INTRODUCTION:

Definition:

Pacemaker is an object or substance that influences the rate at which a certain phenomenon occurs, if it influences heart rate than is called cardiac pacemaker.

1. The natural cardiac pacemaker

2. An artificial cardiac pacemaker

Artificial pacemaker is a medical device, which uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart. Pacemakers are implanted to prevent or treat bradycardia caused by disorders of the cardiac conduction system^{1, 2}.

Need of Artificial Pacemaker:

If a person's natural heart rate (sinus rhythm) is too slow then the heart will not be able to pump enough blood to meet the needs of their body. A pacemaker is a small implantable device that can increase the heart rate by using an electrical stimulus to cause the heart muscle to contract.

The pacemaker can be programmed to stimulate the heart at a desired rate to increase the heart rate and enable cardiac output to be sufficient¹.

In addition to a slow-beating heart, a pacemaker could also be beneficial to a person whose heart beats unevenly. For instance, a person whose heart sometimes beats normally, but often changes to a slow or quick rhythm too frequently may require a pacemaker.

Symptoms, which may signify the need for a pacemaker, include:

1. Dizziness and/or fainting and loss of consciousness.

2. Shortness of breath

3. Significant lack of energy or fatigue

4. Irregular heart rate, tiredness

Design of Cardiac Pacemaker:

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 (circuitry and battery), and the leads are all made with biocompatible materials³. Generally, it has weigh less than 13 grams (less than half an ounce) and are the size of two stacked silver dollars³.

Casing:

Typically, the casing is made of titanium or a titanium alloy. Casing contains battery and circuitry.

Battery:

The primary function of a pacemaker battery is to store enough energy to stimulate the heart with a jolt of electricity. Additionally, it also provides power to the sensors and timing devices.

Since these batteries are implanted into the body designed to meet specific characteristics³:

1. It must be able to generate about 5 volts of power, a level that is slightly higher than the amount required to stimulate the heart.

2. It must retain their power over many years. A minimum period is four years.

3. It must have a predictable life cycle, allowing the doctor to know when a replacement is required.

Finally, they must be able to function when hermetically (airtight) sealed. Batteries have two metals that form the anode and cathode. Charge is transferred through these battery components. Some examples include lithium/iodide, cadmium/nickel oxide, and nuclear batteries. Generally, it is lithium iodide battery. An artificial cardiac pacemaker is a small battery-operated computer, called the pulse generator³.

The battery cannot be recharged. For this reason, the pulse generator must be replaced when the battery's energy is used up. Battery life typically ranges from seven to 15 years, depending on the number of leads the pacemaker is configured with and how much energy the pacemaker uses. When the battery's energy is depleted, a new pacemaker must be implanted. 

Circuitry (Mother Board):

The circuitry is usually made of modified silicon semiconductors. It is programmed for detection of fluctuation of impulse generation and it helps to generate pacing. The circuitry is the control center of the pacemaker. It consists heart monitoring sensors, voltage regulators, timing circuits, and externally programmable controls. The circuitry is composed primarily of resistors, capacitors, diodes, and semiconductors. With the application of semiconductors, circuit boards have become much smaller and also require less energy, produce less heat, and are highly reliable.

Leads:

The lead are thin, made of a metal alloy (coiled metal conductor), but it is insulated by a polymer such as polyurethane and anchored to the inner wall of the heart with either soft plastic hooks or a very short metal screw³. Only the metal tip of the lead is exposed. There are many styles of leads available, with primary design differences found at the exposed end.

BASIC PACEMAKER CHARACTERISTICS:

Pacemakers, both internal and external, have quite similar output characteristics³

Ø Pulse waves of from 1.5 to 2.0 milliseconds duration

Ø Energy outputs from 65 to 200 micro joules

Ø Peak currents in the range of 7.5 to 14 milliamperes

This provides sufficient energy to pace the heart in the majority of patients by epicardial or endocardial electrodes

TYPES OF PACEMAKERS:

1. Single chamber pacemakers - only one chamber is regulated, usually the ventricles. Pacemaker has one lead to carry signals to and from one chamber of patient’s heart --either the right atrium or the right ventricle³.

2. Dual chamber pacemakers - two leads are used the tip of one lead positioned in the right atrium and the tip of the other lead located in the right ventricle. Information from the atria regulates the contractions of the ventricles³.

MECHANISM OF IMPULSE GENERATION:

The pulse generator sends an electrical signal down the lead to a bare metal electrode, which is fixed against the heart, and the targeted heart chamber is prompted to contract. The system relies on feedback, which means the artificial pacemaker 'listens' to the heart and supplements the heart's natural rate. For example, the heart rate of a person with sick sinus syndrome may not increase during physical exertion. The artificial pacemaker recognizes this and boosts the heart rate to an appropriate level. In order to do this, the pulse generator may have sensors to detect physical exertion. Such sensors may detect activity or changes in breathing.

