Also called first-degree AV block is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds.
This lengthening of the PR interval is caused by a delay in the electrical impulse from the atria to the ventricles through the AV node.
Normally, and in the case of ACLS, first-degree heart block is of no consequence unless it involves myocardial infarction or an electrolyte imbalance.
Although first-degree heart block is not clinically significant for ACLS, recognition of the major AV blocks is important because treatment decisions are based on the type of block present.
There are a number of disorders that can cause first-degree AV block, but it may be a normal variant in the conduction system of the heart. Some of the most common causes are listed below:
Causes of First degree AV block:
- Increased vagal tone (well trained athlete)
- Electrolyte disturbances
- Myocarditis caused by infections
- hypoxemia (see more in infants and children)
- Cardiac surgery
- Congenital abnormalities (see more in infants and children)
- Myocardial infarction
- Medications that inhibit AV node conduction (amiodarone, beta-blockers, calcium channel blockers, digoxin)
- Acute rheumatic fever (see more in infants and children)
Below is a short video which will help you quickly identify first-degree AV block on a monitor. Please allow several seconds for the video to load. (3.40 mb)
Click for next Rhythm Review:
Second Degree Heart Block Type I
Top Questions Asked On This Page
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Q: So would I call that sinus rhythm with a first degree AV block? Or just first degree AV block?
A: You can say it either way. They both are correct.
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Q: What should a nurse do first if there is an abnormal ECG reading. Do you take the pulse first or go ahead and the CPR?
A: An abnormal ECG only indicates that there is an arrhythmia in the heart. You will first look at your patient. If they are awake/responsive, you will not have to check a pulse, and you would not need to perform CPR. If you find a person unresponsive, you would call for help and a defibrillator and then perform a pulse check. If there is no pulse, then begin CPR.
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Q: You had a video on this site that helped with the basics of ECG strip analysis. Can you post that again?
A: Here is a video that will help you with the very basics of ECG strip analysis.
Jesse Sola says
So would I call that sinus rhythm with a first degree AV block? Or just first degree AV block?
Jeff with admin. says
You can say it either way. They both are correct.
Dudu says
Hi Jeff patient is unresponsive and pulselessrhythm change irregular ,chaotic vf like pattern you change to 200 j and press shock but no shock deliver why?
Jeff with admin. says
It sounds like either you did not charge the defibrillator prior to shocking the patient or you had the defibrillator in synchronize mode and the defibrillator could not sync with the patient’s rhythm.
Kind regards,
Jeff
Alniren says
Very helpful and informative. There’s a lot of info here that you will not learn from ACLS.
Kate Igunma says
Hi Jeff. I am preparing to take the Nclex-RN. My question is – what should a nurse do first if there is an abnormal ECG reading. Do you take the pulse first or go ahead and the CPR?
Jeff with admin. says
An abnormal ECG only indicates that there is an arrhythmia in the heart. You will first look at your patient. If they are awake/responsive, you will not have to check a pulse and you would not need to perform CPR. If you find a person unresponsive then at that point you would call for help and a defibrillator and then perform a pulse check. If no pulse then begin CPR.
Does that make sense?
Kind regards,
Jeff
hce9847 says
Good teaching web site. Now I know how to distinguish NSR from First degree AV block.
Thank you.
edith murimi says
very helpful share videos for tachycardia s also
Vnl904177 says
Kudo’s to you Jeff ! Great teaching website ! Thank You ??
LorryKelley says
Amazing way to teach and educate.
carlafussy says
Hi Jeff,
On Sept. 12, 2013 you had a video on this site that helped with the basics of ECG strip analysis. Can you post that again?
Thank you,
Carla
Jeff with admin. says
Here is a video that will help you with the very basics of ECG strip analysis:
Kind regards,
Jeff
CyndiSood says
The PR interval confuses me. It looks more like a PQ interval. I thought the R wave was the peak of the QRS complex. What am I missing?
Jeff with admin. says
The name is a bit confusing. The PR interval or PRI is measured from the beginning of the P-wave to the beginning of the QRS complex. This can be confusing because the beginning of the QRS complex is at Q.
Some healthcare providers do refer to it as PQ interval and this would still be considered correct. It’s more common name is PRI or PR interval. It is kind of like EKG when really it should be ECG. There is absolutely no good reason to call ECG an EKG, but we do.
Kind regards,
Jeff
Ben says
Jeff, great explanation about the PRI. However, just to throw out some cool trivia: there is meaning behind saying “EKG”. The inventor of the ECG, as we know, it was a Dutch guy back around 1900. The German word is abbreviated as EKG, while in English it is abbreviated as ECG. So if you say EKG, you are paying homage to the original German term which I won’t butcher the spelling of. The more you know!!!
Ben
Jeff with admin. says
Thanks for sharing that interesting fact. Kind regards, Jeff
jangrossberg says
Thank you for clarifying that piece of tradition! I always thought I was missing something there….?? 🙁
im1coolrn says
In all the ACLS classes I have had, you are the first person to clarify the block vs a NSR. It makes it so much easier to understand the rest of the blocks too. Another thank you.
docro10 says
Clears things up greatly
Zaba says
Thanks great help !
Susan says
Very helpful. format is perfect for isolating essential information. Comparison with NSR just adds to it all. Thank you.
hassan says
Thanks