SSCTS

1.   Introduction

Electric pacing is one of the most common therapeutic or prophylactic strategies in the management of patients with cardiac problems at present. Temporary cardiac pacing is often needed in the acute management of myocardial infarction compounded by conduction system injury. Likewise, it is also regularly utilized in the peri-operative setting of open-heart surgery. Permanent cardiac pacing is a very common cardiac surgical procedure performed at present with about 548,000 pacemakers implanted worldwide in 1998 as reported by Cardiac Pacing Incorporated. Moreover, more than 200,000 pacemakers were implanted in the United States in 2000 costing a colossal $2 billion for pacemakers and leads alone. (1, 2)

This paper aims at providing an outline of the fascinating journey that led to the invention and evolution of the cardiac pacemaker.

2.   What is a pacemaker?

A pacemaker generator is a complex electronic instrument that consists of 3 essential components which are the metal encasement of the electronic circuit, the electronic circuit and a battery. The generator is then attached to pacing leads which conduct electrical impulse to the myocardium. (1)

The size of the pacemaker is about the size of a man’s wristwatch. It is made up of titanium and contains a lithium battery along with the electronic circuitry that controls the pacing system. The lifespan of the battery usually varies from 5 to 10 years. The pacemaker system is implanted following venous access through the subclavian or cephalic veins and giving rise to a subcutaneous device pocket in the subclavian region via a small cutaneous incision. The leads are passed transvenously into the expected cardiac chambers and anchored to the myocardium by a tiny screw or soft tines. (3)

3.   Function of pacemaker

The basic function of the pacemaker is to pace the heart in the absence of intrinsic impulses and to recognize intrinsic cardiac electrical activity if present and restrain pacing consequently. Pacemaker functions within each chamber depend on the mode of programmed operation. Pacemakers are coded according to the type of pacemaker and mode of pacing as defined by British Pacing and Electrophysiology group and North American Society of Pacing and Electrophysiology. The mode is usually characterized by a 3 or 4 designation. The first letter pertains to the chamber(s) being paced (Atrium, Ventricle or both-labelled dual) and the second letter refers to the chamber(s) being monitored for intrinsic electrical activity. The third letter attributes to the response to a sensed event (Inhibit pacing output, Triggered pacing after a sensed event or Dual response), the fourth letter represent the presence of rate responsiveness. (R) Hence, a pacemaker programmed to a DDDR mode would have the capacity to pace in both the atrium and ventricle, sense in both the atrium and ventricle be both inhibited and triggered by sensed events. Single chamber pacing is often a prudent intervention for management of some cardiac disorders. Dual-chamber pacing regulates the delivery of ventricular stimuli with respect to sensed atrial depolarizations to maintain atrio-ventricular (AV) synchrony. (3)

4.   Indications For Implantation

The commonest rationale for pacemaker implantation is sinus node dysfunction. The sinus node is the primary pacemaker of the heart and is responsible for the regular, rhythmic heart beat. It is made up of a collection of specialized cells found at the top of the right atrium. These cells generate regular electric impulses that spread thereafter through the atria and pumping ventricles and bring about the muscular contractions for the pumping function of the heart. (4)

Sinus node dysfunction can manifest as sinus bradycardia, asystole, sinus arrest, sino-atrial block etc. It can occur in individuals of any age but is more often seen in elderly people because the number of cells in the sinus node decreases over time as the body ages. Hence, pacemaker implantation in the elderly population is perceived as a means of preventing, treating or preserving a normal heart rate. (2, 3)

5. Period before pacemakers

Before the advent of pacemakers, only two methods were employed in an attempt to restore the normal cardiac activity following a cardiac arrest. These were the mechanical stimulation of the heart and the intracardial therapy. Mechanical stimulation of the heart was practiced following accidental cardiac arrest in patient being operated under general anaesthesia. This involved either applying pressure on the diaphragm during the course of a laparotomy or directly massaging the heart-“squeezing, pinching or irritating the heart to recontract.” The intracardial therapy required injecting a drug such as adrenaline through the chest wall. The consequence on the whole was too incoherent to allow the physicians to assess the effectiveness of the procedure. (5-7)

