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

1. 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.

---

2. 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.

---

3. 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.

---

Click to view more top questions

[This content is available for registered users.]

Learn more about the course…