Cardiac Medicine Certification (CMC) Practice Exam

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What is the normal range for the PR interval?

0.06 to 0.12 seconds
0.12 to 0.20 seconds
0.20 to 0.26 seconds
0.40 to 0.44 seconds

The correct answer is: 0.12 to 0.20 seconds

The normal range for the PR interval is between 0.12 to 0.20 seconds. This interval represents the time taken for electrical impulses to travel from the atria to the ventricles through the atrioventricular (AV) node. A PR interval within this range indicates that the conduction through the AV node is functioning properly, allowing for efficient heart rhythm and coordination of contraction. When the PR interval is shorter than 0.12 seconds, it may suggest a pre-excitation syndrome, such as Wolff-Parkinson-White syndrome, where the electrical impulse bypasses the normal conduction pathway. Conversely, a PR interval longer than 0.20 seconds could indicate a first-degree AV block, where there is a delay in the conduction through the AV node. Thus, maintaining a PR interval in the normal range is critical for proper cardiac function and rhythm.