tests, such as the imaging tests with stress,
either exercise stress or a drug stress.
There are some general rules that should be
followed whenever one is thinking about ordering
a test. For example, don’t order a test
that makes no difference. You want to order
a test that’s going to affect what you are
going to tell the patient and, of course eventually,
what therapy you are going to recommend or
If you already know the answer, don’t order
the test because every test has a small chance
of complication and you want to know, if the
complication occur, that you really wanted
to order the test.
Know that some tests give less information
than others. The exercise test with the electrocardiogram
alone does not give us much information as
the exercise test or the drug stress test
when you are also using imaging. For example,
nuclear imaging or echo imaging.
And finally, it’s important to integrate
the test with whatever information you already
have about the patient.
So, remember from our first part, last time,
I talked about how important it was to understand
the history. If you already have a strong
suspicion that the patient has coronary artery
disease, that is atherosclerotic coronary
disease, then your test is going to confirm
that. If you are doing it because you really
don’t think the patient has this disease
and that the chest symptom the patient’s
reporting is really related to something entirely
different, for example arthritis, you may
not even want to do the test because you already
have the answer.
So, you have to integrate your desire for
the test with your clinical suspicions obtained
from the history and the physical examination.
Now, the EKG stress test is the simplest,
the cheapest and the most easily done of all
the tests. The only imaging is with the electrocardiogram.
And there are specific changes in the electrocardiogram
which suggest that there is ischemia present.
It’s the least accurate of the tests, but
it’s the simplest and the cheapest and so,
often, it’s the first test that we do.
So, when we are doing the EKG exercise test,
it’s either done on a bicycle or a treadmill.
We record the electrocardiogram continuously.
And then we decide, based upon the response
of the electrocardiogram, whether there was
a suggestion of ischemia or not.
And here, we see just a little cartoon of
somebody walking on the treadmill. They will
be all hooked up to the electrocardiogram
and we will be looking for the stress-test
Here is two examples of EKG tracings. One
is at baseline at the top and the one at the
bottom is at peak exercise. You will notice
that there is a decrease, a drop, in the ST-segment,
that is the area of the EKG immediately after
the big QRS. That is a so called ‘ischemic
response’ and it suggests that there is
part of the heart muscle that’s not getting
enough blood flow. Remember the motor analogy?
There is not enough gas getting into the motor
and the motor is hurting, it’s not performing
well and it shows you this ST-segment depression.
This is a very typical example of a positive
EKG exercise stress test.
Now, of course, there are other tests that
can be done with exercise or, sometimes with
drugs to stress the heart to bring out ischemic
One of these is the echo. When the heart doesn’t
get enough blood flow, of course we talked
about this before, it doesn’t contract well.
So, if you start off with a normal echo showing
the heart functioning fine, the patient exercises
and following exercise, there is an area of
the wall that doesn’t move normally. That
strongly suggests that there is lack of blood
flow there and that the patient has atherosclerotic
So, this is an imaging test that goes with
exercise that’s one step beyond the plain
EKG test. We also record the ECG, by the way,
during this so we have both the ECG information
and the echo information.
And here, we see the patient getting an echocardiogram.
They may have just finished exercise,
they quickly lie down and we record the echocardiogram
with a very modern echo machine.
Now, we don’t do this with stress, but occasionally,
we want to get a more elaborate picture of
the heart than we can get by putting the jelly
and the probe on the chest wall. We want to
get closer to the heart. It turns out we have
a little echo on the end of a catheter that
can be threaded down the throat behind the
heart in the esophagus. So, you can see that
the probe is right next to the heart and we
get exquisitely detailed images here. This
is not so much a stress test, but it’s more
a very detailed anatomical test.
I will just show you some examples. Here is
an echo in a patient with a large dilated,
poorly contracting heart that was done transthoracically.
And, of course, these are movies, so the heart’s
moving, you can actually see the motion of
the heart and the motion of the valves. During
this time, there are parts of this test where
we can see whether the valves are leaking
or whether they are stuck and so forth.
Here you can see the contrast between the
image you get with a transthoracic, that is
when you put the probe right on the chest
with some jelly as opposed to putting the
probe down the esophagus with a tube. You
can see, on the left, the transthoracic image
of the aortic valve and on the right, you
can see the transesophageal image - much more
detail, much clearer look at the aortic valve.
This is particularly useful if we think there’s
an infection on one of the heart valves. You
get a much better picture of the heart valve
when you use the transesophageal echo.
And we can even, in these days, we can do
three-dimensional echocardiography. And I
am going to show you an example of that in
By the way, here is a transesophageal echo
that shows a small blood clot in the heart.
And this patient would need to be on blood
thinners - anticoagulants, to prevent that
little blood clot from breaking off and going
to the brain and causing a stroke.
As promised, here is a three-dimensional colorized -
this is not the natural color. The computer
enters the color to show contrast of depth
and so forth. This is a three-dimensional
echocardiogram of the aortic valve. And you
can see that it’s quite detailed. We really…
It’s a really excellent picture.
Now, going back to the stress test, we can