Unit 1 - Cardiac Care Units

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UNIT ICARDIAC CARE UNITS

Pace makers different types, batteries for pace makers. ACdefibrillators, asynchronous and synchronous DC defibrillators,

patient monitoring systems.

Pace makersdifferent types1.What is pace maker?Device that used to apply a strong electrical shock to the heartmuscle undergoing a fatal arrhythmia is called pace maker. Theshock changes ventricular fibrillation to an organized ventricularrhythm or changes a very rapid and ineffective cardiac rhythm toslower, more effective rhythm.2.What is Normal Heart-Beat Cycle? / What are cardiac cycles

two distinct phases? / What do you mean by heartspacemaker?

The cardiac cyclehas two distinct phasesthe diastole phase andthe systole phase. In the diastole phase, the heart ventricles arerelaxed and fill with blood. In the systole phase, the ventriclescontract and pump blood around the body through a system ofarteries. These events are triggered by the sinoatrial node acollection of modified myocytes that acts as the hearts pacemaker.

3.What is Ventricular Fibrillation or defibrillation?Normally the pulse rate (heartbeat rate) is appropriate for the bodysoxygen demand. Problems can arise if the heart rate is too low ortoo high. If the speed is very high it can lead to ventricularfibrillation (VF) in which the heart muscle quivers and does notpump efficiently, if at all. This condition is generally fatal if nottreated quickly. Normal heart-beat can be restored by delivery of acontrolled electric shock. This process is called defibrillation.4.What is a Defibrillator?

Defibrillators have been in use for about sixty years. The earliermachines were comparatively large and not really portable.Emergency portable defibrillators (also called AEDs or automaticexternal defibrillators) are today available in many public buildings,


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schools, clubs etc. and small defibrillators can now be implantedsurgically in patients with certain chronic heart problems.5.What is Intelligent Defibrillators?

Over recent decades there have been major advances in the designof defibrillators. Much of this work stemmed from efforts to produceimplantabledevices. Modern defibrillators include sensorsthat candetect the cardiac rhythm and are programmed to decide whethera shock is required and to deliver it correctly.

6.Write short notes on Pacemaker.

A pacemaker is a device that helps regulate the the rhythm of the

heart as well as the rate at which it beats. It may be usedtemporarily, such as after open heart surgery, or placedpermanently, with a minimally invasive procedure.

A normal heart beats at a steady pace, but there are manyconditions that can make the heart beat irregularly. The rate maybe too fast or too slow, or the heart may no longer beat in thenormal "lub-dub" fashion. If the heart is not beating properly, apacemaker can be used to regulate the rhythm.

A pacemaker sends an electrical impulse to the muscle of the hearttelling it when to beat. If one of the chambers of the heart isworking improperly, the pacemaker can be attached there, or tomultiple chambers if necessary.

Conditions that can be treated with a pacemaker include atrialfibrillation and bradycardia (slow heart rate). In some cases, thepacemaker can help insure the left and right atrium or ventriclescontract at the same time. There is also a defibrillator/pacemaker

combination available, which is used to treat abnormal tachycardia(an irregular and overly fast heart rate).

7.What are the types of Pacemakers?There are two primary types of pacemakers:


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a)A standard pacemaker that triggers the chambers of theheart, and

b)An internal defibrillator/pacemaker combination knownas a cardioverter defibrillator.

The standard type of pacemaker sends an electrical impulse viaspecial wires that are attached to the heart. This replaces the signalthat is sent by the heart, which is faulty in patients who need apacemaker.A second type of pacemaker, the internal defibrillator/pacemakercombination, sends an electrical impulse to the heart to control thehearts rate and rhythm, just as a standard pacemaker does. Inaddition to that function, it can also deliver a shock to stop alethal rhythm, a heart rhythm that does not allow the heart toeffectively function.The idea of the shock is the same as the shock with paddles thatyou may have seen on television. However, because the device isattached to the heart with wires, the shock is much less powerfulthan what you may imagine.Single-Chamber PacemakersThe heart has four chambers. The left and right ventricle moveblood outside the heart; the left and right atrium move the bloodback in. There are also four valves that keep the blood flowingthrough the heart. Single-chamber pacemakers have just one wire,

known as a pacing lead. Once the pacemaker is surgicallyimplanted, the pacing lead extends from the device along a vein.The pacing lead extends through one of the valves before finallyattaching to a heart chamber. Since a single-chamber pacemakercan connect to only one chamber, these devices are normallyreserved for patients who do not have severe cardiac problems, andonly an occasional need to stabilize their heart rates.Dual-Chamber PacemakersDual-chamber pacemakers have two pacing leads connecting to two

heart chambers. Most pacemakers implanted in the United Stateseach year are dual-chamber devices. Dual-chamber cardiacpacemakers more closely mimic the hearts natural beating than thesingle-chamber pacemaker. Dual-chamber pacemakers are moreexpensive than single-chamber pacemakers, but there is someindication that they may actually be more cost effective. In the
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January 2005 issue of Circulation, Dr. David Cohen, director ofcardiovascular research at Saint Luke's Mid America Heart Institutein Kansas City, Missouri, writes that while the dual-chamberdevices cost $3,000 more initially, the total lifetime cost mirrors

that of the single-chamber devices. Patients with dual-chambercardiac pacemakers are also less likely to be hospitalized for heartfailure than patients with single-chamber devices, according to Dr.Cohen.Triple-Chambered PacemakersTriple-chambered pacemakers have three pacing leads, two for eachventricle and one to an atrium. Typically, triple-chamberedpacemakers are reserved for patients with congestive heart failure,a condition that arises when the heart experiences difficultyperforming its most basic function, pumping blood. These devices

help improve blood flow through the heart by properly syncing theventricles.Rate-Responsive PacemakersThanks to their special activity and breathing sensors, rate-responsive pacemakers have the ability to self-adjust based on apatients current level of physical activity, emotional state andmetabolic needs. These devices respond to physiological changes inthe body rather than to atrial rate, or heart rhythm.

