Artificial pacemaker
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A pacemaker (or artificial pacemaker, so as not to be confused with the heart's natural pacemaker) is a medical device designed to regulate the beating of the heart. The purpose of an artificial pacemaker is to stimulate the heart when either the heart's native pacemaker is not fast enough or if there are blocks in the heart's electrical conduction system preventing the propagation of electrical impulses from the native pacemaker to the lower chambers of the heart, known as the ventricles.
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[edit] History of the artificial pacemaker
In 1889 J A McWilliam reported in the British Medical Journal of his experiments in which application of an electrical impulse to the human heart in asystole caused a ventricular contraction and that a heart rhythm of 60-70 beats per minute could be evoked by impulses applied at spacings equal to 60-70/minute.[1]
In 1926 Albert Hyman created an electro-mechanical instrument which may have been the first true external artificial pacemaker.[2]
In 1928 anaesthetist Mark Lidwell [assisted by physicist Edgar Booth] devised a device which "ran on alternating current and required a needle to be inserted into the patient's ventricle". "He used electrical stimulation of the heart to save the life of a child born in cardiac arrest". Lidwell reported his work to the Third Congress of The Australian Medical Society in 1929, but little more is known of his work.[citation needed]
An external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950 based upon observations by cardio-thoracic surgeon Wilfred Bigelow at Toronto General Hospital . A substantial external device using vacuum tube technology to provide transcutaneous pacing, it was somewhat crude and painful to the patient in use and, being powered from an AC wall socket, carried a potential hazard of electrocution of the patient by inducing ventricular fibrillation.
A number of innovators, including Paul Zoll, made smaller but still bulky transcutaneous pacing devices in the following years using a large rechargeable battery as the power supply.
In 1957 engineer Earl Bakken of Minneapolis, Minnesota, produced the first wearable external pacemaker for a patient of Dr. C. Walton Lillehei. The pacemaker, housed in a small plastic box, had controls to permit adjustment of pacing heart rate and output voltage and was connected to electrode leads which passed through the skin of the patient to terminate in electrodes attached to the surface of the myocardium of the heart.
The first clinical implantation into a human of a fully implantable pacemaker, was in 1958 at the Karolinska University Hospital in Solna, Sweden, using a pacemaker designed by Rune Elmqvist and Åke Senning connected to electrodes attached to the myocardium of the heart by thoracotomy . The device failed after three hours. A second device was then implanted which lasted for two days. The world's first implantable pacemaker patient, Arne Larsson, survived the first tests and died in 2001 after having received 22 different pacemakers during his lifetime. In February 1960, an improved model relying on better materials was implanted in Montevideo, Uruguay. That device lasted until the patient died of other ailments, 9 months later. The early Swedish-designed devices used rechargeable batteries, which were charged by an induction coil from the outside.
In 1959 temporary transvenous pacing was first demonstrated by Furman et al in which the catheter electrode was inserted via the patient's basilic vein. "Furman S, Schwedel JB : An intracardiac pacemaker for Stokes-Adams Seizures.(see Stokes-Adams attack). N Eng J Med 1959; 261:943-948"
Implantable pacemakers constructed by the American Wilson Greatbatch entered use in humans from April 1960 following extensive animal testing. The Greatbatch innovation varied from the earlier Swedish devices in using primary cells (mercury battery) as the energy source. The first patient lived for a further 18 months.
The first use of transvenous pacing in conjunction with an implanted pacemaker was performed at the Hopital Tenon of Paris, France, in 1963 by Dr Jean-Jacques Welti. The transvenous, or pervenous, procedure involved incision of a vein into which was inserted the catheter electrode lead under fluoroscopic guidance, until it was lodged within the trabeculae of the right ventricle. This method was to become the method of choice by the middle 1960's.[3]
The preceding implantable devices all suffered from the unreliability and short lifetime of the available primary cell technology which was mainly that of the mercury battery. In the late 1960's several companies, including ARCO in the USA, developed isotope powered pacemakers, but this development was overtaken by the development in 1970 of the lithium-iodide cell by Wilson Greatbatch. Lithium-iodide or lithium anode cells became the standard for future pacemaker designs.