IMPLANTATION PROCEDURE:

Procedure:

The typical hospital stay for artificial cardiac pacemaker implantation is between one to two days³. A pacemaker is typically inserted into the patient through a simple surgery using a local anesthetic. The patient is usually given a drug for relaxation, and an antibiotic to prevent infection. An incision is made in the left shoulder area below the collarbone where the pacemaker is actually housed in the patient's body. The lead or leads (the number of leads varies depending on the type of pacemaker) are fed into the heart through a large vein using fluoroscope (using x-ray control) to monitor the progress of lead insertion. A temporary drain may be installed and removed the following day³.

The leads are tested before the pulse generator is attached and the incision is closed. A pocket is formed under the skin of the upper chest. The pulse generator, which is about the size and weight of three 50-cent coins, is generally implanted under the skin just below the collarbone in this pocket. The pacemaker is then connected to its leads. There are other sophisticated pacing systems, used in special circumstances that require more than two leads and may involve pacing the left side chambers. Usual activities such as working, driving a car and light exercise can resume after one to two weeks recuperation³.

Chance of failure:

Almost 70% of pacemakers are implanted in the operating room by surgeons⁴. There is a remote possibility that any electronic device can fail, but technical advances in recent years have made it possible to make pacemakers very reliable⁴. If patient’s pacemaker should fail to function properly, patient may experience the same symptoms that patient had before patient received the pacemaker³. If patient ever have these symptoms, contact patient doctor as soon as possible.

Programmer:

Pacemakers are checked with a special device called a programmer³. A portion of the programmer is simply held over the pacemaker and is able to communicate with the pacemaker. It can obtain information about the function of the pacemaker. It can also change certain functions of the pacemaker to whatever the doctor, nurse, or technician feels is most appropriate. A special magnet may also be used during the pacemaker evaluation, and if transtelephonic monitoring is part of the follow-up, a magnet will probably be given to the patient to use during the telephone evaluations³.

LIVING WITH A PACEMAKER:

Periodic Pacemaker Checkups:

Once the pacemaker is implanted, it is periodically checked to ensure the device is operational and performing appropriately. Depending on the frequency set by the following physician, the device can be checked as often as is necessary. During a visit, a programmer is used⁵. A programmer is a special computer that receives information stored in the pacemaker. It can also be used to change some pacemaker settings - without surgery. Routine pacemaker checks are typically done in-office every six (6) months, though will vary depending upon patient/device status and remote monitoring availability. At the time of in-office follow-up, the device will be interrogated to perform diagnostic testing.

CHECKING THE PACING SYSTEM INCLUDES:

Checking information about patient’s heart:

The clinician uses the programmer to look at information patient’s pacemaker has collected and stored since patient’s last visit. This information is about how patient’s heart and pacemaker are working together.

Checking the pacemaker’s settings:

The clinician also checks the current pacemaker settings with the programmer. If patient’s lifestyle or medical condition has changed, these settings can be changed using the programmer. These tests include⁵:

Ø Sensing: the ability of the device to "see" intrinsic cardiac activity (Atrial and ventricular depolarization).

Ø Impedance: (In electrical science impedance is a ratio of the voltage phasor to the electric current phasor) A test to measure lead integrity. Large and/or sudden increases in impedance can be indicative of a lead fracture while large and/or sudden decreases in impedance can signify a breach in lead insulation.

Ø Threshold: this test confirms the minimum amount of energy (Both volts and pulse width) required to reliably depolarize (capture) the chamber being tested. Determining the threshold allows the Allied Professional, Representative, or Physician to program an output that recognizes an appropriate safety margin while optimizing device longevity.

Checking battery status:

The status of the battery in patient’s pacemaker can also be checked using the programmer³¹. How long patient’s battery lasts depends on several factors. Some of these factors include the type of pacing system patient have and the nature of patient’s heart condition. When patient’s pacemaker battery is low, patient’s physician decides when to replace patient’s pacemaker. Because the battery is sealed inside the pacemaker, the entire pacemaker is replaced.

Frequency of follow-ups:

How often patient have follow-up appointments depends upon the type of pacemaker, patient’s medical condition, patient’s health plan, and the usual practice of patient’s clinic or doctor's office. Ask patient’s doctor about scheduling these appointments. The frequency of monitoring will change during the lifetime of patient’s pacemaker, with more frequent checks as patient’s pacemaker nears its expected replacement time⁵.

