Cardiac Glycosides: Inotropic, Chronotropic, Dromotropic

In our previous lectures, we have started discussing the different types of drugs used for heart failure or other heart-related conditions, namely: inotropic, chronotropic, and dromotropic. A quick way to remember these drugs is to categorize them into A, B, C, D, and E. Since we’ve already discussed A and B, we’ll focus on the C.

The “C” stands for two things: calcium-channel blockers and cardiac glycosides. Calcium channel blockers are anti-hypertensive drugs, while cardiac glycosides (Digoxin) are mainly utilized for heart failure, atrial fibrillation, and atrial flutter.

Digoxin

Digoxin is an inotropic drug that helps the heart contract forcefully. On the other hand, digoxin is also a negative chronotropic drug.

To elaborate further, digoxin is an inotropic drug because it causes the forceful contraction to help the atriums squeeze out blood efficiently. Think of digoxin as the force that is used to squeeze the last portions of ketchup out of the bottle. Due to the atrial kick caused by digoxin, heart rate decreases.

Why would you want to decrease the heart rate?

In cases of atrial fibrillation, there is increased excitability from pacemaker cells inside the atrium. The SA node does its best to control the rhythm; however, there will be times when the SA node breaks down due to drug toxicity or hypoxia. Therefore, increased electrical impulses coming from the atrium happens. To keep this from happening, digoxin is given to help facilitate smoother contractions.

Digoxin as a Dromotropic

Digoxin as a dromotropic drug causes diminished impulses from the AV node. Therefore, digoxin brings down electrical conductivity which leads to atriums to contract adequately.

Digoxin Administration Prerequisites

There are a few important things that you must consider when handling a client taking digoxin.

First, you have to monitor the client’s apical heart rate closely. This is done by using a stethoscope to listen to the heart rate between the fourth and fifth intercostal space for a whole minute. This is process is important and is a prerequisite to making sure that the client is stable before giving the drug.

Second, if the client is on digoxin treatment, there is a high chance that the client is also taking a warfarin-type of anticoagulant to make sure that blood clots are not formed inside the heart, especially in cases of atrial fibrillation.

The Apical Heart Rate

As stated, an important prerequisite is to make sure that the apical heart rate is monitored to prevent digoxin toxicity. Remember, digoxin’s therapeutic level is between 0.8 and two (2) ng/mL.

How does digoxin toxicity occur?

When a client with heart failure is taking loop diuretics like furosemide (Lasix), which is a potassium-wasting drug, this technically means that the client is losing potassium from the body. Anytime potassium levels in the body go down, while the client is taking digoxin, there is an increased chance that the client will experience digoxin toxicity.

NCLEX® Sample Question

When assessing a client for digoxin toxicity, you noted that the level is between 1.5 and 1.9 ng/mL. Would you still give digoxin?

Answer: Yes.

If the client’s digoxin level is still within its therapeutic level (0.8 – 2 ng/mL), you can still give digoxin because it has not reached toxicity level yet.

Just remember that you have to check the potassium levels, apical heart rate, and heart rhythm on the monitor to assess if it’s safe to give the cardiac glycoside, digoxin.

In our next lecture, we’ll be discussing calcium-channel blockers as a hypertensive medication.

Cardiac Glycosides: Inotropic, Chronotropic, and Dromotropic Drugs

In your NCLEX® reviews, one of the most common discussions that you’ll encounter is cardiac glycosides.

So, what are cardiac glycosides? What are the different types of cardiac glycosides? How are these types of cardiac glycosides distinctive from one another?

When we talk about cardiac glycosides, we are mainly referring to your heart’s vascular perfusion. Now, when remembering the different types of cardiac glycosides, you have to remember this: I Know! Sax 5th Avenue. This mnemonic will help you easily recall crucial details of our cardiac glycoside review.

The different types of cardiac glycosides are:

  1. Inotropic
  2. Chronotropic
  3. Dromotropic

As mentioned, these can be remembered by the mnemonic: I Know! Sax 5th Avenue. If asked, there are actually five major classifications of your inotropic, chronotropic, and dromotropic drugs (A, B, C, D, and E). You can remember that because of the “5th” in your mnemonic. We will be discussing what these five classifications are later on; but first, let’s focus on your inotropic drugs.

Inotropic Drugs

Inotropic simply means that there is the presence of forceful heart contraction. If you administer an inotropic drug to your client, it primarily means that you wanted the heart to contract forcefully.

In your mnemonic, your inotropic drugs stand for “I Know!” Since Mike is Puerto Rican, he would remember “I Know!” being forcefully uttered by his aunt who wanted to make a strong point of knowing something. Therefore:

            Inotropic = forceful heart contraction = I Know!

But why would we want your heart to contract forcefully?

Due to conditions like atrial fibrillation, wherein the atriums are not adequately contracting due to fibrillation or what is also known as arrhythmia (irregular heartbeat).

If you would review the three processes or steps that the atriums contract, one of which would be the filling phase.

In your filling phase, there’s the rapid, moderate and atrial kick. During the atrial kick, that’s when excess blood flows down into the ventricles and is the time when your valves are supposed to close. With atrial fibrillation, this atrial kick is weak which is why an inotropic drug is necessary to ignite forceful contraction.

The most popular inotropic drug is Digoxin. Apart from being an inotropic drug, Digoxin is also a negative chronotropic drug. So, what are negative chronotropic drugs?

            Inotropic drug = Digoxin

Negative Chronotropic Drugs

Going back to our mnemonic, after I Know!, we have SAX. How can you relate negative chronotropic drugs to the SAX mnemonic?

Chronotropic is basically the rate of contraction that’s primarily concerning the SA node. So, SAX mainly stands for SA node and the number of times (X) it’s contracting, thus SA + X.

            Chronotropic drugs = SA node + number of times (X) the heart contracts = SAX

The scenario for this is when the heart is increasingly contracting, either due to heart failure, hypertension, or whatever state that the heart is experiencing for as long as it’s contracting too many times, negative chronotropic drugs are given.

Another way to remember chronotropic drugs as “the number of times a heart contracts,” is by basing it on the Greek word “Chronos” that means time.

Negative chronotropic drugs consist of the following:

  • Beta-blockers – drugs ending in “lol” like Metoprolol or Atenolol
  • Calcium channel blockers– drugs ending in “pine” or “zem,” like Cardizem
  • Antidysrhythmic drugs – Amiodarone

On our next discussion, we will be focusing on dromotropic drugs and calcium channel blockers.

See you there!