8.How Does a Defibrillator Work?

In essence the shock circuit in a defibrillator has three keycomponents: a high voltage source, a capacitor and switches.The Voltage SourceModern defibrillators use direct current (dc) rather than thealternating current(ac) which earlier models used. This poses a problem for designers

of battery-operated devices. Transformers cannot step up directcurrent.The problem is solved as follows.


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A battery drives an oscillator circuit; in effect this produces acurrent that is switched on and off at a high frequency (e.g. 1000times per second), although it is still going in one direction only. Ifthis pulsed direct current is fed into a suitable transformer therequired output voltage can be generated. The factor by which thevoltage is stepped up is the ratio of the number of turns on theinput and output coils of the transformer. For example, if the inputcoil (primary) has 200 turns and the output coli (secondary) has20,000 turns then the voltage is stepped up by a factor of 100. A 5V input would then result in a 500 V output. The alternating outputvoltage is rectified by means of a diode and fed into a capacitorwhich stores the high voltage charge.

The CapacitorA capacitor consists of two flat conductors or plates (usually ofaluminium foil) with an insulator between them. A conducting leadis attached to each plate. In practice the whole capacitor assembly

is often rolled and inserted in a can with two connections.

CircuitThe diagram shows a simplified version of a defibrillator circuit.With all switches open the paddles are attached across thepatients chest. S1is then closed in order to charge the capacitor. S1is then opened and S2 is closed; this causes the capacitor to


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discharge through the patient, hopefully restoring normal cardiacrhythm.Energy ConsiderationsThe capacitance of a capacitor is the amount of electric charge it

can store for every volt applied to it. The unit of electric charge isthe coulomb (symbol: C). The unit of capacitance is called a farad(symbol: F). One farad = 1 coulomb per volt. With regard todefibrillators the amount of energy stored in a capacitor is veryimportant. It can be calculated as follows: E = C V2, where E isthe energy in joules, C the capacitance in farads and V the electricpotential (voltage) measured in volts. This energy, which may bemore than 100 J, is dissipated in the patients body over a smalltime interval (about 10 milliseconds or one hundredth of a second).For example, if the capacitance is 1000 F (microfarad) and thevoltage is 500 V then the stored energy is 125 J [E = C V2 = (1000 106)(5002) = 125 J]. Early defibrillators delivering about400 joules sometimes caused further cardiac injury.Electric CurrentThe electrical resistance of the skin is the main contributor to thehuman bodys resistance. If the skin is dry the resistance from onehand to the other might be over 100, 000 ohms. This isdramatically reduced if the area of contact is large and the skin ismoistened with a suitable conductive paste or gel. The electrodes

provided with AEDs are generally self-adhesive and are pre-coatedwith conductive gel. They can reduce the bodys resistance (acrossthe chest) to about 20 ohms. Using V=IR we can calculate the peakdefibrillation current. If V = 500 volts then the current is 25amperes. The pulse lasts only about a hundredth of a second (10ms) and so the risk of surface burns to the skin is reduced.WaveformsAs a capacitor discharges its voltage falls and so does the currentthrough the patient. Plotting the voltage or the current against time

gives a characteristic graph or waveform. The waveform resultingfrom a single capacitor discharge is monophasic, i.e. the current ison one direction only. Modern defibrillators are generally biphasic;successive current pulses are in opposite directions. Biphasicdefibrillators are considered to be more effective and today virtuallyall new defibrillators are of this type.


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Monophasic (left) and Biphasic (right) waveforms

Batteries for pace makersBatteries used in Implantable cardiac pacemakers-present uniquechallenges to their developers and manufacturers in terms of highlevels of safety and reliability. In addition, the batteries must havelongevity to avoid frequent replacements. Technological advances inleads/electrodes have reduced energy requirements by two orders ofmagnitude. Micro-electronics advances sharply reduce internal

current drain concurrently decreasing size and increasingfunctionality, reliability, and longevity. It is reported that about600,000 pacemakers are implanted each year worldwide and thetotal number of people with various types of implanted pacemakerhas already crossed 3 million. A cardiac pacemaker uses half of itsbattery power for cardiac stimulation and the other half forhousekeeping tasks such as monitoring and data logging. The firstimplanted cardiac pacemaker used nickel-cadmium rechargeablebattery, later on zinc-mercury battery was developed and used

which lasted for over 2 years. Lithium iodine battery invented andused by Wilson Greatbatch and his team in 1972 made the realimpact to implantable cardiac pacemakers. This battery lasts forabout 10 years and even today is the power source for manymanufacturers of cardiac pacemakers. This paper briefly reviewsvarious developments of battery technologies since the inception ofcardiac pacemaker and presents the alternative to lithium iodinebattery for the near future.Introduction

Cardiac PacemakerThe pacemaker unit delivers an electrical pulse with the properintensity to the proper location to stimulate the heart at a desiredrate. The cardiac pacemaker comprises of a pulse generator and alead system. The pulse generator houses electrical componentsresponsible for generating the pulse (via output circuits) at the