An additional aspect of the in-office check is to examine any events that were stored since the last follow-up. These are typically stored based on specific criteria set by the physician and specific to the patient. Some devices have the availability to display intracardiac electrograms of the onset of the event as well as the event itself⁶. This is especially helpful in diagnosing the cause or origin of the event and making any necessary programming changes. A survey of pacemaker follow-up programs was conducted in 1997 to determine current follow-up practices, 49% of respondents indicated a need for pacemaker follow-up guidelines⁶.

LIFESTYLE CONSIDERATIONS:

A patient's lifestyle is usually not modified to any great degree after insertion of a pacemaker³. There are a few activities that are unwise such as full contact sports and activities that involve intense magnetic fields.

The pacemaker patient may find that some types of everyday actions need to be modified. For instance, the shoulder harness of a vehicle seatbelt may be uncomfortable if the harness should fall across the pacemaker insertion site.

Any kind of an activity that involves intense magnetic fields should be avoided. This includes activities such as arc welding possibly, with certain types of equipment, or maintaining heavy equipment that may generate intense magnetic fields. In vitro investigation⁷ of an implantable cardiac pacemaker exposed to low frequency magnetic fields. The method used in this study is based on the interaction by inductive coupling through the loop formed by the pacemaker and its loads and the surrounding medium. This interaction results in an induced electromotive force between the terminals of the pacemaker, which can potentially disturb its operation. The studied frequencies are 50/60 Hz and 10/25 kHz. The experimental tests were carried out on several cardiac pacemakers, single chamber, and dual chamber. The results show a window effect of the detection circuits of cardiac pacemakers for the four studied frequencies⁷.

A 2008 U.S. study has found that the magnets in some portable music player headphones may interfere with pacemakers when placed in close proximity.

AHA (American Heart Association) Recommendation:

If patient have an artificial pacemaker, be aware of patient’s surroundings and the devices that may interfere with pulse generators³:

Home appliances and Pacemaker:

Ø CB radios, electric drills, electric blankets, electric shavers, ham radios, heating pads, metal detectors, microwave ovens, TV transmitters and remote control TV changers, in general, have not been shown to damage pacemaker pulse generators, change pacing rates or totally inhibit pacemaker output.

Ø Several of these devices have a remote potential to cause interference by occasionally inhibiting a single beat. However, most people can continue to use these devices without significant worry about damage or interference with their pacemakers.

Ø Power-generating equipment, arc welding equipment, and powerful magnets (as in medical devices, heavy equipment, or motors) can inhibit pulse generators. Patients who work with or near such equipment should know that their pacemakers might not work properly in those conditions.

A 2008 U.S. study has found that the magnets in some portable music player headphones may interfere with pacemakers when placed in close proximity⁷.

Medical equipments and Pacemaker:

Ø Magnetic resonance imaging (MRI)⁹ uses a powerful magnet to produce images of internal organs and functions. Metal objects are attracted to the magnet and are normally not allowed near MRI machines. The magnet can interrupt the pacing and inhibit the output of pacemakers. If MRI must be done, the pacemaker output in some models can be reprogrammed. Discussion with doctor the possible risks and benefits before undergo MRI scanning. Therefore, all physicians performing MRI on pacemaker patients must be very cognizant of possible thermal myocardial injury resulting in loss of capture and of possible pacemaker inhibition during MR imaging, both of which may lead to patient morbidity¹⁰_.

Ø Extracorporeal shock-wave lithotripsy (ESWL) is a noninvasive treatment that uses hydraulic shocks to dissolve kidney stones. This procedure is safe for most pacemaker patients⁹, with some reprogramming of the pacing. Patient will need careful follow-up after the procedure and for several months, to be sure patient’s unit is working properly. Patients with certain kinds of pacemakers implanted in the abdomen should avoid ESWL. Discuss patient’s specific case with patient’s doctor before and after the treatment.

Ø Radiofrequency (RF) ablation uses radio waves to manage a wide variety of arrhythmias. Recent studies of patients with implanted pacing systems measured the units before, during, and after RF catheter ablation. They showed that most permanent pacemakers are not adversely affected by radio frequencies during catheter ablation⁹. A variety of changes in patient’s pacemaker can occur during and after the treatment. Patient’s doctor should carefully evaluate patient’s pacing system after the procedure.

Ø Transcutaneous electrical nerve stimulation (TENS) is used to relieve acute or chronic pain. Several electrodes are placed on the skin and connected to a pulse generator. Most studies have shown that TENS rarely inhibits bipolar pacing⁹. It may sometimes briefly inhibit unipolar pacing. This can be treated by reprogramming the pulse generator.

