Effects of Calcium Channel Blockers as Negative Chronotropic Drugs

When someone says “calcium channel blockers,” the first impression that would come to mind is that it blocks the channels responsible for calcium absorption. Yes, that’s what calcium channel blockers primarily do. But the question now is, how and why?

Before we dig deeper into calcium channel blockers, here’s a quick trivia question related to cardiac glycoside medications. One of the biggest questions that usually appear on nursing exams is:

Q: A client comes in complaining seeing halos, mostly green halos, what is the client experiencing and what is the nursing intervention?

A: Digitalis or Furosemide toxicity, monitor potassium.

This is especially a common inquiry on cardiac tests. Nurses need to monitor potassium for heart failure clients on Lasix, Furosemide, or other loop diuretics that wastes potassium.

So, that’s a bit of a refresher question that you should remember.

Now, let’s go into your calcium channel blockers.

The Cellular Channel

One should understand that calcium channel blockers act directly on the channels of the cells.

So, what are these cellular channels? If you wish to know more about the basics structure of the cell in a simplified manner, simplenursing.com has a video of Mike explaining the cells effortlessly, comparing it to a city that has the following structures:

• The gates (channels)
• A city hall (nucleus)
• Bills and laws (DNA and RNA)
• A post office (Golgi apparatus)
• Power plants (mitochondria)
• Trashmen (lysosomes)

Check that video out; it takes the stress off of memorizing the cellular structure and just have some fun working through the cell.

Calcium Channels

The cell’s city gates have channels, these channels are primarily responsible for letting things inside the cells and one of which is calcium.

Calcium is not bad for the body, especially the heart. However, if the client has hypertension, that’s when increased calcium consumption becomes dangerous since calcium is an electrolyte that causes electrical excitability or the state of being excited. So, calcium causes muscle spasms or constrictions.

That’s when calcium channel blockers come in – to block the channels so calcium won’t enter the cells and preventing spasms from occurring.

Calcium and Hypertension

On application, we can make sense of calcium by thinking about what calcium does to the body. The calcium deposits of the bones contribute to its hardened structures. Therefore, if you have increased calcium in your cells, the blood vessels become hard, and if that happens, the heart compensates by increasing the pressure to push on the hardening vessels. This is the reason why we need to block calcium from entering the cells – to soften the vessels and decrease hypertension.

So, calcium channel blockers:

• Do not cause a force on the heart
• Is a negative chronotropic drug – decreases the rate of contraction
• Causes decreased cardiac output
• Ceases arterial spasms (softening things up)
• Causes vasodilation
• Is not a dromotropic drug on the AV node level

So basically, calcium channel blockers are decreasing the rate regarding SA node output and electrical excitability. The direct mechanism of calcium channel blockers on the vascular beds is to block those electrolytes from getting inside, thereby softening the heart.

Critical Thinking Question

How do calcium channel blockers affect EKG readings?

Hypercalcemia causes sluggish ST waves which are just fancy terms for the heart becoming very hard and is not relaxed. Increased calcium causes increased constriction and excitability; therefore, it would show that there will be:

• Sluggish or too much ST contractions
• The absence of a good T-wave
• No repolarization
• ST elevation

This, however, does not necessarily mean that the client is having a heart attack or a STEMI, it just means that there is too much calcium. Blood tests and EKG readings are important to draw cardiac enzyme and to make sure that the client is not experiencing myocardial infarction (MI).

Simplenursing.com has tons of videos that primarily focuses on EKG readings that can immensely help students to be familiar with the P, T, and QRS waves. So, might as well check that out.