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t o r e g . c o m
Dr. Mete ALPASLAN
PR Interval (PQ Interval)
Last update: May 2020
PR (PQ) interval starts from the beginning of P wave and ends at the beginning of QRS complex.
When measuring the PR interval, the lead with the longest PR interval should be chosen (in some leads, initial part of the PR interval may be isoelectric; this may be misinterpreted as short PR interval).
Normal PR interval is between 0.12 s and 0.2 s.
PR interval = P wave + PR segment. PR segment is the isoelectric line which is from the end of P wave to the beginning of QRS.
During PR segment, the impulse travels the AV node, His bundle, bundle branches and Purkinje fibers.
The PR interval in children is shorter than that of the adults since children have lower myocardial mass.
The normal PR interval in NEWBORNs is 70-140 msec (average 100 msec).
In children, PR interval lengthens as age increases while it shortens as heart rate increases.
Normally, TP segment is the isoelectric baseline. During tachycardia, P wave may merge with the preceding T wave. Then the PR segment is chosen as the isoelectric line (baseline).
PR interval displacement (localized PR segment elevation or depression) is an important ECG finding of atrial infarction. PR interval displacement during atrial infarction is best appreciated in patients with 2nd or 3rd degree AV block.
During treadmill exercise test, observation of downsloping PR segment in inferior leads is a normal finding.
It has been reported that 81% of patients with short QT syndrome reveal PQ depression.
Remember
When its rate is slowed by medication, atrial flutter may mimick sinus rhythm with 1st degree AV block, at first glance (flutter wave may be mistakenly perceived as P wave).
Click here for Short PR interval
References
Surawicz, Knilans. Chou's electrocardiography in clinical practice. 6th edition. Saunders. Philadelphia 2008.
Heart Rhythm 2014;11:1024-1030.
American Journal of Emergency Medicine 2008;26:221-228.
ECG 1. When measuring the PR interval, the lead with the longest PR interval should be chosen.
In the ECG tracing above, the PR interval of the lead I is clearly shorter than that of the leads II and III.
This difference is due to the isoelectric segment of the first part of the P wave in lead I.
Click here for a more detailed ECG
ECG 2a. The ECG above belongs to a 66 years-old woman with coronary artery disease and mitral valve prosthesis.
She had undergone coronary artery bypass grafting operation and mitral valve replacement 2 weeks ago.
She had experienced inferoposterior wall myocardial infarction before the operation.
Now she has left ventricular systolic dysfunction with Ejection Fraction (EF) of 35%.
She is under Bisoprolol (beta blocker) therapy.
Her heart rate is 110/minute.
What is the rhythm? Is it sinus tachycardia? Is the PR interval prolonged?
Click here for a more detailed ECG
ECG 2b. The ECG above belongs to the same woman. It was recorded 3 weeks after the ECG 2a.
This ECG was recorded at a standard calibration of 10 mm/mV and at a paper speed of 25 mm/second.
After 3 weeks, her heart rate is almost the same: 111/minute.
She is still taking Bisoprolol (beta blocker).
What is the rhythm? Is it sinus tachycardia?
Do you see P waves? Are they P waves? Is there a normal PR interval?
Click here for a more detailed ECG
ECG 2c. The ECG above belongs to the same woman. It was recorded immediately after the ECG 2b.
To see the details clearly, the calibration was now set at 20 mm/mV.
Her heart rate is 110/minute.
Seemingly P waves in lead V1 are in fact flutter waves.
Flutter waves deform terminal portion of the QRS complexes in inferior leads.
The rhythm is atrial flutter, not sinus tachycardia.
Click here for a more detailed ECG
ECG 2d. The ECG above belongs to the same woman.
It was recorded 24 hours after the onset of intravenous Amiodarone infusion.
This ECG was recorded at a standard calibration of 10 mm/mV and at a paper speed of 25 mm/second.
Now the heart rate is 92/minute.
Is it sinus rhythm with prolonged PR interval (1st degree atrioventricular block)?
Please look at the ECG 2e below.
