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First Degree Atrioventricular (AV) Block
Diagnostic criteria
PR interval is prolonged: >200 ms (5 small squares).
Every P wave is followed by a QRS complex.
PR interval is fixed.
Block is at the level of AV node.
Sometimes, PR interval prolongation may coexist with 2:1 second degree AV block.
Clinical significance
Prolonged PR interval (>200ms) is seen in approxiamtely 1-2% of the population.
Usually has a benign course.
In patients under Digoxin, beta blocker, Diltiazem,
Verapamil or Amiodarone therapy, emergence of first degree atrioventricular block may call for a revision of the therapy.
Extreme forms of first-degree AV block (PR interval >300 ms) can cause symptoms due to inadequate timing of atrial and ventricular contractions, similar to the so-called pacemaker syndrome. This is called pseudo-pacemaker syndrome.
Remember
When its rate is slowed by medication, atrial flutter may mimick sinus rhythm with 1st degree AV block, at first glance (flutter waves may be mistakenly perceived as sinus P waves).
References
Eur Heart J. 2013 May 14. doi:10.1093/eurheartj/eht176
Ann Noninvasive Electrocardiol 2013;18(3):215-224.
Clin Cardiol 1991;14:336-340.
Europace 2010;12(4):594-596.
HeartRhythm Case Rep 2018;4(3):98-101.
BMC Res Notes 2014;7:781.
ECG 1. First degree AV block in a coronary artery disease patient under Digoxin therapy.
Click here for a more detailed ECG
ECG 2a. First degree AV block in a patient with acute inferior myocardial infarction.
Click here for a more detailed ECG
ECG 2b. Half an hour after the beginning of treatment, the PR interval decreased but there is still first degree AV block.
Click here for a more detailed ECG
ECG 3a. First degree AV block in a patient with coronary artery disease. PR interval is very long. The P waves are so small
that they are visible only in leads C1 and C2. Besides, P waves are absent where they are expected to be in leads I and II.
Click here for a more detailed ECG
ECG 3b. The ECG of the same patient next day. First degree AV block still persists but the PR interval is shorter this time.
P waves are more close to the QRS complex.
Click here for a more detailed ECG
ECG 3c. The ECG of the same patient after two days. First degree AV block is not seen. P waves are hardly seen in leads C1
and C2.
Click here for a more detailed ECG
ECG 4. The above ECG, belongs to a 6 years-old girl with first degree AV block.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.
Click here for a more detailed ECG
ECG 5. The ECG above belongs to a 3 years-old boy. He had undergone complete correction for ToF two years ago. His recent
echocardiography showed mild dilation of right atrium and right ventricle, 3rd degree pulmonary regurgitation and 2nd degree
tricuspid regurgitation. This ECG is also remarkable for prolonged PR interval , prolonged QT interval and
right bundle branch block . The bottom rhythm strip also shows sinus arrhythmia.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.
Click here for a more detailed ECG
ECG 6. The ECG above belongs to a 4 years-old boy who had undergone operation for ToF when he was 4 months-old.
PR interval is prolonged and there is also right bundle branch block.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.
Click here for a more detailed ECG
ECG 7a. The above ECG is from a 63 years-old hypertensive diabetic woman. There is low voltage in limb leads.
Also the PR interval is prolonged : first degree atrioventricular (av) block.
The low voltage makes it difficult to recognize the prolonged PR in interval in limb leads at first glance.
Click here for a more detailed ECG
ECG 7b. Then the ECG was recalibrated at 20 mm/mV .
Now P waves and the prolonged PR interval are easily discernible in limb leads.
Click here for a more detailed ECG
ECG 8a. At a first glance, the ECG above looks like an ECG with first degree AV block. The P waves seem to have prolonged
PR interval. Careful inspection shows that the P waves are getting closer to the QRS complexes This ECG is from a man with
VVI type pacemaker. The pacemaker senses from and paces only the ventricle. Therefore P waves are not related to the
pacemaker-induced QRS complexes. Small pacemaker spikes are seen on some precordial leads.
