ECG of Myocardial Infarction (MI): STEMI vs. NSTEMI

00:01 So now let's look at some ECGs of acute myocardial infarction.

00:04 By the way, just to bear in mind that not only does the ECG help you in terms of the diagnosis of MI, but depending upon the extent of number of the changes, it gives you prognostic information.

00:18 In other words, how bad is this heart attack? We have some EKGs that are - looked like small amount of injury to the heart and some EKGs that looked like big bad injury to the heart.

00:28 This is really gonna be dangerous and may impair the patient's ability to survive down the road.

00:34 Acute MI presents as either ST segment elevation or ST segment depression and often associated with inverted T waves as you're going to see.

00:45 Depending on where the changes occur, it gives us a rough idea of the location of the myocardial infarct.

00:54 So, the leads that look at the bottom of the heart.

00:57 Remember lead II, lead III and lead aVF from down below, those show us heart attacks on the inferior or posterior of the back.

01:07 Either the underside or the back of the heart that's the inferior leads.

01:11 The leads V1 and V2 show us the anteroseptal region that is the - partly the septum and part of the interior wall.

01:21 Leads V3 and V4 generally show you the main area of the anterior wall.

01:26 And five and six show you the anterior wall and some of the lateral wall.

01:32 Leads I and aVL show you the lateral wall.

01:36 So, you can see we get a rough idea of where the infarct is from where the abnormalities occur with that heart attack.

01:45 And again, here's just a little review.

01:47 Leads II, III and aVF, inferior or sometimes called inferior posterior.

01:53 Leads V1, V2: septal, anteroseptal. V3, V4: anterior. V5 and 6 lateral.

02:02 Also leads I and aVL: lateral. So very often, a lateral infarct, you'll see leads - changes in lead I, aVL, V5 and V6.

02:13 ST elevation myocardial infarction are the worst.

02:18 They imply a large amount of myocardium that's ischemic with considerable damage and have a worse prognosis than the ST depression, so-called non-ST elevation MIs.

02:30 As stated here, the non-ST elevation MIs show ST segment depression.

02:37 They're smaller than the ST elevation MIs.

02:40 By the way, ST segment depression can occur with myocardial ischemia, with angina and then goes back to baseline when the patient rests.

02:49 And it's also a finding when we do an exercise test.

02:52 The ST segments depressed when there's ischemia and then in the rest period after the exercise test, they come back to normal.

02:59 So, let's go over a little bit about the ST segments. They should normally be flat.

03:04 They should be the same flat and direction as the segment - the PR segment, nice and flat.

03:10 And in fact, there are multiple causes of ST segment depression as I mentioned in the very first lecture.

03:17 Ischemia is the one we're most interested in. Electrolytes like hypokalemia can cause ST segment changes, and digitalis therapy, we can do the same.

03:27 You've seen this slide before, remember? The digi-effect causes a sort of rounded sagging of the ST segment.

03:34 Ischemia caused a flattened - a squared off ST segment depression.

03:39 And hypokalemia, usually a sort of somewhat slow or downward slope with a flattened T-wave and sometimes a U wave following.

03:49 Here's some more examples. Here's minimal ST segment depression.

03:54 So, this might be associated with a very small infarct.

03:57 Here's what I call big leak ST depression going to be associated with a much larger non-ST elevation MI.

04:04 The minor amounts of ischemia you saw above can be seen with a positive exercise test or with angina that reverses itself.

04:15 The kind of ST depression you see down below; the huge amounts, are usually going to cause some cell death and a myocardial infarct.

04:25 Again, reviewing where the occlusion may have occurred, here, the inferior wall is often supplied by the right ventricle - by the right coronary artery in 90% of patients.

04:38 In 10% of patients, it's the left circumflex that supplies the inferior surface.

04:42 So, if you see an infarct pattern, an ST elevation or depression in leads II, III and aVF, it's usually gonna be the right coronary artery that's involved. If it's any one of the V leads, either the septal, anterior or lateral, then it's usually going to be the left anterior descending that's doing it.

05:03 And if it's pure lateral, it's usually the left circumflex.

05:06 It's not 100%, but it gives you a rough idea.

05:09 And like people in the Cath Lab who are gonna be going in to open up the artery will look at the EKG to decide which artery they're gonna look at first to consider opening up with an angioplasty.