 Welcome back to ACS Part 2. In this section, we'll discuss how to use the ECG in a patient who you're suspecting of an ACS. This is not a comprehensive review of how to read an EKG. ECG is the cornerstone diagnosis for ACS. Keep in mind that if your first ECG did not show any abnormalities and the patient is still having symptoms, we often repeat it. This is a normal 12-lead ECG. When we're approaching a 12-lead ECG, we often start with right rhythm, axis, and so on. Once we make sure those are okay, we're going to move on to more specific details. These specific details include SD elevation and SD depression with or without T-wave inversion. In the patient that we're worried about acute coronary syndrome, SD elevation means an acute infarct. You can also get SD elevation in patients without an infarct. They include benign early repolarization, which should not be giving patient chest pain. A left-bundle branch block, which you may or may not be able to find out if it's new or old. LVH, or LV aneurysm, which should not be giving patient chest pain. And the last reason for SD elevation is pericarditis. That will give patient chest pain. However, we'll look at the criteria to decide whether this is infarction versus pericarditis. For now, let's look at SD elevation in patients with acute myocardial infarction and learn their patterns first. Acute myocardial infarct follows two rules on the ECG. One, it's territorial. Second, there are reciprocal changes. We'll go through them one by one. First, territorial. Each coronary artery and its branches supply specific area to the heart. If one of the arteries or the branches is blocked, it will make sense that all the territory of the heart that is being supplied by this branch will not be getting oxygen. That the whole territory is being affected. And so when we're looking at SD elevation, we want to look at them in territories. Specifically, we want to look at the different territories of the heart. On the 12 lead ECG, inferior part of the heart is looked at by lead 2, 3 and AVF. Lateral part of the heart is looked at by leads 1, AVL, V5 and V6. V1, V2, V3 and V4 comprises the anterior part of the heart. This is important when looking at patient with potential ACS. In terms of coronary artery supplies, the inferior part of the heart is mostly supplied by the right coronary artery. The anterior portion of the heart is being supplied by the left anterior descending artery. The lateral wall of the heart is supplied by the branches of the left anterior descending artery, and the left circumflex arteries. If we see SD elevations on the 12 lead ECG, we want to ask, do these elevations belong to the same territory of the heart? Let's see a few examples. We'll focus on SD elevations for now. Which leads do you see SD elevations? Lead V1, and that's the baseline. V2, V3, V4 and V5 are fairly obvious. Do you see SD elevation anywhere else? There's a very subtle SD elevation in AVL. So the question is, do the SD elevations belong to the same territories? If so, which ones? They include the anterior territory and two of the leads in the lateral territory. Therefore this is an acute interlateral myocardial infarction. Let's look at this ECG. You can pause here to decide where the SD elevations are and whether it belongs to the same territory. SD elevations are in 2, 3 and AVF. That is the inferior portion of the heart. Therefore this is an acute inferior SD elevation myocardial infarction. What about this ECG? Again, just look at the SD elevations and decide whether they belong to the same territories. There are SD elevations in multiple leads. You see them in the interior portion of the heart. Pay special attention to the way the SD elevations look like in the interior leads. You see that they have those rounded tops. These are also known as tombstones and are particularly worrisome for infarcts. Where else do you see SD elevations? You see them in the lateral leads as well. You can also see tombstones' SDs in those leads as well. This is an acute entrolateral SD elevation my. Every time you see SD elevations belonging to the same territory you have to think there is a blocked vessel and therefore there is an infarction. The second part of an SD elevation my has to do with reciprocal changes. It refers to the fact that if you have SD elevation going on in one territory of the heart the ECG leads corresponding to the opposite territory should show SD depression almost like a mirror image of the SD elevation. This is a schematic of a heart. You can see that the lateral wall of the heart is directly opposite to the interior wall of the heart and the anterior wall of the heart is opposite to the posterior wall of the heart which will be behind the slide. The rules of reciprocality in SD elevation means that if there is an SD elevation my in one of the territories of the heart the opposite territory should show SD depression picking up the mirror changes. Therefore in a patient with SD elevation in say the inferior leads the lateral leads should be showing SD depression and if there are SD elevation in the lateral leads there should be SD depression in the inferior leads. These two territories always reciprocate with each other. The same vein also goes for anterior and posterior leads that is if there is SD elevation in the interior leads if we do posterior leads we will see SD depression. These two territories always reciprocate with each other. Let's go through some examples. Here I want you to pick out the SD elevation and the SD depression. Where are the SD elevations? They're in the inferior leads. They belong to the same territory. Do you see the SD depressions? Where are they? They're in one NAVL and the depression in one is very subtle. That corresponds to the lateral leads. Therefore this is a acute inferior SD elevation MI. What about this one? We've seen this one before. You notice that there are SD elevation in the interior leads and the lateral leads. Do you see any SD depression? You can see SD depressions in two, three NAVF corresponding to the inferior part of the heart. That makes sense because the inferior part of the heart reciprocates with the lateral SD changes. What about changes in the posterior leads? Well in a standard 12 lead EKG we don't do posterior leads. If we were to do them using a 15 lead we would be able to see SD depression in the posterior leads. Let's try this one. Where are the SD elevations? In the inferior leads? And some in the interior leads. A bit more subtle. This time where are the SD depressions? We expect them to be in the lateral leads since the inferior part reciprocates with the lateral. Are there SD depression? Yes, there are some in one NAVL. Therefore you can explain all the EKG changes with regard to the STs by an antero-infero SD elevation MI with reciprocal changes in the lateral leads. How about this one? Where do you see the SD elevations? There are some in the inferior leads. They're very subtle. Do you see any SD depressions? There are some in the one to be four in the anterior leads. Are these reciprocal changes? We know that the inferior wall reciprocates with lateral, not with anterior. And therefore the anterior SD depression must be coming from something else. It can either be ischemic changes that we'll discuss later. The second possibility is that we are looking at reciprocal changes in the anterior leads as a reflection from posterior lead SD elevation MI. And therefore this is one of the reasons we will do a 15 lead ECG. It will be looking for posterior leads. To do posterior leads EKG leads are put in the back part of the body just underneath the scapula. It is usually denoted by V7, V8 and V9. Often in the 15 lead only V8 and V9 are being performed. This is what the patient with the SD depression in V1 to V4 look like with V7, V8 and V9. Do you see the SD changes? You see the SD elevation in V7 to V9 the posterior part of the heart and that corresponds exactly to the SD depressions in V1 to V4. The anterior and the posterior part of the heart reciprocates. Therefore the patient is having an acute inferior posterior SD elevation MI. And we wouldn't have picked that up had we not done the 15 lead. After we look for SD elevation and seeing whether they are territorial or reciprocal on the 12 lead ECG we then look for SD depression or T wave inversion in patients with potential ACS. The difference between SD depression is that it denotes ischemia. It is not territorial or reciprocal like infarct. Let's look at this ECG. Do you see SD depression? You kind of see them everywhere. It's not territorial and not reciprocal. If there are no SD depression the second thing we look for is T wave inversion or flip T's. Where do you see the flip T's in this ECG? They're in multiple leads. If they are new then we have to be very concerned about ischemia. In summary we talk about how to approach the IGG of a patient suspicious of having ACS. Remember that we look for SD elevation to see whether they are territorial and reciprocal. If there is no SD elevation we will look for SD depression and T wave inversion. In the next section we'll discuss how to use other diagnostic modality in the patient with ACS. Thank you for watching.