Pacemaker, by Chris Carr
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 (1, pg 472).
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 (1, pg 472).
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 (1, pg 483).
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 (1, pg 483).
1958 - First implanted cardiac pacemaker. 
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