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proper time (via timing and control circuits) based on events sensed(via sensing circuits). It also contains a power supply (battery) andmay include other elements such as telemetry for testability andprogrammability and memory (ROM or RAM) to store data for

diagnostic purposes.Impulses are transmitted to the heart by means of a lead, which isattached to the pulse generator via the connector block. A lead iseither unipolar or bipolar; a unipolar lead contains one insulatedcoil, whereas a bipolar lead contains two coils, separated by aninner insulation. An outer insulation shields a lead from theenvironment. The tip of a lead, which contains an electrode, isimplanted into the inner, endocardial surface of the heart, theactual location depends on the type of pacemaker. The pacemakerunit is usually implanted in the pectoral region, with the lead

running through the right subclavian vein to the internal surface ofthe heart. A pacemaker is programmed by means of a programmer,a computer with a special user interface for data entry and display,and with special software to communicate with the pacemaker. Thetelemetry head is placed above the location of the pacemaker;information from the programmer to the pacemaker, and back, istransmitted by means of telemetry.The casing of the pulse generator functions as housing for thebattery and all other electronic and electrical circuits. A connector

block, made of polyurethane, (glass materials were used to comprisethe connector block in earlier models) is located at the top of thepacemaker. It serves to attach the pacemaker to the pacemakerlead(s). The present day pulse generator case is made of titanium, ametal that is ten times as strong as steel, but much lighter.Titanium and two of its alloys, niobium and tantalum, arebiocompatible, they exhibit physical and mechanical propertiessuperior to many other metals. The modulus of elasticity (measureof stiffness) of titanium and its alloys range between 100-120GPa.

Extreme resistance to corrosion and durability make titanium andits alloys ideal materials for hermetically sealed pulse generatorcases for cardiac pacemakers.Titanium replaced ceramics and epoxy resin with silicone rubber,which were used for encapsulation of some pacemakers in the past.To assemble the pulse generator, the hybrid circuits and the battery


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are placed in the titanium case (ASTM Grade 1) in a speciallydesigned clean room that has no static charge (less than 1%moisture) and no dust in it. Once the hybrid circuits and thebattery are in the casing, the casing is welded shut with a high-

powered laser beam. This laser beam gives the pulse generator ahermetic seal, which means that the device is airtight and liquid-tight. After welding, the top, or header of the pacemaker is attachedand the entire device is covered in a thin layer of plastic (epoxyplastic). This plastic coating further seals the pacemaker.The casing is a given a kind of elliptical shape and a typicalpacemaker diagram is shown in Figure 1. This upgrade to titaniumallowed patients to safely use appliances such as microwave ovensbecause titanium helps to shield the internal components andreduce the external electromagnetic interference. In addition,

titanium casing shields from ground level cosmic radiation.

Figure 1: Typical Pacemaker DiagramBatteries for Cardiac PacemakersIn 1958, Ake Senning, a thoracic surgeon at the KarolinskaHospital in Stockholm, implanted myocardial electrodes and a pulsegenerator with a rechargeable nickel-cadmium battery in a 40-year-old patient. Senning and his associate, Rune Elmquist, an engineerwith the Swedish firm Elema Schonander, had developed and testedthis pacemaker between 1956 and 1958. The pulse generator failed

within a few hours; a successor lasted about 6 weeks. The history ofthe implantable cardiac pacemaker is traced from its inception in1951, through its development and trials in 1958, to its successfulimplantation in 10 patients in 1960, and on to its commercialrealization. The usage of implanted pacemakers has been everincreasing since then. The battery occupies major portion of the
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pulse generator in terms of weight, volume, and size. The mostimportant factor for a cardiac pacemaker battery is its reliability.Unlike many consumer products, batteries in implantable devicescannot be replaced. They are hard wired at the time of manufacture

before the device is hermetically sealed. From that point on, thebattery is expected to power the device during final testing at thefactory, during the shelf life and throughout the useful life of thedevice while it is implanted. In general the power source of theimplantable device is the only component, which has a knownpredictable service life, which in turn determines the service life ofthe implanted device itself.It is indeed fascinating to see the breadth and the vision of the earlyinvestigators of implantable power sources in the almost desperatesearch for a power source that would enable the pacemaker to last

as long as the expected lifetime of the average patient. This paperpresents a brief history and review of various types of batteries usedin cardiac pacemakers since beginning. The smooth transition fromzinc-mercury, nuclear batteries to the lithium-iodine batteries arepresented along with product information obtained from themanufacturers. The technical advantages of lithium iodine batteryin terms of its longevity, no gas generation, adaptable shapes andsizes, corrosion resistance, minimum weight, excellent currentdrain characteristics suitable to cardiac pacemakers are highlighted

in this paper. The future of cardiac pacemaker batteries in terms ofalternatives to lithium iodine battery is also presented.Electrochemical Power sourcesWe need to generate electrical energy from some other source ofenergy. Chemical energy is the most practical source and isgenerally used in one of two possible ways. Fuels can be burnt in aheat engine or fuel cells can be used. Fuel cells have no movingparts and do not require the mechanical energy to generateElectrical energy. Chemical energy can also be stored in two types

of electrochemical power sources, primary cells or batteries, andsecondary cells or batteries. Primary cells are those used once andthen discarded, whereas secondary cells can be discharged andrecharged many times. In theory, many electrochemical reactionsare reversible. In practice, only a few systems are worthwhile and


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safe. In general, electrochemical power sources have developed inan evolutionary manner.Battery Performance ParametersThe definitions for some of the important parts of a battery and its

performance parameters like voltage, duty cycle, temperature, shelflife, service life, safety and reliability, internal resistance, specificenergy (watt-hours/kg), specific power (watts/kg), etc are wellknown. A good battery design is a compromise between variousperformance parameters to meet the requirements of the specificapplication. Critical factors in selecting a cardiac pacemaker batterytechnology are: minimum and maximum voltage, initial, average,and maximum discharge current, continuous or intermittentoperation (size and duration of current pulses), long shelf andservice life, high specific energy and specific power, impact, and

good performance in a variety of conditions (temperatures, dutycycles, etc.). Cardiac pacemaker battery design poses specialchallenges in development of biocompatible materials, corrosionand sealing, light weight and flat type, high reliability, accurate endof life battery predictions, etc.Early DevelopmentsRechargeable (secondary batteries) nickel-cadmium batteries wereused in the beginning (in 1958) of pacemaker implants in humanbeings. They were inductively recharged by the transmission of

