The human body is amazing, and it houses many organs, vessels, cells, nerves, muscles, and systems that all work together to keep us alive. One of these systems is known as the heart conduction system, also known as the cardiac conduction system. Read on to learn more!
What Is the Heart Conduction System?
The heart conduction system is made up of cells, nodes, and signals that help your heart to beat. In fact, the cardiac conduction system is responsible for our heart beating around 2.5 billion times during the average human lifespan.
The conduction system, also called the cardiac electrical system, helps the heart contract, thus pumping blood through the body. It is made up of several different parts, including a sinoatrial (sinus) node. The sinus node is a small collection of tissue. It can be found in the heart's upper right chamber.
The sinus node powers electrical stimulation through the heart, causing it to contract, first the upper chambers and then the lower chambers. The heart’s contraction is what causes it to beat. Because the sinus node keeps the heart beating normally, it is often referred to as a natural pacemaker.
By helping your heart to beat, the conduction system also helps your heart send blood flowing to the rest of your body.
Cardiac Conduction System Anatomy
There are quite a few cells and nodes in your heart’s conduction system, and each has its own cardiac conduction system function, including:
- Sinoatrial node: As mentioned before, the sinoatrial node is your heart’s natural pacemaker. How fast or slow your sinoatrial node sends your heart the signal to contract depends on your autonomic nervous system. Based on your level of physical activity, the autonomic nervous system manages hormones that control your cardiac activity.
There are two components of the autonomous nervous system: the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system controls fight or flight responses, increasing your heart rate. The parasympathetic nervous system controls your rest and digestive responses, decreasing your heart rate.
- Atrioventricular bundle: The atrioventricular bundle is also known as the Bundle of His. It contains several nerve cells and receives electrical input from the atrioventricular node. The bundle has two branches: left and right. They send electrical signals to the left and right ventricles found in the chamber at the bottom of your heart.
- Atrioventricular node: The atrioventricular node delays the sinoatrial node’s signal by a fraction of a second to ensure no blood is left in your heart when the contraction stops. It’s located near the center of the heart.
- Purkinje fibers: Purkinje fibers, similar to the atrioventricular bunch, send electrical signals to your heart ventricles. They do so quickly, causing the ventricles to contract. When this happens, blood flows through your pulmonary arteries and into your aorta.
These cells and nodes make up your heart conduction system pathway.
Conduction System of the Heart Steps
The main function of your heart’s conduction system is to contract and relax your heart, which causes your heart to beat and helps pump blood through your body.
Each heartbeat is accompanied by electrical signals that travel along the conduction pathway. Here are the steps involved:
- The sinoatrial node sends out an electrical signal.
- The top of your heart chambers (the atria) receives the signal and contracts.
- The signal is delayed by the atrioventricular node until your atria are emptied into the ventricles.
- The atrioventricular bundle carries the signal to the Purkinje fibers.
- The Purkinje fibers send the signal to your ventricles, or bottom heart chambers, telling them to contract as well.
Cardiac Conduction Conditions
Many conditions can affect the heart conduction system and lead to serious health issues such as heart attack or stroke. Some conditions can also lead to irregular heartbeats.
One condition affecting the cardiac conduction system is known as heart block. Heart blocks are categorized as first-degree, second-degree, or third-degree.
First-degree heart blockage can be caused by medications such as beta-blockers and calcium blockers. Treatment isn’t often required, and symptoms are limited to dizziness and lightheadedness. In fact, many show no symptoms at all.
Second-degree heart blockers are slightly more serious and are classified as Mobitz Type 1 and Mobitz Type 2. In the case of type 1, symptoms may not be present, but monitoring the condition is important as it can often develop into type 2. Type 2 is more serious and may require a pacemaker to help the heart beat and keep blood flowing effectively. Symptoms such as chest pain, breathing difficulties, and fainting can occur.
Third-degree heart blocks occur when some openings of the heart are fully blocked, so blood is pumped slower than normal. Heart conditions can cause third-degree blocks, and certain medications can contribute in rare cases. Typically, individuals with third-degree blocks need immediate medical attention, as third-degree heart blocks can lead to cardiac arrest. Symptoms include chest pain, fainting, excessive fatigue, and shortness of breath.
Another condition that affects the heart conduction system is called sick sinus syndrome (SSS) or sinus node disease. It affects the sinoatrial node and causes the heart to beat slower or faster than normal. It can also contribute to an increased heart rate during exercise.
Ion channels, tiny pores located on the heart’s muscle, are also prone to disorders such as long QT syndrome. It is referred to as a long QT system because of how it is viewed on an electrocardiogram as a longer interval between heartbeats. It causes problems with the electrical system that causes your heart to beat, sometimes leading to cardiac arrest.
Electrocardiograms (ECGs) are often used to the heart’s rhythm. If an abnormal rhythm is present, your doctor may prescribe medicine or recommend a procedure.