Otis Singleton
The heart's electrical system is a network of nodes, cells, and signals that controls the heartbeat. The heart is a pump made of muscle tissue, and it needs a source of energy and oxygen to function. The heart's electrical conduction system coordinates the contraction of the heart chambers and regulates blood flow through the heart and body. The sinus node, also known as the sinoatrial node (SA node), is a small mass of specialized tissue located in the upper right chamber (atrium) of the heart. It generates an electrical stimulus, which causes the heart to contract and pump blood. The electrical system of the heart is critical to its function, and disruptions can lead to serious complications such as cardiac arrest.
| Characteristics | Values |
|---|---|
| Purpose | 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 |
| Heart rate | 60 to 100 times per minute under normal conditions |
| Heartbeat | Each contraction of the ventricles represents one heartbeat |
| Contraction | The atria contract a fraction of a second before the ventricles so their blood empties into the ventricles before the ventricles contract |
| Electrical system | Controls the heartbeat |
| Components of the electrical system | Sinus node (SA node), atrioventricular node (AV node) |
| Sinus node | A small mass of specialized tissue located in the right upper chamber (atria) of the heart; often referred to as the heart's "natural pacemaker" |
| Atrioventricular node (AV node) | Located in the middle of the heart between the upper and lower chambers; helps manage the electrical activity as it travels from the atrium to the ventricles |
| Bundle branches | Part of the electrical system of the heart |
| Bundle of His | Part of the electrical system of the heart; a collection of cells |
| Heart block | A conduction disorder in which the heart's electrical signals are unable to move from the atria to the ventricles |
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What You'll Learn
The sinus node: the heart's pacemaker
The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of its chambers. The sinus node, also known as the sinoatrial node or SA node, is a small mass of specialised tissue located in the right upper chamber (atria) of the heart. It is a crescent-like cluster of myocytes, or pacemaker cells, that generate electrical impulses.
The sinus node acts as the heart's pacemaker by producing electrical impulses that travel through the heart's electrical conduction system, causing myocardial contraction and blood distribution to the rest of the body. These impulses are generated regularly, 60 to 100 times per minute under normal conditions, and result in the heart contracting in a coordinated manner. The sinus node sets the rhythm and rate of a healthy heart, typically between 60 and 100 beats per minute, depending on a person's age.
The autonomic nervous system controls input into the sinus node, allowing the heart to adapt to various physiological stressors. Parasympathetic input slows down the rate of action potential production, decreasing the heart rate, while sympathetic input has the opposite effect, increasing the rate of action potential production and the heart rate. The sinus node's function can be disrupted by sick sinus syndrome, which is caused by age, medication, myocardial infarction, or coronary artery disease. This can lead to an abnormally slow or fast heartbeat, or a combination of both.
In cases of sinus node dysfunction, a pacemaker may be recommended to regulate the electrical impulses of the heart and control its rate and rhythm.
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Electrical conduction system
The heart's electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat. Each time the heart beats, electrical signals travel through it, causing different parts to expand and contract. This regulates blood flow through the heart and body. The heart's electrical system coordinates the pumping of the four chambers of the heart and controls the heart rate, allowing the heart to speed up or slow down as the body's demands change.
The sinus node, or sinoatrial node (SA node), is a small mass of specialized tissue located in the upper right chamber (atrium) of the heart. It is often referred to as the heart's ""natural pacemaker"" as it generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The SA node creates an excitation signal, which is like electricity travelling through wires to an appliance. This electrical impulse then spreads across the right and left atria, causing both atria to contract and push blood into the right and left ventricles. This is known as atrial depolarization.
The AV node, or atrioventricular node, is the second major part of the heart's electrical system. It is located in the middle of the heart between the upper and lower chambers and helps manage the electrical activity as it travels from the atria to the ventricles. The AV node slows down the electrical message, allowing time for the heart's valves to open and let blood travel into the ventricles. In some cases, the AV node can act as a ""backup"" pacemaker when there are problems with the sinus node.
The bundle branches and the bundle of His are also parts of the heart's electrical system. The electrical signals travelling through the ventricles generate the "QRS complex" on an electrocardiogram (EKG) or electrocardiogram. An EKG traces the movement of electrical signals across the heart and allows for the assessment of irregularities in the heart's electrical system and related medical conditions.
