Cardiac Glycosides: Inotropic, Chronotropic, and Dromotropic Drugs
One of the most common nursing discussions you’ll encounter is cardiac glycosides – particularly of the inotropic, chronotropic, and dromotropic types.
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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 mainly refer 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.
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.
Inotropic vs Chronotropic Drugs
Inotropic drugs increase the strength of the heart’s contractions, resulting in increased cardiac output. They work by altering the calcium levels within the cardiac cells, which leads to an increased force of contraction.
Inotropic drugs include digoxin, dobutamine, and milrinone. These drugs are used to treat heart failure, cardiogenic shock, and certain arrhythmias.
Chronotropic drugs affect the heart rate. They increase or decrease the heart rate by altering the electrical impulses that regulate the heart’s rhythm. These drugs are used to treat conditions such as hypertension, angina, and arrhythmias.
Inotropic Drugs
Inotropic simply means modifying the force of contractions of the heart.
Inotropes are drugs that tell your heart muscles to beat or contract with more power or less power, depending on whether it’s a positive or negative inotrope.
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 the heart to contract forcefully?
Such as in conditions like atrial fibrillation, where the atria 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?
There’s the rapid, moderate, and atrial kick in the filling phase. During the atrial kick, excess blood flows down into the ventricles, and is when the valves are supposed to close. This atrial kick is weak with atrial fibrillation, so an inotropic drug is necessary to ignite forceful contraction.
The most popular inotropic drug is Digoxin. It’s 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 the rate of contraction 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 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,” which 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
Dromotropic Drugs
Dromotropic drugs affect the speed at which the electrical impulses travel through the heart, and the degree to which they are delayed or accelerated.
Dromotropic drugs can be further divided into two categories: positive and negative dromotropic drugs. Positive dromotropic drugs, such as epinephrine, increase the speed of electrical conduction in the heart, while negative dromotropic drugs, such as beta-blockers, slow down electrical conduction.
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