Beatrice Lang
The human heart is a pump made of muscle tissue. Like all muscles, it requires oxygen and energy to function. The heart's pumping action is controlled by an electrical conduction system that coordinates the contraction of its chambers. Electrical impulses are generated by the sinus node, a small mass of specialised tissue located in the upper right chamber of the heart. These impulses travel through the heart's chambers, causing them to contract and pump blood. This electrical system is critical to the heart's function, and disruptions to it can lead to serious complications, including cardiac arrest.
| Characteristics | Values |
|---|---|
| How the electrical system of the heart works | The electrical impulse starts in the sinus node, located in the upper right chamber of the heart, and travels through the right and left atria, causing them to contract and pump blood into the ventricles. |
| The electrical impulse then reaches the atrioventricular (AV) node, where it is slowed down before continuing into the ventricles. | |
| The AV node splits the signal into right and left pathways to provide electrical stimulation to both ventricles, causing them to contract and pump blood throughout the body. | |
| Heart rate regulation | The sinus node acts as the heart's pacemaker and controls the heart rate, generating an electrical stimulus 60 to 100 times per minute under normal conditions. |
| The heart rate varies depending on factors such as age, physical activity, excitement, and rest. | |
| Bradycardia | Bradycardia is a condition associated with a slow heartbeat, caused by a dysfunctional sinus node or heart block, resulting in symptoms like fatigue, dizziness, and fainting. |
| Tachycardia | Tachycardia refers to a rapid heart rate caused by the SA node firing at an increased rate, which can lead to abnormally fast heartbeats. |
| Heart block | Heart block occurs when electrical signals are weakened or blocked, preventing them from reaching the ventricles. |
| Conduction disorder | A disruption in the heart's electrical pathway can increase the risk of major complications, including cardiac arrest. |
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What You'll Learn
Electrical impulses trigger heartbeats
The electrical system of the heart is critical to how it functions. The cardiac conduction system, the network of nodes, cells, and signals, controls the heartbeat. The electrical impulses in the heart can be too slow or fast, causing a decrease or increase in heart rate, respectively. Bradycardia refers to a slow heart rate, while tachycardia indicates a rapid heart rate.
The heart requires an electrical impulse to initiate a heartbeat. This impulse originates in the sinus node, located in the upper portion of the right atrium, and spreads across the heart. The sinus node acts as the heart's natural pacemaker, regulating the heart rate according to the body's needs, such as during exercise or rest.
As the electrical impulse travels through the heart, it causes the atria to contract and squeeze blood into the lower chambers, known as ventricles. The impulse then reaches the atrioventricular (AV) node, where it is briefly delayed before spreading through the ventricles, resulting in their contraction and the subsequent pumping of blood throughout the body.
The cardiac electrical signal controls the heartbeat by determining the heart rate and ensuring the correct sequence of muscle contractions. Each electrical impulse generates one heartbeat, and the conduction system helps maintain a steady and coordinated rhythm. This process of contracting and relaxing the heart regulates blood flow within the heart and to the rest of the body.
Disruptions in the electrical system of the heart, such as conduction disorders or heart block, can lead to serious complications, including cardiac arrest. These issues can arise from an extra electrical pathway or an abnormal "focus" that acts like a second pacemaker, causing rapid heartbeats.
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Impulse problems
The heart's electrical system controls the electrical impulses that make the heart beat and regulate its conduction, which organises the beating of the heart. This electrical system is critical to how the heart functions. The heart is a pump made of muscle tissue, and its pumping action is regulated by electrical impulses.
The electrical impulse originates in the sinus node, which is located in the upper portion of the right atrium. 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. This electrical stimulus travels down through the conduction pathways and causes the heart's ventricles to contract and pump out blood. This is referred to as atrial depolarization, an action that pushes blood into the right and left ventricles, the bottom two chambers of the heart.
However, the electrical impulses in the heart can sometimes be too slow, causing a decrease in heart rate, or bradycardia. In some cases, the impulses can be abnormally fast, which is called tachycardia. This can be caused by an extra electrical pathway in addition to the normal path, allowing the electrical impulse to make a continuous loop. In other cases, an abnormal "focus" acts like a second sinus node or natural pacemaker, causing the heart to beat much faster than the sinus node normally would.
Problems with the heart's electrical system can lead to arrhythmias, disturbances in the rhythm of the heartbeat. This can cause the heart to race so fast that it might suddenly stop. Heart block is another condition that can result from electrical problems in the heart, where the electrical signal that starts in the upper portion of the heart cannot get through to the lower chambers.
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The sinus node
Sinus node dysfunction (SND), also known as sick sinus syndrome, is a group of irregular heartbeat conditions caused by faulty electrical signals of the heart. When the heart's sinoatrial node is defective, the heart's rhythms become abnormal, typically too slow or exhibiting pauses in its function, and very rarely faster than normal. SND is the most common reason to have a pacemaker implanted, accounting for 27.5% of all pacemakers implanted in the UK. Implantable electronic pacemakers are currently the only effective treatment for SND.
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Heart block
There are three degrees of heart block severity: First-degree heart block is the least severe, where electrical signals are slowed but still reach the ventricles. Treatment may not be necessary. Second-degree heart block is more serious, with some electrical impulses from the atria reaching the ventricles, while others are blocked. This can lead to an intermittent failure of conduction, causing the heart to skip beats. Depending on the underlying cause, a pacemaker may be required. The third-degree heart block is the most severe, where electrical signals completely fail to reach the ventricles, resulting in a dramatic slowing of the pulse or even the absence of a pulse. In this case, a pacemaker is typically necessary.
Diagnosis of heart block is typically done through an electrocardiogram (ECG) that measures the electrical activity of the heart. Treatment depends on the severity and symptoms, ranging from no treatment for mild cases to pacemaker implantation for more severe cases.
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Bradycardia and tachycardia
Bradycardia is when the heart beats abnormally slowly, fewer than 60 times per minute. It is the most common cause of a low heart rate and is caused by the SA node firing at a reduced rate. It is not always a cause for concern, such as when a person is sleeping, and it is common in athletes. However, it can also be caused when the central nervous system is not sending the proper message to the heart due to damage.
Tachycardia is when the heart beats faster than 100 times per minute. This is also referred to as a rapid heart rate and can be caused by the SA node firing at an increased rate. This is normal and necessary when a person is exercising. There are many types of tachycardia, but the most common and severe form is ventricular tachycardia.
Both conditions can turn into severe issues if not treated properly. Treatment depends on the underlying cause and severity of the condition.
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Frequently asked questions
The heart requires a source of energy and oxygen to function. Electrical impulses trigger heartbeats. These impulses start in the sinus node, which is located in the upper right chamber of the heart. The sinus node acts as the heart's pacemaker and controls the heart rate.
Electrical signals in the heart can be too slow or blocked, causing a decrease in heart rate or even stopping the heart. This is called bradycardia. Heart block occurs when the electrical signal that starts in the upper portion of the heart cannot get through to the lower chambers.
Pacemakers are used to treat heart block and sinus node dysfunction. They provide electrical stimulation to the heart, allowing it to contract and pump blood effectively.
