Otis Singleton
The heart is a muscular pump, and its pumping action is controlled by electrical impulses. These impulses trigger heartbeats and cause the heart to contract. Normally, the heart contracts 60 to 100 times a minute at rest, but this can vary with age. An abnormality in the electrical pathway can cause the heart to beat too fast (tachycardia) or too slow (bradycardia). An ECG (electrocardiogram) can be used to assess the rhythm of the heart and detect any abnormalities.
| Characteristics | Values |
|---|---|
| Definition | Electrical impulses regulate the pumping action of the heart. |
| Heartbeat | Each time an electrical impulse completes a circuit, the heart beats. |
| Normal Heart Rate | The heart contracts about 60 to 100 times a minute at rest, depending on a person's age. |
| Atria and Ventricles | The atria contract a fraction of a second before the ventricles, allowing blood to empty into the ventricles before they contract. |
| Abnormal Heart Rate | An extra electrical pathway between the atria and ventricles can cause a very rapid heartbeat (tachycardia). |
| Abnormal Heart Rate | An abnormal "focus" can act like a second pacemaker, causing a faster heart rate. |
| Abnormal Heart Rate | Certain conditions cause a slow heartbeat (bradycardia), e.g., heart block, which is when the electrical signal can't get through to the lower chambers. |
| Diagnosis | An ECG (electrocardiogram) can assess the rhythm of the heart by recording its electrical activity. |
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What You'll Learn
Electrical impulses trigger heartbeats
The heart is a pump made of muscle tissue, and its pumping action is regulated by electrical impulses. These impulses trigger heartbeats. As the electrical impulse moves through the heart, the heart contracts, and each contraction of the ventricles represents one heartbeat. Normally, at rest, the heart contracts about 60 to 100 times a minute, depending on a person's age. 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 impulse flows through the heart in a specific pathway. It first goes from the atrium to the ventricle, then to the AV node, where it is slowed down for a very short period. After passing through the AV node, the electrical current continues down the conduction pathway, through a pathway called the bundle of His, and into the ventricles. The bundle of His divides into right and left pathways (bundle branches) to give electrical stimulation to the right and left ventricles.
Sometimes, there can be an extra electrical pathway between the atria and ventricles, causing an abnormally fast heartbeat. This extra pathway allows the electrical impulse to make a continuous loop, resulting in a very rapid heartbeat. In other cases, instead of an extra pathway, there may be an abnormal "focus," which can act like a second sinus node or natural pacemaker, causing the heart to beat much faster than normal. Certain conditions are associated with a slow heartbeat, or bradycardia, such as heart block, which occurs when the electrical signal cannot get through to the lower chambers of the heart from the upper portion.
Symptoms of an irregular heartbeat, or arrhythmia, can include a feeling that your heart is fluttering (heart palpitations), shortness of breath, dizziness, or fainting. If you are experiencing these symptoms, it is important to see a doctor, who may perform an ECG (electrocardiogram) to assess the rhythm of your heart. This test involves recording the electrical activity of the heart with small stickers attached to the chest, and it can help determine if medicine or a procedure is needed to treat the arrhythmia.
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The AV node slows impulses
The heart is a pump made of muscle tissue, and its pumping action is controlled by electrical impulses. These impulses trigger heartbeats, and problems with these impulses can cause the heart to beat too fast (tachycardia) or too slow (bradycardia).
The heart's electrical conduction system is a network of nodes, cells, and signals that controls the heartbeat. The sinoatrial (SA) node, located in the upper part of the right atrium, acts as the heart's natural pacemaker, sending electrical impulses that initiate the heartbeat. The autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems, regulates the speed at which the SA node sends electrical signals. During physical activity, the sympathetic nervous system increases the heart rate, while the parasympathetic nervous system slows it down during rest.
The atrioventricular (AV) node, situated near the heart's central area, plays a crucial role in slowing down the electrical impulses generated by the SA node. This delay ensures that the atria, the upper chambers of the heart, are empty before the contraction stops. The AV node consistently slows each electrical signal by a fraction of a second, allowing the atria to empty blood into the ventricles (the lower chambers) before the ventricles contract. This coordinated delay is essential for the efficient pumping of blood and maintaining a healthy heartbeat.
The AV node's function is further supported by the bundle of His, a branch of nerve cells that extends from the AV node. This bundle receives the electrical signal from the AV node and transmits it to the Purkinje fibers, which spread the signal throughout the heart. The bundle of His, along with its branches and the Purkinje fibers, resembles an upside-down tree, with the bundle of His forming the tree trunk and the Purkinje fibers creating the tree's canopy. This intricate network ensures the timely and controlled propagation of electrical impulses, facilitating the heart's rhythmic contractions.
Any disruptions or abnormalities in the AV node's function can have significant implications for the heart's electrical system and overall cardiac health. Conditions such as arrhythmia, atrial fibrillation, bundle branch block, and long QT syndrome are often associated with impaired electrical signals between the heart's atria and ventricles. Therefore, the AV node's role in slowing impulses is vital to maintaining the proper timing and coordination of the heart's contractions, ensuring efficient blood circulation throughout the body.
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Impulse problems cause tachycardia
The heart is a pump made of muscle tissue, and its pumping action is regulated by electrical impulses. These impulses trigger heartbeats. When a person is at rest, the heart normally contracts about 60 to 100 times a minute, depending on their age.
