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Pacemaker of Heart: Natural, Artificial, Types, Working, Significance, Practice Problems, and FAQs

Pacemaker of Heart: Natural, Artificial, Types, Working, Significance, Practice Problems, and FAQs

We all know the importance of heart. It is the major organ in our body which works continuously to make us live. You know this fist-sized organ beats 100,000 times per day and pumps about 2,000 gallons of blood per day. Have you ever thought what would happen if it stopped working? Yes, we will die. You might have seen in movies that suddenly a person collapses and the people giving CPR. Cardiopulmonary resuscitation or CPR is a lifesaving technique which is useful in emergencies, such as a heart attack, cardiac arrest or in drowning cases in which breathing or heartbeat has stopped.

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Fig: Cardiac arrest

Now you understand that the heart can also fail. The most common cause is some type of blockage or the case where the natural pacemaker stops functioning. Both of which you might have seen in movies. To treat the problem of blockage of blood vessels, doctors place stents during angioplasty. On the other hand, if the natural pacemaker stops functioning, an artificial pacemaker is placed in the body with the help of a catheter.

Do you know what are the major functions of an artificial pacemaker or how does it work? How many types of artificial pacemakers does a doctor use? You will find the answers to all these questions in this article. So, let’s take a deep dive into the details of pacemakers both natural and artificial in depth in this article.

Table of contents

Pacemaker

A pacemaker is a tiny device that is implanted in the chest to assist in heartbeat regulation. It serves as a protection against the heart beating too slowly. The placement of a pacemaker in the chest requires surgery. A pacemaker is also known as a cardiac pacing device. When the heart does not beat normally, the pacemaker provides electrical stimulation. It is powered by batteries and is connected to the heart by a long, and thin wire.

Fig: Pacemaker of heart

Types of pacemaker

Pacemakers are of two types as follows:

Natural pacemaker

The natural pacemaker of the heart is the sino-atrial node which is located in the upper right chamber of the heart called the atrium. It sends an electrical impulse to make the heart beat.

Artificial pacemaker

The job of a pacemaker is to artificially take over the role of the sino-atrial node if it is not working properly in the body.

SA Node - Natural pacemaker

The SA node (SAN) of the heart is considered as the natural pacemaker or ‘heart of heart’.

The sino-atrial node consists of a group of crescent shaped myocytes that are divided by connective tissue. It is situated in the upper part of the wall of the right atrium or auricle of the heart. Due to its location in the right atrium, it is referred to as the sino-atrial node.

The SA node is responsible for generating nerve impulses at the highest rate, that is 70 - 75 per minute and carrying out contraction of the atria (upper chambers of the heart). The impulses are then carried to the AVN or atrioventricular node. It is the node where the impulses then carry out the contraction of the both ventricles (lower chambers of the heart). It is also called the pace setter of the heart.

Fig: Nodal tissues of the heart

Pacemaker potential

Pacemaker cells in the sino-atrial node do not have a resting phase, in contrast to atrial and ventricular cells. The ability of these cells to depolarise automatically when an action potential finishes is known as the pacemaker potential.

Mechanism of working of SA node

The SA node also referred to as the sino-atrial node, is a cluster of myocytes in the shape of a crescent that is separated by connective tissue and occupies a few square millimetres. It can be found where the superior vena cava opening meets the crista terminalis in the right atrium's top wall. These cells have the capacity to produce an electrical impulse on their own. The SA node is formed by the coordinated activity of these so-called pacemaker cells. Perinodal cells, also known as transitional (T) cells, then convey this electrical impulse to the right atrium and the rest of the heart's electrical conduction system, where it is finally converted into myocardial contraction which results in the blood distribution to the rest of the body. The sino-atrial node continuously produces electrical impulses, which establishes a healthy heart's normal rhythm and pace.

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GIF: Mechanism of working of SAN and AVN

Regulation of heart beat

Depending on a variety of physiological and environmental conditions, the heart rate can vary remarkably. The SA nodal myocytes depolarize intrinsically between 60 and 100 beats per minute while at rest, which is typically regarded as a normal heart rhythm. The sino-atrial node's input is regulated by the autonomic nervous system. The firing of the sino-atrial node, which starts following cardiac cycles, is controlled by the autonomic fibres, which also have an impact on heart rate. The pace of action potential production is slowed by parasympathetic input, which lowers the heart rate; on the other hand, the rate of action potential production is accelerated by sympathetic input, which raises the heart rate. Parasympathetic regulation of the heart occurs via the vagus nerve and is the main mechanism that regulates beat-to-beat control of the heart rate.