6. Invention of first cardiac pacing- Mark C. Lidwill 

Mark C. Lidwill, a physician-anaesthetist described an electrical apparatus that he had designed to drive the human heart at a meeting of the Australasian Congress in Australia in 1929. Apparently, Lidwill intended to use his machine only for emergencies when surgical patients went into cardiac arrest while under general anaesthesia. Likewise, he told his audience that using a slightly more primitive model of the electrical equipment in 1925 or 1926, he attempted to revive several stillborn infants. One of these infants had “recovered completely and is quite healthy.” He mentioned that this child did not respond to any other treatments such as injection of adrenaline that was commonly done in those days. So, Lidwill inserted a needle electrode first into the right atrium and then when atrial pacing failed, into the right ventricle. After about ten minutes of ventricular pacing, the pacemaker was turned off and the child’s heart continued on its own. Hence, an Australian baby was the first human being to undergo successful heart pacing and Lidwill’s apparatus was the first artificial pacemaker.

But Lidwill acknowledged the fact that pacing might be successful only occasionally, “but one life in fifty or even a hundred is a big advancement when there is no hope at all.” Unfortunately, Lidwill’s work seemed to be an isolated investigation that stimulated no interest and led nowhere. (8)

7. Hyman’s artificial pacemaker-1930s 

While suing the intracardial therapy for cardiac arrest, Albert Hyman, at the New York Beth David Hospital noticed that the success of such a procedure irrespective of the drug used was principally attributable to the prick of the needle inserted into the heart.  Furthermore, he inferred that during prolonged asystole, the electrodynamic balance of the heart may be too disturbed to allow a single prick to result in a myocardial contraction. Multiple pricks would have been useful potentially but surely prove hazardous. Since the mechanical stimulus finally acted by variations in electric potential, Hyman thought of directly stimulating the myocardium with electrical impulses passed through needle electrodes, with the benefit of repeated stimulation without posing any hazard. This led to the impressive design of Hyman’s pacemaker in 1932. It consisted of a magneto generator to produce direct current voltage for supplying power to the electrodes. Two large U-shaped magnets supplied the required magnetic flux to induce current in the generator. An interrupter disc was used to control the duration of the electrical impulse supplied to the electrodes. The entire apparatus which was portable weighed 7.2 kg as is shown below. (5)

The Hyman Pacemaker from 1932.

However, contemporary researchers who experimented with Hyman’s pacemaker found it to be ineffective because of a low voltage output of the pulses generated by the generator. Hyman himself conceded the shortcomings of his pacemaker. (9)

8. J. A. Hopps’ s Pacemaker- After 1945 

 

It is only after a decade or so, after the Second World War that interest in artificial pacemakers in the practice of cardiology was rekindled again by Callagan, Bigelow and Hopps at the University of Toronto in Canada. During their investigations about general hypothermia, it was noticed that cardiac arrest took place often during the hypothermic state. Furthermore, control of the heart rate was found crucial for survival during the rewarming period, when the metabolic rate of the body tissues increased. To accomplish this, John A. Hopps, an engineer at the National Research Council of Canada designed an artificial pacemaker that could produce impulses at a desired rhythm through an electrode placed in the region of the SA node after carrying out a thoracotomy. The apparatus was successfully tested on four dogs who suffered from cardiac arrest under general hypothermia. (10) Swiftly after that, it was realized that such a pacemaker could be used equally efficiently to control heart rate at normal body temperature. The device was successful in controlling cardiac rate in animals at normal temperature but it failed when utilized in patients who had suddenly collapsed because of atrio-ventricular block following myocardial infarction. The failure was probably attributed to the fact that only the atria and never the ventricles were paced. (11-13)

 

 

 

 

9. Zoll’s pacemaker and first clinical application




The first clinical application of the pacemaker took place in 1952. It occurred following the admission of a 75- year old man in Boston Beth Israel Hospital with two episodes of Stokes Adams attacks and a complete heart block for the past two years. His condition worsened and he continued to experience episodes of ventricular asystole despite being administered 34 intracardiac injections of adrenaline over a 4 hour period. Dr Paul M. Zoll, the attending physician applied “external electrical stimulation” to this patient and successfully paced this patient’s heart over the next 25 minutes. (14) Unfortunately, this patient succumbed to cardiac tamponade because of perforation of one of the cardiac veins by multiple intracardiac injections that had been injected in order to resuscitate him.  However, Zoll managed to successfully pace the heart of another 65 year old man with similar episodes of ventricular standstill for 5 days by external electrical stimulation. At the end of the fifth day, the patient reached an immediate idioventricular rhythm of 44 beats per minute and was discharged. (13)