Click here for a more detailed ECG
ECG 8b. Another ECG from the same patient is seen above. This time it looks like Wenkebach AV block at first glance.
The timing of P waves is so that it gives the impression of gradual prolongation of the PR interval . The timing is accidental
and actually the P waves are not related to the pacemaker-induced QRS complexes. Small pacemaker spikes are seen on
some precordial leads.
Click here for a more detailed ECG
ECG 9. The ECG above belongs to a 13 years-old boy.
His ECHOcardiogram showed a tumor in the posterior mitral annulus.
PR interval is slightly prolonged (first degree AV block).
Pediatric Cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website..
Click here for a more detailed ECG
ECG 10. The ECG above belongs to a 14 years-old boy. His ECHOcardiogram was normal.
PR interval prolongation with incomplete right bundle branch block is seen
Pediatric Cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.
Click here for a more detailed ECG
ECG 11. The ECG above belongs to a 76 years-old hypertensive woman.
Low amplitude P waves make it difficult to detect the prolonged PR interval.
Click here for a more detailed ECG
ECG 12. The ECG above is from a 73 years-old man.
Because of baseline drift, the rhythm seems like atrial fibrillation at first glance.
P waves are best seen in precordial leds.
First degree AV block is also present.
Click here for a more detailed ECG
ECG 13. The above ECG is from a 63 years-old apparently healthy woman. Mild prolongation of the PR interval (220 ms) is seen.
She has no known heart disease. She is also not using any medicine that can result in PR interval prolongation.
Prolongation of the PR interval is seen in approximately 1-2% of the general population.
Click here for a more detailed ECG
ECG 14. Oscillating irregular baseline and irregular RR intervals do not always denote atrial fibrillation.
In the presence of baseline drift and/or tremor artifact P waves may be difficult to detect at first glance.
In the 6-channel ECG above, the basic rhythm is sinus with first degree AV block ( prolonged PR interval )
The precordial recording shows two VPCs. Terminal portion of the first VPC and the second VPC are seen.
Click here for a more detailed ECG
ECG 15a. The ECG above belongs to a 47 years-old apparently healthy and asymptomatic woman with no known structural
heart disease. The low amplitude P waves may be difficult to notice at first glance, resulting in a false diagnosis of nodal
rhythm. In fact, the low amplitude P waves are barely noticeable in leads V3 and V4.
The PR interval is prolonged (1st degree AV block). There is also baseline drift artifact in precordial leads.
The above ECG was recorded at a standard calibration of 10 mm/mV.
Click here for a more detailed ECG
ECG 15b. The compact ECG above is the computer interpretation of ECG 15a.
The computer failed to recognize PR interval prolongation.
Also a false diagnosis of "anteroseptal myocardial infarction, age undetermined" is made.
Her ECHOcardiogram showed normal left ventricular systolic function (no sign of old myocardial infarction).
ECG 15c. Another ECG with a different ECG machine was recorded from the same woman, on the same day.
This time the ECG calibration is at 20 mm/mV.
To be able to accomodate all QRS complexes on a narrow ECG paper, the ECG machine has depicted some leads
at a calibration of 10 mm/mV.
Now the P waves are easily noticed on leads with a calibration of 20 mm/mV.
The P waves are barely noticeable at a calibration of 10 mm/mV.
Click here for a more detailed ECG
ECG 16a. The ECG above belongs to a 33 years-old apparently healthy and asymptomatic man without structural
heart disease. It was recorded just before the treadmill exercise test. The PR interval is prolonged.
Click here for a more detailed ECG
ECG 16b. The ECG above was recorded 1 minute after termination of his treadmill exercise test.
The heart rate is about 167/minute.
Now, the P waves are not visible since they coincide with the preceding T waves.
Click here for a more detailed ECG
ECG 16c. The ECG above was recorded 2 minutes after termination of his treadmill exercise test.
The heart rate is about 143/minute.
The P waves started to reappear.
