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Hey guys in this lesson we are going to talk about first degree AV heart block, can also be called just 1st degree block. We are going to talk about the characteristics of it, and nursing interventions and treatments. So let’s get started.
So in first degree AV heart block the SA nodes initiates the impulse, it travels across the atria and then down to the AV node. Now remember the AV node naturally slows down the impulse so the atria fully contract. Well in 1st degree block the AV node will slow down the impulse too much so it takes longer than normal, so the signal from the atria to the ventricles takes longer. This is measured with the PR interval, remember that normally it takes 0.12-0.20 seconds. So in 1st degree block, the PR interval is greater 0.20 seconds, meaning it takes the electricity longer from the SA node to the ventricles because the AV node slows things down. So let’s break it down a little further.
So in step 1 we need to look at the rhythm and find out if it is a regular rhythm or an irregular rhythm. So we count the boxes in between the R waves and we have 27 consistently our rhythm is regular. Sometimes it can be irregular, again it depends on the underlying rhythm. An example would be if I have a sinus arrhythmia, it would be irregular. Ok so let’s do step 2 and count our heart rate, so we have 5 R waves and we multiply it by 10 since it is a 6 second strip and we get 50 beats per minute. In the 1500 method we divide 1500 by 27 and get 55 beats per minute which again is more accurate. So in step 3 we need to look at the P to QRS ratio, do we have 1 P wave followed by 1 QRS and we do, every P wave has a QRS behind it. In step 4 we look at the PR interval and we have 6 small boxes so our PR interval is 0.24 seconds. In step 5 we look at the QRS complex and we have about 1 and a half boxes so our QRS complex is 0.06 seconds. So step 6 would be to identify the rhythm and it is a Sinus bradycardia with a first-degree AV heart block. So always know the underlying rhythm. So let’s recap the characteristics, the rhythm is regular for the most part but it can be irregular depending on the underlying rhythm. The heart rate varies but usually with a first-degree AV block it’s a slower rate. There P:QRS ratio is 1 to 1. The PR interval is longer than 0.20 seconds and that is the biggest characteristic of 1st degree block and the QRS complex is normal. This is relatively a harmless rhythm unless the patient is really bradycardic and symptomatic. So let’s talk about managing it.
So usually when patients present with 1st degree AV block they are asymptomatic for the most part, may become symptomatic with bradycardia. Nursing interventions are to just continue to monitor them. If we can find out the cause we can try to treat it. Some of the possible causes are electrolyte imbalances or medications that slow down the AV node like calcium channel blockers or heart problems like an MI. Again this rhythm is harmless, if they become bradycardia and are symptomatic, we can follow ACLS guidelines for the most part we just continue to monitor the patients and rhythm.
So the key points that you need to remember from this lesson are the abnormalities of 1st degree AV heart blocks which like the name says, the AV node is slowing down the conduction and delays the impulse from the atria to the ventricles so the PR interval is going to be greater than 0.20 seconds. The nursing interventions are to just continue to monitor the patients, if they become symptomatic with bradycardia follow ACLS guidelines, if you can identify and treat the cause to improve 1st degree heart block
So I hope this little lesson makes it easier to understand 1st degree AV heart block. Make sure you check out all of the resources attached to this lesson. Now, go out and be your best self today! And, as always, happy nursing!