 

In an epochal publication in 1952, Zoll described cardiac resuscitation via electrodes on the bare chest with 2-milli second duration pulses of 100-150 volts across the chest, at some 60 stimuli per minute. This initial clinical description provided the impetus for the extensive evaluation of pacing and the recognition by the medical profession and the public that the asystolic heart could be stimulated to beat. This represented the foundation on which all future developments lie. (14)










Zoll demonstrating his external pacemaker, from the mid-1950s

















10. Mid 1950s. Heart paced through an external pulse generator and internal leads




During the mid 1950s, the early years of open heart surgery, post-operative complete heart block proved to be a particularly complex dilemma for cardiac surgeons. External electric stimulation could not be used in these patients as they required continuous stimulation for prolonged periods of time. Dr W. Lillehei, Dr W. Weirich and their colleagues, working at the University of Minnesota Medical School set out to develop a better system. Also involved with them were engineers from Medtronic, one of the world’s famous firms in pacemaker technology at present. By 1957, the research team discovered that by combining a pulse generator with a wire electrode attached directly to the heart of a dog, it could be possible to control the heart rate. (15, 11)

 

On 30^th January 1957, Lillehei used this technique to pace the heart in the first human patient, a child with post-operative complete heart block after repair of a ventricular septal defect. The heart was activated by impulses lasting for 2 milliseconds at a voltage ranging from 1.5 to 4.5 volts much lower than that used by Zoll in pacing the heart by external electric stimuli. This method proved to be effective and was well tolerated by patients. (18)

 

Bakken’s pacemaker

Both Zoll and Lillehei used a particular physiological stimulator (device which transforms alternating current into direct current) to power their pacemakers. In 1957, following a power failure in Minneapolis and in the absence of backup power supply in hospitals in those days, most patients could not be paced. Lillehei turned to Earl Bakken and Medtronic for battery backup for the AC pacemakers. Over the next few weeks, Earl designed a new pacemaker that was miniaturized similar to the size of a packet of cigarette.  After testing the original Bakken pacemaker in the University of Minnesota’s laboratory, the newly apparatus was applied to a patient with heart block. The pacemaker spontaneously restored the child’s heart beat to normal and within a few days, the child’s heart resumed to a normal rhythm on its own and the pacemaker was consequently removed. This transistorized pacemaker conferred a flurry of advantages such as being less compact and it increased patient safety. (16)

 

 

 

 

11. 1958- Ake Senning and Rune Elmqvist - Birth  of Implantable pacemakers

 

The techniques of cardiac pacing employed by Lillehei could not be maintained for long because of the risk of peri-electrode infection, discomfort of carrying the pacemaker externally and ineffectiveness of pacemaker stimulation after a few months. The only way to prevent infection due to wires brought out of the body through skin incisions appeared to be the development of an implantable pacemaker. The initial attempts towards this endeavour were made by surgeon Ake Senning and engineer Elmqvist at the Karolinska Hospital in Sweden. (17)

 

The first pacemaker was implanted on 8^th October 1958 in a 43 year old man called Arne Larsson with complete heart block and Stokes-Adams attacks. However, the pacemaker broke down three hours after the implantation. A similar unit was implanted the following day but that did not work either. Finally, it was decided to abandon pacemaker therapy for this patient until better leads were developed. Fortunately, the Stokes-Adams attacks did not recur for the following three years when the patient received a second pacemaker implant. Eventually, he underwent 24 surgical interventions and survived till 2001 when he died of an unrelated malignancy. (18, 19)

 

Dr. Robert Rubio in Uruguay implanted a pacemaker unit similar in design as that implanted by Senning in a 41 year old lady on 3^rd February 1960. This unit considered to be the first successful pacemaker implant served its purpose until the patient died of sepsis about nine months later due to infection at the region of the thoracic incision. (20) This effort played a significant role in the creation of a pacemaker industry to supply pacemakers at a reasonable price and to serve as a financial support for research projects in cardiology and pacing in Uruguay. Manufacture of pacemakers began in 1970. (21) 

 