Click here for a more detailed ECG
ECG 17. The ECG above shows extremely long PR interval (440 milliseconds).
This may result in pseudo-pacemaker syndrome.
Dr. Peter Kukla has donated the above ECG to our website.
Click here for a more detailed ECG
ECG 18. The ECG above belongs to a 85 years-old man with prolonged PR interval and 2:1 AV block.
Some P waves are conducted to the ventricles while some are blocked.
One of every two P waves can be conducted to the ventricles.
Heart rate (ventricular rate) is bradycardic (33/minute) but it is not sinus bradycardia since P wave rate (atrial rate) is 66/minute.
Atrial rate is normal but its conduction to the ventricles is the problem.
If you see P waves and the heart rate (ventricular rate) is < 50/minute, then search for a second (blocked) P wave
before diagnosing sinus bradycardia.
The conducted P waves and the blocked P waves have similar configurations, since they originate from the same focus.
Click here for a more detailed ECG
ECG 19a. 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 with 1st degree AV block?
Click here for a more detailed ECG
ECG 19b. The ECG above belongs to the same woman. It was recorded 3 weeks after the ECG 19a.
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? Is there a normal PR interval?
Click here for a more detailed ECG
ECG 19c. The ECG above belongs to the same woman. It was recorded immediately after the ECG 19b.
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 19d. 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 28e below.
Click here for a more detailed ECG
ECG 19e. The ECG above belongs to the same woman. It was recorded just before the ECG 19d.
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).
When slowed by medication, atrial flutter may mimick sinus rhythm with 1st degree AV block, at first glance.
Click here for a more detailed ECG
ECG 20. The above ECG belongs to a 78 years-old man who had undergone coronary artery bypass surgery in the past.
Left bundle branch block is seen.
His ECHOcardiogram was normal: no valvular heart disease, no systolic heart failure.
He is under Amiodarone therapy.
Amiodarone therapy has resulted in PR interval prolongation, QT interval prolongation and bradycardia.
Click here for a more detailed ECG
PR interval is prolonged: >200 ms (5 small squares).
Every P wave is followed by a QRS complex.
PR interval is fixed.
Block is at the level of AV node.
Sometimes, PR interval prolongation may coexist with 2:1 second degree AV block.
Clinical significance
Prolonged PR interval (>200ms) is seen in approxiamtely 1-2% of the population.
Usually has a benign course.
In patients under Digoxin, beta blocker, Diltiazem,
Verapamil or Amiodarone therapy, emergence of first degree atrioventricular block may call for a revision of the therapy.
Extreme forms of first-degree AV block (PR interval >300 ms) can cause symptoms due to inadequate timing of atrial and ventricular contractions, similar to the so-called pacemaker syndrome. This is called pseudo-pacemaker syndrome.
Remember
When its rate is slowed by medication, atrial flutter may mimick sinus rhythm with 1st degree AV block, at first glance (flutter waves may be mistakenly perceived as sinus P waves).
References
Eur Heart J. 2013 May 14. doi:10.1093/eurheartj/eht176
Ann Noninvasive Electrocardiol 2013;18(3):215-224.
Clin Cardiol 1991;14:336-340.
Europace 2010;12(4):594-596.
HeartRhythm Case Rep 2018;4(3):98-101.
BMC Res Notes 2014;7:781.
ECG 1. First degree AV block in a coronary artery disease patient under Digoxin therapy.
Click here for a more detailed ECG
ECG 2a. First degree AV block in a patient with acute inferior myocardial infarction.
Click here for a more detailed ECG
ECG 2b. Half an hour after the beginning of treatment, the PR interval decreased but there is still first degree AV block.
Click here for a more detailed ECG
ECG 3a. First degree AV block in a patient with coronary artery disease. PR interval is very long. The P waves are so small
that they are visible only in leads C1 and C2. Besides, P waves are absent where they are expected to be in leads I and II.
Click here for a more detailed ECG
ECG 3b. The ECG of the same patient next day. First degree AV block still persists but the PR interval is shorter this time.