energy to the implanted receiver. The cell voltage was 1.25 V andthe capacity was 190 mAh. The major problems were two fold, thefirst being very short life time and the second was to place theresponsibility for recharging in the hands of patients, which is not agood medical practice. It was well known that primary or non-rechargeable batteries would give longer lifetime compared tosecondary batteries. There are still some rechargeable pacemakersin use though not sold any more.Some of the early pulse generators constructed mainly from discrete

components were powered by series-wired mercury-zinc batteries.Three to six cells in series provided 4-8 V. They were widely used atthat time (around 1960s). Such mercury-zinc batteries were cast inepoxy, which was porous to the discharge of the battery releasedhydrogen and permitted its dissipation, which required venting andhence could not be hermetically sealed. This allowed fluid leakage


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into the pacemaker at times that caused electrical shorting andpremature failure. The terminal voltage decay characteristic of themercury-zinc battery is such that normal battery depletion resultsin little change in the terminal voltage until the end of batterys

useful life. This makes failure difficult to anticipate. This batterywas improved in its design and still the life was only about twoyears with an abrupt drop in voltage as they become depleted. Nodevice of this type is currently in use.Biological batteries (which use power from within the human body)were experimented unsuccessfully1 for practical use in pacemakers.Nuclear batterieswere tried successfully for some period. Practicalnuclear batteries use plutonium (238Pu). It has a half-life of 87 yearsso the output degrades only by 11% in 10 years. However it ishighly toxic and 1g in the blood stream could be fatal. Early

pacemakers used metallic plutonium whereas later ones usedceramic plutonium oxide. The plutonium emits alpha particles,which impact upon the container and generate heat. Thermopiles ofdissimilar p- or n-doped bismuth telluride generate the electricityfor the pacemaker circuits. Though these nuclear power sourceshad very long life, they were large and created problems whentravelling between states and countries due to the presence of theirradioactive fuel. They also must be removed at the time of deathand returned for proper disposal. Nuclear powered pacemakers are

no longer sold but still a small number of implanted nuclear devicesthat remain in use. Nuclear power sources became obsolete withthe development of lithium batteries.Lithium BatteriesLithium has the highest specific energy of all but it has only becomepossible since mid 1970s to manufacture practical batteries.Because lithium reacts violently with water, non-aqueouselectrolytes must be used. Organic solvents such as acetonitrile andpropylene carbonate, plus inorganic solvents such as thionyl

chloride (SOCl2) are typical, with a compatible solute to provideconductivity. Many different materials such as sulfur di, thionylchloride, manganese dioxide, and carbon monofluoride, are used forthe active cathode material.


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IntroductionIntroduction of a lithium iodine battery in 1975 greatly extendedthe pacemaker battery life (more than 10 years for some models)and replaced the mercury-zinc battery. Lithium Primary batteries

are used in pacemakers since they meet the requirements of longlife, low drain current and voltage characteristics. The shelf life ofprimary lithium cells is typically equivalent to a 10% loss ofcapacity over five years. This compares with a similar loss foralkaline cells over only one year. The long shelf life of lithiumbatteries arises from the lithium metal surface becoming passivatedby reaction with the electrolyte. All lithium systems are said to bethermodynamically unstable but kinetically stable. They produce nogas and hence they can be hermetically sealed. In addition, theterminal voltage decay characteristic is well behaved, falling slowly

enough for battery end-of-life(EOL) to be anticipated in routinefollow up.Lithium batteries are categorized under liquid cathode cells, solidcathode cells, and solid electrolyte cells.The liquid cathodesystems, Li/SO2, Li/SOCl2 and Li/SO2Cl2, plustheir derivatives, are capable of higher discharge rates than thesolid cathode systems such as Li/MnO2 and Li/CFX. These are notsuitable for applications in implanted cardiac pacemakers. Howeverlithium sulfur dioxide batteries are used in automated external

defibrillators (AEDs) that can restore a normal cardiac rhythm tovictims of sudden cardiac arrest. Solid Cathode Lithium Cells usesolid cathode materials such as MnO2, CuO, V2O5 and carbonmonofluoride, (CF)n. They have the advantage of not beingpressurized, although they cannot be discharged as rapidly asliquid cathode cells. They are available in button and cylindricalforms. About 80% (by number) of all lithium batteries in use are ofthe Li/MnO2 type. The energy density is similar to that of theLi/SO2 cells when discharged slowly and their slow self-discharge

characteristic make them suitable for memory backup, watches,calculators, cameras, mines and munitions, etc. Voltage delayappears to be less of a problem with solid cathode cells.The solid cathode cells do not support currents as high as the liquidcathode ones. This is because the liquid cathode undergoes adischarge at the surface of the electrode (which comprises a high


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surface area carbon supported on a metal mesh) where thedischarge products are deposited. In contrast, discharging at a solidcathode involves diffusion of lithium ions into the bulk of thecathode, which is a slower process.