Ø Diagnostic radiation (such as screening X-ray) appears to have no effect on pacemaker pulse generators⁹. However, therapeutic radiation (such as for treating cancerous tumors) may damage the pacemaker's circuits. The degree of damage is unpredictable and may vary with different systems. However, the risk is significant and builds up as the radiation dose increases. The American Heart Association recommends that the pacemaker be shielded as much as possible, and moved if it lies directly in the radiation field. If patient depend on patient’s pacemaker for normal heart pacing, the electrocardiogram (ECG) should be monitored during the treatment, and patient’s pulse generator should be tested often after and between radiation sessions.

Ø Dental equipment does not appear to affect pacemakers adversely. Some patients may feel an increase in pacing rates during dental drilling.

Ø Electroconvulsive therapy (such as for certain mental disorders) appears to be safely used in patients with pacemakers.

Ø Short wave or microwave diathermy uses high frequency, high-intensity signals. These may bypass patient’s pacemaker's noise protection and interfere with or permanently damage the pulse generator.

Cellphones and Pacemaker:

Ø In certain cases, a cellular phone could affect patient’s pacemaker's operation if it is closer to it than six inches⁸. This interaction is temporary, and moving the phone away from the pacemaker will return it to proper function⁹.

ü To reduce the chance of interaction, maintain a distance of at least six inches between the cellular phone and patient’s pacemaker;

ü Hold the cellular phone on the opposite side of patient’s body from patient’s pacemaker;

ü Do not carry a cellular phone in a breast pocket or on a belt if that places the phone within 6 inches of patient’s pacemaker.

Ø Cellphones available less than 3 watts do not seem to damage pulse generators or affect how the pacemaker works. Technology is rapidly changing as the Federal Communications Commission (FCC) is making new frequencies available. Newer cellphones using these new frequencies might make pacemakers less reliable. A group of cellophone companies is studying that possibility.

Microwave ovens and Pacemaker:

At one time, there was concern that leakage from microwave ovens could interfere with certain electronic cardiac pacemakers. Similar concerns were raised about pacemaker interference from electric shavers, auto ignition systems, and other electronic products. Although no recent studies have been performed which test the effect of household microwave energy on pacemakers and ICDs, it is widely believed and accepted that all modern pacemakers are adequately shielded from microwave energy produced by modern appliances¹¹. Extremely high-powered pulses and low power pulses microwave induced changes in the pacemaker rhythm of isolated frog heart preparation were identical and could be entirely attributed to microwave heating independent of its power¹². The problem has been largely resolved because pacemakers are now designed to be shielded against such electrical interference. However, patients with pacemakers may wish to consult their physicians if they have concerns.

Other electronic equipments and Pacemaker:

Ø Anti-theft systems which are also known as electronic article surveillance (EAS)

Ø Metal detectors for security are detecting pacemaker as a metal can create inconveniency to patients

PACEMAKER - PATIENT IDENTIFICATION CARD:

Pacemaker Patient Identification Cards carry information such as¹³:

1. Model and serial numbers of patient’s pacemaker and lead(s)

2. Patient’s name, address and phone number

3. Patient’s social security number, if available

4. The date patient’s device was implanted

5. The hospital where the implant was performed

6. The implanting doctor’s name, address and phone number

7. Patient’s follow-up doctor’s name, address and phone number

8. Patient data (between others, symptom primary, ECG, aetiology)

9. IPG (rate, mode, date of implantation, MFG, type and lead details)

Advice to patient:

Patient is asked always to carry his/her identification card. In an accident, I.D. card will tell the people helping patient that patient have a pacemaker. Patient’s card can be particularly handy if patient travel by air. The metal-detection devices in airports may detect the metal in patient’s pacemaker¹⁴, although they will not damage it. Showing patient’s card may save patient some inconvenience. The Pacemaker Wallet Identification Card is available as a PDF. Print it out and carry it with patient¹⁴.

PRIVACY AND SECURITY:

Security and privacy concerns have been raised with pacemakers that allow wireless communication. Unauthorized third parties may be able to read patient records contained in the pacemaker, or reprogram the devices, as has been demonstrated by a team of researchers¹⁵. The demonstration worked at short range; they did not attempt to develop a long-range antenna¹⁵. The proof of concept exploit helps demonstrate the need for better security and patient alerting measures in remotely accessible method.

Risks of artificial pacemaker:

Possible complications of pacemaker surgery are¹⁶:

Ø Abnormal heart rhythms

Ø Bleeding

Ø Punctured lung. This is rare.

Ø Infection

Ø Puncture of the heart, which can lead to bleeding around the heart but it, is rare.

