Artificial pacemaker

This article is about a medical device which electrically stimulates the heart. For a similar device that stimulates the brain, see brain pacemaker.

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.

History of the implantable pacemaker

The first external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950. A substantial external device, it was somewhat crude and painful to the patient in use. A number of inventors, including Paul Zoll, made smaller but still bulky external devices in the following years. The pacemakers built in the late 1950s were bulky, relied on external electrodes, and had to be plugged into a wall outlet. External electric shocks were frequently too traumatic for young heart block patients, and the AC-operated pacemaker could fail during a power blackout.

The first implantation into a human was made in 1958 by a Swedish team using a pacemaker designed by Rune Elmqvist and Åke Senning. 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.

Devices constructed by the American Wilson Greatbatch entered use in humans from April 1960 following extensive animal testing. The first patient lived for a further 18 months. The early devices suffered from battery problems - every patient required an additional operation every 24 months to replace the batteries. 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 Berkowits and Sheldon Thaler of American Optical, Geoffrey Wickham of Telectronics Australia, Walter Keller of Cordis Corp. of Miami, Hans Thorander who joined previously mentioned Rune Elmquist of Elema-Schonander in Sweden, Janwillem Van den Berg of Holland and Manuel A. Villafaña of Cardiac Pacemakers Inc.

Pacemakers require wires (called leads) to both send the pacing pulses to the heart and sense the intrinsic rhythm of the heart. The first pacemakers required these leads to be placed surgically on the outer surface of the heart. In the mid 1960s, the first transvenous leads were placed. This allowed the placement of pacemakers without opening the thoracic cavity and therefore without the use of general anaesthesia.

The first American-made nuclear-powered pacemaker was developed and implanted by Victor Parsonnet at Newark Beth Israel Medical Center in Newark, New Jersey.

The first pacemaker implanted into an infant was July 26, 1974 to Jason A. Haines when he was 16 hours old.

Applications

Artificial pacemakers can be used in order to help with and/or treat these conditions:

Arrhythmias - an abnormal heartbeat
Sick sinus syndrome - when the sinoatrial node does not fire properly to contract the heart

Methods of pacing

External pacing

External pacemakers can be used for initial stabilization of a patient, but implantation of a permanent internal pacemaker is usually required for most conditions. External cardiac pacing is typically performed by placing two pacing pads on the chest wall. Usually one pad is placed on the upper portion of the sternum, while the other is placed along the left axilla, near the bottom of the rib cage. When an electrical impulse goes from one pad to the other, it will travel through the tissues between them and stimulate the muscles between them, including the cardiac muscle and the muscles of the chest wall. Electrically stimulating any muscle, including the heart muscle, will make it contract. The stimulation of the muscles of the chest wall will frequently make those muscles twitch at the same rate as the pacemaker is set.

It was first invented by Canadian doctor John Hopps in 1950. He studied as an electrical engineer at the University of Manitoba.

Pacing the heart via external pacing pads should not be relied upon for an extended period of time. If the person is conscious, he or she may feel discomfort due to the frequent stimulation of the muscles of the chest wall. Also, stimulation of the chest wall muscles does not necessarily mean that the heart is being stimulated as well.

Temporary internal pacing

An alternative to external pacing is the temporary internal pacing wire. This is a wire that 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. Temporary internal 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.

Permanent pacemaker placement

Placement of a permanent 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.

Basic pacemaker function

Modern pacemakers all have two functions. They listen 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 heart with a set amount of energy, measured in joules.

Pacemaker naming code

The NASPE/BPEG generic (NPG) code is a pacemaker naming convention originally developed in 1974 that uses a 3-5 letter code to describe the main features of an artificial pacemaker. Each of the 5 positions signifies a particular aspect of pacemaker functionality. Using this scheme, a designation of VATOO would describe, for example, a pacemaker that sensed the atria and paced the ventricles in a triggered mode with no rate response or multisite pacing.

Position	I	II	III	IV	V
Category	Chamber(s) Paced	Chamber(s) Sensed	Response to Sensing	Rate Response	Multisite Pacing
Code	O = none, A = atrium, V = ventricle and D = dual (A + V)	O = none, A = atrium, V = ventricle and D = dual (A + V)	O = none, T = triggered, I = inhibited and D = dual (T + I)	O = none, R = rate modulation	O = none, A = atrium, V = ventricle and D = dual (A + V)
Manufacturer's designation only	S = single (A or V)	S = single (A or V)

Table I. The Revised NASPE/BPEG Generic Code for Antibradycardia Pacing

Bi-Ventricular Pacing (BVP)

A bi-ventricular 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 has three leads, one in the Atrium, one in the right ventricle, and the last 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.^2,3

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 trial⁴ 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 what is available in standard pacemakers. This extra wire is implanted to improve symptoms in patients with severe heart failure.

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 for sudden cardiac death. An ICD has the ability to treat many types of heart rhythm disturbances by means of pacing, cardioversion,or defibrillation.

References

1. Berstein, A. D., Daubert, J., Fletcher, R. D., Hayes, D. L., Luderitz, B., Reynolds, R. D., Schoenfeld and M. H., Sutton, R.: The Revised NASPE/BPEG Generic Code for Antibradycardia, Adaptive-Rate, and Multisite Pacing. Journal of Pacing and Clinical Electrophysiology, Volume 25, No. 2 (2002). ^*

2. 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.

3. 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

4. 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. ^*

External links

Cardiac electrophysiology | Embedded systems | Implants | Canadian inventions

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