00:01
So, let’s start talking then about the
drugs. The first class of drugs that I am
going to talk about are so-called “beta
blockers.” What do I mean by a “blocker”?
What’s a blocker? Well, it turns out that
on the surface of heart cells, as well as
other cells in the body, there are little,
let’s call them “keyholes”, in which
certain keys are fit which then result in
changes going on within the cell. So, let
me tell you one example. One example… example
would be adrenaline. Adrenaline is released
from nerve endings and it’s released from
the adrenal glands. We are going to talk
about that system in just a moment. But, it’s
important to realize that when adrenaline
plugs into the keyhole, into the receptor
on the cell membrane, it results in a number
of biochemical changes within that cell. And
those biochemical changes are not just restricted
to heart cells, but throughout the body, and
of course, that can lead to the side effects
or the complications that we just talked about.
So, why are beta blockers useful? Beta blockers
are useful because they decrease heart rate,
they decrease blood pressure and they decrease
heart contractility. And you are going to
see, what they do is they block some of the
actions of the autonomic nervous system.
Beta blockers were discovered by this man,
Dr. James Black, who was a chemist with Imperial
Chemistry Company in England in the 1960s.
01:36
And by the way, for discovering beta blockers,
he won the Nobel Prize in 1988.
01:43
So, what was the reason for developing beta
blockers? Well, I think most of you are aware
is that our entire circulatory system, our
digestive system, many of the organs in the
body are controlled by the brain. And one
of the ways that the brain controls things
is through something called the “autonomic
nervous system.” I like to call it the “automatic
nervous system.” It has two parts - a sort
of an accelerator system and a brake system.
02:13
The accelerator system, also called the “flight-or-fight
system”, is the sympathetic nervous system.
02:19
That’s the one that squeezes out adrenaline
when you are in a near car accident or when
you are threatened by somebody. It revs up
your blood pressure, it revs up your energy;
you are ready to flight or fight. Now, the
opposite effect occurs from the parasympathetic
nervous system. That’s when you eat a meal
and you feel a little sleepy and you lie back
and you relax. That nervous system increases the
digestive activities, which of course, are
the exact opposite of what you would want if
you were flying or fighting. You would want
to be revved up, not lying back, relaxing
and digesting. And these two nervous systems
interact constantly depending upon what you are
doing. If you are vigorously exercising,
you are going to be turning on the sympathetic
nervous system. If you are relaxing after
eating a large meal, you are going to be
turning off the sympathetic nervous system
and turning on the parasympathetic nervous
system. The parasympathetic nervous system
is also run through a very large nerve that
runs throughout the body called the “vagus
nerve”. And sometimes, it will actually
activate at a time where it drops blood pressure
and even can cause people to feel
lightheaded or faint. That’s a little excessive
activity by the parasympathetic nervous system.
Now, the excess activity on the part of the
vagus system or the parasympathetic system
can slow the heart. It can decrease the blood
pressure and it basically sets you up for
what we call a “vegetative state”, that
is for a digestive resting state. The sympathetic
nervous system, of course, does the opposite.
04:01
It revs you up, ready to fight or to flee
depending upon the circumstances. Raises your
blood pressure, increases your heart rate,
increases the pumping activity of the heart
and starts putting a lot more blood flow into
the muscles to get you ready to run away.
04:17
So, what do beta blockers do? Beta blockers
block the effect of the sympathetic nervous
system so that you can’t increase your heart
rate so much, you can’t increase your contractility,
you can't increase your blood pressure. Why
would that work in a patient with ischemic
heart disease, a patient with coronary artery
disease? Of course. Remember, we talked about
the imbalance between the demand on the heart
in terms of metabolic supply and the supply,
because of a blocked artery, there’s decreased
supply. So, what beta blockers do is by decreasing
the metabolic demand of the heart, they reestablish
the balance between cardiac demand and cardiac
nutritional supply - oxygen and nutrients.
They plug into the little receptors in the
heart that speed up the heart and when they
do that, they stop adrenaline from getting
into those receptors and therefore, the heart
rate doesn’t increase, even though the sympathetic
nervous system is pushing. Now, it turns out
that there have been three levels or three
classes of beta blockers. There are ones that
are a little more specific for the heart.