In 1960, William Chardack implanted pacemakers that were designed by Great bath. The doors were now opened for the pacemaker industry. The first implanted pacemakers were short-lived. Arne Larsson, himself eventually received a total of 27 pacemakers and survived for many years until he died in 2001 at the age of 86. (22, 23) Likewise, during that same period, in 1962 pacemaker implantation without thoracotomy was carried out by Ekestrom, Johannson and Lagergren who introduced the electrode transvenously with its tip in the right ventricle. (24) 

 

 

 

 

1970s - Advancement in implantable pacemakers

 

Lithium batteries

 

Technological innovations between 1973 and 1980 rendered obsolete the reliable pacemaker of 1970. The interest of manufacturers was now focused on improving the power source used in these pacemakers. Power supply was important because it determined longevity, reliability coupled with the type of battery to be used and thereafter the weight and volume of pacemaker. (25, 26) After multiple unsuccessful attempts with nickel-cadmium, zinc-mercury oxide batteries, the lithium battery was accepted as a long-lived power source.

 

Apart from ensuring a long pacemaker life, lithium halide batteries also allowed hermetic sealing of the pulse generators. It is this source which evolved over the next years as the preferred fuel alternative for implantable cardiac pacemakers. (27)

 

 

Nuclear energy - fuelled pacemakers  

During the 1970s, interest was directed towards the use of nuclear energy fuelled cardiac pacemakers. In these pacing devices, the energy of radioisotope decay which was mostly plutonium-238 was transformed to electrical energy. Even if these pacemakers ensured a remarkable lifespan (10 to 20 years) and reliability of 99%, they had the inherent drawback of radiation exposure, contamination of tissues with radioisotope in case of capsule leak, safety concerns of pacemaker disposal after use and cost implications. Thus these pacemakers could not attain widespread acceptance. A study conducted on 132 patients from 1973 to 1987 by Parsonnet et al revealed that the use of nuclear energy-fuelled pacemakers was not recommended. (28)

 

 

Programmability and integrated circuits

 

The first attempts towards programmability, that is to modify implantable pacemaker to work non-invasively were made as early as 1931. The General Electric Company manufactured a pacemaker in which the impulse rate could be varied by a magnetic “bistable” switch. (29) The patient could choose between a rate of either 70 per minute at rest or 100 per minute during activity by altering the switch with the help of an external magnet. After this no further notable developments took place in pacemaker programmability until 1972 when Medtronic introduced a programmable pacemaker that had a gear train attached to small bar magnets inside an implanted pulse generator. (30) In 1973, Medtronic introduced another pacemaker where the rate could be varied by radiofrequency signals transmitted through the programmer. After this numerous other programming systems appeared and soon programmability became a standard feature of pacemakers manufactured by all major companies. (31) Likewise, a hybrid circuit drew less power from the battery because it used power only when performing an action like opening or closing a switch. Hybrid circuitry made possible for manufacturers to downsize their generators while also providing reliability at no sacrifice of pacemaker longevity. (32)

 

Besides, in 1974, the Inter-Society Commission on Heart Disease Resources introduced a three-letter pacing-mode code for antibradycardia pacing systems to convey their functions by simple conversational means. (33) This mode-code system was further lengthened to a five-letter one in 1981 to incorporate programmability and antitachycardia functions. (34) This code has been adopted and modified by the North American Society of Pacing and Electrophysiology (NASPE) (now the Heart Rhythm Society) Mode Code Committee and the British Pacing and Electrophysiology Group (BPEG), and is designated the NASPE/BPEG generic (NBG) code. Since its introduction, the code has undergone multiple revisions; the last in 2002. (35)  Use of this code by medical and nursing intensive care personnel is recommended, both to facilitate communication and also to accurately describe pacemaker function.







Microlith-P Pacemaker and Model 2000 Programmer, from 1978.











