Pacemakers, by Chris Carr, Anthony LaViola, David Triffletti, and Denise Buciuman-Coman
An artificial pacemaker is a device that is placed inside the chest to control the rhythm of the heart. It works by sending electrical pulses to various regions of the heart to cause the contractions leading to the heart beat. Usually the sinoatrial node, located in the right atrium of the heart, would act as a natural pacemaker for the heart. However, when this specialized tissue malfunctions or deteriorates in the body, the pacemaker device can be used as a replacement. 
- 1 Background
- 2 History
- 3 How Pacemakers Work
- 4 Types of Pacemakers
- 5 What Pacemakers Treat
- 6 Implanting Procedure
- 7 Side Effects
- 8 Battery Technology
- 9 Resources
The Cardiovascular System
The pacemaker, once placed inside the body, plays a key role in sustaining the cardiovascular system. The cardiovascular system is made up of the heart and it's connected arteries and veins. The cardiovascular system a part of the circulatory system, which is responsible for controlling the flow of blood, nutrients, hormones, oxygen, and other gases throughout the body. 
A pacemaker is placed inside the chest and is directly connected to the heart. The heart is responsible for facilitating blood flow in the body using contractions.
The heart can be sectioned into four chambers separated by two sides, the left and the right. The left chambers are the left atrium and left ventricle. The right chambers are the right atrium and right ventricle. Separating these four chambers are four valves, the tricuspid, pulmonary, mitral, and aortic valves. The blood flow is from right to left and alternates between atrium and the ventricle. The oxygenation of blood beings by the entering of deoxygenated blood into the right atrium, then passing the tricuspid valve into the right ventricle, followed by passing through the pulmonary valve to the pulmonary artery where the blood enters the lungs. The lungs oxygenate the blood and it then enters the left atrium, next into the mitral valve, and then to the left ventricle. Finally, the blood reaches the aortic valve into the aorta where it then begins its journey through the rest of the body. 
The heart wall is made up of endocardium (inner), myocardium, epicardium (outer), and pericardium layers. The inner endocardium layer is composed of endothelial cells and the myocardium, or middle layer, is made up of cardiac muscle. Myocardium is an aerobic muscle (it uses oxygen to function) where it's composition is 99% contractile cells, 1% autorhythmicity cells.
How It Works
These contractile cells are stimulated by the sinoatrial node (SA), which has an average natural rate of 80-100 A.P. per minute, and surrounding autorhythmic cells.  The first electrical signal that the SA sends causes the depolarilization of the cardiac myocytes, which in turn causes the contraction of the heart chambers. After the initial electrical impulse, the signal flows through both the atria which also causes them to contact. It then reaches the atrioventricular node (AV), where the signal is then sent again and spread through the ventricles creating the second contraction. 
1791 – Galvani discovered that an eel could electrically stimulate frog legs, starting the research on how electricity effects dead organisms. [1,8]
1802 - First successful experiments to electrically stimulate the heart of animals by Aldini in Paris 
1862 – Walshe suggests that heart could be electrically stimulated 
1889- McWilliam discovered the electrical impulses of the heart using an EKG type device 
1927 – Hyman designs an apparatus that could be used to maintain heart function called the "artifical pacemaker" but was very large and originally had a hand crank [1,16]
1932- Hyman improves the artificial hand crank making it battery powered 
1951 – Callahan and Bigelow conducted experiments stimulating sinoatrial nodes in dogs to restore natural rhythmic heart beat during hypothermia 
1954 – Hopps performed experiments on animals to test snaking wires through veins 
1958 – First successful external implanted pacemaker, Furman found that placing electrodes internally that less energy could be used, Arne Larrson received the first internal pacemaker [1,16,10]
1975- Lifespan increased using lithium batteries. 
2001 - First wireless pacemaker was produced by BIOTRONIK 
How Pacemakers Work
A pacemaker is composed of a computerized generator, a battery, and leads. The leads are the long electrodes that are fed through the veins of the body to reach inside the heart. Each lead is at a different location and can either sense the hearts electrical signals or send an electrical impulse directly to the heart tissue. The generator is receiving that information sent from the electrodes and sends the correct electrical voltage to the correct lead and therefore correct part of the heart. The battery stores the energy needed for the electrical impulses to occur. 
Types of Pacemakers
There are three different types depending on what is required for the patient.
Demand pacemakers monitor the heart and only send an impulse when the heart slows below average.
