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.
Vicki says
agree with all above. I am finally understanding blocks thanks to your easy explanations! Yes would have been nice to have this site 20 years ago when I started Nursing, but I will share this site with my daughter whom is a new nurse, who is required to be ACLS certified for her present position. There should be no fear only learning and a good learning experience! We all want the same for our patients! Many Thanks again
sajauna says
love it
Dr Ghazwan says
Amazing site
thanks Jeff for everything
Jennebah Dorley says
This is an amazing site. I am a senior B S Nursing student and this site has been my number one resource this semester. Thank you so much.
alleas says
You cannot believe how much this site is helping me to prepare for recert!! I wish that this site had been available way back when I started my critical care nursing career 24 years ago. God bless you for this!!
Carol says
A friend led me to this site. Thank you so much for giving me something to study besides the ACLS book. Other people’s questions have also helped me. Thank you! Thank you! Thank you!
jeannie says
I love this!!!! Thank You!!
shanthi says
very helpful site. i would have been better i knew about this site earlier
sunitha george says
REALLY HELPFULL
Christian Hurano says
Very nice illustration..:) it will really help me recognize the heart rythm of my patients.
AL-Ameri Nader says
Thank you for this nice illustration.
ashley says
fantastic website, very helpful in studying!
wmjarvis says
Jeff I love this site. The music to the videos for Asystole, and Ist degree AV block is fantastic. What is it?
I find it helps very much to ID the rhythms. Love it!
Jeff with admin. says
The music was composed by a friend (Jared Kraft). His website is here.
Kind regards,
Jeff
mylee belle says
great vid^^ it does help a lot!!!^^ i have a question though..is the lengthening of the PR interval a definitive sign to diagnose 1st DEGREE AV BLOCK?
Jeff with admin. says
Yes, this is the criteria that is used to determine 1st degree block. 1 degree AV block is a conduction problem and this can only be seen on an ECG and it therefore essential to use the ECG for clinical diagnosis.
1st degree block is usually benign.
Kind regards, Jeff
DeannaWheeler says
What electrolyte imbalance induces first degree block?
Jeff with admin. says
Hyperkalemia can be a contributing factor for all of the heart blocks. Regards, Jeff