Fig: Regulation of heart beat

The sino-atrial node is closely regulated and under tight control, which enables the heart to adjust to different physiologic stimuli. For instance, the heart reacts to the body's increased need for oxygen during exercise, as well as the body's increased sympathetic input and heart rate.

GIF: Heart beat increases during exercise

Pacemaker shift

Since there are several myocytes in the sino-atrial node, they are not necessarily generating the same electrical impulse. This is known as a pacemaker shift. The heart rate might increase within normal limits if one myocyte produces an action potential that is quicker than the myocyte that generated the preceding action potential. This is recognised as a superior shift. Action potentials that are slower than the previous action potential can also be created by myocytes. This would result in a drop in heart rate that is still within normal range and is regarded as an inferior shift.

Artificial pacemaker

Pacemakers are medical devices that can be inserted into your body, typically through surgery, to support the electrical system in your heart. They can control unnatural cardiac rhythms and stop issues before they disrupt or risk your life. The weight of the pacemakers is as little as one ounce or 28 grams normally.

Fig: Artificial pacemaker of heart

Parts of artificial pacemaker

Most artificial pacemakers are composed of two parts:

  • Pulse generator
  • Leads or electrodes

Pulse generator

A pulse generator is considered as a small metal case that contains an electronic circuit with a small computer and a battery that regulates the impulses that are sent to the heart. This electrical circuit normally regulates the frequency of electrical pulses delivered to the heart. The internal pulse generator or IPG is placed in the subcutaneous tissue normally at the abdominal level. It is then connected to the electrode using tunnelled extension leads.

Leads or electrodes

The electrical pulses necessary to modify heart rate are delivered by one to three flexible, insulated wires that are individually inserted into one or more heart chambers. Some modern pacemakers do not require leads. Direct implantation of these leadless pacemakers is done within the cardiac muscles.

Types of artificial pacemaker

A particular pacemaker with one to three wires may be utilised, depending on the type of heart issue. There are different types of pacemakers as follows:

  • Single chamber pacemaker
  • Dual chamber pacemaker
  • Biventricular pacemaker
  • Leadless pacemaker

Single chamber pacemaker

This type of pacemaker carries electrical impulses from the right ventricle to the heart. This is because this type of pacemaker has one lead that connects the pulse generator to one chamber of the heart. The single-chamber pacemaker is used commonly to regulate the pacing of a heartbeat. This can be done by connecting the lead to the right ventricle. The connection of a lead to the chamber of the heart can be altered and this depends on the symptoms and the type of pacing required. The lead can also be connected to the right atrium to accelerate the pacing in that chamber.

Fig: Single chamber pacemaker

Dual-chamber pacemaker

This type of pacemaker carries impulses from the right ventricle and the right atrium to the rest of the heart. It aids in controlling the pace of contractions between two chambers. The dual-chamber pacemaker helps the chambers to work together. It allows the chambers to contract and relax in the proper rhythm. The right atrium and right ventricle can effectively exchange blood due to contractions.

Biventricular pacemaker

This type of pacemaker is also known as a cardiac resynchronisation therapy (CRT) device. It has three leads that are connected to the right atrium and both the ventricles. The biventricular pacemaker is used to treat patients with advanced heart failure-related arrhythmias or an irregular heartbeat. Many heart failure patients do not have simultaneous pumping of the left and right ventricles. To overcome this problem, doctors program the biventricular pacemaker in such a way that the contractions of the ventricles are coordinated so that they can both pump together. Your heart pumps blood more effectively when the ventricles are coordinated, which can relieve the symptoms of heart failure. It synchronises the ventricles' pumping function and hence the procedure is referred to as cardiac resynchronisation therapy.

Leadless pacemaker

A compact, and a battery-operated device called a leadless pacemaker. It causes the heart to receive gentle, and painless electrical signals. This keeps the heartbeat consistent. This pacemaker is implanted into the heart by the doctor using a catheter. Leadless pacemakers are suitable for those patients that have permanent atrial fibrillation with bradycardia (It occurs when the heart beats fewer than 60 times a minute) or tachycardia ( It occurs when the heart rate is over 100 beats a minute). These are also suitable for those who require pacing sometimes.

