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.
QUEENARDA Brown says
So is sinus Brady the same as sinus Brady w/ 1st degree AV block?
ACLS says
The two are different. The main difference between sinus bradycardia and sinus bradycardia with a first-degree block lies in the presence of the AV block. In sinus bradycardia, the electrical impulses from the sinus node reach the ventricles without any conduction delay. In sinus bradycardia with a first-degree AV block, there is a delay in the conduction of these impulses, which is evident by a prolonged PR interval on the ECG.
It’s important to note that both conditions can occur independently of each other, and the presence of a first-degree AV block in sinus bradycardia does not necessarily imply a more severe or concerning condition. Sinus bradycardia with a first-degree AV block is typically benign.
Kind regards,
Jeff
Janice Schoeneck says
You had a video on this site that helped with the basics of ECG strip analysis. Can you post that again?
Jeff with admin. says
Basic ECG interpretation
Kind regards,
Barrett Mey says
Thank you. Great help in understanding an ECG strip
Rachel Jolokai says
When reading the comments I must have missed something or it still to come. What is the NSR the comments are talking about?
Jeff with admin. says
NSR stands for normal sinus rhythm.
Kind regards,
Jeff