Click here for a more detailed ECG
ECG 2e. The ECG above belongs to the same woman. It was recorded just before the ECG 2d.
This time, the calibration was set to 20 mm/mV to see the details clearly.
Her heart rate is 93/minute.
Seemingly P waves in lead V1 are in fact flutter waves.
Some flutter waves deform terminal portion of the QRS complexes, especially in lead V1.
The rhythm is atrial flutter (slowed by Amiodarone), not sinus rhythm with 1st degree atrioventricular block.
Flutter waves may mimick P waves, resulting in a false diagnosis of PR interval prolongation.
Click here for a more detailed ECG
ECG 3. Congenital short QT syndrome. There is almost no ST segment. Narrow-based, tall and peaked T waves are observed in chest leads. Precordial leads and leads II and aVF show PQ depression while lead aVR shows PQ elevation. Congenital short QT interval syndrome was first described by Dr. Preben Bjerregaard in 1999.
Prof Dr. Preben Bjerregaard has donated this ECG to our website.
Click here for a more detailed ECG
Click here to visit Prof Dr. Preben Bjerregaard's website on Short QT Interval Syndrome.
ECG 4a. The above ECG shows both complete AV block and interatrial block. It was recorded during acute inferior wall myocardial infarction. P waves are not related to the QRS complexes. Therefore, some P waves are buried in QRS complexes. The P wave width is slightly more than 120 milliseconds: interatrial block. This ECG was recorded at a calibration of 20 mm/mV to show interatrial block. The P wave morphology and PR interval are also compatible with atrial infarction. Displacement of the PQ interval is considered the most useful sign of atrial infarction. The displacement of PQ interval during atrial infarction is best appreciated in patients with AV block.
Click here for a more detailed ECG
A close-up view of PR segment elevation from the ECG 4a is seen above. This is a magnified view of the P wave before the 8th QRS complex in lead II from the ECG 4a. The PR segment is elevated when compared with the baseline (TP segment).
ECG 4b. Above is his ECG at a standard 10 mm/mV calibration.
It is difficult to see interatrial block, PR segment elevation and complete AV block, at first glance.
Click here for a more detailed ECG
PR (PQ) interval starts from the beginning of P wave and ends at the beginning of QRS complex.
When measuring the PR interval, the lead with the longest PR interval should be chosen (in some leads, initial part of the PR interval may be isoelectric; this may be misinterpreted as short PR interval).
Normal PR interval is between 0.12 s and 0.2 s.
PR interval = P wave + PR segment. PR segment is the isoelectric line which is from the end of P wave to the beginning of QRS.
During PR segment, the impulse travels the AV node, His bundle, bundle branches and Purkinje fibers.
The PR interval in children is shorter than that of the adults since children have lower myocardial mass.
The normal PR interval in NEWBORNs is 70-140 msec (average 100 msec).
In children, PR interval lengthens as age increases while it shortens as heart rate increases.
Normally, TP segment is the isoelectric baseline. During tachycardia, P wave may merge with the preceding T wave. Then the PR segment is chosen as the isoelectric line (baseline).
PR interval displacement (localized PR segment elevation or depression) is an important ECG finding of atrial infarction. PR interval displacement during atrial infarction is best appreciated in patients with 2nd or 3rd degree AV block.
During treadmill exercise test, observation of downsloping PR segment in inferior leads is a normal finding.
It has been reported that 81% of patients with short QT syndrome reveal PQ depression.
Remember
When its rate is slowed by medication, atrial flutter may mimick sinus rhythm with 1st degree AV block, at first glance (flutter wave may be mistakenly perceived as P wave).
Click here for Short PR interval
References
Surawicz, Knilans. Chou's electrocardiography in clinical practice. 6th edition. Saunders. Philadelphia 2008.
Heart Rhythm 2014;11:1024-1030.
American Journal of Emergency Medicine 2008;26:221-228.
ECG 1. When measuring the PR interval, the lead with the longest PR interval should be chosen.
In the ECG tracing above, the PR interval of the lead I is clearly shorter than that of the leads II and III.
This difference is due to the isoelectric segment of the first part of the P wave in lead I.