ADVANCEMENTS IN FUNCTION:

When first invented, pacemakers control only the rate of the only single the ventricles beat. Much advancement has been made to enhance the control of the pacemaker once implanted. Many of these enhancements have been made possible by the transition to microprocessor-controlled pacemakers. Pacemakers that control not only the ventricles but the atria as well have become common. Pacemakers that control both the atria and ventricles are called dual-chamber pacemakers. Although these dual-chamber models are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure.

Biventricular Pacing (BVP):

Cardiac resynchronization therapy (CRT) was conceived in the mid-1990s. It offered not only atrioventricular (AV) synchronization as had previously been used in dual-chamber pacing but also synchronization of the two ventricles¹⁶.

(Figure –: Biventricular pacing)

Three leads can be seen in this example of a cardiac resynchronization device:

1. Right atrial lead (solid black arrow)

2. Right ventricular lead (dashed black arrow)

3. Coronary sinus lead (right arrow)

The coronary sinus lead wraps around the outside of the left ventricle, enabling pacing of the left ventricle. Note that the right ventricular lead in this case has two thickened aspects that represent conduction coils and that the generator is larger than typical pacemaker generators, demonstrating that this device is both a pacemaker and a cardioverter-defibrillator, capable of delivering electrical shocks for dangerously fast abnormal ventricular rhythms.

A biventricular pacemaker, also known as CRT (cardiac resynchronization therapy) is a type of pacemaker that can pace both the septal and lateral walls of the left ventricle. By pacing both sides of the left ventricle, the pacemaker can resynchronize a heart whose opposing walls do not contract in synchrony, which occurs in approximately 25-50 % of heart failure patients.

CRT devices have at least two leads, one in the right ventricle to stimulate the septum, and another inserted through the coronary sinus to pace the lateral wall of the left ventricle.

Often, for patients in normal sinus rhythm, there is also a lead in the right atrium to facilitate synchrony with the atrial contraction. Thus, timing between the atrial and ventricular contractions, as well as between the septal and lateral walls of the left ventricle can be adjusted to achieve optimal cardiac function.

CRT devices have been shown to reduce mortality and improve quality of life in patients with heart failure symptoms¹⁷ a LV ejection fraction less than or equal to 35%¹⁸ and QRS duration on EKG of 120 msec or greater¹⁹. CRT can be combined with an implantable cardioverter-defibrillator (ICD)^{18, 20}.

Early studies with CRT demonstrated its ability to improve the symptoms, the exercise capacity, and the feeling of well-being of many patients with moderate to severe heart failure. Additional studies showed that CRT could improve both the anatomy and function of the heart - tending to reduce the size of the dilated left ventricle, and improving the energy usage of the heart.

In the fall of 2003, the COMPANION trial showed that CRT can reduce the need for hospitalization, and may improve survival in patients with heart failure. In the COMPANION trial, over 1600 patients with significant heart failure (including recent prior hospitalizations for heart failure, and intraventricular conduction delays, were randomized to receive optimal drug therapy, or optimal drug therapy plus CRT. (Half the patients receiving CRT got a CRT device that also acts as an implantable defibrillator; the other half-got CRT pacing alone.)

Results from COMPANION confirm that patients receiving either kind of CRT device had more than a 20% reduction in the composite endpoint of the study (i.e., total hospitalizations and death from any cause.) Furthermore, patients who received the CRT-plus-defibrillator showed a 36% reduction in mortality alone. Those who received CRT without the defibrillator showed a trend toward a 24% reduction in mortality alone, though the trend did not quite reach statistical significance.

The DAVID trials²¹ have shown that unnecessary pacing of the only right ventricle can lead to heart failure and an increased incidence of atrial fibrillation. The newer dual chamber and biventricular devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease²¹.

Current pacemaker technology has evolved such that modern pacemakers have high-density, low-power consumption memory and are capable of automatically recording and storing episodes of spontaneous atrial tachyarrhythmias according to programmable detection criteria. Such episodes may be recorded as interval data, local electrograms, or both²².

Rate responsive pacing allows the device to sense the physical activity of the patient and respond appropriately by increasing or decreasing the base pacing rate via rate response algorithms. Previously, the rate of cardiac stimulation had been determined either at pacemaker manufacture, by programming a single rate, or by sensing the atrium. More recently, sensing another physiological or nonphysiological function that changes in response to body need has become possible²³.