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Electrocardiogram (EKG)
The heart's electrical system is critical to its functionality, controlling the electrical impulses that cause the heart to beat and coordinating the pumping of the four chambers of the heart. An electrocardiogram (EKG or ECG) is a test used to evaluate the electrical activity of the heart. This test is simple and fast and involves placing electrodes (small, sticky plastic patches) on the chest, arms, and legs. These electrodes are connected to an ECG machine by lead wires and measure, interpret, and record the electrical activity of the heart. The development of the electrocardiogram was made possible by Willem Einthoven's 1903 string galvanometer, for which he received the 1924 Nobel Prize.
The heart's electrical impulse originates in the sinus node (also called the sinoatrial node or SA node), a small mass of specialized tissue located in the upper right chamber (atrium) of the heart. The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. This electrical signal then spreads across the right and left atria, causing them to contract and push blood into the ventricles. The ventricles then contract, sending blood to the organs of the body (via the left ventricle) and to the lungs (via the right ventricle).
An EKG records the movement of electrical signals across the heart, producing a trace known as an electrocardiogram. This trace typically displays a regular, identifiable pattern: the P wave, the QRS complex, and the T wave. The QRS complex is generated when the electrical signal travels through the ventricles. The EKG allows for the assessment of irregularities in the heart's electrical system and any related symptoms or medical conditions. For example, heart block is a conduction disorder where the electrical signals are unable to move from the atria to the ventricles, preventing the atria from signalling the ventricles to contract and pump blood.
Advancements in electrocardiography have led to the development of smaller devices for inclusion in fitness trackers and smartwatches. Additionally, the term "EKG" is derived from the German acronym "Elektrokardiogramm," reflecting the pioneering role of German physicians in the field of electrocardiography.
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Conduction disorders
The heart's electrical system is critical to its function, controlling the electrical impulses that cause the heart to beat and their conduction, coordinating the beating of the heart. The cardiac conduction system is a network of nodes, cells, and signals that controls the heartbeat.
Some common conduction disorders include bundle branch block, heart block, and Long QT Syndrome (LQTS). Heart block is a conduction disorder in which the heart's electrical signals are unable to move from the atria to the ventricles, preventing the atria from telling the ventricles when to contract and pump blood. There are three degrees of heart block severity, with the first being the least severe, and the third being a complete heart block, in which no signals reach the ventricles. LQTS can cause abnormal heart rhythms in response to exercise or stress, and it can be hereditary.
Other conduction disorders include sick sinus syndrome (SSS), which can cause a slow or fast heart rate, and atrioventricular (AV) block, which has three degrees of severity depending on how serious the condition is. Beta blockers and calcium channel blockers can also cause first-degree heart block by slowing down electrical conduction within the heart.
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The cardiac conduction system
The sinus node, also called the sinoatrial node or SA node, is a small mass of specialised tissue located in the right upper chamber (atria) of the heart. It is often referred to as the heart's "natural pacemaker". The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The atria are then activated, and the electrical stimulus travels down through the conduction pathways, causing the heart's ventricles to contract and pump out blood. The upper chambers of the heart (atria) are stimulated first and contract briefly before the lower chambers (ventricles). This is referred to as atrial depolarisation, which pushes blood into the right and left ventricles.
The electrical impulse originates in the sinus node and spreads across the right and left atria, causing them to contract. Upon reaching the atrioventricular (AV) node, the signal is delayed for a very short period before continuing down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways, called bundle branches, to stimulate the right and left ventricles. The bundle of His and the Purkinje fibres spread the wave impulses along the ventricles, causing them to contract.
The electrical system of the heart controls the heartbeat and the movement of electrical signals across the heart, which can be traced on an electrocardiogram (EKG). The EKG allows for the assessment of irregularities in the heart's electrical system and any related symptoms and medical conditions.
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Frequently asked questions
The heart's electrical system controls the electrical impulses that cause the heart to beat. This regulates blood flow through the heart and body.
The sinus node, also called the sinoatrial node (SA node), is a small mass of specialized tissue located in the right upper chamber (atria) of the heart. It acts as the heart's natural pacemaker by generating an electrical stimulus that causes the heart to beat.
The electrical system ensures that the heart contracts in a coordinated manner. The electrical impulse originates in the sinus node and spreads across the right and left atria, causing them to contract and push blood into the ventricles. The ventricles then contract to pump blood out to the body.
The electrical system helps regulate heart rate by controlling the speed and timing of the electrical impulses. The sinus node can increase or decrease the rate at which it fires, influencing the heart rate.
Problems in the electrical system, such as arrhythmias or conduction disorders, can be detected through an electrocardiogram (EKG or ECG) that records the electrical activity of the heart. Treatment options may include medication or procedures, such as the implantation of a permanent pacemaker.