However, when there are problems with these electrical impulses, it can cause tachycardia, a condition characterised by a heart rate of more than 100 beats per minute at rest. Tachycardia is an abnormal heart rhythm that can prevent the heart from filling up with enough blood to supply all the cells with the blood and oxygen they need.
There are several types of tachycardia, and they can be caused by various factors. One type is supraventricular tachycardia (SVT), which often affects people who smoke, drink excessive alcohol, or consume a lot of caffeine. SVT is also more common in women and children. It is also associated with heart attacks and atrial fibrillation. SVT can be further classified into paroxysmal supraventricular tachycardia (PSVT), where electrical signals repeat, causing a fast heartbeat that starts and stops suddenly.
Another type is ventricular tachycardia, which is associated with abnormal electrical pathways present at birth, structural heart problems, medications, or electrolyte imbalances. Ventricular tachycardia can be life-threatening and requires immediate medical attention.
Sinus tachycardia is another form of tachycardia that can be caused by strenuous exercise, fever, fear, stress, anxiety, certain medications, or street drugs. It can also be triggered by anaemia, an overactive thyroid, or damage from a heart attack or heart failure.
In some cases, there may be an extra electrical pathway between the atria and ventricles, allowing the electrical impulse to create a continuous loop, resulting in a very rapid heartbeat. Additionally, an abnormal "focus" may act as a second pacemaker, causing the heart to beat faster than normal.
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Heart block impedes electrical signals
The heart is a pump made of muscle tissue. Its pumping action is controlled by electrical impulses. Normally, these electrical signals travel from the heart's upper chambers (atria) to the lower chambers (ventricles). The signal moves through the AV node, a cluster of cells that link the electrical activity from the top to the bottom chambers. Each contraction of the ventricles represents one heartbeat.
Heart block, or atrioventricular (AV) block, is a conduction disorder that disrupts the normal pathway of these electrical signals. It is characterised by a delay or blockage of the electrical impulses travelling from the atria to the ventricles. Heart block can range from mild to severe, depending on the extent to which the electrical signals are impeded.
There are three degrees of heart block, classified according to the severity of the blockage. In first-degree heart block, the electrical impulse still reaches the ventricles but moves more slowly than normal through the AV node. This typically results in a slower heart rate but may not cause any noticeable symptoms. Certain medications, such as digitalis, beta-blockers, and calcium channel blockers, can cause first-degree heart block as a side effect.
Second-degree heart block occurs when only some electrical signals from the atria reach the ventricles. This can cause the heart to miss beats and beat slowly and irregularly. There are two types of second-degree heart block: Mobitz Type I and Mobitz Type II. In Mobitz Type I, also known as Wenckebach's AV block, the electrical signal gradually slows down until the heart skips a beat. Mobitz Type II is more serious, with some electrical signals failing to reach the ventricles, resulting in an irregular and slower heart rate.
Third-degree heart block, or complete heart block, is the most severe form, characterised by a complete blockage of electrical signals from the atria to the ventricles. This negatively affects the heart's ability to pump blood effectively, leading to serious symptoms such as a very slow heart rate, fainting, chest pain, and shortness of breath. Treatment for third-degree heart block typically involves the implantation of a pacemaker to ensure the heart continues to beat regularly.
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ECGs assess heart rhythm
The heart is a pump made of muscle tissue. Its pumping action is controlled by electrical impulses, which trigger heartbeats. These impulses cause the heart to contract about 60 to 100 times a minute when the body is at rest. The atria contract a fraction of a second before the ventricles so that blood empties into the ventricles before they contract.
An electrocardiogram (ECG) is a quick, non-invasive, and low-risk test used to evaluate the heart's function. It measures and records the electrical activity of the heart, which can be used to assess its rhythm. Small plastic patches with electrodes are placed on the skin of the chest, arms, and legs. These electrodes are connected to an ECG machine by lead wires, which measure, interpret, and print out the electrical activity of the heart.
ECGs can be performed while a patient is lying down and resting or during exercise as part of a stress test. The test can be conducted in an ambulance, emergency room, or during a scheduled appointment. Certain personal devices, like smartwatches, can also take an ECG, but it is best to have a healthcare provider perform the test. A typical ECG only tracks the heart's electrical activity for a very short time, usually about 10 seconds.
An ECG records the electrical impulses in the heart to show how fast it is beating, the rhythm of the beats (steady or irregular), and the timing of the impulses as they move through the heart. A normal ECG will show a regular series of waves that repeat: a small bump (P wave), a spike (QRS complex), and another small bump (T wave). These waves should be repeated at the same distance from each other, indicating a regular heart rate and normal rhythm. Unusual wave patterns can indicate a problem, and abnormal ECG results can help healthcare providers identify which part of the heart is affected.
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Frequently asked questions
Electrical impulses are what trigger heartbeats. They cause the heart to contract and pump blood.
At rest, the heart contracts about 60 to 100 times a minute, depending on a person's age.
An ECG is a painless test that involves recording the electrical activity of your heart with several small stickers attached to your chest.
Arrhythmia is when your heart beats either too fast (tachycardia) or too slow (bradycardia).
Arrhythmia can be caused by an extra electrical pathway between the atria and ventricles, allowing the electrical impulse to make a continuous loop.
