Diagnostic criteria

  PR interval >200 ms (5 small squares).

  Every P wave is followed by a QRS complex.

  PR interval is fixed.

  Block is at the level of the AV node.




Clinical significance

  Prolonged PR interval (>200ms) is seen in approxiamtely 1-2% of the population.

  Usually has a benign course.

  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.

  In patients under digoxine, beta blocker, diltiazem, verapamil or amiodarone therapy,

      emergence of first degree atrioventricular block may call for a revision of the therapy.




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.






ECG 1. First degree AV block in a coronary artery disease patient under Digoxin therapy.

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ECG 2a. First degree AV block in a patient with acute inferior myocardial infarction.

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ECG 2b. Half an hour after the beginning of treatment, the PR interval decreased but there is still first degree AV block.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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..

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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




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