An implantable cardiac stimulator having a bradycardia pacer and a defibrillator in a common housing and sharing common atrial and ventricular sense circuits includes circuitry for defining a dynamic paced refractory interval that is inversely proportional to the pacing rate to thereby allow adequate time in the cardiac cycle for sensing ventricular events even at elevated pacing rates such as when the atrial tracking rate approaches a programmed upper rate limit for the pacemaker or a sensor driven rate approaches the programmed upper rate limit. Exercise changes blood oxygen saturation, central venous pH, central venous temperature, minute ventilation and respiratory rate, stroke volume, circulating catecholamines, QT interval, evoked endocardial response to a stimulus, and the mechanics of myocardial contraction²³.

An unrealized advancement in pacemaker function could mimic nature by utilizing various bodily input parameters such as

1. CO₂ - O₂ at in arterial-vein system

2. Body temperature

3. Respiratory rate

4. ATP levels

5. Body hormone levels like Adrenaline, etc.

Instead of producing a static, predetermined heart rate, or intermittent control, a Dynamic Pacemaker could compensate for both actual respiratory loading and potentially anticipated respiratory loading.

A Dynamic Pacemaker would require sensory technology for which heart-rate regulation parameters must first be acutely identified. Dynamic Peacemaking technology could also be applied to future artificial hearts. Advances in transitional tissue welding would support this and other artificial organ/joint/tissue replacement efforts. Stem cells may or may not be of interest to transitional tissue welding.

Cardiac Pacemaker Regulated by Respiratory Rate and Blood Temperature:

In patients with complete heart block with normal sinoatrial function, dual chamber pacing can main- thin atrioventricular synchrony and provide for chrono- tropic response during exercise. However, its use can be limited in patients with sinoatrial disease, which has been reported to be associated with complete heart block in 30 to 40 percent of patients also, atrial sensing can predispose to the development of pacemaker-mediated tachycardia²⁴. Although the use of a long atrial refractory period can reduce this problem, this leads to a limitation of the upper rate response of the pacemaker. Thus, in a subset of patients, dual chamber pacing may not be the ideal pacing method during respiration of a patient, the electrical impedance between two electrodes on the chest of the patient changes. By monitoring this impedance, it is thus possible to calculate the respiration rate and deepness of breathing of the patient. The ventilated breath volume per minute can in turn be calculated.

A new method using respiratory rate and temperature as the guides for optimal pacing is proposed. A pacemaker was fabricated which senses these two parameters simultaneously. The pacemaker functions by calculating the cardiac rate, which would he derived from the respiratory rate and the blood temperature. The higher of the two rates is adopted as the cardiac pacing rate, i.e., at which stimuli will be delivered.

The operation was tested in a mongrel dog with complete atrioventricular block. After the induction of anesthesia, a thermistor temperature probe was inserted into right atrium and a respiratory rate sensor was attached around the chest. After administration of a pyrogenic drug, both respiratory rate and blood temperature increased²⁴.

The pacing rate was increased from 178 beats/minute (bpm) at 36.4°C blood temperature, and 26.5 acts/minute (apm), respiratory rate, to 233 bpm at 40.1°C and 40.0 apm. Cardiac output was increased from 2.25 liters/minute (1/pm) at the beginning to 2.50 l/pm at maximum. The transition of the guide from respiratory rate to temperature was observed at about 38°C.

The respiration-controlled cardiac pacemaker includes a stimulation pulse generator generating stimulating pulses at a controllable basic stimulation rate, a rheography pulse generator producing rheography pulses of constant amplitude and a respiration detector, which, as a function of the impedance data of the rheography pulses, generates a respiration signal representing the respiratory rate and/or the depth of respiration. Control device control the basic stimulation rate of the stimulation pulse generator in accordance with a predetermined respiration signal--basic stimulation rate--characteristic as a function of the respiration signal. The rheography pulse generator generates the rheography pulses to timing dependent upon the stimulating pulses and/or inhibiting pulses, preferably within the refractory time intervals in each case associated with the individual stimulating pulses or inhibiting pulses and in which the stimulation pulse generator is blocked. It is convenient that the rheography pulses are generated within the refractory time intervals preceding the individual stimulating pulses. Associated with each stimulating pulse or inhibiting pulse is a single rheography pulse. In this way, stimulation upsets, disturbances of the ECG by the rheography pulses are avoided, and in the event of hyperventilation, any undesired rise in basic stimulation rate is avoided²⁴.

ADVANCEMENT IN DESIGN:

As research efforts continue, future devices promise to be longer lasting, more reliable, and more versatile. Advances in battery technology, such as using radioactive isotopes for power, will undoubtedly improve the longevity of implanted pacemakers. Developments in microelectronics should provide even smaller devices, which are less prone to environmental interferences.

