular rhythm with a consistent PR interval would indicate a more organized atrial contraction pattern, which is not present in AFib. Consistent QRS morphology typically signifies a regular conduction pattern, which again is not the case in AFib due to varying rates of conduction. Finally, uniform firing from the AV node would suggest a stable control over