Click here for a more detailed ECG
ECG 2a. The ECG above belongs to a 66 years-old woman with coronary artery disease and mitral valve prosthesis.
She had undergone coronary artery bypass grafting operation and mitral valve replacement 2 weeks ago.
She had experienced inferoposterior wall myocardial infarction before the operation.
Now she has left ventricular systolic dysfunction with Ejection Fraction (EF) of 35%.
She is under Bisoprolol (beta blocker) therapy.
Her heart rate is 110/minute.
What is the rhythm? Is it sinus tachycardia? Is the PR interval prolonged?
Click here for a more detailed ECG
ECG 2b. The ECG above belongs to the same woman. It was recorded 3 weeks after the ECG 2a.
This ECG was recorded at a standard calibration of 10 mm/mV and at a paper speed of 25 mm/second.
After 3 weeks, her heart rate is almost the same: 111/minute.
She is still taking Bisoprolol (beta blocker).
What is the rhythm? Is it sinus tachycardia?
Do you see P waves? Are they P waves? Is there a normal PR interval?
Click here for a more detailed ECG
ECG 2c. The ECG above belongs to the same woman. It was recorded immediately after the ECG 2b.
To see the details clearly, the calibration was now set at 20 mm/mV.
Her heart rate is 110/minute.
Seemingly P waves in lead V1 are in fact flutter waves.
Flutter waves deform terminal portion of the QRS complexes in inferior leads.
The rhythm is atrial flutter, not sinus tachycardia.
Click here for a more detailed ECG
ECG 2d. The ECG above belongs to the same woman.
It was recorded 24 hours after the onset of intravenous Amiodarone infusion.
This ECG was recorded at a standard calibration of 10 mm/mV and at a paper speed of 25 mm/second.
Now the heart rate is 92/minute.
Is it sinus rhythm with prolonged PR interval (1st degree atrioventricular block)?
Please look at the ECG 2e below.
Click here for a more detailed ECG
ECG 2e. The ECG above belongs to the same woman. It was recorded just before the ECG 2d.
This time, the calibration was set to 20 mm/mV to see the details clearly.
Her heart rate is 93/minute.
Seemingly P waves in lead V1 are in fact flutter waves.
Some flutter waves deform terminal portion of the QRS complexes, especially in lead V1.
The rhythm is atrial flutter (slowed by Amiodarone), not sinus rhythm with 1st degree atrioventricular block.
Flutter waves may mimick P waves, resulting in a false diagnosis of PR interval prolongation.
Click here for a more detailed ECG
ECG 3. Congenital short QT syndrome. There is almost no ST segment. Narrow-based, tall and peaked T waves are observed in chest leads. Precordial leads and leads II and aVF show PQ depression while lead aVR shows PQ elevation. Congenital short QT interval syndrome was first described by Dr. Preben Bjerregaard in 1999.
Prof Dr. Preben Bjerregaard has donated this ECG to our website.
Click here for a more detailed ECG
Click here to visit Prof Dr. Preben Bjerregaard's website on Short QT Interval Syndrome.
ECG 4a. The above ECG shows both complete AV block and interatrial block. It was recorded during acute inferior wall myocardial infarction. P waves are not related to the QRS complexes. Therefore, some P waves are buried in QRS complexes. The P wave width is slightly more than 120 milliseconds: interatrial block. This ECG was recorded at a calibration of 20 mm/mV to show interatrial block. The P wave morphology and PR interval are also compatible with atrial infarction. Displacement of the PQ interval is considered the most useful sign of atrial infarction. The displacement of PQ interval during atrial infarction is best appreciated in patients with AV block.
Click here for a more detailed ECG
A close-up view of PR segment elevation from the ECG 4a is seen above. This is a magnified view of the P wave before the 8th QRS complex in lead II from the ECG 4a. The PR segment is elevated when compared with the baseline (TP segment).
ECG 4b. Above is his ECG at a standard 10 mm/mV calibration.
It is difficult to see interatrial block, PR segment elevation and complete AV block, at first glance.
Click here for a more detailed ECG