Continuous operation of liquid and solid cathode cells above 2A willlead to a significant rise in cell temperature, so this needs to beborne in mind for a particular battery application, the temperaturerise being of more importance for the high pressure Li/SO2 cells.Possible hazards, like explosions associated with lithium liquid andsolid cathode batteries are still a concern for absolute safety and lotof research is still going on to stipulate the rules and regulations asto how they must be disposed off towards the end of their life.Solid electrolyte lithium cells:Several solids, such as lithium iodide,are electronic insulators but reasonably good ionic conductors and

can be used as the electrolyte in solid electrolyte batteries. Suchbatteries are characterized by extremely long service life at lowdrain currents, even at high temperatures. They are very muchsuitable for applications such as cardiac pacemakers, and forpreserving volatile computer memory.Since 1972, a variety of lithium batteries have been used. Theseinclude Li/SOCI2, Lithium-silver chromate cell [Li/Ag2CrO4],lithium copper-sulfide cell[ Li/CuS], lithium thionyl chloride cell,Li/I2-Polyvinylpyridine (PVP), and, in more limited use,

Li/LiI(Al2)3/PbI2,PbS, Pb. In addition to their widespread use inconsumer products, lithium primary batteries are the power sourceof choice for a range of medical implants.The lithium iodine-polyvinylpyride (PVP) is the principal cardiacpacemaker battery that has been in long use. The internalimpedance (The resistance of a cell to an alternating current of aparticular frequency) of the lithium iodine cell is an importantfactor in battery performance. The greater the impedance, the moredifficult it is to pass current through the cell. Increased cell

impedance corresponds to a decreased power source at the cellterminals. The beginning-of-life (BOL) impedance ranges from 50 to100 Ohms. The impedance increases during service to values from20,000 to 30,000 Ohms during the accumulation of dischargeproduct.


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Lithium Iodine Battery for Cardiac PacemakerThe lithium / iodine-polyvinylpyridine battery, first implanted in1972 has become the power source of choice for cardiac pacemaker.Since then, improvements in cell chemistry, cell design, and

modeling of cell performance have been made. Cells today exhibitan energy density over three to four times as great as cells producedin 1972. Well over 3 million pacemakers have been implanted withthis chemistry, and the system has exhibited excellent reliability.The battery chemistry provides a long shelf life and high energydensity. Lithium cupric sulfide was used in some pacemakersmanufactured by the Cordis Corporation due to its excellent energydensity. However, due to the corrosive nature of this compoundmany abrupt pacemaker failures occurred when the batterychemicals ate through their containment. It is still present in some

of the already implanted pacemakers but lithium cupric sulfide isno longer used.Lithium Iodine has two characteristics that make it an excellentpower source for cardiac pacemaker applications. The self-discharge rate is very low resulting in a long shelf life. It has astable voltage through much of the useful life then tapers down in agradual and predictable manner. This makes predicting the electivereplacement time safe and easy.The cathode is a complex of iodine and poly-2-vinyl pyridine (P2VP).

Neither conducts electricity, but when mixed and heated at 149Cfor 3 days, they react into a black viscous paste that conductselectricity. This is poured into the battery when molten and cools toform a solid. When this paste contacts metallic lithium, amonomolecular layer of crystalline lithium iodine forms. It is amolecular semiconductor that passes lithium ions, as required forcurrent flow, but not iodine moleculesChemical ReactionsConventional current flows through a device from anode to cathode.

For a battery, the current flows from the negative anode, throughthe battery, to the positive cathode. Oxidation of metal occurs at theanode,

and reduction of halide occurs at the cathode,


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. The combined reaction is,

Conventional current flows from anode to cathode. The lithiumreacts with iodine to form lithium-iodide, which grows in volume

and increases the resistance.Internal ResistanceThe internal cell resistance (Rdc, The resistance to flow of anelectric current within a cell; the sum of the ionic and electronicresistance of the cell components) as a function of capacity for PVP-coated and uncoated (see below) lithium anode are shown in Figure2. The open circuit voltage (OCV) and voltage at 20 A loadcharacteristics are shown in Figure 3. It is seen that the voltageabove 2.2V (required minimum by the pacemaker electronics) is wellmaintained until the 2.5 Ah rating of the battery.

Figure 2: Capacity vs Internal resistance
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Figure 3: Run down characteristicsManufacturingLithium is easily formed into sheets that can be cut to the requiredsizes. It is easily pressed into specific anode shapes. The lithiumanode is coated three times with a solution of PVP. The solvent isevaporated to leave a contiguous film of pure PVP on the anodesurface. The precoated central lithium anode is corrugated toincrease its area and lower battery impedance. To obtain lower

impedance, newer designs use more concentrated active materialsand larger anode surface areas. Multiple anode surfaces may beused to lower the impedance. The complex of iodine and poly-2-vinyl pyridine (P2VP) is poured into the cathode case and allowed tocool.TestingTo maintain high reliability (of the order of 0.005 % failures permonth), cells are designed conservatively. They are manufacturedunder stringent quality controls, as demanded by the GoodManufacturing Practices (GMP) issued by the Food and DrugAdministration (FDA), USA. The qualification testing is performedunder accelerated test conditions specified for Li/I2-PVP cells. Thelist includes Non-destructive examinations, thermal cycling, highpressure, mechanical vibration, temperature / humidity,mechanical shock, voltage / temperature, seal terminal strength,
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elevated temperature discharge, destructive analysis, and solventresistance.Longevity and Battery life estimationLongevity

The pacemaker battery provides energy required for the operation ofthe circuitry of a pacemaker, which includes the control, sensingand pulse-generating units. A major concern in using battery is itslongevity. Longevity of a battery can be determined knowing batterycapacity (Ah) and current drain (microamperes). The current drainis dependent on the type of electrode as well as the circuitry andtype of pulse generation of the pacemaker.Life EstimationSince the longevity of a cardiac pacemaker means its battery life, itis essential to have the circuitry to identify the remaining useful life

of battery in a simple and reliable manner. Monitoring of internalresistance is a convenient tool for estimation of discharge level andfor predicting the approaching end-of-service.In many pacemaker systems, circuits are provided to measure theinternal resistance of the battery to deduce the remaining life. Withthis circuit1, the pacemaker is first switched to test mode and aresistive load is applied to the battery to measure the voltage drop.The status of the battery is indicated by generating a series of testpulses. Depending on the internal voltage drop, and thus the

internal resistance, the frequency of the stimulation pulse ischanged, which is measured externally. However, this circuit canonly be used for batteries with increasing internal resistance as thebattery discharges.To overcome the limitations of the above technique and to measurethe life expectancy of a battery with constant internal resistance,another technique was proposed. The battery test circuit is providedwith a pulse counter and input logic to measure the consumedcharge from the operating parameters of the pacemaker and the

number of pulses delivered over a period of time. During each test,the charge delivered since the last battery test is calculated basedon the count in the pulse counter, which is then summed to thecontents of the charge counter in memory. The content of thecharge counter is a measure of the total charge consumed andprovides information about the remaining life of the battery.


