Pacemaker

Excerpt

The true beginning of the concept of a pacemaker began over 200 years ago. In the late 1700s, Luigi Galvani discovered that he could cause contraction of a frog heart simply by passing an electrical current through the heart. This concept was further realized nearly 100 years later with the first successful resuscitation of a child by Guilliame de Boulogne utilizing electricity. He was able to accomplish this by introducing an electrical current to the patient's chest with a return electrode on the leg after a drowning. After this feat, many successful resuscitations were reported, leading to the term "artificial cardiac pacemaker" by Dr. Hyman in 1932.

Pacemakers are adjustable artificial electrical pulse generators, frequently emitting a pulse with a duration between 0.5 and 25 milliseconds with an output of 0.1 to 15 volts, at a frequency up to 300 times per minute. The cardiologist or pacemaker technologist will be able to interrogate and control the pacing rate, the pulse width, and the voltage, whether the device is temporary or permanent. Pacemakers are typically categorized as external or internal. The external variety is almost always placed for temporary stabilization of the patient or to facilitate some type of surgical procedure. The implantable type is usually permanent and often, significantly more complex than the temporary, external variety.

Pacemakers are one type of cardiac implantable electronic devices (known as CIED). This broad category also includes implantable cardioverter-defibrillators (ICDs). Collectively, this group of devices was first introduced in the 1950s, shortly after the advent of the transistor. As technology has improved, so has the pacemaker device. The first implantable ICD was developed in 1980, and since that time, it has become more difficult to differentiate between pacemakers and ICDs. This is because every ICD currently implanted has an anti-bradycardia pacing function. It is critical for the patient and any health care provider to understand which device has been implanted to prevent unnecessary ICD therapy. This is most likely to occur with any electromagnetic interference (EMI) and could lead to activation of the device (if it is an ICD). Most types of CIED use several insulated lead wires with non-insulated tips that are implanted in the heart, either by percutaneous vein insertion or directly by a cardiac surgeon. Cardiac pacemakers are made up of two parts: the pulse generator and the leads or electrodes.

The North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and Electrophysiology Group (BPEG) jointly developed a generic pacemaker code, utilized worldwide, that would allow providers and manufacturers to describe the characteristics of the device. This was last updated in 2002 and is shown below in the Pacemaker Table.

The first letter in the code indicated which chamber is paced; the second letter indicates which chamber is being sensed by the device; the third letter indicates if there is a response to sensing; the fourth position indicates whether the device will modulate or change the programmed rate independent of the patient's cardiac activity, for example, with exercise; the fifth and last letter of the code indicates additional multisite pacing. The last two letters of the code (in the fourth and fifth position) are rarely used in typical nomenclature.

The latest generation of pacemakers have many capabilities. The simplest settings are AAI and VVI. The AAI mode paces and senses in the atrium and each sensed event triggers the generator to fire within the P wave. The VVI mode paces and senses the ventricle and is suppressed by a sensed ventricular event.