Molly Ayala
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 controlled by an electrical conduction system that coordinates the contraction of the four chambers of the heart. This electrical system allows the heart to speed up and slow down as the body's demands change. The sinus node, or sinoatrial node (SA node), is the heart's natural pacemaker and generates an electrical stimulus, or impulse, that travels through the heart's chambers, causing them to contract and pump blood. The SA node is a small mass of specialised tissue located in the right upper chamber (atria) of the heart.
| Characteristics | Values |
|---|---|
| Purpose | To coordinate the pumping of the four chambers of the heart and to control the heart rate |
| Heart's 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 |
| Heart rate | 60 to 100 beats per minute at rest |
| Heart rate during exercise | Increases to meet the body's needs |
| Heart rate during sleep | Decreases as the body needs less oxygen |
| Heart rate issues | Bradycardia (slow heart rate), Tachycardia (fast heart rate) |
| Diagnosis | ECG (electrocardiogram) to assess the rhythm of the heart |
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What You'll Learn
The sinus node: the heart's pacemaker
The sinus node, also known as the sinoatrial node (SA node) or Keith-Flack node, is a cluster of myocytes with pacemaker activity. It is a small mass of specialised tissue located in the right upper chamber (atria) of the heart. The SA node was first discovered by medical student Martin Flack in the early 1900s.
The sinus node is the heart's natural pacemaker, responsible for generating electrical impulses that cause the heart to contract and pump blood. These electrical impulses are generated regularly, 60 to 100 times per minute under normal conditions. The electrical stimulus travels from the sinus node through the conduction pathways, causing the heart's ventricles to contract and pump out blood. The right and left atria are stimulated first, contracting to push blood into the ventricles. The ventricles then contract, pumping blood out into the body's blood vessels.
The sinus node's function as a pacemaker is critical, as it sets the rhythm and rate of the heart. The rate of action potentials produced by the sinus node influences the heart rate. If the sinus node is not functioning properly, the heartbeat may slow down, leading to a decrease in blood pressure. This condition is known as sinus node dysfunction or sick sinus syndrome, which can cause an abnormally slow heart rhythm called bradycardia. In such cases, implantation of a permanent pacemaker may be required to regulate the heartbeat.
The autonomic nervous system controls input into the sinus node, allowing the heart to adapt to various physiological stressors. Parasympathetic input slows down action potential production, decreasing the heart rate, while sympathetic input increases it. This regulated control enables the heart to respond to the body's changing oxygen demands during exercise or other activities.
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Electrical impulses: the spark plug of the heart
The heart is a pump made of muscle tissue. Like all muscles, it needs a source of energy and oxygen to function. Electrical impulses trigger heartbeats, acting as a spark plug to start a heartbeat. The electrical impulse starts on the right side of the upper chamber in an area called the sinus node. The sinus node is the heart's natural pacemaker and controls the heart rate.
The sinus node generates an electrical stimulus regularly, 60 to 100 times per minute under normal conditions. The right and left atria are stimulated first and contract to push blood from the atria into the ventricles. The electrical impulse then travels from the sinus node to the atrioventricular node (also called the AV node). Here, the impulses are slowed down for a very short period, allowing the atria to contract a fraction of a second before the ventricles.
The electrical current then 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. The ventricles then contract, sending blood throughout the body.
The heart's electrical system controls the timing of the heartbeat by regulating the heart rate and rhythm. The heart rate is the number of times the heart beats per minute, and the rhythm is the synchronized pumping action of the four heart chambers. The heart rate and rhythm change to meet the body's needs, such as during physical activity or sleep.
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Heart rate: controlled by the electrical system
The heart's pumping action is controlled and coordinated by an electrical conduction system. The heart's electrical system controls the timing of the heartbeat by regulating the heart rate and rhythm. The heart rate is the number of times the heart beats per minute, and the rhythm is the synchronized pumping action of the four heart chambers.
The heart's natural pacemaker, the sino-atrial node (SA node), is a small area of specialized electrical tissue located in the right upper chamber (atria) of the heart. The SA 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 right and left atria are stimulated first and contract to push blood from the atria into the ventricles. The ventricles then contract to pump blood out into the blood vessels of the body.
The electrical impulse leaves the SA node and travels a set path through the upper chambers, the atria, causing them to contract and squeeze blood into the lower chambers. The electrical signal then reaches the atrioventricular (AV) node, located between the atria and ventricles. The AV node slows down the electrical impulses for a very short period, allowing the atria to contract a fraction of a second before the ventricles. 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.
