Electrical Conduction System of the Heart

What is the cardiac conduction system?

The human heart is an engine that has to work 24/7 to keep you alive, and it has to be reliable and effective. To do this, it relies on a specialized network of cells called the cardiac conduction system. It’s also known as your heart’s electrical system.

Cells in the cardiac conduction system can generate electrical impulses and then distribute the signal throughout your heart. While all cells in your heart can conduct electricity, the cells in this system conduct it at very specific speeds. This is how different parts of your heart beat at just the right time. The parts of the cardiac conduction system are (in order, starting where electricity is generated):

• The sinoatrial (SA) node.
• The atrioventricular (AV) node.
• The Bundle of His.
• Bundle branches.
• Purkinje fibers.

What does the cardiac conduction system do?

Your body uses electrical impulses to control when your muscles flex and relax, and your heart is no different. However, your heart needs to do this 24/7, whether you’re asleep or awake. To do this, it relies on a specific part of your nervous system called the autonomic nervous system. This is the unconscious part of your nervous system, and it runs the functions of your body that you don’t think about. This includes your heart, breathing, digestion and more.

The timing of your heart muscle’s action is also critical. Rather than your brain firing the electrical impulses, it relies on your heart’s conduction system. To do that, your brain sends signals through your autonomic nervous system to your heart’s electrical system. That system activates, sending an electrical pulse through your heart muscle. This makes the chambers of your heart squeeze in a specific order, creating a heartbeat.

Under normal circumstances, this happens between 50 to 100 times per minute when you're at rest. When you're active, your heart speeds up and beats faster.

Heart muscle and its function

Your body has three types of muscle: smooth, skeletal and cardiac.

What are the parts of the heart’s electrical conduction system?

Knowing the heart's structure helps in understanding your heart's electrical system. Your heart has four chambers. The upper chambers are the left atrium and right atrium (they’re called atria when you refer to them both). The lower chambers are the left and right ventricles.

Blood travels through your heart in the following steps (the steps on the left and right are happening at the same time):

As electricity moves through your heart, it causes each part it passes through to contract. This is called the electrical cascade. While all of the cardiac muscle in your heart can conduct electricity, there are certain areas of your heart — the electrical conduction system — where the cascade travels at different speeds.

The cascade travels through the electrical conduction system in the following order:

Sinoatrial node

The sinoatrial (SA) node is a cluster of cells that act as a natural pacemaker for your heart. The SA node is located in a wall of the right atrium of your heart. This step is where the upper chambers of the heart begin to squeeze.

Atrioventricular node

The atrioventricular (AV) node is located in the wall between the upper chambers of your heart. This node is very similar to the SA node but smaller, and electricity travels slower here. The slowing effect gives the ventricles enough time to expand and fill up with blood.

Bundle of His

The Bundle of His (pronounced “hiss”) is a cluster of cells that extends outward from the AV node and travels down the center of your heart. Because these conduct electricity faster than surrounding tissue, it functions much like a lightning rod, directing the electrical cascade further into the heart.

Bundle branches

The bundle branches are where the Bundle of His splits into two branches. The split happens at roughly the same level where the top and bottom chambers of the heart are divided. The branches carry the electrical cascade to the outer areas of the heart, especially the ventricles.

Purkinje fibers

As the bundle branches fan out, they become a web-like network of conducting segments called the Purkinje fibers. The Bundle of His, bundle branches and Purkinje fibers are often described as the His-Purkinje system, which has a shape like an upside-down umbrella. The Bundle of His is the handle, the bundle branches are the stem and the Purkinje fibers are the umbrella's canopy.

Electricity travels down and then spreads out at the bottom of the heart. Electricity then travels upward and along the outer areas of the heart. This is how the heart pumps blood upward and out of the heart.

What are common conditions and disorders that affect the heart’s electrical system?

The heart conducts electricity in a specific way as described above, and its function works best when it maintains this sequence. Any time there is a disturbance of this sequence, it can cause abnormal heart rhythms and patterns called arrhythmias (irregular heart rhythms).

Arrhythmias mainly happen in two ways:

• Bradycardia: These are slow heart rates that happen with problems related to the SA node, the AV node or the His-Purkinje system. These usually happen due to damage or scarring of the heart’s electrical pathways, which slows or stops electrical current in places.
• Tachycardia: This refers to rapid or fast heartbeats, which often happen because of a phenomenon known as re-entry. When this happens, a persistent electrical loop forms, causing parts of the heart to beat too quickly or out of order. Tachycardia can start in the bottom chambers of the heart (ventricular tachycardia) the level of the AV node or above (supraventricular tachycardia).

