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11Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

PR Intervals

Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program

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PR Intervals

Q

• Another important step of assessing the ECG is analyzing the PR intervals

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33Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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44Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

PR Interval

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

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55Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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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

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77Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

PR Intervals

• Are considered abnormal if they are shorter, longer, progressively longer, vary or absent

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88Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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99Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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1010Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Longer P’R Intervals

• Can occur when there is a delay in impulse conduction through the AV node

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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

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1212Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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1313Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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1414Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Absent PR Intervals

• Also seen in the most severe form of AV heart block

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1515Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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1616Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Practice Makes Perfect

• In this tracing, determine the type of PR interval

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1717Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Practice Makes Perfect

• In this tracing, determine the type of PR interval

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1818Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Practice Makes Perfect

• In this tracing, determine the type of PR interval

I

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1919Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Practice Makes Perfect

• In this tracing, determine the type of PR interval

I

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2020Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

Practice Makes Perfect

• Determine the type of PR interval

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2121Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved.

2222Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

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2323Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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

© 2013 The McGraw-Hill Companies, Inc. All rights reserved.

2424Fast & Easy ECGs, 2EFast & Easy ECGs, 2E

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