How to Measure Intervals

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What are the Intervals including PR interval, QRS interval, and QT interval

PR Interval

To measure the PR interval measure from the beginning of the p wave to the beginning of the QRS. A normal range is between 120ms (3 small boxes) and 200 ms (5 small boxes).

QRS Complex

To measure the QRS complex measure from the beginning of the Q wave to the end of the S wave. A normal range is from 40 to 100 msec (1 small box to 2.5 small boxes)

QT Interval

To measure the QT interval measure from the beginning of the Q wave to the end of the T wave. The normal range is no more than one half the R to R interval or < 440 msec.

Next Lesson

The next step in reading an EKG is How to Look for Hypertrophy.

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