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!