Video
Below is a quick video snap shot of this article.
Definition
When there is a prolonged delay in the AV node.
This is easily identified as a PR Interval longer than 0.20 sec or 5 small boxes.
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/2023/11/first-degree-atrial-contraction-1024x576.png)
AV Node Delay
Next, the AV node delay happens as expected but lasts longer than expected.
This is identified as a PRI greater than 0.20 sec or 5 small boxes.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-AV-delay-1024x576.png)
Ventricular Contraction
The QRS complex should be normal with a First Degree AV Block.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-vent-contraction-1024x576.png)
Ventricular Repolarization
Lastly, the ventricles relax and reset for the next contraction just as the do with NSR.
T waves should be normal
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-vent-relaxation-1024x576.png)
Seven steps of rhythm interpretation
1. Assess the rhythm.
First, the rhythm will be regular.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-rhythm-1024x576.png)
2. Assess the rate.
Next, when assessing the rate it will most likely be WNL.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-rate-1024x576.png)
3. Assess atrial and ventricular rates.
When it comes to assessing atrial and ventricular rates there will be the same amount of P’s and QRS complexes.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-P-and-QRS-1024x576.png)
4. Assess the P waves and PR interval.
With a First Degree AV Block there will be a prolonged delay in the AV node causing a greater than normal PR interval.
![](https://www.nursingunraveled.com/wp-content/uploads/2023/11/first-degree-PRI-check-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/2023/11/first-degree-QRS-check-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/2023/11/first-degree-T-wave-check-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/2023/11/first-degree-ectopy-check-1024x576.png)
Treatments for First Degree AV Block
In most cases first degree AV blocks are benign and do not require treatments, just standard monitoring.