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Step 4 PR interval (PRi) - Cardiac Rhythms


  • Measurement of the PR interval reflects the amount of time from the beginning of atrial depolarization to the beginning of ventricular depolarization.
  • Plainly stated, PR interval measurement is from the beginning of the P wave to the beginning of the QRS complex.
  • The normal range for PR interval is: 0.12 – 0.20 seconds (3 to 5 small boxes)
  • It is important that you measure each PR interval on the rhythm strip.
  • Some tracings do not have the same PRi measurement from one cardiac complex to the next. Sometimes there is a prolonging pattern, sometimes not.
  • If the PR intervals are variable, report them as variable, but note if a pattern is present or not.
measuring pr interval ecg image 113

how to measure pr interval ecg image 114

Measuring PR Interval Practice 1

measuring pr interval image 115

Analyze this tracing. What is the PR interval Measurement?

Reveal Answer 4 small boxes (4 X 0.04 second) = 0.16 second

PR Interval Practice 2

analysis ecg image 116

Analyze this tracing. What is the PR interval Measurement?

Reveal Answer Variable – inverted P wave has shorter PR, plus one complex has no P wave

Authors and Sources

Authors and Reviewers


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