05:31
There are some that are a little less specific
for the heart, but more specific for the lung.
05:37
There are some that are a mixture of heart
and lung and then there are some that are
either a mixture for heart and lung, but also
dilate blood vessels and therefore, even accentuate
the drop in blood pressure. The first group,
β-1 receptor blockers are used for angina
and particularly also, for patients with
heart failure. Again, we are trying to assist
the heart a little bit by not making such
high demands on it. The β-2 receptor blockers
are used in a variety of ways also, sometimes
for heart disease, sometimes for arrhythmias
and sometimes for hypertension. And the β-3
group, the most recent ones, are used for
heart failure patients. Again, they decrease
the contractility of the heart, they decrease
the blood pressure, they decrease the work
of the heart so that a damaged heart can heal
a little bit. We are going to talk about
that some more in a moment.
06:33
I don’t expect you to read and memorize
this list, but here it shows you all of the
actions of the β-1 and the β-2 blockers.
As you can see, they have actions throughout
the body - on blood vessels, on the heart,
on the lungs. And of course, what this means
is, it gives you potential for complications.
Let’s say we have a patient with high blood
pressure and angina - that is the feeling of
chest discomfort when there’s an imbalance
between blood supply and blood demand. We
put the patient on beta blocker. But, we forgot
the patient has a history of asthma in the
past. When we block the β-2 in the lung,
we make their asthma worse. So, we did something
good for the heart, but we did something bad
for the lungs. So again, this list shows you
all the different effects of beta blockers
throughout the body and a lot of them are
potential sources for complications.
07:31
Here, in a little diagram, you see what I
just said. In the top arrow, you can see the
β-1 or heart-blocking effects - reduces contractility,
reduces blood pressure, makes the work of
the heart less. You can also see, in the second
little drawing, the lungs. If there’s β-2
effects, you may increase the bronchial constriction,
that is the constriction of the small tubes
in the lung that lead to asthma. And then
you can see, down below, the beta blockers
that dilate the blood vessels are particularly
good for heart failure.
08:08
Now, let’s think for a second about the
potential of the non-specific beta blockers,
the one that block both β-1 and β-2. These
are the ones that have the greatest potential
for causing lung side effects when given for
the heart. But, it turns out that selectivity
of β-1 and β-2, I call it “semi-selectivity.”
Because if you take a β-1 selective blocker
and you give it at a very low dose, it’s
going to mostly block the beta receptors in
the heart. But, if you need to push the dose
even into moderate levels, there’s some
spillover onto β-2. So, even if you are giving
a β-1 blocker to a patient with heart disease
for angina or for hypertension or for heart
failure and that patient has a tendency to
develop asthma. When you push the dose of
that beta blocker into a reasonable range,
you may well worsen their asthma. And almost
the only way to find that out is to try it
and see what happens, particularly if you
have a real need for that beta blocker. And
the same thing is true, sometimes we give
β-2 stimulants to improve lung function by
dilating the bronchioles and sometimes that
results in cardiac arrhythmias because of
spillover in the β-1 area. So, again, all
of these drugs are not perfectly selective,
they have effects throughout the body. And
again, this relates to the art of using these
drugs because of their potential for effects
in other parts of the body.
09:42
This complex diagram right here shows you
all the effects of beta blockers on the heart.
09:50
I’m not going to spend a lot of time talking
about it. You’re welcome to look at it at
great detail on your own, but you can see
what happens in the heart with beta blockers.
10:00
They decrease contractility, they decrease
the heart rate, they help to prevent certain
kinds of electrical short circuits - cardiac
arrhythmias. We are going to talk about that
later, particularly atrial fibrillation. In
a sense, they quiet the heart down in a number
of ways. They improve the metabolic balance,
right, the demand-supply relationship within
the heart that stabilizes the situation in
patients with ischemic heart disease. It helps
patients who are hypertensive, that is have
too high blood pressure, gets them back down
into a more normal range. And it generally
quiets down the heart. Particularly some individuals
are prone to markedly increase their heart
rate even with small disturbances and beta
blockers also are very, very useful in helping
in that regard.
