Diagnostic criteria

  Only one of every other two P waves can be conducted to the ventricles.

  2:1 AV block may mimick sinus bradycardia, at first glance.

  If you see P waves and the heart rate (ventricular rate) is < 50/minute, then
search for a second P wave

      (not conducted to the ventricles)
before diagnosing sinus bradycardia.



Types of 2:1 AV block

  2:1 AV block can be either Mobitz Type 1 or Mobitz Type 2.

  The following may help to differentiate the two types:



Response to carotid sinus massage: AV block worsens if the block is Wenkebach (block level is intranodal).

                                                                AV block improves if the block is Mobitz Type 2 (block level is infranodal).



Response to atropine : AV block improves if the block is Wenkebach.

                                        AV block worsens if the block is Mobitz Type 2.



Response to exercise: The conduction ratio increases (block improves) if the block is Wenkebach (intranodal).

                                      The conduction ratio either does not change or decreases (block worsens) if the block is

                                      Mobitz Type 2.



QRS width: A QRS complex with a normal width suggests that the block is Wenkebach.

                  If the QRS complex is wider than normal, the block is thought to be Mobitz Type 2.



The PR interval of the conducted P wave: is generally prolonged if the block is Wenkebach.

                                                                          but is normal if the block is Mobitz Type 2.





ECG 1. Only one of every other two
P waves is blocked. Diagnosis is 2:1 AV block.
Narrow QRS complexes suggest Wenkebach type block.

Click here for a more detailed ECG





ECG 2. Mobitz Type 2 second degree AV block. This is a 2:1 block and the presence of
wide QRS complex supports the
diagnosis of Mobitz type 2 block. Of every 2
P wave s, only 1 is conducted to the ventricles.

Dr. Peter Kukla has donated the above ECG to our website.

Click here for a more detailed ECG





ECG 3. Wenkebach type 2:1 AV block. Narrow QRS complexes
suggest Mobitz Type 1, 2:1 AV block.
Of every two P waves
only one is conducted to the ventricles while the other is not .
The above ECG was recorded
at a calibration of 20 mm/mV to show the P waves more clearly.

Click here for a more detailed ECG





ECG 4. The ECG above is from a 6 months-*old infant with non-restrictive type VSD. He has congenital 2:1 AV block.

Of every two P waves, only one can be conducted to the ventricles
. Also, the interval between the first P wave and
the second P wave
is shorter than the interval between the second P wave and the third P wave .

This is called as
VENTRICULOPHASIC SINUS ARRHYTHMIA . It is less pronounced on the left side of this ECG .

Pediatric cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.

Click here for a more detailed ECG





ECG 5a. The ECG above shows 2:1 AV block (congenital) in a 1 year-old child.
Of every 2
P waves only one can be conducted to the ventricles.

Pediatric cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.

Click here for a more detailed ECG




ECG 5b. The ECG above belongs to the same patient and was recorded at an age of 2.5 years.
2:1 AV block persists. Of every 2
P waves , only one can be conducted to the ventricles.
The P waves near the top of the T waves can be missed unless inspected carefully.
Baseline drift is also seen at the beginning and the ending of the tracing.

Pediatric cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.

Click here for a more detailed ECG





ECG 6. The above ECG is from a 72 years-old woman with 2:1 AV block.
Wide QRS complexes and increased PR interval (of the conducted P waves) suggest Mobitz Type 2 block.

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ECG 7. 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