P waves are more close to the QRS complex.
Click here for a more detailed ECG
ECG 3c. The ECG of the same patient after two days. First degree AV block is not seen. P waves are hardly seen in leads C1
and C2.
Click here for a more detailed ECG
ECG 4. The above ECG, belongs to a 6 years-old girl with first degree AV block.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.
Click here for a more detailed ECG
ECG 5. The ECG above belongs to a 3 years-old boy. He had undergone complete correction for ToF two years ago. His recent
echocardiography showed mild dilation of right atrium and right ventricle, 3rd degree pulmonary regurgitation and 2nd degree
tricuspid regurgitation. This ECG is also remarkable for prolonged PR interval , prolonged QT interval and
right bundle branch block . The bottom rhythm strip also shows sinus arrhythmia.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.
Click here for a more detailed ECG
ECG 6. The ECG above belongs to a 4 years-old boy who had undergone operation for ToF when he was 4 months-old.
PR interval is prolonged and there is also right bundle branch block.
Pediatric cardiologist Dr. Mahmut Gokdemir has donated this ECG to our website.
Click here for a more detailed ECG
ECG 7a. The above ECG is from a 63 years-old hypertensive diabetic woman. There is low voltage in limb leads.
Also the PR interval is prolonged : first degree atrioventricular (av) block.
The low voltage makes it difficult to recognize the prolonged PR in interval in limb leads at first glance.
Click here for a more detailed ECG
ECG 7b. Then the ECG was recalibrated at 20 mm/mV .
Now P waves and the prolonged PR interval are easily discernible in limb leads.
Click here for a more detailed ECG
ECG 8a. At a first glance, the ECG above looks like an ECG with first degree AV block. The P waves seem to have prolonged
PR interval. Careful inspection shows that the P waves are getting closer to the QRS complexes This ECG is from a man with
VVI type pacemaker. The pacemaker senses from and paces only the ventricle. Therefore P waves are not related to the
pacemaker-induced QRS complexes. Small pacemaker spikes are seen on some precordial leads.
Click here for a more detailed ECG
ECG 8b. Another ECG from the same patient is seen above. This time it looks like Wenkebach AV block at first glance.
The timing of P waves is so that it gives the impression of gradual prolongation of the PR interval . The timing is accidental
and actually the P waves are not related to the pacemaker-induced QRS complexes. Small pacemaker spikes are seen on
some precordial leads.
Click here for a more detailed ECG
ECG 9. The ECG above belongs to a 13 years-old boy.
His ECHOcardiogram showed a tumor in the posterior mitral annulus.
PR interval is slightly prolonged (first degree AV block).
Pediatric Cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website..
Click here for a more detailed ECG
ECG 10. The ECG above belongs to a 14 years-old boy. His ECHOcardiogram was normal.
PR interval prolongation with incomplete right bundle branch block is seen
Pediatric Cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.
Click here for a more detailed ECG
ECG 11. The ECG above belongs to a 76 years-old hypertensive woman.
Low amplitude P waves make it difficult to detect the prolonged PR interval.
Click here for a more detailed ECG
ECG 12. The ECG above is from a 73 years-old man.
Because of baseline drift, the rhythm seems like atrial fibrillation at first glance.
P waves are best seen in precordial leds.
First degree AV block is also present.
Click here for a more detailed ECG
ECG 13. The above ECG is from a 63 years-old apparently healthy woman. Mild prolongation of the PR interval (220 ms) is seen.
She has no known heart disease. She is also not using any medicine that can result in PR interval prolongation.
Prolongation of the PR interval is seen in approximately 1-2% of the general population.
Click here for a more detailed ECG
ECG 14. Oscillating irregular baseline and irregular RR intervals do not always denote atrial fibrillation.
In the presence of baseline drift and/or tremor artifact P waves may be difficult to detect at first glance.
In the 6-channel ECG above, the basic rhythm is sinus with first degree AV block ( prolonged PR interval )
The precordial recording shows two VPCs. Terminal portion of the first VPC and the second VPC are seen.
