What is a Pacemaker?
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An artificial pacemaker is an electronic medical device which is used to treat abnormalities in the rhythm of the human heart. These devices are used internally inside the body, are usually small and implanted into the chest. The pacemaker provides electrical impulses that allow the heart to beat at its normal rate, if the heart were not able to do so by itself.
Reason for the need of a pacemaker
A pacemaker is used to treat arrhythmias. Arrhythmias are problems or abnormalities in the rhythm of the heartbeat. These problems or abnormalities include an irregular heartbeat, the rate of the heartbeat being too slow or the rate of the heartbeat being too fast. Arrhythmias are a severe condition which causes shortness of breath, fatigue and fainting. It can also lead to serious damage of bodily organs or even death if not treated properly. However these problems can easily be solved with the implementation of a pacemaker. A pacemaker can allow a person with these problems to lead a normal and active lifestyle relieving them of fatigue and fainting.
How an artificial pacemaker functions
The pacemaker is run on batteries and delivers electrical impulses through electrodes, which are connected to the cardiac muscle to regulate the beat of the heart. These electrical impulses regulate the heart beat and maintain the correct rhythm of the heart. The leads which connected between the pacemaker and the heart send electrical signals back and forth and sense when the heart needs some sort of treatment. When it requires treatment, the heart will receive an impulse from the device to correct the problem.
Human Pacemaker
Within the cardiovascular system there are electrical events which cause the contraction and relaxation of the muscles in the heart. The cells of cardiac muscle can be classified as either non-pacemaker cells or pacemaker cells in terms of electrical activity. It is the pacemaker cells that create the impulses and control the heart rate.
The pacemaker cells lie within the sinoatrial (SA) node. This node can be found in the wall of the right atrium. These pacemaker cells cause spontaneous depolarizations which generate action potentials that determine the heart rate under normal physical conditions. Pacemaker cells can also be found at the atrioventricular (AV) node, which lies within the ventricular walls. It is the SA node that generally generates the heart’s electrical impulses and is the reason it is usually called the pacemaker, but if the SA node were not to function or if it was blocked on its path, it would be the AV node that would generate the heart beat and become the new pacemaker.
The failure of the function of these cells results in irregular and abnormal heartbeats which require correction. The artificial pacemaker can provide this correction with its own electrical impulses.
Diseases Related to pacemaker
Arrhythmias
Arrhythmias or cardiac dysrhythmia is the condition in which the electrical activity in the heart is abnormal. The pacemaker is used to treat this condition if the heart is beating too fast, too slow or if the heart is beating irregularly. The heart normally beats between 60 to 100 beats per minute, however different types of arrhythmias can cause the heart to beat below or above this rate. Bradyarrhythmias causes the heart to beat below 60 beats per minute, tachyarrhythmias causes the heart to beat above 100 beats per minute.
Causes of Arrhythmias
There are many causes of arrhythmias occurring, which include:
Injury caused by a heart attack.
Injury during healing after heart surgery.
Coronary artery disease.
A change in the cardiac muscle in the heart.
An imbalance of sodium or potassium in the blood which causes electrolyte imbalances.
Symptoms of Arrhythmias
Many symptoms can arise because of arrhythmias. Chest pains, shortness of breath, dizziness, fainting, fatigue, and palpitations of the heart are all common problems associated with arrhythmias, but if left untreated the problems may become much more severe and may even lead to death. However an arrhythmia may also be silent and a patient may be unaware of this condition as none of the symptoms listed may have occurred. A doctor can detect an arrhythmia with a regular physical examination using an electrocardiogram which measures the pulse of the heart. Any complications in the rhythm of the heart will become apparent and will indicate if a pacemaker is required.
Types of Arrhythmias
As mentioned already arrhythmias can be described as either bradyarrhythmias (heart rate too slow) or tachyarrhythmias (heart rate too fast).
Bradyarrhythmias results in a heart rate lower than 60 beats per minute, the different types include sinus node dysfunction and heart blocks.
Sinus node dysfunction results in slow rhythm as the heart beats because of an abnormal sinus node (SA).
Heart block results in delaying or blocking the electrical impulses which travel from the sinus node to the ventricles.
A pacemaker can be used to treat both of the these conditions
Tachyarrhythmias results in a heart rate higher than 100 beats per minute, the different types of this condition include atrial premature beats, atrial flutter, paroxysmal tachycardias, ventricular premature beats, ventricular tachycardia, and ventricular fibrillation.
Atrial premature beats are earlier than expected extra beats which come from the atria. These do not require treatment.
Atrial flutter is rapid appearing atrial activity. This can cause rates of 250 – 300 bpm and is most common after heart surgery.
Atrial fibrillation is a common irregular heart rhythm. It causes the atria to contract abnormally.
Paroxysmal tachycardis results in a rapid heart rate between 140 and 250 bpm originating from above the ventricles.
Ventricular premature beats are unexpected beats from the ventricles.
Ventricular tachycardia is a series of three or more ventricular premature beats in a row.
