Video
Below is a quick video snap shot of this article.
Definition
When there is a progressively prolonged PR interval that eventually leads to a failed conduction through the AV node.
Another way of thinking of this is there is a progressively prolonged delay in the AV node until there is an instance where the impulse does not pass through the AV node.
A common way to remember this is “longer longer drop, then you got a Wenckebach.”
What’s happening in the heart
Atrial Contraction
First, the impulse originates in the SA node just as it does with a normal sinus rhythm.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/P-wave-1-1024x576.png)
AV Node Delay
Next, there is a delay in the AV node just as there is with a normal sinus rhythm but with each beat this delay becomes progressively longer until it fails to conduct through the AV node to the bundle branches.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/dropped-qrs-1024x576.png)
Ventricular Contraction
Next, the impulse travels through the bundle of HIS to the bundle branches and on to the purkinje fibers causing ventricular contraction.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/qrs-1024x576.png)
Ventricular Repolarization
Lastly, the ventricles relax and reset for the next contraction.
T waves should be normal.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/t-wave-1024x576.png)
Seven steps of rhythm interpretation
1. Assess the rhythm.
First, the rhythm may be regular or just slightly irregular.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/rhythm-1024x576.png)
2. Assess the rate.
Next, when assessing the rate you will find it will be variable like the rhythm. The rate may be regular or brady.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/rate-1024x576.png)
3. Assess atrial and ventricular rates.
When it comes to assessing atrial and ventricular rates there will be more P’s than there are QRS waves.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/ps-and-qs-1024x576.png)
4. Assess the P waves and PR interval.
While the P waves may look normal the PRI will be variable. The PRI will progressively get longer until there is a dropped impulse through the AV node.
After the missed QRS the next PRI will “reset” and be back to it’s original length in the progression.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/pri-1024x576.png)
5. Assess the QRS.
Next the QRS will be within normal limits.
The QRS should be between 0.06 seconds to 0.12 seconds.
Better yet, QRS should be between 1.5 to 3 small boxes.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/qrs-length-1024x576.png)
6. Assess the T waves.
T waves should deflect in the positive direction with no ST-Elevation or ST-Depression.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/t-waves-1024x576.png)
7. Assess for Ectopy.
As you can see on this 6 second strip there are no ectopic beats. This is to say there are no PVC’s or PAC’s present.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/09/ectopy-1024x576.png)
Treatments for Mobitz 1 Wenckebach
Stable
i.e. asymptomatic and normotensive
Unstable
i.e. hypotensive with or without symptoms
Pacing (transcutaneous or transvenous) may be considered for treatment.
Medications:
Atropine. (Note: Atropine may be ineffective in Type 2 AV blocks)
Medication Consideration
If this block is caused by medications dosages should be adjusted.