Molly Ayala
The heart's electrical system is a special system that coordinates the heart's pumping action. The heart is a pump made of muscle tissue, and its pumping action is regulated by electrical impulses. Electrical impulses trigger heartbeats, and the heart's electrical system controls the rate and rhythm of the heartbeat. The heart's electrical system is critical to how it functions, and it controls the electrical impulses that cause the heart to beat and their conduction, which organizes the beating of the heart. The heart's electrical system causes the heart muscle to contract and send blood to the organs of the body and to the lungs.
| Characteristics | Values |
|---|---|
| Purpose | To coordinate the pumping of the four chambers of the heart and to control the heart rate |
| Heart Rate at Rest | 60 to 100 beats per minute |
| Heart Rate During Exercise | Faster |
| Heart Rate During Rest or Sleep | Slower |
| Heart's Natural Pacemaker | Sinus Node (also called the sinoatrial node or SA node) |
| Location of Sinus Node | Upper portion of the right atrium |
| Sinus Node Function | Generates an electrical stimulus 60 to 100 times per minute under normal conditions |
| Electrical Pathway | Sinus Node -> Right and Left Atria -> AV Node (Atrioventricular Node) -> Bundle of His (dividing into right and left bundle branches) -> Ventricles |
| AV Node Function | Slows down electrical impulses for a very short period |
| Conduction Disorder | Heart block, which prevents electrical signals from moving from atria to ventricles |
| Diagnosis of Electrical Irregularities | Electrocardiogram (EKG or ECG) |
| Conditions Affecting Electrical System | Arrhythmia, Atrial Fibrillation, Tachycardia (rapid heartbeat), Bradycardia (slow heartbeat) |
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What You'll Learn
The sinus node
The heart is a pump made of muscle tissue. Its pumping action is regulated by electrical impulses that originate in the sinus node, also known as the sinoatrial node (SAN) or SA node. The SAN is located in the superior right atrium, specifically in the wall (epicardium) of the right atrium, laterally to the entrance of the superior vena cava. It is an oval-shaped region of specialised cardiac muscle, approximately 15 mm long, 3 mm wide, and 1 mm thick.
The SAN is the heart's natural pacemaker, controlling the heart rate. It automatically produces cyclical electrical activity, known as cardiac action potentials, that travel through the electrical conduction system of the heart, causing it to contract and pump blood. The rate of action potentials produced, and therefore the heart rate, is influenced by the nerves that supply the SAN. In a healthy heart, the SAN continuously produces action potentials, setting the rhythm of the heart (sinus rhythm).
The electrical impulse generated in the SAN travels across the cells of the heart's right and left atria to the atrioventricular (AV) node, located in the middle of the heart between the atria and ventricles. At the AV node, the impulse is briefly slowed down, allowing the atria to contract first and squeeze blood into the ventricles before the ventricles contract. The impulse then continues down the conduction pathway through the bundle of His, which divides into right and left bundle branches to stimulate the right and left ventricles.
SAN dysfunction (SND), also known as sick sinus syndrome, can lead to abnormal heart rhythms. SND can manifest as pathological bradycardia (slow heart rate) or asystolic pauses, resulting in symptoms such as dizziness and syncope. SND can be caused by various factors, including inflammatory diseases, certain medications, and abnormal blood electrolyte levels. Treatment options for SND may include the implantation of a permanent pacemaker to regulate heart rhythm.
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Electrical impulses
The heart is a pump made of muscle tissue. Its pumping action is regulated by electrical impulses. The heart's electrical system coordinates the pumping of the four chambers of the heart and controls the heart rate, allowing it to speed up or slow down as the body's demands change.
The electrical impulse originates in the sinus node, a small mass of specialized tissue located in the right upper chamber (atrium) of the heart. The sinus node acts as the heart's ""natural pacemaker"" and controls the heart rate. It generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The electrical impulse then travels from the sinus node across the cells of the heart's right and left atria. This causes the atria to contract and squeeze blood into the ventricles.
The electrical signal then reaches the atrioventricular (AV) node, located between the atria and ventricles. The AV node slows down the electrical impulses for a very short period, allowing the atria to contract a fraction of a second before the ventricles. After passing through the AV node, the electrical current continues down the conduction pathway, through the bundle of His, and into the ventricles. The bundle of His divides into right and left pathways (bundle branches) to stimulate the right and left ventricles. As the electrical signal travels through the ventricles, it causes them to contract and pump blood to the lungs and throughout the body.
The entire heartbeat process starts with an impulse in the sinus node and ends with the contraction of the ventricles. Each contraction of the ventricles represents one heartbeat. Problems with the electrical impulses in the heart can cause it to beat too fast (tachycardia) or too slow (bradycardia). Tachycardia can be caused by an extra electrical pathway between the atria and ventricles, allowing the electrical impulse to make a continuous loop. Bradycardia can be caused by heart block, a conduction disorder where the electrical signals cannot move from the atria to the ventricles.
