3rd Degree AV Heart Block (Complete Heart Block)

Hey guys, so we made it to our last lesson in this EKG section, we are going to finish strong and talk about another deadly arrhythmia. So we are going to talk about 3rd degree AV heart block, it is also called complete heart block. This is a deadly arrhythmia and when you see this you need to do something about it right away before our patients die. So let’s break down the characteristics of this rhythm and talk about it.

So in 3rd degree AV heart blocks the electrical conduction is unable to reach the ventricles, the SA node still initiates the impulse across the atria at a rate of 60-100 beats per minute. So what is supposed to happen is the SA node sends the impulse down to the AV node, down the Bundle of His, right and left bundle branches and purkinje fibers. In complete heart block, the signal is not getting down to the ventricles so the ventricles would not contract and the patient would die, but because the heart is so smart, it picks up its own ventricular rate. If you remember one of the first lessons where we talk about conduction, I mentioned that the SA node initiates the impulse at a rate of 60-100, if it quits working the AV node initiates the impulse at a rate of 40-60 beats per minute, and if the AV node quits working the ventricles pick up the pace at a rate of 20-40 beats per minute. That is what is happening here, since the ventricles are not receiving the signal from the atria it starts beating at its own pace with its own electrical conduction at a rate of 20-40 beats per minute. So the atria are contracting like they should and the signal does not reach the ventricles, they contract at their own pace. So there is no connection or relationship between the atria and ventricles. Since the atria and ventricles contract when they want, cardiac output is significantly decreased, something needs to be done as soon as possible. Now let’s break down each of the steps and talk about the characteristics of 3rd degree heart block.

So in step one we need to see if our rhythm is regular or irregular, and with 3rd degree heart block we need to look at it a little differently. We have more P waves than we do QRS so usually from one P wave to the other it is regular, like look at this P wave and this one and this one we have about the same number of boxes in between and if we march it out, they are regular. The ventricular rhythm can be regular but can be irregular. So the atrial rate is regular, and the ventricular rate is regular or irregular. In step 2 we need to look at the heart rate and we have 40 beats per minute, it is usually slow in 3rd degree heart block. In step 3 we look at the P:QRS ratio, there is not association between the P and QRS, and there are more P waves than QRS, the P:QRS ratio, it is not a 1 to 1 conduction. In step 4 we look at the PR interval and that is not measurable since we have more P waves than QRS. In step 5 we look at the QRS complex so from here to here we have about 3 boxes so it’s 0.12 seconds, it is usually wider in complete heart block. In step 6 would be to identify the rhythm and we have 3rd degree heart AV heart block or complete heart block. So let’s recap the characteristics, ventricular rhythm is regular or irregular, the P to P is regular. The heart rate varies but it is usually low, the P:QRS ratio is not 1 to 1 and the PR interval is not measurable and the QRS complex is wider than normal. In this rhythm you need to remember that there is a complete block from the atria to the ventricles, they are doing their own thing and there is no communication between the upper and lower chambers. So let’s talk about signs and symptoms and treatment measures.

So because the cardiac output is severely decreased in this rhythm, there clinical presentations are fatigue, dizziness, syncope, hypotension, chest pain, and they will be hemodynamically unstable. The priority nursing interventions are to assess the patient determine severity and prepare them for a pacemaker. We will do a temporary pacemaker if unstable until they get a permanent pacemaker inserted.

So the key points to take away from this lesson are to remember the abnormalities of 3rd degree AV heart block, also called complete heart block. The electrical signal from the atria is not reaching the ventricles, there is a dissociation between the atria and ventricles. The atria are contracting at their own pace and the ventricles contract at their own pace, there is no relationship between the P waves and QRS, this causes decreased cardiac output. The pain nursing interventions are to quickly identify the rhythm and prepare for a temporary pacemaker if unstable or a permanent pacemaker for a longer management.
So I hope that you guys have enjoyed this lesson and feel more comfortable identifying 3rd degree AV heart blocks or complete heart blocks. Make sure you check out all of the resources attached to this lesson. Make sure you go back and look at the last lessons regarding the heart blocks and pick out the differences between the 3 blocks so you can identify them. Now, go out and be your best self today! And, as always, happy nursing!