The heart rate can adjust higher or lower to meet the body's needs. For example, during exercise, when the body requires more oxygen to function, signals from the body cause the heart rate to increase to deliver more blood and oxygen to the body. Conversely, during rest or sleep, when the body needs less oxygen, the heart rate decreases.
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Tachycardia: when the heart beats too fast
The heart, a muscle pump, is regulated by an electrical conduction system. This system coordinates the contraction of the heart's chambers, with electrical impulses generated by the sinus node, the heart's natural pacemaker. In a healthy heart, the sinus node generates an electrical stimulus 60 to 100 times per minute. This causes the heart to contract and pump blood out to the body.
Tachycardia is a condition where the heart beats too fast, exceeding the normal rate of 60-100 beats per minute when at rest. This can be caused by a variety of factors, including exercise, stress, fever, smoking, excessive alcohol consumption, caffeine, medications, and street drugs. It is also more common in pregnant women, and in those with structural heart problems or a history of heart attacks.
There are several types of tachycardia, including supraventricular tachycardia (SVT), which is the most common form in infants and children, and ventricular tachycardia (VT). SVT is characterised by a fast heart rate that starts in the upper chambers of the heart, with abnormal electrical signals causing the heart rate to increase. VT, on the other hand, originates in the lower chambers, with electrical signals firing abnormally fast and interfering with impulses from the sinus node.
Tachycardia can cause a range of symptoms, including a feeling of fluttering in the heart, shortness of breath, dizziness, or fainting. In extreme cases, it can lead to unconsciousness or cardiac arrest. Treatment options depend on the specific type of tachycardia and the symptoms experienced, and may include medication or procedures to address the underlying cause.
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Bradycardia: when the heart beats too slow
The heart, a muscle pump, has an electrical conduction system that regulates its pumping action by coordinating the contraction of its chambers. The sinus node, a small mass of specialised tissue located in the upper right chamber of the heart, generates an electrical stimulus, which travels through the conduction pathways, causing the ventricles to contract and pump out blood.
Bradycardia is a type of cardiac arrhythmia where the resting heart rate is below the healthy average of 60-100 beats per minute (bpm). Specifically, this condition applies to a resting heart rate below 60 bpm. A rate below 40 bpm is often considered a threshold for severe bradycardia.
The symptoms of bradycardia are often due to reduced oxygen caused by a low heart rate. When the heart isn't pumping blood fast enough, organs may not get enough oxygen, especially the brain. This can lead to dizziness and fainting spells and, in severe cases, may contribute to the risk of an ischemic stroke.
The causes of bradycardia include medication, age, damage to the heart tissue, congenital heart defects, inflammatory diseases, and metabolic problems such as hypothyroidism. People with heart disease or an increased risk of heart disease are more likely to develop bradycardia. Additionally, certain medications can cause bradycardia as a side effect.
The treatment for bradycardia depends on the circumstances and severity. In cases with minimal to no symptoms, treatment may not be necessary. Lifestyle changes such as quitting smoking, reducing alcohol intake, increasing exercise, and following a healthy diet may be recommended. If medication is causing bradycardia, doctors may adjust or discontinue the medication. In severe cases, a pacemaker may be required to regulate the heart's rhythm and speed up the heart rate.
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Frequently asked questions
Yes, the heart has an electrical conduction system that coordinates the pumping action of the four chambers of the heart and controls the heart rate.
The heart's electrical system is responsible for coordinating the pumping action of the four chambers of the heart and controlling the heart rate so that it can speed up or slow down to meet the body's needs.
The heart's electrical system generates an electrical stimulus in a small mass of specialized tissue called the sinus node or SA node, located in the right upper chamber of the heart. This electrical impulse then travels through the conduction pathways, causing the heart's chambers to contract and pump out blood.
Problems with the heart's electrical system can cause the heart to beat too fast (tachycardia) or too slow (bradycardia). Symptoms of an irregular heartbeat include heart palpitations, shortness of breath, dizziness, and fainting. Treatment options may include medication or procedures such as the implantation of a permanent pacemaker.
Your doctor may perform an ECG (electrocardiogram) to assess the rhythm of your heart. This painless test involves recording the electrical activity of your heart using small stickers attached to your chest.
