0:00

I'm going to talk about medications

0:03

we give in cardiac CT imaging.

0:06

As radiologists, we're used to giving one medication,

0:09

which is iodinated contrast, and of course gadolinium.

0:14

We're not used to giving cardiac medication,

0:16

which sometimes induces fear in us,

0:18

but I want to keep this very simple.

0:22

And so, not to overwhelm you with cardiac pharmacology,

0:27

which, quite honestly, I have forgotten from my

0:29

medical school days, but mostly to tell you about

0:32

a couple of medications we give quite often.

0:34

The first is metoprolol, which is a beta blocker.

0:38

It's a short- to intermediate-acting beta

0:41

blocker that can be given orally or intravenously.

0:45

Oral is the preferred method and the

0:49

guidelines that we use are weight-based.

0:53

Weight-based is not perfect but

0:54

it's still a good heuristic to use.

0:57

Anybody less than 40 pounds gets

0:59

50 milligrams initially of oral.

1:02

Remember, not intravenous, oral.

1:04

Intravenous doses are much lower.

1:05

140 to 160 pounds, they get 75 milligrams

1:09

and 160 pounds, they get 100 milligrams.

1:12

So who gets them?

1:13

Why do they get them?

1:14

So we give the medication to people who have

1:16

heart rates that are greater than 70 beats

1:20

per minute, and there's nothing wrong with

1:23

a heart rate of 70 or 75 beats per minute.

1:25

We just want to get it to lower than 70 beats

1:27

per minute, so that we get an optimal scan.

1:33

So, a lower heart rate is like taking a

1:36

picture of a tree on a moving train,

1:39

and you can imagine that the picture is

1:42

much better when the train is moving slower.

1:45

So, in a sense, we're trying to

1:46

lower the speed of the train.

1:48

The shutter speed, temporal

1:49

resolution, metoprolol, doesn't affect.

1:53

Those are other concepts which

1:54

we will discuss later on.

1:56

So metoprolol is the first-line drug

2:00

and probably the most common drug.

2:02

I would say probably the only drug we should be using.

2:05

If you need to use anything more than that, then

2:08

it's probably best to involve cardiologists.

2:12

I use it if the heart rate is greater than 70.

2:16

And after giving the medication, I have the techs

2:19

check the heart rate in about 20 to 25 minutes.

2:23

And I repeat it

2:25

to a maximum of 150, 200 milligrams

2:28

to get the heart rate less than 70.

2:30

If it's going in the right direction, if it

2:32

starts off, let's say 110 and you're at 75,

2:35

that means it's trending in the right direction.

2:38

Sometimes it just doesn't budge and you

2:41

just have to make a call at that point,

2:42

whether you want to do the scan or not.

2:45

So metoprolol has contraindications, and these

2:52

are cardiac drugs that we're talking about.

2:54

But before I go into that, I'll

2:55

talk about the intravenous method.

2:57

The intravenous method is shorter-

2:59

lasting than the oral method.

3:00

So the oral method should be overwhelmingly

3:04

more preferred than the intravenous.

3:06

And you should never rush these studies.

3:08

These studies should take, should be done,

3:11

without being rushed, because if you rush them,

3:14

then you can get a poor-quality result with intravenous.

3:16

You want to give two and a half milligrams

3:17

every minute to a maximum of 15 milligrams.

3:20

Some might push it to 20, but

3:21

certainly not more than 20.

3:23

You want to check the blood pressure continuously

3:27

because it's an intravenous medication, and you

3:29

want to check the heart rate every five minutes.

3:31

But it's not a course I would recommend,

3:34

I would recommend almost always the oral method.

3:38

So what are the contraindications?

3:40

So it's a beta blocker, so, um, one of the

3:42

contraindications is that if the patient has asthma,

3:46

because, as you know, the beta receptors are present

3:51

also in other smooth muscles, such as in the airway.

3:55

Asthma gets a bit tricky because a lot of people

3:57

are on inhalers, but they're not really asthmatic.

4:01

They might have taken an inhaler 10 years

4:02

ago and then been given a diagnosis of asthma.