 

 

 

13. 1980s-Dual Chamber Pacing

 

 

By 1980, almost all pacemakers relied on hybrid integrated circuitry and lithium batteries that would reliably manage the heartbeat for at least 8 years. As from 1985, some of the US pacemaker manufacturers began to compete in a new technological arena, dual-chamber pacing. Manufacturers and physicians argued that dual-chamber pacing, by providing better coordination between the contractions of the atria and ventricles, more closely emulated nature and conferred notable physiological benefits to the patient. (32) These benefits include haemodynamic advantages over ventricular pacing by coupling the timing of atrial and ventricular contraction. (36) The use of dual chamber pacing in the early 1980s proved to be complicated for doctors to understand and manage because of newer, programmable functions for dual-chamber pacing that now accompanied the more familiar functions for stimulus rate, amplitude and duration. (37)

 

As late as 1989, 75% of the pacemakers commercialized in the US market were still single-chamber devices that operated in VVI mode, a kind of pacing that has been around for more than 20 years. (38) Dual- chamber pacing carried expensive selling prices compared to single-chamber pacemakers.

 

 

 

 

14.  1990s  

The use of pacemakers has continued to grow during the 1990s; unfortunately estimates of the number of implantations vary significantly, ranging from 192,000 to 317,000 for 1997. The rise in the number of pacemaker implantations in the 1990s was due to 3 main reasons. First, older people are at highest risk of cardiac arrhythmias and the population over the age of 65 grew by 11% between 1990 and 1999. Secondly, cardiologists were now entirely well-acquainted with the symptoms and ECG indications of the common forms of bradycardia and were treating a higher proportion of those with slow heart beats. Finally the addition of one accepted indication for implantation, pacing for AV block caused by a new invasive technique called catheter ablation, marginally increased the number of implantations annually. (39, 40)

 

In more than 85% of new cases, the patients received pacemakers for “traditional” indications: heart block, sick sinus syndrome and bradycardia caused by drug treatment. The more exotic indications like anti-tachycardia pacing, accounted for no more than 4% of new implantations, partially because of cost-effectiveness analyses either had not been carried out or did not support pacemaker. Most physicians clearly perceived the pacemaker as a device for which the accepted uses were well established. (41) A survey by Bernstein and Parsonnet in 1997 revealed that on a large scale, surgeons who were older than other pacemaker physicians had withdrawn from the field of pacing during the 1990s. Cardiologists now consisted of more than two thirds of the implanter community and in 80% of cases they implanted dual-chamber pacemakers. (42)
















Guidant Model 2901 Programmer, from 1997.








 

 

 

15.  2000s and beyond

 

Indications for pacemaker therapy have increased remarkably in the past 45 years and at present include the treatment of bradyarrhythmias and electrical therapy of tachyarrhythmias, certain types of syncope and advanced heart failure. Current pacemaker devices include multi-chamber pacemakers, rate responsive units capable of pacing, cardioversion and defibrillation. (43) The decision to implant a pacemaker in a patient with abnormal atrioventricular node (AV) conduction depends on the manifestation of symptoms linked to bradycardia or ventricular arrhythmias and their prognostic implications. Observational studies over the years strongly indicate that permanent pacing improves survival with patients with complete AV block, especially if syncope has occurred. (44-47)

 

Although sinus node dysfunction is the commonest reason for pacemaker implantation, permanent pacing in these patients may not improve survival, despite symptom reduction and improvement in quality of life. (48-50) A recent randomized trial revealed that the risk of atrial fibrillation reappearance decreases with dual-chamber pacing compared with ventricular-based pacing in patients with sinus node dysfunction. (51)

 

 

 

 

Conclusion

 

Pacemakers have seen remarkable advancements ever since their inception. Recent developments include the implantable cardioverter defibrillator during which antibradycardia and antitachycardia pacing is combined with defibrillation capacity. With the use of pacemakers for cardiomyoplasty and cardiac resynchronization therapy pacemaker use is no longer restricted to controlling heart rate. Year after year, pacemakers have witnessed massive technological advancements, sophistication and better patient acceptance and reliance thereby instilling an aura of hope for a healthier and prolonged life for its users.

 

 

 

 

 

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Other resources

 

http://www.biotele.com/pacemakers.htm

 

http://www.medtronic.com/your-health/bradycardia/device/

 

http://www.spiritus-temporis.com/artificial-pacemaker/

 

http://www.springerlink.com/content/l635447254m6473r/ (History of Development of the Manufacture of Implanted Pacemakers: Plans and Reality)

 

http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01636350 (The Evolution of the pacemaker)

 

The Bionic Human: Medical Devices and How They are Powered. http://www.youtube.com/watch?v=Hk-gdpXjito

 

 

 

 

 

 

 

 

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