What are some common signs of problems with my heart’s electrical system?

The common symptoms of arrhythmia could include:

• Heart palpitations. This is an unpleasant ability to feel your heartbeat. This includes feeling like your heart is pounding, racing or skipping beats.
• Dizziness or lightheadedness. This can include fainting and passing out or having instances of nearly passing out.
• Sudden loss of consciousness or passing out.
• Fatigue. More than just feeling tired, this is when you’re exhausted beyond what’s normal. This usually takes place over a longer period (days or more).
• Weakness or drop in stamina or endurance. Feeling like you have little or no strength.
• Shortness of breath. Feeling like you’re struggling to breathe is a common sign of heart problems and should be checked by a doctor.
• Chest pain or discomfort.

Many of these symptoms, especially chest pain, dizziness, syncope, palpitations or sudden shortness of breath are reasons that you need to seek emergency medical care.

What tests are there to check the cardiac conduction system?

A diagnostic tool called an electrocardiogram can analyze your heart’s electrical activity. Abbreviated as ECG or EKG, this is a test that measures your heart’s electrical activity using sensors attached to your chest. There are several ways to perform an EKG.

• Resting. While seated or lying down, several sensors are attached to the skin of your chest. A resting EKG can take as little as a few minutes.
• Stress EKG. This is similar to a resting EKG, but it's done when you are physically active. This is usually done at a hospital or clinic using a treadmill or an exercise bike, and it's done with medical personnel monitoring you.
• Wearable monitor. This type of test attaches sensors to your chest, which feed data to a recording device you carry. This can give medical providers much more data to help them find heart problems that don’t appear regularly. You can wear these monitors for days or even weeks.
• Implantable loop recorder. This is a special monitor implanted under the skin of your chest, just beside your breastbone. They can last for three to five years.
• Electrophysiologic study. This is a special procedure that assesses the electrical system of your heart and any arrhythmias. These tests use catheters (tube-like devices) a provider inserts into major blood vessels and threads toward and into your heart. These devices record electrical activity from inside your heart. Providers also do “pacing maneuvers” to recreate arrhythmias. They then use the results of this test to plan further treatments.

Is there a way to treat problems with my heart’s electrical system?

There are several ways to treat problems with your heart’s electrical system.

• Medication. Several medications can help your heart beat properly. Some of these do so directly by controlling the way your heart's cells function. Others can do this by treating related issues like your blood pressure or keeping your blood from clotting, making it easier for your heart to work.
• Ablation. Pronounced uh-blay-shun, this can happen with surgery or a catheter inserted into the heart through major blood vessels. Providers can artificially cause arrhythmias in a monitored setting and then ablate (damage) the malfunctioning parts of the heart’s electrical pathways. This intentional damage uses radiofrequency or cryo (cold) energy in the narrowest and safest parts of the circuits permanently stop tachycardia from happening.
• Implanted devices. This includes pacemakers or implantable cardioverter defibrillators. A pacemaker is a small device implanted into your chest, which connects to leads (wires) that attach to your heart (in some cases, leadless pacemakers are implantable directly into your heart). These deliver electrical pulses similar to what your heart would produce on its own. An implantable cardioverter defibrillator is similar to a pacemaker but with an additional capability. This device can detect an abnormally fast heart rhythm and deliver a shock to return your heart to a normal rhythm.

What can I do to help my cardiac conduction system?

There are several actions you can take to help your heart’s health.

• Quit tobacco (this includes all forms of tobacco, as well as any kind of vaping).
• Limit how much alcohol you drink. For men, this is two drinks per day and no more than 14 drinks per week. For women, this is one drink per day and no more than seven per week.
• Be careful with over-the-counter products. Some over-the-counter items contain ingredients that can change your heart rhythm. You should always tell your healthcare provider about everything you take — including vitamins, supplements, herbal remedies — not just medicines.
• Avoid drug use. You should only take medications prescribed by your healthcare provider. However, if you do use drugs recreationally, your healthcare provider needs to know about them.
• Limit caffeine use. Caffeine is a stimulant, which can cause your heart to beat faster. If you have problems with your heart’s electrical system, your healthcare provider may tell you to limit or stop taking anything with caffeine.
• Maintain your health overall. Eating a healthy diet, staying physically active and maintaining a healthy weight are all good things when it comes to the health of your heart and its electrical system.

A note from Cleveland Clinic

The electrical conduction system of your heart is a key part of your survival, and it's one that runs automatically. Understanding how it works can help you spot potential problems and seek help. A healthcare provider can often recommend a wide range of treatments, from medications to minimally invasive surgeries, that can help treat or even cure electrical problems in your heart.