A further impediment to reliability of the early devices was the diffusion of water vapour from the body fluids through the epoxy resin encapsulation affecting the electronic circuitry. This phenomenon was overcome by encasing the pacemaker generator in an hermetically sealed metal case, initially by Telectronics of Australia in 1969 followed by Cardiac Pacemakers Inc of Minneapolis in 1972. This technology, using titanium as the encasing metal, became the standard by the mid 1970's.
Others who contributed significantly to the technological development of the pacemaker in the pioneering years were Bob Anderson of Medtronic Minneapolis, Geoffrey Davies of Devices Ltd in England, Barouh Berkovits and Sheldon Thaler of American Optical, Geoffrey Wickham of Telectronics Australia, Walter Keller of Cordis Corp. of Miami, Hans Thornander who joined previously mentioned Rune Elmquist of Elema-Schonander in Sweden, Janwillem van den Berg of Holland and Manuel A. Villafaña and Anthony Adducci of Cardiac Pacemakers Inc.(Guidant)
[edit] Applications
Artificial pacemakers can be used in order to help with and/or treat these conditions:
- Sinus node dysfunction - when the sinoatrial node does not fire properly to contract the heart
- Bifascular block, Trifascicular block, or Complete heart block.
- Stokes-Adams attack involving disruption of conduction between the sinoatrial node and the atrioventricular node
[edit] Methods of pacing
[edit] Transcutaneous pacing
Transcutaneous pacing (TCP), also called external pacing, is recommended for the initial stabilization of hemodynamically significant bradycardias of all types. The procedure is performed by placing two pacing pads on the patient's chest, either in the anterior/lateral position or the anterior/posterior position. The rescuer selects the pacing rate, and gradually increases the pacing current (measured in mA) until electrical capture (characterized by a wide QRS complex with a tall, broad T wave on the ECG) is achieved, with a corresponding pulse. Pacing artifact on the ECG and severe muscle twitching may make this determination difficult. External pacing should not be relied upon for an extended period of time. It is an emergency procedure that acts as a bridge until transvenous pacing or other therapies can be applied.
[edit] Transvenous pacing
Transvenous pacing, or temporary internal pacing, is an alternative to transcutaneous pacing. A wire is placed under sterile conditions via a central venous catheter. The distal tip of the wire is placed into either the right atrium or right ventricle. The proximal tip of the wire is attached to the pacemaker generator, outside of the body. Transvenous pacing is often used as a bridge to permanent pacemaker placement. Under certain conditions, a person may require temporary pacing but would not require permanent pacing. In this case, a temporary pacing wire may be the optimal treatment option.
[edit] Permanent pacing
Permanent pacing with an implantable pacemaker involves placement of one or more pacing wires within the chambers of the heart. One end of each wire is attached to the muscle of the heart. The other end is screwed into the pacemaker generator. The pacemaker generator is a hermetically sealed device containing a power source and the computer logic for the pacemaker.
Most commonly, the generator is placed below the subcutaneous fat of the chest wall, above the muscles and bones of the chest. However, the placement may vary on a case by case basis.
The outer casing of pacemakers is so designed that it will rarely be rejected by the body's immune system. It is usually made of titanium, which is very inert in the body.