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The-circuit is implemented internally in the pacemaker unit and ameans is provided to report the value of the charge counter wheninterrogated by telemetric methods. The advantage of this method isthat there is no need to alter the frequency of stimulation pulses

while testing the battery.In some models-of pacemakers, approximately twice per day thedevice evaluates the battery status, which is reported during follow-up; where as in some other models, battery status is automaticallyevaluated every 11 hours. Battery status may be displayed in theform of a gauge (showing BOL, ERT, and EOL) and longevityremaining (> 5 years to < 0.5 years in 0.5 year increments) at 100%pacing.SpecificationsThe battery should meet the pacemaker pulse requirements in therange of 25 J, a very small power (compared to 15-40 J forImplantable Cardioverter Defibrillators). The following are broadspecifications.

a.Open Circuit Voltage: 2.8 Voltb.Control Circuit minimal voltage: 2.2 Voltc. Control Circuit current drain: 10 Ad.EOL battery resistance: 10 k Ohmse. Chold: 10 Ff. Oscillator frequency: 167 Hzg. Duty Cycle; 16.7 %h.Ah rating: 2 Ah (typical rating)i. Reliability: 99.6% probability of survival beyond 8 yearsj. Failure Rate: 0.005 % failures/month

Weight, Volume, Shape and SizeWeightHalf of the occupied space is consumed by the internal battery14 incardiac pacemaker. Therefore the energy density (energy/volume)and specific energy (energy/mass) are important considerations for

implantable batteries. Compared with lead, the same volume oflithium provides eight times as much electricity, at one-thirtieth theweight. The weight of a lithium-iodine battery varies from about12.5 grams to 15.5 grams for different manufacturers of thepacemaker unit. The variation in weight is primarily due to thelongevity and current drain capabilities of the battery.


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VolumeThe volume occupied by the battery in a pacemaker (pulsegenerator unit) is also about half the total volume. This varies from5 to 8 cc for the units manufactured by different manufacturers.

ShapeMost of the cardiac pacemakers are shaped as variations oncircular or elliptical objects1 to avoid having sharp corners thatmight penetrate the skin or damage surrounding tissues. Therefore,the batteries in these devices are shaped to conform to the overalldevice geometry, and often approximate a semicircle with a radiusof about 3cm and a depth of 6 to 8mm.SizeTypical dimensions of an implantable cardiac pacemaker are in therange of 49 mm x 46 mm x 6 mm / 47 mm x 41 mm x 7 mm / 45

mm x 52 mm x 7 mm / 44 mm x 42 mm x 8 mm / 41 mm x 50 mmx7 mm. The dimensions vary from one model to an another as wellas from one manufacturer to an another. The battery occupiesabout half of the size, and volume given in the table. Most of thecompanies use the lithium iodine battery developed first by WilsonGreat Batch.Future BatteriesNewer designs are aimed at lowering impedance by using moreconcentrated active materials and increasing anode surface area9.

Any increase in service life of implantable medical devices,including cardiac pacemakers is highly desirable and important. Inthis connection it seemed worthwhile to use power sources withhigher energy densities and lower internal resistance. Indeed,batteries based on other lithium systems were also proposed;lithium-silver chromate, lithium-cupric sulfide, lithium-thionylchloride being among them. However all these batteries wererejected.With several features being added to the implantable cardiac

pacemakers and other implanted medical devices, manufacturersare going to need to pull more energy out of the battery morequickly. Today's pacemakers typically use lithium iodine batteriesand defibrillators employ lithium silver vanadium oxide, next-generation systems may slowly migrate toward a newer type oflithium battery: lithium carbon monofluoride (CFx). CFx batteries


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reportedly offer higher energy density and can be pulsed at currentsabove 20 mA, which is slightly better than today's competingbatteries. Such innovations will be necessary, particularly if OEMvisions of patient management come to fruition. Medtronic, for

example, has already embarked on a decade-long program, knownas Vision 2010, which calls for far-reaching use of deviceconnectivity. Ultimately, engineers say they can foresee a day whenan implanted heart monitor will detect a problem and call anambulance; all while the patient lies sleeping.Lithium / carbon monofluoride (Li / CFx): a new pacemakerbatteryThe reduction in pacemaker size coupled with addition of morecurrent demanding functions have motivated the development ofbatteries that can supply higher current densities at useful voltages

than lithium / iodine batteries in use today while retaining thevolumetric energy density of that system. The battery can delivercurrents in the milliampere range without significant voltage drop.The system is compatible with titanium casing, allowing a 50%reduction in weight over the same size lithium / iodine battery.Cells have been designed and tested in these laboratories and havebeen shown to be suitable for advanced pacemaker applications.Lithium-polycarbon fluoride batteryThis type of battery possesses very high energy density and is

capable to ensure pulse discharge current as high as tens ofmilliamps. At the same time, in contradiction to lithium-iodinebatteries, lithium-polycarbon fluoride ones use a liquid electrolyte,specifically 1 M LiBF4 in gamma- butyrolactone. This fact warrantsspecial attention to a problem of sealing batteries for liquids andgases (due to electrolyte impurities). It is very important to checkthe battery leak-tightness, (meeting the reliability standards laiddown for implantable cardiac pacemakers) which would qualify formedical applications. The only volatile component of lithium-

polycarbon fluoride battery is gamma-butyrolactone. For detectingvolatile substances, gas chromatography is viewed as the mostsuitable and most accurate technique. Sadly enough, gaschromatography is not able to be used for gamma-butyrolactonedetection because it decomposes at a temperature below its boilingpoint. However, liquid chromatography is suitable for this analysis,


