Molly Ayala
The heart's electrical system is a complex network of nodes, cells, and signals that work together to regulate the heart rate and coordinate the pumping action of the four chambers of the heart. This system ensures that the heart receives the necessary electrical impulse to contract and pump blood to the body and lungs. The electrical impulse is generated by the sinus node (SA node), which acts as the heart's natural pacemaker. From the SA node, the electrical signal travels through a specific pathway, including the atrioventricular (AV) node, the bundle of His, and the ventricles. Any disruptions to this electrical conduction system can lead to heart block, a condition where the electrical signals are weakened or blocked, impacting the heart's ability to pump blood effectively.
| Characteristics | Values |
|---|---|
| Purpose of the electrical system of the heart | 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's "natural pacemaker" | Sino-atrial (SA) node, a small area of special electrical tissue high on the right side of the heart that starts the electrical signal |
| SA node location | Right upper chamber (atria) of the heart |
| SA node function | Generates an electrical stimulus 60 to 100 times per minute under normal conditions |
| Atrioventricular (AV) node | Located in the middle of the heart, between the atrium and the ventricle |
| AV node function | Slows down the electrical impulse for a very short period before continuing down the conduction pathway |
| Bundle of His | A collection of cells; divides into right and left bundle branches to stimulate the right and left ventricles |
| Heart block | A conduction disorder where the heart's electrical signals are unable to move from the atria to the ventricles; can cause symptoms like fatigue, dizziness, and fainting |
| Types of heart block | First, second, and third-degree heart block, with the third being the most severe |
| Treatment for heart block | Pacemaker placement is often required, especially in the case of third-degree heart block |
| Other conduction disorders | Bundle branch block, sinus arrhythmia, sinus bradycardia, and tachycardia |
| Diagnosis of heart rhythm issues | Electrocardiogram (EKG), heart monitor, electrophysiology study |
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What You'll Learn
The sinus node
The electrical impulse generated by the sinus node travels through the electrical conduction system of the heart, causing it to contract and pump blood. The impulse first travels through the upper chambers (atria), causing them to contract and squeeze blood into the lower chambers (ventricles). The electrical signal then reaches the atrioventricular (AV) node, where it is briefly slowed down before continuing down the conduction pathway into the ventricles. The ventricles then contract, sending blood out to the body.
Sinus node dysfunction (SND), also known as sick sinus syndrome, can occur when the sinus node does not function properly. This can be caused by ischemia or necrosis of pacemaker cells due to a decrease in arterial blood supply, often secondary to worsening coronary artery disease or myocardial infarction. SND can lead to symptoms such as dizziness and syncope due to reduced cerebral perfusion. It is the most common reason for pacemaker implantation, accounting for 27.5% of all pacemakers implanted in the UK.
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Heart block
The heart is a pump made of muscle tissue. Its pumping action is regulated by an electrical conduction system that coordinates the contraction of the heart's chambers. Electrical impulses are generated by the sinus node, 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 electrical impulse then travels from the sinus node to the atrioventricular node (AV node), where it is slowed down before continuing down the conduction pathway via the bundle of His into the ventricles.
The main test used to diagnose heart block is an electrocardiogram (ECG), which measures the electrical activity of the heart. Treatment depends on the type of heart block and the presence and severity of symptoms. First-degree heart block may not require any treatment, while second-degree and severe cases of heart block may require a pacemaker to regulate the heartbeat.
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Wolff-Parkinson-White syndrome
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. The sinus node is the normal pacemaker of the heart and controls the heart rate. The electrical impulse travels from the sinus node to the atrioventricular node (also called the AV node), where it is slowed down for a very short period, and then continues down the conduction pathway via the bundle of His into the ventricles.
Wolff-Parkinson-White (WPW) syndrome is a condition in which there is an extra electrical pathway in the heart that leads to periods of rapid heart rate (tachycardia). This extra pathway may be separate from or within the AV node. In either case, the extra electrical pathway between the atria and ventricles causes an abnormally fast heartbeat by allowing the electrical impulse to make a continuous loop. The impulse flows down the normal path from the atrium to the ventricle, then returns to the atrium along the extra pathway. Each time the impulse completes a circuit, the heart beats. This may result in a very rapid heartbeat, a condition known as supraventricular tachycardia.
WPW syndrome is one of the most common causes of fast heart rate problems in infants and children, and it can sometimes be life-threatening, especially if it occurs with atrial fibrillation. However, this is rare, and treatment can eliminate this risk. Most people with WPW syndrome do not have any other heart problems, and the condition is usually not serious. Many people with WPW syndrome will have no symptoms or only experience occasional, mild episodes of their heart racing.
The treatment for WPW syndrome is often catheter ablation, which involves inserting a tube (catheter) into a vein through a small cut near the groin and guiding it up to the heart area. Once the tip reaches the heart, the small area causing the fast heart rate is destroyed using radiofrequency energy or by freezing it (cryoablation). This procedure has a high success rate, curing the disorder in most people. Open-heart surgery to burn or freeze the extra pathway may also be an option, usually only if heart surgery is required for other reasons.
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Electrocardiogram (EKG)
The heart is a pump made of muscle tissue. Like any other muscle, it requires oxygen and energy to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the heart's chambers. An electrical stimulus is generated by the sinus node, a small mass of specialised tissue located in the upper right chamber (atrium) of the heart. This electrical stimulus travels through the conduction pathways, causing the heart's ventricles to contract and pump blood out of the heart.
An electrocardiogram (ECG or EKG) is a simple and fast test used to evaluate the heart's electrical activity. Electrodes are placed on the skin of the chest, arms, and legs. These electrodes are connected to an ECG machine, and the electrical activity of the heart is measured, interpreted, and printed out. The word electrocardiogram is derived from the Greek words 'electro', meaning related to electrical activity, 'kardia', meaning heart, and 'graph', meaning 'to write'.
The German term 'Elektrokardiogramm' and its English equivalent, electrocardiogram, are derived from the Neo-Latin and international scientific vocabulary elements 'elektro' and 'kardi', which are cognates of 'electro' and 'cardi' respectively. The German acronym EKG, which stands for Elektrokardiogramm, is commonly used in American English, reflecting the pioneering work of German physicians in the field.
Electrocardiograms are recorded by machines consisting of a set of electrodes connected to a central unit. Early ECG machines used analog electronics to drive a motor and print out the signal on 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 and may include a screen, keyboard, and printer on a small wheeled cart. Recent advancements in electrocardiography include the development of smaller devices for integration into fitness trackers and smartwatches.
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The bundle of His
Any damage to the bundle of His can lead to heart block, a conduction disorder where the electrical signals struggle to reach the ventricles. This results in an irregular heartbeat and can cause symptoms such as fatigue, dizziness, and fainting. In some cases, a permanent pacemaker may be required to correct the issue.
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Frequently asked questions
The electrical system of the heart 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 electrical system of the heart involves electrical signals that travel through a network of nodes, cells, and pathways. The sinoatrial (SA) node, or the heart's ""natural pacemaker", initiates an electrical signal that travels through the atria, causing them to contract. The signal then passes through the atrioventricular (AV) node, where it is briefly slowed down, before continuing through the bundle of His and into the ventricles.
In some cases, an extra electrical pathway may exist in the heart, either separate from or within the AV node. This extra pathway can cause an abnormally fast heartbeat by allowing the electrical impulse to travel in a continuous loop. This condition is known as Wolff-Parkinson-White syndrome or AV node reentry, respectively.
