Now, let’s move now from the Statin drugs,
let’s talk about anti-coagulants. As you
probably already are aware, many of the cardiovascular
events that occur with atherosclerosis are
the result of blood clots that form over the
atherosclerotic lesions. When a blood clot
forms in the heart, it causes a myocardial
infarct or heart attack. When a blood clot
forms in the arteries to the brain, it causes
a stroke. And so, one part of the treatment
of these diseases is an attempt to dissolve
the blood clots and a second part is to keep
the blood clots from forming.
We have a variety of drugs that block the
clotting system. The first group are known
as anti-thrombotics. They are very powerful
anti-coagulants. At least one of them - heparin,
can be given intravenously. Many of them can
be given as subcutaneous injections and some
can be given as oral agents. That’s the
second category on this slide, the oral anti-thrombotics.
The oral anti-thrombotics have a similar very
powerful anti-coagulant or blood thinning
effect, often as powerful, for example, as
heparin. The commonly used one is warfarin.
Warfarin blocks a number of the clotting factors
in the clotting cascade - factors II, VII,
IX and X. It’s a very, very effective anti-coagulant.
And then there are some new agents, factor
X blockers and factor II blockers that, in
many ways, are a little more effective than
warfarin because they are little more easily
controlled and there’s a little less bleeding.
Yes, let’s talk about bleeding. Anytime
you thin the blood… what’s the risk for
the major side effect? Bleeding. And sometimes,
that bleeding can be fatal. So, we cardiologists,
we would like to use these drugs, but we use
them very, very carefully. I always think
of them just like firearms, just like guns.
They are useful under some circumstances,
but you have to be very careful with them
and you have to know what you are doing when
you use them.
So, when do we use heparin or two of the others,
fondaparinux or agratropin? We usually use
intravenous heparin in the earliest or acute
phase of a heart attack. When we have done
something to remove the blood clot, either
with drugs, thrombolytic drugs or with angioplasty -
the little balloon catheters and stents that
are used to open up the artery and pull the
blood clot that’s formed in the artery out.
And what we do is we put patients on heparin
for a little while to prevent the blood clot
form reforming. Of course, that would start
the injury to the heart muscle all over again.
Once we are finished with our short course
of heparin, usually and often in these patients,
a stent has been placed - the little wire cage.
We are going to talk a lot more about that
when we talk about coronary artery disease
later in this series. We then put the patients
on anti-platelet agents.
Platelets are the first step in the clotting
cascade. So, when you cut yourself, what happens
is, eventually a little blood clot forms and
a little scab forms, right? Well, the first
step in that is activation of little bodies
that float throughout the bloodstream called
platelets. When they see an injury like that,
they become activated. They release a number
of chemicals that then start a whole series
of chemical reactions that end up in the blood
So, why do we put people on anti-platelet
agents? It’s to prevent blood clots from
forming both on top of a new stent or even
chronically in somebody who already has atherosclerotic
coronary artery disease. Interestingly enough,
the commonest anti-platelet agent is aspirin.
You may have noticed if you cut… if you have
taken some aspirin, let’s say for a headache
and you cut yourself, it takes you a much
longer time to stop bleeding once you are
The commonly used ones are clopidogrel, prasugrel
and ticagrelor and these have been approved
in the United States and also in Europe. They are
used after stents and… and various procedures
in the coronary arteries have been done. They
are used long term in people who are at high
risk for forming blood clots.
The oral anti-coagulants are used to prevent
clots that can form inside the heart, particularly
with an arrhythmia known as atrial fibrillation.
In a few moments, I am going to talk about
that some more, but atrial fibrillation is
an irregular heart beat in which the atria
of the heart, instead of beating nice and
regularly like this, fibrillate, they quiver.
And in that quivering state, blood clots can
form within the left atrium. They can get
out of the left atrium into the circulation
and go to the brain and cause strokes, go
to the kidney and cause kidney damage and
so forth. So, a lot of bad things can happen
with the blood clots when they form in atrial
fibrillation. And it’s been shown that with
blood thinners, with anti-coagulants, oral
anti-coagulants, we can markedly decrease
the risk for these blood clots forming in
the heart and getting out.
Warfarin has been the gold standard for a
long time. It’s a drug that’s… that
is much more complicated to deal with than
some of the newer agents. It requires constant
blood tests, it requires changes in diet and
it is associated with more bleeding, particularly
bleeding in the brain, which is as you can
imagine the worst possible place to bleed.
And that’s why new agents have been developed.