[edit] Basic pacemaker function
Modern pacemakers usually have multiple functions. The most basic form listens to the heart's native electrical rhythm, and if the device doesn't sense any electrical activity within a certain time period, the device will stimulate the vetricles of heart with a set amount of energy, measured in joules. The more complex forms include the ability to sense and/or stimulate both the atrial and ventricular chambers.
| I | II | III | IV | V |
|---|---|---|---|---|
| Chamber(s) paced | Chamber(s) sensed | Response to sensing | Rate modulation | Multisite pacing |
| O = None | O = None | O = None | O = None | O = None |
| A = Atrium | A = Atrium | T = Triggered | R = Rate modulation | A = Atrium |
| V = Ventricle | V = Ventricle | I = Inhibited | V = Ventricle | |
| D = Dual (A+V) | D = Dual (A+V) | D = Dual (T+I) | D = Dual (A+V) |
[edit] Biventricular Pacing (BVP)
A biventricular pacemaker, also known as CRT (cardiac resynchronization therapy) is a type of pacemaker that can pace both ventricles (right and left) of the heart. By pacing both sides of the heart, the pacemaker can resynchronize a heart that does not beat in synchrony, which is common in heart failure patients. CRT devices have three leads, one in the atrium, one in the right ventricle, and a final one is inserted through the coronary sinus to pace the left ventricle. CRT devices are shown to reduce mortality and improve quality of life in groups of heart failure patients.[5][6]
[edit] Advancements in pacemaker function
When first invented, pacemakers controlled only the rate at which the heart's two largest chambers, the ventricles, beat.
Many advancements have 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.
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.
The DAVID trials[7] have shown that unnecessary pacing of the right ventricle can lead to heart failure. New devices can keep the amount of right ventricle pacing to a minimum and thus prevent worsening of the heart disease.
Another 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 more physiological pacing than available in standard pacemakers. The extra wire is implanted to improve symptoms in patients with severe heart failure.
[edit] Devices with pacemaker function
Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter-defibrillators) are implanted. These devices are often used in the treatment of patients at risk from sudden cardiac death. An ICD has the ability to treat many types of heart rhythm disturbances by means of pacing, cardioversion, or defibrillation.
| I | II | III | IV |
|---|---|---|---|
| Shock chamber | Antitachycardia pacing chamber | Tachycardia detection | Antibradycardia pacing chamber |
| O = None | O = None | E = Electrogram | O = None |
| A = Atrium | A = Atrium | H = Hemodynamic | A = Atrium |
| V = Ventricle | V = Ventricle | V = Ventricle | |
| D = Dual (A+V) | D = Dual (A+V) | D = Dual (A+V) |
| ICD-S | ICD with shock capability only |
| ICD-B | ICD with bradycardia pacing as well as shock |
| ICD-T | ICD with tachycardia (and bradycardia) pacing as well as shock |
[edit] See also
[edit] References
- ^ Electricity and the heart: a historical perspective. Heart Rhythm Foundation. [1]
- ^ Furman S et al. Hyman's pacemaker. Heart Rhythm Foundation.[2]
- ^ Jean-Jacques Welti:biography.Heart Rhythm Foundation.[3]
- ^ Bernstein A, Daubert J, Fletcher R, Hayes D, Lüderitz B, Reynolds D, Schoenfeld M, Sutton R (2002). "The revised NASPE/BPEG generic code for antibradycardia, adaptive-rate, and multisite pacing. North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group". Pacing Clin Electrophysiol 25 (2): 260-4. PMID 11916002.
- ^ Cleland JGF, Daubert J-C, Erdmann E, et al; the Cardiac Resynchronization — Heart Failure (CARE-HF) Study Investigators. The effect of cardiac resynchronization on morbidity and mortality in heart failure. N Engl J Med. 2005 March 7 Fulltext. PMID 15753115.
- ^ Bardy GH, Lee KL, Mark DB, et al for the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) Investigators. Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure. N Engl J Med 2005; 352:225–237
- ^ 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: 3115–3123. [4]
- ^ a b Bernstein A, Camm A, Fisher J, Fletcher R, Mead R, Nathan A, Parsonnet V, Rickards A, Smyth N, Sutton R (1993). "North American Society of Pacing and Electrophysiology policy statement. The NASPE/BPEG defibrillator code". Pacing Clin Electrophysiol 16 (9): 1776-80. PMID 7692407.
[edit] External links
- Pacemaker Patient Information at Arrhythmia Alliance