Ventricular fribrillation is the most life threatening type of arrhythmia which results in disorded erratic impulses of the ventricles because the ventricles are unable to contract.
Invention of the Pacemaker
Who invented the first pacemaker?
The first artificial pacemaker to be used in aiding the rhythm of the heart was invented by John Hopps. John Alexander Hopps was born in Winnipeg, Manitoba, Canada in 1919. He attended the University of Manitoba and in 1941 achieved a B.Sc.Eng degree in electrical engineering. In 1942 Hopps became a member of the National Research Council of Canada. Hopps did not produce the first pacemaker with all his own work but had help from both Dr. Wilfred Bigelow, a Canadian heart surgeon and Dr. John Callaghan, a cardiac surgeon also from Canada. In 1949 the first work began with this trio in inventing the first external artificial pacemaker. The research and development for their project was undertaken at the Banting Institute in the University of Toronto with the finishing touches completed in 1951. With both Dr. Bigelow and Dr. Callaghan’s vast knowledge of the human heart, and Hopps’ degree in electrical engineering the first successful pacemaker was invented which lead the way to improve treatment of arrhythmias.
Artificial Pacemaker
How does it work?
The modern implantable artificial cardiac pacemaker consists of two parts, the pacemaker device which generates the impulses and the insulated leads which are connected to the heart via electrodes.
The pacemaker generator device (pulse generator) is run by the use of batteries; these batteries must store enough energy to provide electrical impulses to maintain the rhythm of the heart, they are recharged when required and send electrical signals back and forth to the heart through the leads. This device is relatively small and is implanted into the chest.
The pacemaker leads which are insulated are also implanted into the body. These leads are very thin and are connected to both the heart wall and the pacemaker generator device. The electrical signals which are produced by the pulse generator send small amounts of electrical energy through the leads which prompt the device to send impulses to the heart if the rhythm of the heartbeat is incorrect.
Method of Pacing
The methods of pacing the rhythm of the heart include percussive pacing, transcutaneous pacing, epicardial pacing, and transvenous pacing. However these methods of pacing are only used temporarily in conjunction with an external pacemaker or in an emergency. The method used in the implantable pacemaker is permanent pacing.
Permanent pacing involves placing one or more pacing leads (electrodes) in the chamber/chambers of the heart. The electrode lead is inserted and passed through a vein until it reaches the heart valve, the lead continues to pass through the valve and is placed inside the chamber of the heart. Once the surgeon is pleased with the position of the electrode in heart chamber the opposite end of the lead is connected to pacemaker generator device. The generator device is also implanted into the chest of the body.
Different types of Pacemakers
There are now many different types of pacemakers which assist in treating other heart conditions as well such as combining pacemakers and defibrillators in one device. Some devices only use one electrode while others make use of many electrodes to regulate different positions of the heart.
The three basic types of implantable pacemakers which use permanent pacing include:
Single-chamber pacemakers, this type of pacemaker only uses one pacing lead. The pacing lead is placed in only one chamber, either the atrium or the ventricle.
Dual-chamber pacemakers, this type of pacemaker uses two pacing leads. The pacing leads are placed in two chambers of the heart, with one pacing the ventricle and the other pacing the atrium.
Rate-responsive pacemakers, this type of pacemaker includes a sensor that automatically adjusts due to a change in the activity of the human body.
Materials Used
The materials used for producing the pacemaker generator and electrodes are inert, nontoxic, biocompatible and all function within the body.
The casing of the pacemaker generator is made of stainless steel, titanium or a titanium alloy. The battery requires storing a large amount of energy but cannot be too big because of the small size of the device, for this a lithium battery is used. The electrodes are made from platinum or platinum-iridium alloy but insulated with polyurethane. Sealing of the casing or any other parts is done using silicon rubber or polypropylene.
Methods of production
Pacemaker devices are produced by biomedical engineering companies such as Boston Scientific. There are three main components which must be produced to make a pacemaker.
The main battery used for a pacemaker device is a lithium/iodine cell. The iodine and a polymer are mixed and heated together first. The liquid iodine/polymer solidifies to form the cathode with the lithium forming the anode. Moisture is prevented from entering the battery by hermetically sealing it.
The wires in the leads are produced using a method of extrusion. The wires are bundled together and insulated with polyurethane. One end is shaped to fit the pacemaker and the other to be placed in the heart.
The motherboard used in the pacemaker includes semiconductors, resistors and capacitors which are combined together on a single circuit using hybridization.
Once these components are produced they can all be put together in the casing of titanium or stainless steel, and sealed using the polypropylene or silicon rubber.
Improvements and the future
There have been many improvements in the technology of pacemakers. They have been reduced in size for the comfort of patients, the lithium batteries used have vastly improved the multiyear life spans of the device, better leads and wires along with improved electronics have reduced power consumption, and now the device can treat various types of arrhythmias.
Increasing numbers of patients requiring pacemakers will mean more will have to be produced. Further research will be carried out to improve the existing devices. Future improvements may include longer lasting batteries with the use of radioactive isotopes, smaller devices, and an application of cardiac pace making technology to the brain.