4:04

So you have to use your clinical judgment there.

4:06

So, um, the way to kind of understand the

4:10

significance of the asthma, the first thing

4:12

to ask is, have you ever been admitted to a machine?

4:14

in the intensive care unit with

4:16

an attack of status asthmaticus.

4:18

If that's the answer, then

4:19

yes, it's clearly contraindicated.

4:21

If they take inhalers daily for

4:25

symptom relief, it's contraindicated.

4:28

If they've been given a diagnosis of asthma,

4:30

but you also notice that they're on oral

4:31

metoprolol for heart failure or whatever, then

4:34

of course it's not contraindicated by logic.

4:38

Hypertension, of course, so

4:39

always check the blood pressure.

4:41

So we do this for patients who have heart rates greater

4:44

than 70, but anybody who has a heart rate that is, you

4:49

know, bradycardic, obviously they don't need the

4:51

metoprolol, but it's also a contraindication to it.

4:54

So it's kind of a moot point, but it's a

4:55

contraindication, so you might see somebody with

4:57

heart rates running at 50 to 60 beats per minute with

5:00

a diagnosis of second or third degree heart block.

5:02

Clearly contraindicated and clearly not necessary.

5:05

Pregnancy.

5:07

Tend to avoid aortic stenosis is one of those,

5:10

uh, funny ones where, you know, uh, if it's

5:13

very severe and you lower the blood pressure,

5:15

you can precipitate a hypertensive attack

5:19

because the aortic valve is static as well.

5:23

So, you know, anybody with complex cardiac

5:26

conditions that you're not sure of, just avoid.

5:28

I mean, there's a whole lot of them.

5:29

There are fancy arrhythmias like Wolf-Parkinson-White

5:33

and you can just go through a whole list and

5:35

just the important thing is that you keep it simple.

5:39

People who don't have

5:40

coexisting cardiac disease and

5:42

are generally fit and well.

5:44

There are alternatives, but if you're at that point,

5:47

then you ought to get cardiology consultation for that.

5:53

The other drug we give is nitroglycerin, and we

5:55

give this drug because it's a vasodilator, and the

5:59

idea is that you vasodilate the coronary arteries,

6:03

making them slightly bigger. That slightly works.

6:07

When you make them slightly bigger,

6:09

then it's much easier to see narrowing.

6:11

It's a theoretical advantage.

6:13

It hasn't really been rigorously tested,

6:15

but everybody attests to its greatness.

6:19

So we give the nitroglycerin one

6:22

tablet sublingually under the tongue

6:27

around the time that you start the scan.

6:29

So, the major thing you need to warn the patient

6:33

about is that they can get a headache from it.

6:36

So that's not a catastrophic side

6:42

effect, but it's a very common one and an annoying one.

6:44

So it's best to warn them about that.

6:47

In terms of contraindication, if they are

6:50

on phosphodiesterase inhibitors, better

6:53

known as Viagra, and its, uh, alternatives.

6:57

And yes, remember, it's not just men with

6:59

erectile dysfunction who are on Viagra.

7:01

People with pulmonary hypertension are often on it.

7:04

So you have to be, you know, you have to be careful.

7:07

Avoiding the, I don't want to stereotype type

7:10

of bias, so ask everybody, are you on this or

7:12

not, and remember there are derivatives of that.

7:14

The problem with phosphodiesterase inhibitors

7:16

is that they work also on the same kind of

7:21

mechanism as the nitrates, except they work on

7:24

a different path, so the two are synergistic.

7:29

It's not the same path, they're

7:30

different paths and they add up.

7:32

So you can get very profound hypertension.

7:34

And if you do get that, you will need to, um, get the

7:38

patient lying down with the legs up and, um, with, uh,

7:42

intravenous saline, but you've got to keep this simple.

7:45

Yeah.

7:45

You're, you know, you're a radiologist, you're not cardiologists.

7:46

172 00:07:48,985 --> 00:07:52,295 So, um, keep these medications are overwhelmingly

7:52

safe in people that don't have contraindication.

7:55

So anytime you have any doubts, avoid them.

7:59

Thank you.