THE MILLENIUM PACEMAKER - An Biomedical Instrument

ABSTRACT  
                  More than half-million people fall victim to heart attacks and  thousands more are critically injured in accidents.  Taking care of these patients  in special care units of hospitals involves the use of several types of specialized  equipment.  Among which one of the equipment is pacemaker.
          In the past few years electronic pacemaker systems have become  extremely important in saving and sustaining the lives of cardiac patients who is normal pacing function becomes impaired.  Depending on the exact nature of a  cardiac dysfunction, a patient may require temporary artificial pacing during the  course of treatment or permanent pacing in order to lead an active, productive  life after treatment.

INTRODUCTION  
    In the past few years electronic pacemaker systems have become  extremely important in saving and sustaining the lives of cardiac patients whose  normal pacing function becomes impaired.  Depending on the exact nature of a  cardiac dysfunction, a patient may require temporary artificial pacing during the  course of treatment or permanent pacing in order to lead an active, productive  life after treatment.
   The history of cardiac research has grown in stair-step manner.  Early ideas & inventions led to the development of more complicated instruments  and machines.   The use of electricity for stimulation of the heart in the late  eighteenth and early nineteenth centuries stirred many ideas.  There was much  controversy over who was the first to invent the artificial pacemaker.  Dr. Albert S  Hyman is believed to be the founder of the artificial pacemaker, but there  appears to be evidence that he was not the first.  An Australian physician by the   name of Mark C.Liwill, along with physicist Major Edgar Booth, built a portable  peacemaking unit.  It was demonstrated in 1931, while Hyman developed the  device in 1930-31 Liwill’s apparatus had one pole applied to the skin and another  in the appropriate cardiac chamber.

 WHAT IS PACEMAKER? 
   A device capable of generating artificial pacing impulses and  delivering them to the heart is known as Pacemaker System.  A pacemaker is  small device placed under the skin.  It helps to regulate heart rhythm.  The  pacemaker runs on batteries and sends out electrical impulses that keep the  heart beating at its proper speed.  A pacemaker has two parts:
1) a pulse generator, which is the battery/timer unit.
2) One or more electrodes and wires that carry electrical impulses to heart.
   Pacemakers are used to treat such problems as heart block, in  which the hearts impulses are interrupted, or cardiac arrihythrnias in which the  heart beats abnormally slow or fast.

PACEMAKER SYSTEMS : 

   A  pacemaker is small electronic device that is used to stabilize or  stimulate the heartbeat.  It controls  the heart rate by providing a series of  electrical impulses.   Electrodes in the pacemaker system are those portions of the  system in contact with the electrolyte.  An electrode’s function is to transform the  ionic currents from biochemical and physiological phenomenon into electron  currents in a metal conductor.  The electrode that is implanted with the  pacemaker must satisfy following condition.

• The electrode must not poison the body or be poisoned by the body.  
• The electrode must not he affected by electrochemical action.  

   Pacemakers are available  in  variety of forms.  Following are the  two main forms of pacemakers.
Internal Pacemakers : 

   Internal pacemakers may be permanently implanted in patients  whose SA nodes have failed to function properly or who was suffer from  permanent heart block because of a heart attack.  An internal pacemaker is  defined as one in which the entire system is inside the body.
   Internal pacemaker systems are implemented with the pulse  generator placed in a surgically pocket below the left or right clavicle.  Internal  leads connect to electrodes that directly connect the inside of the right ventricle  or the surface of myocardium.  The exact location of the pulse generator  depends primarily on the type of electrode used, the nature of the cardiac  dysfunction.  Since there are no external connections for applying power, the  pulse generator must be completely self-contained, with a power source capable  of continuously operating the unit for a period of years.