10:51
Here you see a summary of the full spectrum
of cardiovascular effects of the beta blockers
and their indications. Beta blockers are particularly
useful for angina or for ischemic heart disease,
for heart failure. Actually, we have seen
sometimes hearts improve when patients have
been treated with beta blockers for heart
failure, and also for hypertension, all very
effective and then a little less effective
for controlling arrhythmias and some of the
other problems. But, because angina and heart
failure are so common, we use a lot of beta
blockers. Fortunately, almost all of them
now are generic, so they are relatively inexpensive
and usually in moderate doses, they are well
tolerated. When you start to push the doses
up, you increase the risk for effects in other
organ systems and you increase the risk for complications.
11:47
So, let’s talk a little bit about the mechanism
of benefit of beta blockers in ischemic heart
disease - that is hardening of the arteries
with blockage of blood flow into the heart
muscle. Well, what we are trying to do is
rebalance the situation, right? We can try
and improve blood flow down the coronary arteries.
12:07
We will talk about a strategy to do that in
a moment. But, the most important effect is
to try and decrease the demand of the heart
for oxygen and nutrients. We do that by dropping
the heart rate, by dropping the blood pressure
and by dropping contractility. So this is...
12:24
all three mechanisms work in the patient with
ischemic heart disease and very often a patient
who has angina with normal activity. For example,
let’s say, climbing a flight of stairs.
12:35
Oh, they get chest discomfort. When we give
them beta blockers, their heart rate doesn’t
accelerate as much when they go up the stairs,
their blood pressure doesn’t rise as much
and they don’t have angina now when they
go up the stairs. And that’s the goal, as
you will see when we talk about ischemic heart
disease. We want patients who don’t have
symptoms, who can lead a normal active life
as long as they are not trying to race up
and down stairs, but that they can do normal
daily activities without having angina.
13:01
Again, here you see a slide, quite complex,
listing all of the beneficial effects, and
some of the potential non-beneficial effects,
of beta blocker in a patient with ischemic
heart disease. You see the heart rate is down,
the blood pressure is down. Unfortunately,
what happens is sometimes, because of the
decreased contractility, the heart may dilate
a little bit and that has a tendency to increase
myocardial oxygen consumption or myocardial
oxygen demand for nutrients and oxygen. But,
that’s a minor player in comparison to the
decreases in the demand that you get from
lowering heart rate and lowering blood pressure.
13:42
So, again, you might want to peruse this slide
in a little more detail at your leisure and
of course, you can also read further about
this in all the standard textbooks of cardiology
and some of the references which we give at
the end of this lecture.
13:57
Now, what about the so-called “anti-arrhythmic”
effects of beta blockers? We haven’t talked
a lot about arrhythmias. Remember, I showed
you the cardiogram with the P wave, the QRS
and the T; P wave being the atrial depolarization,
the electrical depolarization; the QRS being
the ventricular one. And that’s the normal
sequence of electrical activity passing through
the heart. It turns out, particularly in older
individuals and even occasionally in some
younger individuals, you can have electrical...
what I call “electrical short circuits”,
in which suddenly the heart will start to
race or there will be abnormal activity in
the atria, so you will lose the P wave and
the heart will race in a… in a very abnormal
way. Remember, I showed you an electrocardiogram
of a patient in atrial fibrillation. Instead
of the nice, regular “lub-dub, lub-dub,
lub-dub,” what you had was (fast and inconsistent
heart sounds) and of course, when that happens,
the heart could be going as fast as 150 beats
per minute. Even people with normal hearts
will feel uncomfortable with that and especially
individuals who have a lack of blood flow,
getting… normal blood flow getting into
the heart because of coronary artery disease.
