Coronary artery disease
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Heart attack (myocardial infarct) diagnosis
- [Voiceover] It's really important that Myocardial Infarcts, that heart attacks, are diagnosed as soon as possible. The reason for this is because the longer that the heart goes without getting the proper supply of oxygen it needs, then the more the heart muscle is going to die. This principle is actually so important that in medicine there is a saying that goes, "Time is muscle." That really serves to underscore the importance that the faster you diagnose a heart attack and sort of localize where on the heart the infarct has happened the faster you can treat it. Right, and the faster that you treat it, that means there is a best chance for a good outcome after having a Myocardial Infarct. Time is muscle. Let's say our friend Vinay had a heart attack and he gets himself, or somebody brings him to the hospital. When he gets to the hospital what is going to happen? What are the diagnostic steps that are going to take place? Well, it's an emergency, right? A suspected Myocardial Infarct is an emergency and the hospital staff will really treat it as such because, again it really is understood that time is muscle. The longer you leave the Myocardial Infarct untreated, the more heart muscle you are going to lose. So Vinay will get doctors on his case pretty quickly. Diagnosis is really based on three major things. What's it based on? It's based on a history, that is the first thing. What's a history? A history is just basically talking to the patient and getting an idea of what happened to bring them into the hospital. Another thing and arguably the most important is an ECG. What an ECG is, it's a machine that can measure the electrical activity of the heart. I will explore that in a minute. The third major thing is blood work. Taking a sample of the patients blood and looking for certain proteins in the blood, that can indicate that a heart attack has happened. Those are our three major things. Those are our three pillars in terms of diagnosis. What is a history? Let's sort of delve deeper into each one of these things. A history is basically like a question and answer session between a health care professional and a patient. Really the purpose behind history is to figure out what sort of symptoms the patient had and how long they lasted for. Typically, it's really worrying if the symptoms have lasted for over 20 minutes in the case of a Myocardial, suspected Myocardial Infarct. Why is that worrying? Well that's worrying because it's almost a sign that the heart damaged that has happened is probably irreversible. These sorts of things you try to get out on a history. You'd want to ask about chest pain because people who have had a Myocardial Infarct sometimes report that the pain they feel is almost like someone put a brick on their chest. It's this really sort of heavy crushing pain in the center of their chest. You might be asked if your chest pain radiated anywhere, if it sort of seemed to travel any where else in your body. People who have had Myocardial Infarcts will sometimes report feeling pain travel down their arms or up towards their jaw or to their shoulder tips. You might also be asked if you had any shortness of breath. Sometimes people get short of breath because since their heart is not pumping properly, blood coming back to their heart from their lungs will start to back up and create this sort of pressure in the lungs and that will prevent people from being able to breath properly during a heart attack. You might be asked if you felt nauseated or if you vomited at all. This might happen because part of your nervous system called your Autonomic Nervous System might still be trying to figure out what is going on during your heart attack. You might get feelings of wanting to throw up. You might be asked if you had any dizziness or if you actually lost consciousness. This might happen because your hearts pumping ability is getting compromised so you can't necessarily get blood up to your brain, so you might feel a bit dizzy. Or you might lose conscious entirely. You might be asked if you started to sweat a lot. A lot of people who have Myocardial Infarcts will all of a sudden break out in a sweat. So, two caveats to sort of talk about. First, both men and women will experience all of these symptoms that I just listed. But statistics actually show that women seem to experience the nausea and vomiting and the dizziness and the blacking out more often than men do. The second sort of little caveat is that in people that have diabetes, the nerves that conduct pain from the heart may have become damaged as part of a complication of their diabetes. Sometimes people who have diabetes don't actually get chest pain because they actually can't sense the pain signals coming from their heart, coming from their chest. That is the second caveat. But these are really some of the key parts of a history that you would want to ask about in someone you are suspecting of having a Myocardial Infarct. That is one of our three pillars. We have done history, now we need to move onto ECG. ECG, what is an ECG? An ECG is basically a machine that can detect the electrical activity of our hearts. Since we know what the normal electrical activity of our heart looks like, so with each heart beat we actually get a pattern like this, that