 BLOCK DIAGRAM OF PACEMAKER  

   The timing circuit which consist of an RC network, a reference  voltage source, and a comparator determines the basic pacing rate of the pulse  generator.  Its output signal feeds into the second RC network, the pulse width  circuit, which determines the stimulating pulse duration.  A third RC network, the  rate limiting circuit, disables the comparator for a present interval and thus limits  the pacing rate to a maximum of 120 pulses per minute for most single-  component failures.  The output circuit provides a voltage pulse to stimulate the  heart.   The voltage monitor circuit senses cell depletion and signals the rate  slowdown circuit and energy compensation circuit of this event.  The rate  slowdown circuit shuts off some of the current to the basic timing network to  cause the rate to slow down 8 ± 3 beats per minute, when cell depletion has
occurred.  The energy-compensation circuit causes the pulse duration to  increase as the battery voltage decreases, to maintain nearly constant  stimulation energy to heart.
   There is also feedback loop from output circuit, to the refractory  circuit, which provides a period of time following and out put or a sensed R-wave  during which the amplifier will not respond to outside signals.  The sensing circuit  detects a spontaneous R wave and resets the oscillator timing capacitor.  The  reversion circuit allows the amplifiers to detect a spontaneous R wave the  presence of low-level continuous wave interference.  In the absence of an R  wave, this circuit allows the oscillator to pace at its present rate ± 1 beat par  minute.
   Pulse generators for external placement are marketed by a large  number of manufactures.  They can be worn in the pocket or strapped to a limb  or the torso.  They are designed to function in the asynchronous (fixed rate) and  synchronous (demand) modes.  Some units also operate in a synchronous   triggered mode.  This feature is useful for temporary pacing in the presence of an  inhibiting non-cardiac signal such as emanating from an implanted pulse  generator which is producing pulses hut not capturing the myocardium.
 
What things about the pacemaker can be programmed ? How is it done? 
   Pacemakers are indeed very advanced devices.  One of their most  desirable features is the ability to program them to behave in different manners  according to the needs of the patient.  This allows for the function of the device to  be individualized for you.  No surgery is necessary to do is it is done through the skin, and indeed even through your clothes.  The programmer talks to the pulse  generator using radio frequencies.  A typical device being used is illustrated  below.
   The most easily understood aspect or a parameter that can be  changed is the lower rate of the pacemaker that is, the rate at which the  pacemaker will “kick in” to prevent the heart from going slower than this rate.
This is usually set at 50,60 or 70 beats per minute.
   Many other aspects can be programmed, including the strength and  duration of the impulses delivered to the muscle, how fast the pacemaker will go,  and the pause between stimulating the atrium and the ventricle.  This is just the  start of the possibilities.

 THE MILLENIUM PACEMAKER : 

   Pacemakers are small electrical generators that control your heart  beat.  They are often just called pacers.  You may need a pacemaker if you have  a chronic rhythm problem.  The pacemaker is one sealed unit with a battery, and  some circuitry inside.
    The battery supplies the power.  The circuitry is like a little  computer inside the pacemaker it changes energy from the battery into tiny  electrical pulses that go to your heart through wires called leads.  The connector block is plastic, on top of the pacemaker.  That’s  where the leads connect to the generator unit one specific kind pacemaker can  help about 1 in  5 heart failure patients feel a lot better.  Although many types of  heart problems may require a pacer, I am concentrating on one kind  the type  specifically for CHfers.  This kind of pacemaker therapy is called VRT for “  ventricular resynchronization therapy” or  CRT for “ cardiac resynchronization  therapy.” The kind of pacemaker used is called a “ biventricular pacemaker”  because it “paces” both your heart’s ventricles (pumping chambers).    CRT is when a pacemaker is use to coordinate your heart’s 4  chambers to act together as a team, making them pump blood more efficiently.

   Many CHFers hearts don’t have all chambers firing at just the right time to beat  effectively.  Re-timing the beat of some of the chambers can restore that needed  teamwork, making your heart function better, which makes you feel better.
   Getting the right and left ventricle to beat with proper timing can  really improve your heart function, if they aren’t already beating properly.  Not  everyone with heart failure will improve with CRT.

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