Fixed-rate pacemakers send a pulse at a fixed rate to maintain a normal heart rate.
Rate-responsive pacemakers monitor factors such as body temperature, oxygen levels and carbon dioxide levels to adjust the rate of pulses sent. This is based off of the demand of the body depending on physical activity at that moment.
There are three different ways the pacemaker can be set up.
Single-chamber has one lead coming from the pacemaker either leading to the right atrium or right ventricle.
Dual-chamber has two leads coming out of the pacemaker that attach to the right atrium and right ventricle.
Triple-chamber or biventricular pacemaker has three leads, one attached to the right atrium, one attached to the right ventricle and one attached to the left ventricle. 
What Pacemakers Treat
Arrhythmia is a heart condition in which the heart beats in an irregular rhythm, too fast or too slow. Arrhythmia is caused by many different issues and most forms of arrhythmia are not big deal and can be cured by medicine. Different things that cause arrhythmia can be damage heart tissue from heart attack, congenital heart disease, missing or even extra functionalities. If the condition is serve enough a pacemaker is a great way to help elevate the severity of the Arrhythmia. 
Ventricular Arrhythmias start in the ventricles and are very dangerous if not treated immediately since there will not be proper flow of blood out of the heart and into the body. There are two types of ventricular arrhythmia which consists of either a fast regular rhythm or a fast irregular rhythm. Ventricular tachycardia is regular fast beating while ventricular fibrillation is a fast irregular heart beat which is more severe than the ventricular tachycardia. 
Supraventricular arrhythmia are fast heart rates that originate at locations other than the sinoatrial node. They are characterized by having fast rhythms which results in build up of blood within the heart which could clot and lead to strokes or heart attacks. Atrial fibrillation is the most common severe arrhythmia and is when the atrium has a very fast erratic rhythm. Similar to atrial fibrillation is atrial flutter which is also a fast rhythm but is instead a regular rhythm. Paroxysmal Supraventricular Tachycardia or PSVT is a very fast heart rate which can generally be stopped quickly with medicine and relaxation. Wolff-Parkinson-White syndrome is a form of PSVT that is extremely dangerous and is caused by an extra electrical pathway from the left ventricle to the right atrium which circles the current in an irregular way. This causes the entire heart to function improperly. 
How Arrhythmia is Treated
Arrhythmias can be treated in a myriad of ways many of them are treated qwith use of medicine when possible. Medicine is generally only used to heal tachycardia or sped up hear rhythm. Other times a pacemaker is the only way to control the irregularity of the cardiac conductive system. 
Other Reasons a Pacemaker May Be Used
One reason doctors recommend a pacemaker is for bradycardia. This is the slowing of the heartbeat to well below average. Beta blockers, a medication for cardiac arrhythmia control may also affect the heart rate and necessitate the use of a pace maker. One consequence of a low heart beat can be a Strokes-Adams attacks, which is where a victim repeatedly has fainting spells due to low amounts of oxygen getting to the brain from the low heart rate. [2, 3] Another reason for getting a pacemaker is due to a heart block. Heart block is where the artioventicular node or signal transduction to the ventricles fails to be transmitted resulting in unresponsive ventricles of the heart. The heart’s sinoatrial node may also become damaged and in that case be replaced with a pacemaker. Sometimes if the heart is physically damaged it can affect heart rate and require the implantation of a pacemaker.  Certain heart surgeries can be grounds for implanting a pacemaker into a patient. 
1. Drugs to help the patient relax will be administered through an IV line.
2. Local anesthesia will be administered to the patient to numb the area.
3. The doctor will insert a needle into a vein near the collarbone where the wires will be inserted.
4. These needles will be used to guide the leads into the veins and heart.
5. The wires are inserted and guided by an x-ray machine that will be in real time.
6. After the wires are in place, a small incision in the chest for the pacemaker is made.
7. The pacemaker, which holds the battery and the generator, will slip through the incision and be placed under the skin
8. The wires will be attached to the main body of the pacemaker and tested.
9. The patient is kept overnight in the hospital for observation.
10. Patients can resume normal activity in as little as two days after the surgery.
11. Any heavy lifting may need to be put off for up to a month after the surgery.
12. Periodically the doctor will check the status of the pacemaker over the phone.
This whole procedure is done while the patient is awake but on local anesthesia. The procedure itself does not take long only a few hours and the patient will be able to leave the hospital with in one to two days. Normal activity can be completed within just a few days of the surgery. When the pace maker is about to die, within a few years of implantation, it must be replaced. This process is less intrusive since the leads are already in place just the computer and battery section will be replaced. 