When you increase the heart rate like that,
it’s very likely that they will develop
an imbalance in the supply-demand relationship,
angina, and they might even have a small heart
attack. So, we try and also control the…
the arrhythmias, these atrial arrhythmias,
and also some ventricular arrhythmias and
beta blockers often help with that. For example,
early on in the phase of a heart attack - a
myocardial infarction, the administration
of beta blockers decreases the chance that
the patient will have a cardiac arrest. We are
going to talk a lot about arrhythmias in a
total unit where we talk about diseases of
the heart and I’ll also be talking about
some therapy at that time. But, it’s important
for you to realize that the beta blockers
not only help to control the supply–demand
imbalance in the heart with ischemic heart
disease, not only can they help with high
blood pressure, but they also can help control
arrhythmias. They are not a powerful controller
of arrhythmia, but they are much more benign
than many of the other drugs that we use that
have a lot of side effects. More about that
in a later lecture.
Let’s talk about heart failure. This is
a revolution that’s occurred in the last
15 to 20 years. When I was in training, we
were told, “Don’t ever give a beta blocker
to a patient with heart failure because it
depresses the contractility - the 'oomph' of
the ventricle, and you are going to make the
heart failure worse.” Well, it turned out
that in Sweden, the doctors weren’t so convinced
that beta blockers were a bad idea and they
did a series of large clinical trials in which
they demonstrated that actually, early on
in heart failure, the beta blockers might
have made things a little worse. But long-term,
many of the hearts remarkably improved. Well,
this was a revolutionary thought. Something
I had been taught in medical school and training,
“Don’t ever give a beta blocker to a patient
with heart failure!”, was now the exact opposite,
“You better be sure and give a beta blocker
to a patient with heart failure.” So, what
was the benefit there? Well, there were several
benefits. First of all, again, even if the
heart failure wasn’t due to ischemic heart
disease - to lack of blood flow in the heart,
but was due to sick heart cells. By decreasing
the work of the heart, decreasing the heart
rate, decreasing the blood pressure, you actually
allowed some of those heart cells to recover.
17:30
In addition, by blocking the beta receptors
on the surface of these heart cells - the myocardial
cells, it actually caused the cells to produce
more beta receptors and then there was effect
from the adrenaline hitting those beta receptors
that increased the contractility of the heart
when this was done long term. And of course,
then, there was a decrease in arrhythmias
as well. All that put together, beta blockers
turned out to be a huge benefit in heart failure
patients. And recently, over the last 10 to
15 years, the beta blockers that also dilate
blood vessels and therefore, lower the blood
pressure have been shown to be the best beta
blockers for patients with heart failure.
I can tell you, and when I saw this the first
time, I thought, “I made a mistake.” A
patient that had terrible heart function,
six months later had normal heart function
after being put on beta blockers. When this
happened, I said to myself, “I must have
misremembered. I must have made a mistake.
18:32
It couldn’t have been that the heart function
was that bad early on and now became normal.”
When we checked back, it turned out I was
absolutely right. The heart failure state
had been associated with bad left ventricular
function initially and it became normal after
six months. And I’ve now seen that happen
a number of times in a number of patients.
18:51
Of course, the patients and their families
are ecstatically happy when this happens,
but even in people who don’t totally normalize,
there’s often an improvement in heart function
with beta blockers. It’s the most important
advance in heart failure therapy in the history of cardiology.
19:07
In patients with heart
failure,
data blockers are not used globally
but are part of the initial therapy
for most patients with heart failure
with a reduced ejection
fraction, less than 50% HFrEF.
19:20
Beta blockers are not recommended
as part of the primary therapy for heart
failure with a preserved ejection
fraction of 50% so-called HFpEF.
19:29
Trials have been done
and they have not been effective.
19:33
Unfortunately, they're very good
for HFrEF not good for HFpEF.
19:37
And the same is true for the angiotensin
renin blockers on ACE inhibitors and RB.
19:44
They have been shown
not to be helpful in patients with HFpEF.
19:49
You know,
they can occasionally be used in HFpEF
to help treat angina or hypertension
but they're but it's just HFpEF. alone.
19:59
They're not shown to be beneficial.
20:02
And in fact, if you look at Eugene Braunwald,
who is probably the number one cardiologist
in the world and one of my mentors and teachers,
if you look in his textbook, he says, “Beta
blockers are first choice, of course, for
heart failure, of course, for ischemic heart
disease, and for hypertension and arrhythmias
as well.” Although hypertension and arrhythmias,
they are sort of in second place. But, for
angina and heart failure, they are number one.