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but it is a much more sophisticated and expensive technique. Ofinterest, is a simple method of gamma-butyrolactone detection thatwas developed

DefibrillatorsDefibrillators are devices that apply sharp electrical shocks to theheart when its beating becomes dangerously rapidly or chaotic. Theshocks can restore normal heart rhythms before the malfunctioningheart suffers sudden cardiac arrest, a seizure than can lead todeath within minutes.Implanted defibrillators have become a multibillion dollar businessfor medical device makers following clinical trials showing that theycould save thousands of lives annually among patients with weak or

damaged hearts who are at heightened risk of sudden cardiacarrest. They consist of small battery-powered canisters implantedinto muscle under the collarbone (usually on the right side for left-handed patients and the left for those who are right-handed), whichare connected to the heart by insulated wires known as leads.An implantable cardioverter-defibrillator (ICD) a pager-sizeddevice which is implanted in your chestmay reduce your risk ofdying if your heart goes into a dangerous rhythm and stops beating(cardiac arrest). You may need an implantable cardioverter-

defibrillator if you have a dangerously fast heartbeat (ventriculartachycardia) or a chaotic heartbeat that makes it so your heart can'tsupply enough blood to the rest of your body (ventricularfibrillation).Implantable cardioverter-defibrillators work by detecting andstopping dangerous, abnormal heartbeats (arrhythmias). Animplantable cardioverter-defibrillator continuously monitors yourheartbeat and delivers electrical shocks to restore a normal heartrhythm when necessary.

The leads are used both to sense when the heart is experiencing arhythm that requires a shock and to deliver the shock. Defibrillatorcanisters need to be replaced when batteries are depleted --currently every four to seven years -- but leads are left in placeunless fractures or infections require them to be removed.


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Many defibrillators are designed to be multi-purpose devices thatcan also deliver low-powered stimulation to pace slow-beatinghearts or to help the four chambers of the heart contract in moresynchronized rhythms.

External defibrillators, which deliver life-saving jolts throughpaddles applied to the chest, are standard equipment inambulances and many other emergency response vehicles. In recentyears, simpler models of such devices known as automated externaldefibrillators, or A.E.D.'s, have been placed on commercial aircraft,in offices and schools for public use by citizens who are trained touse them.External DefibrillatorsExternal defibrillators are medical devices that diagnose life-

threatening abnormal heart rhythms, or cardiac arrhythmia, anddeliver electrical energy to the heart to restore its normal rhythm.They are used in emergency situations on patients who havecollapsed due to sudden cardiac arrest. When used in the first fewminutes following collapse, these devices often save lives.External defibrillators are used in many settings by medicalprofessionals, emergency responders, and by trained and untrainedbystanders. The technology is based on decades of research andevolving knowledge.

There is risk associated with all medical devices, and externaldefibrillators can malfunction. The defibrillator industry hasconducted dozens of recalls for external defibrillators, affectinghundreds of thousands of devices. Additionally, the FDA hasreceived thousands of reports of external defibrillator malfunctions.While the FDA continues to advocate use of these important life-saving devices and is not recommending any change to currentclinical practices, we believe the devices can be improved in waysthat improve patient safety.

FDA is taking steps to foster the development of safer, moreeffective external defibrillators.How an ICD worksWhen you experience a rapid heartbeat, the wires from your heartto the device transmit signals to the ICD to send electrical pulses to


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regulate your heartbeat. Depending on the problem with yourheartbeat, your ICD could be programmed for these therapies:

Low-energy pacing therapy. You may feel either nothing or a

painless fluttering in your chest when your ICD responds to milddisruptions in your heartbeat.Cardioversion therapy. A higher energy shock is delivered to dealwith a more serious heart rhythm problem. You might feel as ifyou're being thumped in the chest.Defibrillation therapy. This is the strongest form of electricaltherapy used to restore a normal heartbeat. During this therapyyou may feel as if you're being kicked in the chest. It may knockyou off your feet. The pain from this therapy typically lasts only asecond. There should be no discomfort after the shock is over.

Usually, only one shock is needed to restore a normal heartbeat.Sometimes, however, you may have two or more such shocksduring a 24-hour period. Frequent shocks in a short time period areknown as ICD storms, and they may understandably cause you toworry. If you experience ICD storms, you should seek emergencycare to see if your ICD is working properly or if you have a problemthat's making your heart beat more abnormally. If necessary, theICD can be adjusted to deliver the appropriate number of shocks.Additional medications may be needed to make your heart beat

regularly and decrease the chance of an ICD storm.

Who needs an ICD?You're a prime candidate for an ICD if you've had ventriculartachycardia, survived a cardiac arrest or have fainted from aventricular arrhythmia. You may also benefit from an ICD if youhave:

A history of coronary artery disease and prior heart attack that has

led to a weak heart.A heart condition that involves abnormal heart muscle, such asenlarged (dilated cardiomyopathy) or thickened (hypertrophiccardiomyopathy) heart muscle.An inherited heart defect that makes your heart beat abnormally.These include long QT syndrome, which can cause ventricular


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fibrillation and death even in young, active people with no signs orsymptoms of heart problems. Having other rare conditions such asBrugada syndrome and arrhythmogenic right ventricular dysplasiaalso may mean you need an ICD.

There are three major components to consider when studying adefibrillator: a capacitor, an inductor, and a power supply. Thesethree components will be explored in depth. Specifically, theinteraction between these three components is what allowsdefibrillators to effectively restore proper cardiac rhythms.

