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PR Intervals

8. PR Intervals. Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program. PR Intervals. Another important step of assessing the ECG is analyzing the PR intervals. Q. PR Interval. Distance from the beginning of the P wave to the beginning of the Q wave

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PR Intervals

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  1. 8 PR Intervals Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program

  2. PR Intervals • Another important step of assessing the ECG is analyzing the PR intervals Q

  3. PR Interval • Distance from the beginning of the P wave to the beginning of the Q wave • Morphology is a P wave and a flat line I

  4. PR Interval • Denotes depolarization of the heart from the SA node through the atria, AV node and His-Purkinje system

  5. PR Intervals • Their presence or absence as well as duration can help us identify if and how well the impulses are traveling through the heart’s conductive pathway • Important to know because delays or interruption of conduction through AV node and/or junction can lead to serious or even life-threatening conditions

  6. Measuring PR Intervals • If the PR intervals are identifiable, measure from where the P wave begins to where the Q wave begins • To make it easier, find a P wave that begins on a vertical line and then measure to where the Q or R wave begins

  7. PR Intervals • Are considered abnormal if they are shorter, longer, progressively longer, vary or absent

  8. Shorter P’R Intervals • Shorter P’R intervals occur when the impulse originates in the atria close to the AV junction or in the AV junction

  9. Shorter P’R Intervals • Can occur when an impulse arises from a supraventricular site but travels through abnormal accessory pathways to the ventricles • Leads to premature ventricular depolarization called preexcitation

  10. Longer P’R Intervals • Can occur when there is a delay in impulse conduction through the AV node

  11. Varying P’R Intervals • Can occur when the pacemaker site moves from beat to beat causing the P’ waves to appear different and the P’R intervals to vary

  12. Varying P’R Intervals • In one form of AV heart block, the PR intervals are progressively longer until a QRS complex is dropped and then the cycle repeats

  13. Absent PR Intervals • Occurs with: • atrial rates that exceed 250 BPM and produce flutter waves or a chaotic baseline and absence of P waves preceding the QRS complexes • ventricular dysrhythmias

  14. Absent PR Intervals • Also seen in the most severe form of AV heart block

  15. More P Waves and Constant PR Intervals • In on form of AV heart block, some sinus beats are blocked in the AV node and do not reach the ventricles • PR intervals associated with P waves that are conducted through to the ventricles are constant

  16. Practice Makes Perfect • In this tracing, determine the type of PR interval I

  17. Practice Makes Perfect • In this tracing, determine the type of PR interval I

  18. Practice Makes Perfect • In this tracing, determine the type of PR interval I

  19. Practice Makes Perfect • In this tracing, determine the type of PR interval I

  20. Practice Makes Perfect • Determine the type of PR interval I

  21. Summary • Another important step of analyzing an ECG rhythm is examining the PR intervals • PR interval is the distance from the beginning of the P wave to the beginning of the Q wave • Duration of the PR interval is normally 0.12 to 0.20 seconds • PR intervals are considered abnormal if they are shorter, longer, absent or vary

  22. Summary • Shorter P’R intervals occur when the impulse originates in the atria close to the AV junction or in the AV junction itself • AV heart block is the most common cause of longer PR intervals • When the pacemaker site moves from beat to beat it causes the P’ waves to appear different and the P’R intervals to vary

  23. Summary • In one for of AV heart block, the PR intervals are progressively longer until a QRS complex is dropped and then the cycle repeats • There is an absence of PR intervals in atrial rates that exceed 250 BPM producing flutter waves or a chaotic looking baseline and with ventricular dysrhythmias • In the most severe form of AV heart block the PR intervals are not measurable

  24. Summary • In one form of AV heart block, some of the sinus beats are blocked in the AV node and do not reach the ventricles. The PR intervals associated with the P waves that are conducted through to the ventricles are constant in duration

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