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Heart rate
The heart's electrical system is critical to its function, controlling the electrical impulses that cause the heart to beat and coordinating the pumping of its four chambers. The heart's rate and rhythm are controlled by this electrical system, known as the cardiac conduction system.
The heart is a hollow muscle, a little larger than a clenched fist. It acts as a pump, made up of four chambers or compartments. The two upper chambers are called the atria, and they receive blood from the body and lungs. This blood then travels through valves to the two lower chambers, the ventricles, which pump the blood to the lungs and the rest of the body.
The heart's electrical system coordinates the pumping action of these chambers. An electrical stimulus is generated by the sinus node, a small mass of specialized tissue located in the right upper chamber (right atrium). The sinus node is the heart's "natural pacemaker", controlling the heart rate. It generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions when the body is at rest. The rate increases during exercise or excitement to supply more oxygen to the muscles.
The electrical impulse travels from the sinus node across the cells of the heart's right and left atria, causing them to contract and squeeze blood into the ventricles. The atria contract a fraction of a second before the ventricles, so the blood empties into the ventricles before they contract. The electrical signal then reaches the atrioventricular (AV) node, where it is briefly delayed before continuing down the conduction pathway through the bundle of His into the ventricles. The bundle of His divides into right and left pathways, stimulating the right and left ventricles, which then contract and pump blood out to the body and lungs.
The electrical system of the heart ensures that the heartbeats are regular, efficient, and coordinated. An abnormality in the electrical system can cause an irregular heart rhythm, known as arrhythmia. This can be assessed through an electrocardiogram (EKG), which traces the movement of electrical signals across the heart.
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Electrocardiogram (EKG)
An electrocardiogram (ECG or EKG) is a simple, fast, and painless test used to evaluate the heart's electrical activity. Electrodes, or small plastic patches, are placed on the chest, arms, and legs. These electrodes are connected to an ECG machine by lead wires, and the electrical activity of the heart is then measured, interpreted, and printed out.
The heart's electrical activity was first discovered in the late 19th century, leading to the development of the electrocardiograph. Willem Einthoven's 1903 string galvanometer enabled precise measurement of these signals, for which he received the 1924 Nobel Prize. Early ECG machines were analog, printing the signal onto paper. Modern electrocardiographs use analog-to-digital converters to convert the electrical activity of the heart into a digital signal. Many ECG machines are now portable, often including a screen, keyboard, and printer on a small wheeled cart.
The heart's electrical system is regulated by electrical impulses. The electrical impulse starts in the sinus node, located in the right upper chamber (atria) of the heart. The sinus node acts as the heart's pacemaker, generating an electrical stimulus 60 to 100 times per minute under normal conditions. The electrical signal then travels to the atrioventricular (AV) node, where it is briefly delayed. This delay allows the atria to contract a fraction of a second before the ventricles, so blood empties into the ventricles before they contract. After the AV node, the electrical current continues down the conduction pathway, through the bundle of His, and into the ventricles.
An abnormal electrical rhythm, or arrhythmia, can cause the heart to beat too fast (tachycardia) or too slow (bradycardia). An EKG can be used to assess the rhythm of the heart and determine if medicine or a procedure is necessary.
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Conduction disorders
The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart. An electrical stimulus is generated by the sinus node, a small mass of specialized tissue located in the right upper chamber (atria) of the heart. This electrical impulse travels from the sinus node to the atrioventricular node (AV node), where it is slowed down for a very short period before continuing down the conduction pathway via the bundle of His into the ventricles.
- Bundle branch block: This occurs when electrical signals travel more slowly in one side of the heart than the other, resulting in a delay in the conduction of electrical impulses to the ventricles.
- Heart block: This occurs when the electrical signal that starts in the upper portion of the heart cannot get through to the lower chambers, resulting in a decreased heart rate. There are three degrees of heart block, with the third degree being the most serious and referred to as complete heart block.
- Long QT Syndrome (LQTS): LQTS is a disorder of the heart's electrical system that can cause abnormal heart rhythms in response to exercise or stress. The heart's lower chambers take too long to contract and release, leading to a prolonged QT interval on an electrocardiogram (EKG).
- Sick sinus syndrome (SSS): SSS affects the SA node, which controls the rate and rhythm of the heartbeat. It can cause a slow or fast heart rate and problems with increasing the heart rate during exercise or other activities.
- Ion channel disorders: These disorders involve the tiny pores on the surface of each heart muscle cell that help produce the heart's electrical activity. The most common type is long QT syndrome, but other types include Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome.
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Frequently asked questions
The heart's electrical system is critical to how it functions. It controls the electrical impulses that cause the heart to beat and their conduction, which organises the beating of the heart.
The purpose of the electrical system of the heart is to coordinate the pumping of the four chambers of the heart and to control the heart rate so that the heart speeds up and slows down as the demands of the body change.
Electrical impulses start in the sinus node, a small area of special electrical tissue high on the right side of the heart. The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The electrical impulse then travels across the heart, causing it to contract and pump blood.
