Rhythm InterpretationQuestion 1 of 100
A technician measures the distance from the beginning of the P wave to the beginning of the QRS complex on a strip and counts four small boxes. What is the PR interval, and is it normal?
a.0.04 second, which is shorter than normal
b.0.08 second, which is normal
c.0.16 second, which is normal
d.0.40 second, which is longer than normal
Explanation
Each small box equals 0.04 second at the standard paper speed of 25 mm/sec, so four small boxes equal 0.16 second. The normal PR interval is 0.12 to 0.20 second, so 0.16 second falls in range. The 0.04 and 0.08 answers miscount the boxes, and 0.40 second would require ten small boxes and would indicate a first-degree AV block.
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