I.) Capacitors:One of the key components of a defibrillator is a capacitor. The capacitor of

a defibrillator stores a large amount of energy in the form of electrical charge.Then, over a short period of time, the capacitor releases the stored energy. The

capacitor itself contains numerous components: a pair of metal plate conductors

and an insulator. The insulator is in the middle of the conductors and does not

loose electrons. On the other hand, conductors easily loose electrons and promote

current flow.

To quantitatively describe a capacitor, one calculates the capacitance, the

ability to store charge. The formula to calculate capacitance relates charge (Q),

voltage (V), and capacitance (C):

C = Q/VA capacitor has 1 farad of capacitance if a potential difference of 1 volt is

present across its plates, when they hold a charge of 1 coulomb. Capacitors

typically have values of microfarads (F = 106

F). According to the equation,

capacitance is directly proportional to charge and indirectly proportional to

voltage.For a parallel plate capacitor, as in the case of a defibrillator, a relationship

can be established between the capacitance, the dielectric constant, the area of plate

overlap, and the distance between plates. Capacitance is directly proportional to

area and indirectly proportional to distance between plates:C = (Eo x A) / d


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The mechanism of action of a defibrillator is depicted below in Figure 1.

When the switch is in position 1, direct current from the power supply is

applied to the capacitor and electrons flow. Therefore current flows and a charge

begin to build up on each electrode of the capacitor. Specifically, the lower plate is

more negative and the upper plate is more positive. The build-up of opposing

charges creates a potential difference across the plates (V) that opposes theelectromagnetic force of the power supply (E).

Additionally, the electromagnetic force (E) can also be related to the area of

plate overlap (A), the charge (Q), and the dielectric constant (Eo) with the

following equation:E = Q / (Eo x A)

Charging a Capacitor:Charging a capacitor is an exponential process. Specifically, the work done

(W) to move charge (Q) through a potential difference V is: W = VQ. Therefore, as

the voltage increases more work is required.


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The charged capacitor is a store of potential energy, which may be released

on discharge. Thus, the amount of energy stored in a capacitor is CV and in order

to store energy, work must be done.Discharging a Capacitor:

In a defibrillator, the circuit (depicted in Figure 2) is completed when

paddles are applied to the patients switch. Electrons on the negative, lower platemove through the patient and then to the upper plate. Thus three key steps happen

in sequence: electric current flows, electrical energy is released, and the potential

energy between the upper and lower plates is zero. As the electrons are transferred

from the lower plate, the potential difference decreases. The rate of discharge

declines as the potential difference between the upper and lower plates falls.A graphical image differentiates between the chagrining and discharging of

a capacitor. Permission was obtained to reproduce this image.

Source:http://www.tpub.com/neets/book2/3d.htmEnergy Delivery:

The energy that is delivered can be calculated using the following

relationship: Energy = QV/2. Thus the energy delivered is directly proportional to

stored charge and voltage. Additionally, the energy stored in a capacitor can be

related to the electric field, area, and distance:U = energy = (Eo) E

2(Ad)

Thus, the energy of a capacitor is directly proportional to area of the plates

and distance between the plates. Additionally, if the electric field doubles, the

energy will quadruple.
http://www.tpub.com/neets/book2/3d.htmhttp://www.tpub.com/neets/book2/3d.htmhttp://www.tpub.com/neets/book2/3d.htmhttp://www.tpub.com/neets/book2/3d.htm


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II.) Inductors:Defibrillators are needed to shock the heart back in regular rhythm. Thus,

the current that is delivered must last for a several milliseconds. However, a

discharging capacitor delivers charge and current very fast. Inductors, coils of wire

that produce a magnetic field when current flows through them, prolong the

duration of current flow. Specifically, inductors generate electricity that opposes

the motion of current passing through it. This opposition is called inductance.

Inductors typically have values of microhenries (H).III.) Power Supply:

Step-up transformers are transformers that increase voltage. In the case of

defibrillators, step-up transformers are used to convert the main voltage of 240 VAC to 5000 VAC. A step-up transformer is used in defibrillators because this

allows the doctor to choose among different amounts of charge. The control switch

is calibrated in energy delivered to the patient (J), because this determines the

clinical effect or physical impact that a patient will experience. As an additional

energy source, many defibrillators also have internal rechargeable batteries.

What are the patient and safety issues associated with defibrillators?I.) Patient Issues:

Successful defibrillation depends on delivery of the electrical charge to the

myocardium. Only part of the total current delivered (about 35 A) flows through

the heart. The rest is dissipated. First, the skin and the rest of the body counteract

the flow of the current. The skin and thoracic wall act as resistors in series.R (eq) = R1 + R2 + R3

Other intrathoracic structures act as resistors in parallel.R (eq) = (1/R1) + (1/R2) + (1/R3)

The total impedance is about 50150 ohms; however, repeated

administration of shocks in quick succession reduces impedance.


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II.) Safety:Key safety concerns exist regarding the use of defibrillators. These concerns

must be taken into account before using a defibrillator on a patient with irregular

cardiac rhythms:The patient must not already be in sinus (normal) rhythm.The leads of the defibrillator must be properly connected, ensuring current

flow.Placement of paddles should follow specific guidelines: they should be

placed along the long axis of the heart, they should not cover the transdermal

patches because they are flammable, they should not be placed near metal

objects because currents will travel through the metal (path of least

resistance) and cause burning.All sources of oxygen must be removed from the patient during

defibrillation, because it supports combustion.No one from the medical staff should touch the bed, patient or any

equipment connected to the patient during defibrillation.Fluids may conduct electricity; therefore it is important to ensure that the

immediate area is clean and dry.The defibrillator should not be charged until the paddles are applied to the

patients chest, because accidental discharge from open paddles may cause

injury.

Documents

Unit 1 - Cardiac Care Units