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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 - PowerPoint PPT Presentation
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
11Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
PR Intervals
Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program
88
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
22Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
PR Intervals
Q
• Another important step of assessing the ECG is analyzing the PR intervals
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
I
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
66Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
77Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
PR Intervals
• Are considered abnormal if they are shorter, longer, progressively longer, vary or absent
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
1111Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
1414Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
Absent PR Intervals
• Also seen in the most severe form of AV heart block
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
1616Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
Practice Makes Perfect
• In this tracing, determine the type of PR interval
I
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
1717Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
Practice Makes Perfect
• In this tracing, determine the type of PR interval
I
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
1818Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
Practice Makes Perfect
• In this tracing, determine the type of PR interval
I
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
1919Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
Practice Makes Perfect
• In this tracing, determine the type of PR interval
I
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
2020Fast & Easy ECGs, 2EFast & Easy ECGs, 2E
Practice Makes Perfect
• Determine the type of PR interval
I
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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
© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
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