A 49 year old female is brought to the
emergency room at 4 AM by her husband,
complaining of crushing pain in her chest located
behind her sternum and radiating to the left arm.
She is overweight and has
a history of diabetes.
Myocardial infarction is suspected.
An ECG is performed which reveals ST segment elevation
and T-wave inversion in leads II, III and aVF.
Which of the following is the
most probable diagnosis?
Answer choice (A) - inferior
wall myocardial infarction or MI
Answer choice (B)
- lateral wall MI
Answer choice (C) -
posterior wall MI
Answer choice (D)
- anteroseptal MI
or Answer choice (E) -
right ventricular MI
Now take a moment to come to a conclusion yourself
before we go through the answers together.
Okay, let's tackle this
First thing we have to determine is what
subject are we talking about with this question?
Well, we're concerning the heart the pathology of
the heart, so this is cardiovascular pathology.
Now this is a 2-step question.
The first thing we have to do
is determine what is the diagnosis.
And this case, I mean it looks
like a myocardial infarction
but the second step is to determine where in the
heart are we gonna localize where the lesion is?
And the stem is absolutely required in this case
because we need it to help determine the diagnosis
but also then we need the ECG results
to localize the lesion in the heart.
Now let's start with the first step
in this question in our walkthrough
which is determining wether myocardial
infarction is the most likely diagnosis.
Well this patient absolutely has risk
factors for ischemic heart disease.
She has both obesity and diabetes.
Now this patient also presents with a very typical
clinical presentation for an acute myocardial infarction.
She has crushing substernal chest pain, some patients will
even say they feel like an elephant sitting on their chest
and the pain is substernal, and in this
case it's radiating to her left arm,
very classic for a
traditional or typical MI
Now we also see that the patient has
ST elevation and T wave inversion
which is also typical of an acute
myocardial infarction on the EKG.
Now that we think the diagnosis
is a myocardial infarction,
we need to be able to look at the EKG and then
determine where in the heart we see the lesion.
Well the question stem says that there is ST segment
elevation and T wave inversion in leads II, III, and aVF.
Now this is the inferior wall of the heart, so thus the answer in this
case is answer choice (A) - an inferior wall myocardial infarction.``
Now let's refer to the image for this question as it is an
extremely high-yield image and vital for every student to know.
It is absolutely critical as a doctor, that you can
look at an EKG and quickly be able to determine
what type of pathology we're looking at and
where in the heart you see that pathology.
And if you look at how the location of the MI by EKG
leads is set up in the diagram, you'll see 12 boxes.
And this is set up just like a clinical 12 lead EKG where
each leads corresponds to a certain section on the heart
except for aVR - that's a non-diagnostic lead,
it's just needed to come up with a 12-L EKG.
Now if you look, leads II, III
and aVF are our inferior leads.
leads V5, V6, I and aVL
are lateral leads.
V1, V2 are septal and
V3 and V4 anterior.
It is absolutely vital that you simply memorize
this and put it to memory, ingrain it in your head
because this information is not only vital to USMLE
exam but it's also vital to basic clinical practice.
And as you can see above the images of the heart,
it dictates where you have the different lateral,
inferior and anterior segments of
the heart and also the septal wall.
Now let's go through some high-yield facts
regarding an acute myocardial infarction
and also lcoalization of an
acute myocardial infarction.
Now typical clinical symptoms that one can see with a
patient presenting with an acute myocardial infarction
include severe crushing substernal chest pain
that can radiate to the left arm or into the jaw,
and the pain can often be associated with
sweating, nausea and even shortness of breath.
An important risk factors for patients with an acute MI, are
smoking, obesity, hyperlipidemia, hypertension and diabetes.
And general changes that you can see in an ECG
includes ST segment elevation and T wave inversion,
or you can have what is called a STEMI which
is ST segment elevation myocardial infarction.
Now when looking at a EKG, it's extremely important to be able to
localize where we have different localization within the heart.
And very important to understand, V1-V2 are your
septals, V3 and V4 anterior, V5, V6, I and aVL are lateral
and II,III and aVF are inferior - absolutely vital
information for localizing a myocardial infarction.