Although the risks are low (about 7%), there can be various physical complications either during or after the implanting of the pacemaker and therefore possible negative side effects. To name a few there have been cases of skin necrosis, suture line failur, or lead eroision due to the formation of a pocket hematoma. The formation of a pocket hematoma is one of the most frequent complication, statistically reaching 5% of all cases. These complications can lead to prolonged hospital stay. In older patients, such as this 85 year old patient, the pacemaker's generator can undergo exterisation and skin erosion. In this case the pacemaker was removed due to a high risk of infection.  Twiddler's Syndrome was first described in 1968 when there was a permanent malfunction of a pacemaker because of the patients manipulation of the generator. The pacemaker's leads in this case migrate to other places in the patient resulting in uncomfortable twitching and continuous muscle pulsations. During surgery there can also be possible complications if the placement of the pacemaker leads or generator are not correct or if the generator. The placement of the leads are especially important because they may block valves or disrupt blood flow and eventually cause tears or punctures. The precision and accuracy of surgery are also important so that there are no punctures in the heart organ as well as neighboring arteries. After surgery it is important for daily wound care to occur to decrease the risk for infection. 
A pacemaker uses its battery half for cardiac stimulation and the other half for monitoring and data logging. The history of the battery went from a nickel-cadmium rechargeable batter, to a zinc-mercury batter. The most recent upgrade of the pacemakers battery is the lithium iodine battery, which was developed in 1972 and is still being used.  Pacemaker batteries last between 5 and 15 years depending on it's type and function. The lithium iodine battery extended the life of the battery more than 10 years for some pacemaker models. They are preferred over other batteries for it's high energy density, low discharge, and therefore long shelf life.
However, the battery of a pacemaker could still have room for improvement based on more recent research. The pacemaker's battery could have the potential to not have to be replaced over an entire lifetime thus preventing patients form undergoing multiple invasive surgeries and release the stress of having the pacemaker run out of battery. The main characteristic that a battery should have to last a long while is to have a high energy density. Although the main focus of battery technology improvements is for prolonged cell phone use, the battery research can be applied to pacemakers as well because the phones are also requiring a smaller battery for the thinner designs.
The best thing about these batteries is that they are rechargeable. The lithium-ion battery works using the interaction between an anode and a cathode as well as a lithium-ion salt solution in between the two. The anode in this case is made from carbon and the cathode can be a metal oxide like cobalt oxide. The positive charged lithium ions are then attracted by the cathode that is negatively charged and once they interact, the cathode becomes more positively charged than the anode and then attracts charged electrons. These free flowing electrons are now used as electrical power. 
Fuel Cell Battery
A fuel cell is an electrochemical device. It takes both hydrogen fuel and oxygen to produce electricity, heat and water. The process can be considered electrolysis, but in reverse. The negative electrode, or anode, receives the hydrogen and the positive electrode, cathode, collects oxygen. The hydrogen is separated into hydrogen ions and electrons by the catalyst on the negative electrode while the oxygen is ionized and reaches the electrolyte where it combines with the hydrogen. This battery would be rechargable and be able to last a longer time than the lithium battery. However some limitations would include; the cost, which is very expensive and has not been commercially used until recently because of that reason, also the fact that the fuel cell expels water vapor and heat. In order for this battery to be incorporated into the pacemaker, the pacemaker would have to have an outlet for the water vapor to escape. But, because it is just water vapor, it seems as though that would be the safest to be used by the body. Recharging the battery would have to be through an outside wire fed to be outside the body for easier access. Because this battery would need less charges for something as minimally powered as a pacemaker, the recharges would be less frequent and could be less invasive than the lithium battery changes. The fuel for the fuel cell is also renewable hydrogen and no matter where the water vapor emissions go they are also completely non-hazardous. 
To give an idea of how long the fuel cell battery would last, a company by the name of Intelligent Energy designed a new iPhone fuel cell that claimed to have run the device for up to a week. However this was with the supplement to having lithium batteries. Perhaps the same technique could be used with pacemakers to extend their battery life. 
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Natural and Artificial Pacemaker: https://www.youtube.com/watch?v=xYtJK9JdAN0
Explaining Pacemakers-Khanacademy Style:https://www.youtube.com/watch?v=b3xMC6zdrvM