Wiktor Wise
The heart is a pump made of muscle tissue. Like all muscles, it requires oxygen and energy to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of its chambers. This electrical system controls the electrical impulses that cause the heart to beat and their conduction, which organises the beating of the heart. The cardiac conduction system is a network of nodes, cells, and signals that controls the heartbeat.
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What You'll Learn
The sinus node
The electrical impulses generated by the sinus node spread across the heart, causing the cells of the heart muscle to contract in the correct sequence. This coordinated contraction ensures regular and efficient heartbeats. The sinus node is influenced by the autonomic nervous system, which controls the rate of action potential production and, consequently, the heart rate. Parasympathetic input slows down action potential production, resulting in a decreased heart rate, while sympathetic input has the opposite effect, increasing the heart rate.
Sinus node dysfunction (SND), also known as sick sinus syndrome, can occur when the SA node does not function properly. This can be caused by ischemia, necrosis of pacemaker cells, or changes in the electrophysiology of the SA node. SND can lead to symptoms such as dizziness and syncope due to reduced cerebral perfusion. Implantable electronic pacemakers are currently the only effective treatment for SND.
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Electrical impulses
The heart's electrical conduction system is a network of nodes, cells and signals that controls the heartbeat. Electrical signals move through the heart, causing it to beat. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart.
The electrical impulse starts on the right side of the upper chamber in an area called the sinus node or sinoatrial node (SA node). This is a small mass of specialized tissue located in the right upper chamber (atria) of the heart. The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The sinus node is often referred to as the heart's "natural pacemaker". The SA node is in the upper part of the heart's right atrium, near the superior vena cava, a large vein that brings oxygen-poor blood from the body to the heart. The autonomic nervous system controls how quickly or slowly the SA node sends electrical signals.
The electrical impulse leaves the sinus node and travels a set path through the upper chambers, the atria, causing them to contract and squeeze blood into the lower chambers. The atria contract a fraction of a second before the ventricles so that their blood empties into the ventricles before the ventricles contract. The electrical signal then reaches the atrioventricular (AV) node, which is in the middle of the heart, between the atrium and the ventricle. The signal is delayed in the AV node and then spreads through the lower chambers.
Each electrical impulse generates one heartbeat, so the number of electrical impulses determines the heart rate. The sinus node signal also controls electrical conduction as it "spreads" across the heart. It causes the cells of the heart muscle to contract in the correct sequence, ensuring regular, efficient, and coordinated heartbeats.
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Heart rate
The heart's electrical conduction system is a network of nodes, cells and signals that controls the heartbeat. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the various chambers of the heart. The electrical system of the heart controls the electrical impulses that cause the heart to beat and their conduction, which organises the beating of the heart.
The heart's electrical conduction system sends out thousands of signals per day to keep the heart beating. Each time the heart beats, electrical signals travel through the heart, causing different parts of the heart to expand and contract. These actions regulate blood flow through the heart and body. The cardiac electrical signal controls the heartbeat in two ways. Firstly, since each electrical impulse generates one heartbeat, the number of electrical impulses determines the heart rate. Secondly, the sinus node signal controls electrical conduction as it "spreads" across the heart.
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. The sinus node is the heart's normal pacemaker and controls the heart rate. The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The atria are then activated. The electrical stimulus travels down through the conduction pathways and causes the heart's ventricles to contract and pump out blood. The two upper chambers of the heart (atria) are stimulated first and contract for a short period of time before the two lower chambers of the heart (ventricles).
The heart normally beats faster during exercise or excitement and more slowly when at rest or sleeping. Certain conditions are associated with a slow heartbeat, or bradycardia. One of the causes of bradycardia is heart block, which occurs when the electrical signal that starts in the upper portion of the heart cannot get through to the lower chambers. Another form of bradycardia may be caused when the heart's normal "pacemaker," the sinus node, does not work with regularity. This is known as sinus node dysfunction.
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Heart's electrical conduction system
The heart's electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat. This system is essential to cardiac function, regulating the heart rate and the contraction of the heart muscle. The cardiac electrical signal controls the heartbeat in two ways. Firstly, the number of electrical impulses generated determines the heart rate. Secondly, the sinus node signal controls electrical conduction as it spreads across the heart, ensuring regular, efficient, and coordinated heartbeats.
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 acts as the heart's natural pacemaker, generating an electrical stimulus 60 to 100 times per minute under normal conditions. The right atrium is one of the four chambers of the heart, with two atria at the top and two ventricles at the bottom. The electrical stimulus first activates the atria, causing them to contract for a short period before the ventricles.
The electrical signal then travels from the sinus node through the conduction pathways, reaching the atrioventricular (AV) node in the middle of the heart. The AV node is separated from the atria by a layer of fibrous tissue, ensuring the electrical signal passes through it. The signal is briefly delayed in the AV node before spreading through the lower ventricles. The ventricles then contract and pump blood out of the heart.
The heart's electrical conduction system is critical to its functioning, and disruptions to this system can lead to serious complications, including cardiac arrest. Conditions such as heart disease, high blood pressure, congenital heart defects, and heart attacks can cause disruptions in the electrical conduction system. Bradycardia, a slow heartbeat, can be caused by heart block or sinus node dysfunction, where the electrical signal cannot pass from the upper portion of the heart to the lower chambers. Treatment for these conditions often involves the implantation of a permanent pacemaker.
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Electrocardiogram (EKG)
The heart's electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat. The cardiac electrical system is essential to cardiac function, controlling the heart rate and the contraction of cardiac muscle. The electrical system of the heart controls the electrical impulses that cause the heart to beat and their conduction, which organises the beating of the heart.
An electrocardiogram (EKG or ECG) is a test that measures the electrical activity of the heartbeat. Each time the heart beats, electrical signals travel through it, causing different parts of the heart to expand and contract. These actions regulate blood flow through the heart and body. An EKG is used to diagnose many heart conditions, including heart attacks. It can also be used to assess irregularities in the heart's electrical system and any related symptoms and medical conditions.
The EKG machine records the electrical activity of the heart but does not send electricity into the body. Small stickers or electrodes are placed on the chest, arms, and legs, and connected to the EKG machine by lead wires. The electrical activity of the heart is then measured, interpreted, and printed out.
The heart generates its own electrical signal, which is produced by a tiny structure known as the sinus node, located in the upper portion of the right atrium. The sinus node is often referred to as the heart's "natural pacemaker". It sends electrical impulses that start the heartbeat. These impulses are generated 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 ventricles to contract and pump out blood.
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Frequently asked questions
It is a network of nodes, cells and signals that controls the heartbeat.
Nodes are groups of cells that can be either nerve or muscle tissue.
An electrical impulse starts in the sinus node (also called the sinoatrial node, or SA node) and travels through the heart, causing it to contract and pump blood.
A normal sinus rhythm is between 60 and 100 beats per minute.