Click here for a more detailed ECG
ECG 15a. The ECG above belongs to a 47 years-old apparently healthy and asymptomatic woman with no known structural
heart disease. The low amplitude P waves may be difficult to notice at first glance, resulting in a false diagnosis of nodal
rhythm. In fact, the low amplitude P waves are barely noticeable in leads V3 and V4.
The PR interval is prolonged (1st degree AV block). There is also baseline drift artifact in precordial leads.
The above ECG was recorded at a standard calibration of 10 mm/mV.
Click here for a more detailed ECG
ECG 15b. The compact ECG above is the computer interpretation of ECG 15a.
The computer failed to recognize PR interval prolongation.
Also a false diagnosis of "anteroseptal myocardial infarction, age undetermined" is made.
Her ECHOcardiogram showed normal left ventricular systolic function (no sign of old myocardial infarction).
ECG 15c. Another ECG with a different ECG machine was recorded from the same woman, on the same day.
This time the ECG calibration is at 20 mm/mV.
To be able to accomodate all QRS complexes on a narrow ECG paper, the ECG machine has depicted some leads
at a calibration of 10 mm/mV.
Now the P waves are easily noticed on leads with a calibration of 20 mm/mV.
The P waves are barely noticeable at a calibration of 10 mm/mV.
Click here for a more detailed ECG
ECG 16a. The ECG above belongs to a 33 years-old apparently healthy and asymptomatic man without structural
heart disease. It was recorded just before the treadmill exercise test. The PR interval is prolonged.
Click here for a more detailed ECG
ECG 16b. The ECG above was recorded 1 minute after termination of his treadmill exercise test.
The heart rate is about 167/minute.
Now, the P waves are not visible since they coincide with the preceding T waves.
Click here for a more detailed ECG
ECG 16c. The ECG above was recorded 2 minutes after termination of his treadmill exercise test.
The heart rate is about 143/minute.
The P waves started to reappear.
Click here for a more detailed ECG
ECG 17. The ECG above shows extremely long PR interval (440 milliseconds).
This may result in pseudo-pacemaker syndrome.
Dr. Peter Kukla has donated the above ECG to our website.
Click here for a more detailed ECG
ECG 18. The ECG above belongs to a 85 years-old man with prolonged PR interval and 2:1 AV block.
Some P waves are conducted to the ventricles while some are blocked.
One of every two P waves can be conducted to the ventricles.
Heart rate (ventricular rate) is bradycardic (33/minute) but it is not sinus bradycardia since P wave rate (atrial rate) is 66/minute.
Atrial rate is normal but its conduction to the ventricles is the problem.
If you see P waves and the heart rate (ventricular rate) is < 50/minute, then search for a second (blocked) P wave
before diagnosing sinus bradycardia.
The conducted P waves and the blocked P waves have similar configurations, since they originate from the same focus.
Click here for a more detailed ECG
ECG 19a. 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 with 1st degree AV block?
Click here for a more detailed ECG
ECG 19b. The ECG above belongs to the same woman. It was recorded 3 weeks after the ECG 19a.
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? Is there a normal PR interval?
Click here for a more detailed ECG
ECG 19c. The ECG above belongs to the same woman. It was recorded immediately after the ECG 19b.
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 19d. 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 28e below.
Click here for a more detailed ECG
ECG 19e. The ECG above belongs to the same woman. It was recorded just before the ECG 19d.
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).
When slowed by medication, atrial flutter may mimick sinus rhythm with 1st degree AV block, at first glance.
Click here for a more detailed ECG
ECG 20. The above ECG belongs to a 78 years-old man who had undergone coronary artery bypass surgery in the past.
Left bundle branch block is seen.
His ECHOcardiogram was normal: no valvular heart disease, no systolic heart failure.
He is under Amiodarone therapy.
Amiodarone therapy has resulted in PR interval prolongation, QT interval prolongation and bradycardia.
Click here for a more detailed ECG