A cardiac pacemaker uses half of its battery power for cardiac stimulation and the other half for housekeeping tasks such as monitoring and data logging⁴. The first implanted cardiac pacemaker used nickel-cadmium rechargeable battery, later on zinc-mercury battery was developed and used which lasted for over 2 years⁴. Lithium iodine battery invented and used by Wilson Greatbatch and his team in 1972 made the real impact to implantable cardiac pacemakers. This battery lasts for about 10 years and even today is the power source for many manufacturers of cardiac pacemakers. This paper briefly reviews various developments of battery technologies since the inception of cardiac pacemaker and presents the alternative to lithium iodine battery for the near future⁴.

Six hermetically sealed single cell rechargeable mercury-zinc pacemakers (B.T.) that will run continuously for over 4 years between rechargings have paced dogs with complete heart block for from 2 to 3 years. To maintain full cell capacity (over 1,000 mA hours) requires recharging for from 2-3 min/day to 60 to 80 hr once every 4 years, with any variation between these extremes being acceptable²⁵. Six realtime bench tests continue after over 7 years and accelerated tests have simulated a minimum of 50 years continuous pacing. Battery voltage is assessed by direct telemetry, eliminating the risk of patient intrinsic rhythm-pacemaker competition which is present with all current indirect (stimulation rate change) battery assessment techniques²⁵.

(Figure: X-ray image of installed pacemaker showing extra wire routing)

Advancement in pacemaker technology is left ventricular pacing. A pacemaker wire is placed on the outer surface of the left ventricle, with the goal of physiological pacing than what is available in standard pacemakers. This extra wire is implanted to improve symptoms in patients with severe heart failure.

A late-breaking development in the field is the application of cardiac Pacemaking technology to the brain. In this system, scientists connect the lead wires to a specific site on the brain and stimulate it as needed to regulate heartbeat. This device has been shown to be particularly effective in calming the tremors associated with Parkinson's disease.

Technology is rapidly changing as the Federal Communications Commission (FCC) is making new frequencies available. Newer Cell phones using these new frequencies might make pacemakers less reliable. A group of cellophanes companies is studying that possibility. Advancement concern has been raised with pacemakers that allow wireless communication for physician/technician. They can follow pacemaker information even if patient does not come to clinic visit²⁶. The demonstration worked at short range; they did not attempt to develop a long-range antenna. Unauthorized third parties may be able to read patient records contained in the pacemaker, or reprogram the devices, as has been demonstrated by a team of researchers. The proof of concept exploit helps demonstrate the need for better security and patient alerting measures in remotely accessible method. Researchers are working on improvement of security and privacy concern²⁶.

Summary:

Artificial pacemakers were implanted since middle of the 20^th century. Dr. Hopps invented first implantable artificial pacemaker in 1958. A patient's lifestyle is little bit modified. Few activities those are unwise such as full contact sports and activities that involve intense magnetic fields. Security and privacy concerns have been raised with pacemakers that allow wireless communication. Modern pacemakers are externally programmable and allow the cardiologist to select the optimum pacing modes for individual patients. Like, some combine a pacemaker and defibrillator in a single implantable device. Others have multiple electrodes stimulating differing positions within the heart to improve synchronization of the lower chambers of the heart. A Biventricular Pacemaker (BVP), also known as CRT (cardiac resynchronization therapy) by pacing both sides of the left ventricle, the pacemaker can resynchronize right atrium, right ventricle and left ventricle. An unrealized advancement in pacemaker function could mimic nature by utilizing various bodily input parameters such as CO2 - O2 level at in arterial-vein system, Body temperature, Respiratory rate, Body hormone levels like Adrenaline, etc. Advancement in design - as research efforts continue, future devices promise to be longer lasting, more reliable and versatile. Advances in battery technology, such as using radioactive isotopes, will undoubtedly improve the longevity of implanted pacemakers. Still further advancements are under research for better convenience of patients and security concern.

REFERENCES:

1. Lamas GA, Pashos CL, Normand ST, McNeil B. Permanent Pacemaker Selection and Subsequent Survival in Elderly Medicare Pacemaker Recipients. Circulation. 1995; 91:1063-9.

2. Guidelines for implantation of cardiac pacemakers and antiarrhythmic devices. A report of the American College of Cardiology/American Heart Association Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures (Committee on Pacemaker Implantation). Dreifus LS, Fisch C, Griffin JC, Gillette PC, Mason JW, Parsonnet V. Special report. Circulation. 1991; 84:455-67.

3. Pacemakers, Patient and Public Information Center: Heart Rhythm Society available at http://www.hrspatients.org/patients/treatments/pacemakers.asp. (Assesd on April 30, 2009).

4. Mallela VS, Ilankumaran V, and Rao NS. Trends in Cardiac Pacemaker Batteries. In Pacing and Electrophysiol J. 2004; 4(4): 201-12.

