Heart attack (myocardial infarct) diagnosis | NCLEX-RN | Khan Academy

Heart attack (myocardial infarct) diagnosis | NCLEX-RN | Khan Academy


– [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.