Working of artificial pacemaker

A pacemaker is a small device whose weight varies in a range of 20 - 50g. It consists of one or more wires known as pacing leads that attach to the heart and a pulse generator with a battery and a small computer circuit. The heart receives electrical impulses from the pulse generator via the connections. The pacing rate refers to the frequency at which electrical impulses are transmitted. Nearly all modern pacemakers operate on demand. The discharge rate can thus be adjusted to change in accordance with the body's requirements. The pacemaker transmits signals steadily if it detects that the heart has skipped a beat or is beating too slowly. It doesn't send any messages if it detects that the heart is beating regularly on its own. A unique sensor found in most pacemakers that may detect body movement or the breathing rate. By doing this, they might increase the discharge rate while a person is active.

Significance of pacemaker

Pacemakers are designed to raise the standard of living and stop disturbances brought on by heart issues. The pacemaker is essential for heart patients in the following contrasts:

  • Reducing the number of cardiac rhythm disorder symptoms, such as confusion, nausea, palpitations, chest pain, and more.
  • Avoid unpleasant side effects brought on by arrhythmias, such as fainting.
  • Preserve one's life by avoiding a heart attack.
  • Pacemaker will prolong life.

Risks

Complications related to the pacemaker surgery or having a pacemaker are uncommon. These include the following:

  • Collapsed lung.
  • Presence of blood in the space between chest wall and the lung.
  • Movement of the device or leads.
  • Infection near to the site in the heart where the pacemaker is implanted.
  • Swelling or bruising at the pacemaker site.
  • Bleeding at the pacemaker site.
  • Blood clots near the pacemaker site.
  • Damage happening to nerves or blood vessels present near the pacemaker.

Practice Problems

Q1. What are the components of an artificial pacemaker?
Answer: The artificial pacemaker is composed of two main parts as follows:

  • Pulse generator - It is considered as a small metal case that contains an electronic circuit with a small computer and a battery that regulates the impulses that are sent to the heart. This electrical circuit normally regulates the frequency of electrical pulses delivered to the heart. The internal pulse generator or IPG is placed in the subcutaneous tissue normally at the abdominal level. It is then connected to the electrode using tunnelled extension leads.
  • Leads or electrodes - The electrical pulses necessary to modify heart rate are delivered by one to three flexible, insulated wires that are individually inserted into one or more heart chambers. Some modern pacemakers do not require leads. Direct implantation of these leadless pacemakers is done within the cardiac muscles.

Q2. Which part of the heart is considered the natural pacemaker of the heart?

A. heart?AV
B. SA node
C. Purkinje fibres
D. Right ventricle

Solution: The sino-atrial node continuously produces electrical impulses, which establishes a healthy heart's normal rhythm and pace. As a result, the SA node is referred to as the heart's natural pacemaker. The SA node is responsible for generating nerve impulses at the highest rate, that is 70 - 75 per minute and carrying out contraction of the atria (upper chambers of the heart). Hence, the correct option is b.

Q3. In which chamber of the heart is the SA node situated?

A. Right atrium
B. Left atrium
C. Right ventricle
Left ventricle

Solution: A human heart is made up of four chambers that include two auricles and two ventricles. A myogenic heart is one that is capable of self-excitation. The contractions of the human heart originate in its muscle and hence it is myogenic in nature. A modified muscle called the sino-atrial node, which starts electrochemical impulses, regulates the heartbeat in a myogenic heart. The pacemaker, also known as the sino-atrial node, is located in the upper corner of the right atrium. Hence, the correct option is a.

Q4. Pacemaker is an electronic device. So, what is the source of power in pacemakers?
Answer:
The battery is the power source of the pacemaker. It supplies the necessary energy or power for the pacemaker's entire circuit to function.

FAQs

Q1. What is the general lifespan of a pacemaker?
Answer:
Depending on usage, most device batteries, such as pacemakers have a minimum lifespan of 5 to 7 years. The pulse generator or battery will then need to be changed.

Q2. Which element is used while making a pacemaker?
Answer:
The pacemaker consists of a radioactive element called plutonium-238.

Q3. How long has a person living with a pacemaker?
Answer:
The lifespan of a person with a pacemaker totally depends on the health and disease condition of that person. One known example of the longest working pacemaker is 37 years and 251 days. This was achieved by Stephen Peech as of 7 June 2021. The pacemaker was implanted on 29th September 1983 in him.

Q4. What is the world's smallest pacemaker?
Answer:
Micra™ is considered the world's smallest pacemaker. Most of the pacemakers are placed in the patient's chest with leads running to the heart whereas the Micra is a leadless pacemaker and is implanted directly into the heart.

 

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