5. http://www.cardioassoc.com/patient_pgs/pacericd.asp. (Assessed on May 3, 2009).

6. Fraser JD, Gillis AM, Irwin ME, et al. Guidelines for pacemaker follow-up in Canada: A consensus statement of the Canadian Working Group on Cardiac Pacing. The J of Canadian Cardiovas Soc. 2000; 16(3): 355-76.

7. Babouri A, Hedjeidj A, Guendouz L. Experimental and theoretical investigation of implantable cardiac pacemaker exposed to low frequency magnetic field. J Clin Monit Comput. 2009; 23(2):63-73.

8. MP3 Headphones Interfere With Implantable Defibrillators, Pacemakers - Beth Israel Deaconess Medical Center. www.bidmc.org. (Retrieved on 08 July, 2009).

9. Testing of work environments for electromagnetic interference. PACE. 1992; 15(10): p 163-6.

10. Naehle CP, Litt H, Lewalter T, Sommer T. Do we need pacemakers resistant to magnetic resonance imaging? Europace. 2006; 8:388.

11. Roguin, A., Schwitter, J., Vahlhaus, C., Lombardi, M., Brugada, J., Vardas, P., Auricchio, A., Priori, S., Sommer, T. (2008). Magnetic resonance imaging in individuals with cardiovascular implantable electronic devices. Europace 10: 336-346.

12. Pakhomov AG, Mathur SP, Doyle J, Stuck BE, Kiel JL, Murphy MR. Comparative effects of extremely high power microwave pulses and a brief CW irradiation on pacemaker function in isolated frog heart slices. Bioelectromagnetics. 2000 ;21(4): 245-54.

13. European Pacemaker Patient Identification card available at http://www.xs4all.nl/~fbaart/aktueel/pm.pdf. (Assessed on August 16, 2009).

14. Copperman Y, Zarfati D, Laniado S. The effect of metal detector gateways on implanted permanent pacemakers. Pacing Clin Electrophysiol 1988; 11:1386-138

15. Daniel H; Thomas S, Benjamin H, Benjamin R, Shane S, Defend B, et al. "Pacemakers and Implantable Cardiac Defibrillators: Software Radio Attacks and Zero-Power Defenses" (PDF). IEEE Symposium on Security and Privacy.2008.

16. http://www.righthealth.com/topic/Pacemaker_Battery/overview/adam20?fdid=Adamv2_007369. (Assessed on September 23, 2009)

17. Cleland JG, Daubert JC, et al. "The effect of cardiac resynchronization on morbidity and mortality in heart failure". N. Engl. J. Med. 2005; 352 (15): p 1539–49.

18. Bardy GH, Lee KL, Mark DB, et al. "Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure". N. Engl. J. Med. 2005; 352 (3): p 225–37.

19. Bristow M, Saxon L, Boehmer J, Krueger S, et al. "Cardiac-resynchronization therapy with or without an implantable defibrillator in advanced chronic heart failure". N Engl J Med. 2004; 350 (21): p 2140–50.

20. Erdmann E, Freemantle N, et al. "The effect of cardiac resynchronization on morbidity and mortality in heart failure". N Engl J Med. 2005; 352 (15): p 1539–49.

21. Wilkoff BL, Cook JR, Epstein AE, et al. "Dual-chamber pacing or ventricular backup pacing in patients with an implantable defibrillator: the Dual Chamber and VVI Implantable Defibrillator (DAVID) Trial". JAMA. 2002; 288 (24): p 3115–23.

22. TV, Glotzer, AS. Hellkamp, J Zimmerman, MO Sweeney, R Yee, R Marinchak, et al. Atrial High Rate Episodes Detected by Pacemaker Diagnostics Predict Death and Stroke: Report of the Atrial Diagnostics Ancillary Study of the MOde Selection Trial (MOST). Circulation. 2003; 107: 1614 - 9.

23. S Furman. Rate-modulated pacing. Circulation. 1990; 82: 1081 - 94.

24. Lau CP, Ward DE and Camm AJ. Single-chamber cardiac pacing with two forms of respiration-controlled rate-responsive pacemaker. Chest. 1989; 95; 352-8.

25. HC Hughes, RR Brownlee, and GF Tyers. Two to three years of failure-free testing of a rechargeable pacemaker in experimental complete heart block. Circulation, 2008; 54: 263-6.

26. Bilitch M, Lau FYK, Cosby RS. Recent Advances in Artificial Pacemakers. Calif Med. 1967; 107(2): p 164-70.

Received on 25.01.2010 Modified on 28.02.2010

Research J. Pharm. and Tech. 3(2): April- June 2010; Page 390-398