What is a Cardiac Arrhythmia?

Instructor: Jennifer Mitchell

Jennifer is a clinical professor for nursing students in critical care and has several years of experience in teaching nursing.

So you feel a fluttering in your chest. It's unnerving. What is a cardiac arrhythmia, anyways? We will review the basics of cardiac arrhythmias in this lesson.

What is a Cardiac Arrhythmia?

You decide to go to your healthcare provider because you've been feeling fluttering in your chest. It's a strange, scary feeling, isn't it? They tell you that you have a cardiac arrhythmia. What does this mean? Let's review the basics of cardiac rhythms before we talk about cardiac arrhythmias.

Basics of Cardiac Rhythms

Heart Conduction System
heart conduction system

The heart is a pretty magical organ because of the way it works. It has an electrical conduction system, as you see in the image, that conducts each and every heartbeat. Pretty cool, huh? Let's look at the diagram and review the different parts of the conduction system.

The conduction starts at the top of the heart in the sinoatrial (SA) node, which is sometimes called the pacemaker of the heart. Then it travels down through pathways in the atria (top 2 chambers of the heart) to the atrioventricular (AV) junction. From the AV junction, the conduction travels through the HIS bundle (between the 2 ventricles, or larger bottom chambers of the heart) all the way to the Purkinje fibers in the ventricles themselves.

When the electrical conduction follows the pathway as just described, the heart chambers contract normally, and you've got a normal heartbeat. Any time there is a deviation from the normal pathway, you've got a cardiac arrhythmia.

What Causes a Cardiac Arrhythmia?

There are many factors that can cause the electrical conduction to take an alternate route through the heart. Let's talk about a couple of them.

Electrolyte Imbalance

Your muscles require a certain balance of sodium (Na) and potassium (K) in order to contract normally. When there is an electrolyte imbalance in the bloodstream, such as hypernatremia (elevated Na), hyponatremia (decreased Na), hyperkalemia (elevated K), or hypokalemia (decreased K), then muscles cannot contract normally. This also effects the electrical conduction system and muscles of the heart. This is why you should visit your healthcare provider at least annually to have blood tests to check these electrolyte levels.

Conduction System Issues

There can also be problems within the conduction system itself that will cause cardiac arrhythmias. Sometimes a location other that the SA node will pace the heart, usually because the SA node is conducting impulses too slowly. This can be caused by some medications, or there may be a site somewhere in the heart muscle that decides to go rogue and conduct impulses. It sounds weird, but it happens!

Myocardial Infarction

Heart Attack
Heart attack

A myocardial infarction is medical jargon for heart attack. During a heart attack, blood flow to the heart muscle is blocked. This interrupts the oxygen flow to the heart muscle, which is required for it to work properly. When the heart muscle doesn't get the oxygen it needs, a portion of it dies. It dies? Yes it does. Dead heart muscle cannot conduct or be stimulated by the electrical impulses required for a normal heartbeat. That's a good reason to watch what you eat and get regular physical activity!

Types of Cardiac Arrhythmias

There are many types of cardiac arrhythmias, so we will review a couple of them here.

Atrial Fibrillation

One of the most common arrhythmias is called atrial fibrillation. In this arrhythmia, the top 2 chambers, or atria, flutter like sheets in the wind. This is not normal! There is utter chaos being conducted throughout the atria with this arrhythmia. This puts someone at risk for blood clots and stroke. Atrial fibrillation is long term in a lot of people, but some people can be converted back to a normal rhythm with drugs or medical intervention.

Atrial Flutter

This is a less common arrhythmia, but still one to be concerned about when it occurs. With atrial flutter, the atria are contracting regularly, but at a rate faster than the ventricles. For example, the person's heart rate may be 80, which means the ventricles are contracting 80 times a minute, but the atria are contracting 160-320 times per minute. So, for every 1 ventricular beat, there are 2-4 atrial beats. Atrial flutter is usually a short-term arrhythmia and converts back to a normal rhythm on its own. That's crazy, isn't it? But it happens!

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