The factor Xa blockers, there are now three
of them approved in the United States - rivaroxaban,
apixaban and edoxaban. And then there’s
a factor II blocker, only one there, that’s
dabigatran. And each of these agents are approximately
equal in efficacy. They are just as good as
or maybe a little better than warfarin and
they are associated with a little less brain
Well, let’s talk a little bit about the
atherosclerotic process itself. We are going
to come back to talk about this again, but
remember that inflammation is the factor that
starts the whole injury in the arteries that
then leads downstream to atherosclerosis.
It’s felt that what happens is the endothelium
which is the small skin on… lining the arteries
is injured by a variety of things. Maybe a
viral infection, maybe cigarette toxins - toxic
things that are in cigarette smoke, maybe
high blood pressure, but once there’s a
little injury to the endothelium, it becomes
then more permeable to substances in the blood.
Guess what... which one gets in? Cholesterol.
When cholesterol gets in onto the endothelium,
it sets off an inflammatory reaction. Just
like a mosquito bite, for example, is an inflammatory
reaction. Inflammatory cells and inflammatory
chemicals are released by the body, that’s
what makes it itch and you scratch at it.
Well, of course, you can’t scratch the inside
of your coronary artery, but the same inflammation
process starts there and unfortunately, cholesterol
is a very potent stimulus for inflammation.
And once it gets started, it doesn’t stop.
And consequently, once it keeps going, more
cholesterol is able to get in there. There’s
more inflammation. Eventually, you end up
with an atherosclerotic plaque. These can
be very large or they can be small. Sometimes
the small ones are very friable or very tender
and they can break and suddenly, that sets
off the clotting cascade and a blood clot
forms and the artery is blocked.
Now, here is an anatomical picture from somebody
who died, not from a heart attack, but from
something else. But you can see, it’s a
cross section of a coronary artery and you
can see at the bottom there, there is a little
collection, sort of looks like a cottage cheese.
That’s cholesterol in a large atherosclerotic
The good news is in this patient, you can
see that the channel, which is the black area,
is still open. So, there’s plenty of blood
flow going down there, but what can happen
is, the little cap - the little endothelial
cap that’s covering that cholesterol can
crack or break exposing the bloodstream to
the underlying cholesterol and a blood clot
can form and here we see an example.
You can see that there has been a little bit
of the endothelium peeled off into the lumen,
and that black substance is not an open channel.
It’s a blood clot in this patient who had
a fatal myocardial infarction, a fatal heart
attack from the blockage of the artery by
the blood clot.
Now, as we talked about before, when a patient
has a myocardial infarct or often when they
have a stroke and we get rid of the blood
clot, either mechanically or with drugs, we
then put the patient on heparin for a while.
We can give that intravenously and for a few
days or it can be given subcutaneously with
injections. Usually, for myocardial infarction,
we don’t put patients on the long term chronic
agents like warfarin or the newer agents I
talked about - rivaroxaban, apixaban and edoxaban.
Why not? Because the data has not shown that
long term treatment with those agents prevents
a second heart attack.
In fact, it turns out that the data from the
randomized controlled… double-blind controlled
trials show that the anti-platelet agents
are more effective. It is true that the anti-coagulants
like warfarin and rivaroxaban and so forth
do prevent blood clots, but they increase
bleeding, sometimes with fatal bleeding, so
you end up with no benefit. Whereas the platelet
agents have much less problem with bleeding.
And so, therefore, even though they are not
quite as effective at decreasing clots, they
are much safer. So, you end up with a positive
benefit in the end using the anti-platelet
agents. And they are all so much easier to
use, of course, because they can be taken
Now, let’s talk then about evidence based
medicine in other things for… other aspects
of evidenced based medicine for the patient
with coronary artery disease or strokes.
First of all, we have already of course,
talked about the Statins. We also usually
put these patients on aspirin. If they have
had a stent placed or a procedure done in
their coronary arteries, even coronary bypass,
they may end up on a double program of anti-platelet
agents. that is aspirin plus clopidogrel or
one of the newer anti-platelet agents - prasugrel
Stroke patients sometimes end up on aspirin
and dipyridamole, that’s another combination
that works as anti-platelet. And the newest
agents - prasugrel and ticagrelor are slightly
more effective than the older agent clopidogrel
when combined with aspirin, but maybe associated
with more bleeding. And that’s not a surprise,
of course, because the more effective any
anti-coagulant is, the more likely you are
to see bleeding complications.
Let’s talk for a few minutes about arrhythmias.