 Hi and welcome to nursing school explained into this video in the EKG interpretation playlist about the atrium ventricular blocks and specifically about third degree or complete heart block. If you haven't already done so I highly recommend watching my basic EKG interpretation series as well as the videos on first and second degree heart blocks so that you can follow along in the progression of how the delays in the conduction system here happen. In a third degree or complete heart block the atria and ventricles repeats completely independent of each other. There is absolutely no connection. It is therefore also called an AV dissociation which means that there's a complete heart block. This also means that the SA known impulses are blocked before they reach the ventricles. So some conduction is happening. Something is happening in here in this conduction system that the impulses are not going through. But remember the basic principles of all the cardiac cells is any cardiac cell can act as the pacemaker. So now because there is no communication between the atria and ventricles any pacemaker cell from the ventricle usually takes over. That's usually either in the AV junction or the ventricle and stimulates the ventricles. So the ventricular response is completely unrelated to the impulses that come in through the AV nodes. So now the P waves are independent from the QRS complexes and we will look at this here shortly. So in a third degree heart block the rate is usually less than 60. The rhythm of regularity is that there's an irregular ventricular response. P waves are usually upright but again because of this AV dissociation there is no relationship between the P wave and the QRS complexes. Therefore the PRI is not measurable and the QRS can either be less than 0.12 or greater depending on where this response comes from, what part of the conduction system. And this is the only heart block that is a complete and as you can imagine it is the most severe of the heart blocks. So looking at this rhythm strip here we can see the P waves. P wave, P wave, and so forth. There are all these P waves but if we would really look at the QRS is there any pattern to it? So this P has a QRS following. This QRS follows this P wave but this distance is completely different than this distance here. And so there can be an argument made here that there is also a P wave hidden right here, actually right here in this QRS. Remember the ventricular response is always going to be greater than the atrial response. So if there is an atrial response happening it might be hidden in this QRS complex. So we could really march out these P waves and see that this is a pretty regular pattern. But again there is no relationship to this QRS because this wave has no QRS. This P wave has a QRS but we don't really know what the relationship is here. This next P wave is missing a QRS. This P wave, this distance is much greater to the next QRS. So there is really no rhyme or reason to the relationship of the P waves to the QRS complexes which means that there is this association between the atria and the benthicles. Therefore, because we have no relationships from the P to the QRS complexes, the PRI is not measurable. And in this case when we look at the QRS complex, so really it goes from the Q, the R and the S and the ST segment here. So we can look at starting here 1 which makes this 0.20 which is definitely more than the normal QRS length which is usually less than 0.12. So we know that this is a ventricular response and that the response is not coming from the junction. So it's coming down from deeper down in the benthicles and there is absolutely no relationship. Now if we also look at these QRS's, the R waves that are pointed out to us here, they are fairly regular. And then as we said before, the P waves are fairly regular but there is no relation between the two at all. Hence the term complete heart block. Causes of a third degree heart block is usually MI, inferior wall or posterior wall MI, which are pretty serious. And then therefore signs and symptoms are those associated with MI such as chest pain, dyspnea, shortness of breath, dizziness, altered level of consciousness, dioporesis and every other symptom that the patient might have when they present with an acute MI. For interventions, there is nothing else to do but to insert a temporary pacemaker until a permanent pacemaker can be placed because the SA note is unreliable in making its way or making the impulses conduct in the normal way through the conduction system. Therefore an artificial pacemaker has to be inserted and usually because this is an emergency, the patient will be very symptomatic and the atrium ventricles are not responding. They will need a temporary transcutaneous pacemaker until that permanent pacemaker can be implanted. Here are some references and also resources for test strips because again the more you can practice these rhythm strips the better you'll get at it. Please also watch my other videos specifically the ones on the other AV blocks first and second degree blocks types one and types two so you gain a better understanding. Look at any of the other EKG interpretation playlist videos so you can really get a good grasp on what it takes to read rhythm strips. Please subscribe to my channel give me a thumbs up leave any comments below also follow me on Instagram and refer to those quizzes that I post every Monday so you can keep up to date and up to speed with EKG interpretation and any other NCLEX questions. Thanks for watching Nursing School Explained.