07-02-2013, 04:36 PM
PACEMAKER
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ABSTRACT
If you have a condition called bradycardia, otherwise known as a slow heart beat, you and your doctor may decide an implantable heart device called a pacemaker is the right option for you. When people refer to a pacemaker, they are actually discussing a pacing system, which includes the pacemaker and leads.
(a) A pacemaker is the small device that is implanted under the skin, most often below the collarbone on the left or right side of your chest. The pacemaker continuously monitors your heart, and if it detects a slow rhythm problem, it sends out small undetectable electrical signals to correct it.
(b) Leads are thin, soft, insulated wires about the size of spaghetti noodles. The leads carry the electrical impulse from the pacemaker to your heart and relays information about the heart’s natural activity back to your pacemaker.
Introduction:
The pacemaker is an electronic biomedical device that can regulate the human heartbeat when its natural regulating mechanisms break down. It is a small box surgically implanted in the chest cavity and has electrodes that are in direct contact with the heart. First developed in the 1950s, the pacemaker has undergone various design changes and has found new applications since its invention. Today, pacemakers are widely used, implanted in tens of thousands of patients annually.
Background:
The heart is composed of four chambers, which make up two pumps. The right pump receives the blood returning from the body and pumps it to the lungs. The left pump gets blood from the lungs and pumps it out to the rest of the body. Each pump is made up of two chambers, an atrium and a ventricle. The atrium collects the incoming blood. When it contracts, it transfers the blood to the ventricle. When the ventricle contracts, the blood is pumped away from the heart.
History:
The idea of using an electronic device to provide consistent regulation of the beating heart was not initially obvious to the early developers of the pacemaker. The first pacemaker, developed by Paul Zell in 1952, was a portable version of a cardiac resuscitator. It had two lead wires that could be attached to a belt worn by the patient. It was plugged into the nearest wall socket and delivered an electric shock that stimulated the heart of a patient having an attack. This stimulation would usually be enough to cause the heart to resume its normal function. While moderately effective, this early pacemaker was primarily used in emergency situations.
Raw Materials:
The materials used to construct pacemakers must be pharmacologically inert, nontoxic, sterilizable, and able to function in the environmental conditions of the body. The various parts of the pacemaker, including the casing, microelectronics, and the leads, are all made with biocompatible materials. Typically, the casing is made of titanium or a titanium alloy. The lead is also made of a metal alloy, but it is insulated by a polymer such as polyurethane. Only the metal tip of the lead is exposed. The circuitry is usually made of modified silicon semiconductors.
Design:
Many types of pacemakers are available. The North American Society of Pacing and Electrophysiology (NASPE) has classified them by which heart chamber is paced, which chamber is sensed, how the pacemaker responds to a sensed beat, and whether it is programmable. Despite this vast array of models, all pacemakers are essentially composed of a battery, lead wires, and circuitry.