looks sort of like this on an ECG. What we can do is do an ECG on someone who has had a heart attack or someone who we think of has had a heart attack and we can compare what their pattern looks like to what a normal pattern should look like. Depending on what sort of pattern they have, we will look at a few patterns in a second, we can sort of get an idea of what type of heart attack they have had and where on the heart they have had it. So let's look at the parts of a ECG trace. By the way, yeah, this pattern here is called an ECG trace and it actually represents one heart beat. Let's label it first, so this is the P-wave. This is called a P-wave, representing the electrical activity behind atrial contraction. This is a Q-wave, this is R, S, and this QRS segment, this represents ventricular contraction and atrial relaxation. What do you think this is? A T-wave, signifying ventricular relaxation. To preempt your question, they were just sort of named arbitrarily, P, Q, R, S, T, are just sort of letters assigned to this curve without any real reason. They are just there to make it easy to refer to. I won't actually get into the specifics behind how to read an ECG but suffice to say that comparing the pattern of an ECG taken from someone who you are suspecting of having a heart attack and comparing that to a normal ECG, that will give you a very good idea as to whether or not this person has had a heart attack or not. For example, in one type of heart attack, an ST-elevation Myocardial Infarcts or STEMI, you actually get elevation of the segment between S and T, they actually elevate. Here you can see that they have sort of moved up. This actually tells you a little bit about what sort of heart attack you have had. This means by having an ST-elevation Myocardial Infarct, it means that you have had a full thickness Infarct. So here is a cross section of the heart here and here is a right ventricle and here is a left ventricle. A STEMI means that you have had a full thickness Infarct of the heart. All of this, this entire wall would be, it would have died because of lack of oxygen. Again, this is just an example. It doesn't have to be in that particular part of the heart. I'm just showing you that it's a full thickness. The entire wall of the heart in whichever area it happens in. So we have a ST- elevation. Do we also have a ST-depression? Yes we do. Let's look at ST-depression now. This is actually our other major type of heart attack. But it's actually not called an ST-depression Myocardial Infarct, it's called a non-ST elevation Myocardial Infarct or an N-STEMI. Actually, in N-STEMIs you can also see inversion of this T-wave here. So what does an N-STEMI tell us? What does that mean, functionally? That actually means that we've had a partial thickness Infarct of the heart muscle. For example, you might have this bit of Myocardium, of heart muscle that has died off and not actually a full thickness. Not a full thickness but just this bit right here. Those are really the two major types of Myocardial Infarcts, STEMIs and N-STEMIs. ECGs are really, really helpful in helping us decide which kind we are dealing with here with any given patient. Alright, so what is our third pillar in diagnosis of heart attacks. Well, blood work, blood tests. What sort of blood work do we do? Well, we look for things called Cardiac Markers. You might remember that when a Cardio Myocyte, a heart muscle cell, dies, it sort of, it's membrane sort of leaks. It's membrane sort of ruptures and all these proteins sort of spill out of it. There's a couple different types of proteins that spill out. You have these proteins up here and these proteins are called Troponins and you would have another protein called Myoglobin and then you would have another protein as well called Creatine Kinase MB or CKMB. MB just refers to the shape of the protein on a molecular level. Now all of these spill out of your heart muscle cells once they sort of start to die. They spill out and they enter your blood stream. What sort of blood work gets done? Which ones get looked for? Well, Myoglobin is found elsewhere in the body as well as in your heart muscles, so that one is not very specific to your heart muscles, so we don't typically test for that. Creatine Kinase MB, sometimes that is looked for in blood work because it's more specific than Myoglobin. But troponins, troponins specifically troponins T and I, those are specific subtypes of troponins and those ones are actually exclusively found in your cardiac muscle and they should only be in your cardiac muscle. So we know if that these troponins end up in your blood, you must have had heart muscle damage because then they would have leaked out of your cells and ended up in your bloodstream. Troponins are the most specific cardiac marker that you can find doing blood work in diagnosing a Myocardial Infarct. Let's quickly recap here. To diagnose a Myocardial Infarct, we can take a history, a clinical history, specifically to find out if the patient has had symptoms for more than 20 minutes. We can do an ECG or we can do blood work. According to the World Health Organizations, guidelines on diagnosing Myocardial Infarcts, if two of these three sort of diagnostic tests or procedures are positive, then it's probable that you have had a heart attack. If three out of three of these are satisfied, then you have definitely had a heart attack.