Pacemaker, by Chris Carr
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Revision as of 16:04, 20 February 2013
The heart is one of the most vital organs in the body responsible for the circulation of blood throughout the whole body. The heart is made up of four chambers and separated into two sides, left and right. These chambers are the left atrium, left ventricle, right atrium and right ventricle. The separations between these chambers are made up of four different valves. These four valves consist of the tricuspid, pulmonary, mitral and aortic valves .
The flow of blood goes in the order from right to left alternating between atrium and ventricle. The flow consists of two main steps; bringing the deoxygenated blood to the lungs and bringing the oxygenated blood to the rest of the body. Starting with the collection of the deoxygenated blood in the right atrium, it then passes by the tricuspid valve into the right ventricle. From here it can then pass through the pulmonary valve to the pulmonary artery into the lungs where CO2 can be released. Next the now oxygenated blood flows from the lungs into the left atrium and through the mitral valve to the left ventricle. Lastly, the blood can then flow through the aortic valve into the aorta to the rest of the body .
This whole process is made possible by the initial electrical signal from the sinoatrial node (SAN) and the depolarization of cardiac myocytes. This is because the electrical impulse causes the depolarization of the cardiac myocytes which then causes the contraction of the heart’s chambers. After the SAN creates its initial impulse, it flows through both of the atria causing them to contract. It then reaches the second node, atrioventricular node (AVN). From here the electrical impulse can then spread through the ventricles creating the second contraction .
A pacemaker is a small implanted device that sends electrical impulses to your heart in order to create an adequate heart rate. These devices replace the SAN’s signal and create a small 2-4 mA current in order to contract the heart. Currently there are more than half a million people in the United States with a pacemaker with an average of over 150,000 new ones implanted every year .
1971 - Galvani published his discovery on the electrical stimulation of frog legs from an electric eel 
1802 - First successful experiments to electrically stimulate the heart of animals by Aldini in Paris 
1862 - Walshe states that it is possible to treat cardiac arrest with electrical stimulation of the heart 
1872 - Boulogne successfully stimulates the human heart of a person suffering from arrhythmias 
1927 - Hyman developed an apparatus to stimulate the heart and give it a normal beat 
1932 - First artificial pacemaker was developed by Hyman and New York University [B]
1958 - 1958: First implanted external cardiac pacemaker by Furman, Verzeano, Webb and Kelly [1,3]
1959 - Elmqvist and Senning developed the first completely implanted pacemaker 
1959-Present Day - Increased batter life and monitoring, decreased size
2001 - First wireless pacemaker was produced by BIOTRONIK 
There are quite a few cardiac diseases that require a pacemaker; a few of the common ones include cardiac arrhythmias, syncope, and heart failure. Most of these issues are closely connected and can cause one of the other issues as a side effect. One of the broadest issues that create other problems is cardiac arrhythmias. This is when the heart can’t correctly coordinate the hearts beats, whether it’s an irregular beat, too fast or too slow. One type of these arrhythmias is bradycardia; this is where the heart beats too slowly at less than 60 beats per minute. Reasons behind this can be due to a malfunctioning sinoatrial node and heart block. The first one is just when the main signaling node isn’t working properly. Heart block on the other hand is when the electrical impulses are being blocked from the main sinoatrial node and require the atrioventricular node instead (which is slower). This is a perfect example of where a pacemaker can be of aid by stimulating the heart when it’s not beating fast enough. [1,8,10,11]
The other two diseases mentioned relate a lot to bradycardia and its side effects. Syncope is another name for fainting which occurs when there is not enough blood bringing oxygen to the brain. This is typically due to decreased circulation from the heart which is a symptom of bradycardia. There are two main types of heart failure, systolic and diastolic failure. Systolic failure is when the heart can’t pump out blood out of the heart too well. Diastolic failure is when the heart can’t fill up with as much blood as needed. These issues can cause blood to back up into other areas around the body which is known as congestive heart failure. [7,9,10]
Implanting a pacemaker is a relatively short procedure and typically takes around 1 hour for completion. The patient starts off by taking sedatives and then being put under by anesthesia. Next the doctor makes a small incision, 2-3 inches long, in the upper chest region right under the collar bone. With the help of a real time x-ray (fluoroscopy) he or she guides the leads through a vein into the heart. After attaching the leads to the pacemaker, the surgeon programs the device for the appropriate medical condition. Along with this, the pacemaker is also tested before being placed into the patient. Lastly, the doctor inserts the pacemaker right beneath your skin and stitches the incision back up. On average the patient stays in the hospital overnight for monitoring. [C]
 BIOMATERIALS BOOK
 the artificial cardiac pacemaker book
[A] http://accesstomedicine.files.wordpress.com/2011/11/ heart.gif