1. Anything that influences the rate and rhythm of occurrence of an activity or process.
2. In cardiology, a specialized cell or group of cells that automatically generates impulses that spread to other regions of the heart. The normal cardiac pacemaker is the sinoatrial node, a group of cells in the right atrium near the entrance of the superior vena cava.
SYN: SEE: pacer
3. A generally accepted shorthand term for an artificial cardiac pacemaker.
SEE: artificial cardiac pacemaker
PACEMAKER A magnet placed directly on top of a pacemaker, to check its function
A device that can trigger mechanical contractions of the heart by emitting periodic electrical discharges. Pacemakers are used most often to treat patients with symptomatic slow heart rates or long pauses between heart beats (such as patients with third-degree heart block, symptomatic second-degree heart block, bifascicular block with first-degree heart block, carotid sinus hypersensitivity, and tachybrady syndrome) and slow ventricular response rates. Occasionally they also are used for other purposes, such as to capture and override some tachyarrhythmias.
PACEMAKER Pacemaker defibrillator beneath the skin
All artificial cardiac pacemakers have a pulse generator (a device that gives off an electrical impulse at prescribed intervals), electrical leads (which transmit the impulse to the myocardium), and a battery (usually made of lithium iodide) encased in titanium and implanted surgically in a subcutaneous pocket (usually in the chest). The pacing leads are threaded through a subclavian vein into the right heart, with the primary lead placed in the ventricle, and the second lead (if required) in the atrium. For biventricular pacing, a third lead is placed in the left ventricle. A biventricular pacemaker also may have a built-in cardiovertor-defibrillator. Pacemakers typically have the ability to pace the ventricle, the atrium, or both; to sense electrical discharges coming from cardiac chambers; and to respond to sensed beats. Most pacemakers in the U.S. also are programmable, and many are rate responsive. The features of each pacemaker are identified in its three- to five-letter NASPE/BPG code (developed and revised by the North American Society of Pacing & Electrophysiology and the British Pacing & Electrophysiology Group). The five positions describe the pacer's functions as follows:
A pacemaker that stimulates breathing by delivering electrical pulses to both phrenic nerves from an external radio transmitter to an implanted receiver. It is used in patients with quadriplegia or sleep apnea.
SEE: radiofrequency electrophrenic respiration
A rate-adaptive artificial cardiac pacemaker. It senses and paces both atrial and ventricular events, triggering the atrioventricular (AV) interval so that AV synchrony is maintained over a wide range of heart rates. This type of pacing has reduced the incidence of pacemaker syndrome. It is the most versatile pacing device used.
SEE: pacing code; SEE: pacemaker syndrome
An artificial cardiac pacemaker that senses both atrial and ventricular events but can inhibit only atrial impulses. This type of pacing is used only when atrioventricular conduction is intact. It may be suitable when frequent atrial tachyarrhythmias cause rapid ventricular rates.
An artificial cardiac pacemaker designed to permit its electrical output to be inhibited by the heart's electrical impulses. This decreases the chances for the pacemaker to induce discomfort or dysrhythmias.
An artificial cardiac pacemaker that stimulates both atria and ventricles sequentially.
SYN: SEE: atrioventricular sequential pacemaker
Any endogenous cardiac pacemaker other than the sinoatrial node.
An artificial cardiac pacemaker that stimulates the heart at a predetermined rate.
SEE: Internal pacemaker
An artificial cardiac pacemaker placed within the body.
SYN: SEE: implantable pacemaker
An artificial cardiac pacemaker implanted directly into the right ventricular apex. Unlike conventional pacemakers, which use wires to carry electrical signals from a surgically-implanted pulse generator placed in the upper chest, a leadless pacemaker is anchored directly into the heart by a catheter that ferries the device there from an artery.
An artificial cardiac pacemaker for permanent cardiac pacing. The leads are usually inserted transvenously through the subclavian or cephalic veins with leads positioned in the right atrium for atrial pacing or in the right ventricular apex for ventricular pacing. The leads are connected to the pulse generator, which is implanted in a subcutaneous pocket below the clavicle.
A permanent artificial cardiac pacemaker in which one or more settings can be changed electronically.
An artificial cardiac pacemaker that senses changes in the body's need for adjustment of the cardiac rate as can occur in sleeping, waking, sitting, walking, or running. The device alters cardiac rate by sensing body motion, changes in breathing, or slight changes in blood temperature, which improves the quality of life for active patients. It is also called a rate-adaptive pacemaker.
An artificial cardiac pacemaker for temporary cardiac pacing, as during cardiac surgery and emergencies. The device consists of an electrode catheter inserted transvenously in the right ventricular apex that receives impulses from an external generator.
An artificial cardiac pacemaker that is located outside the body. The electrodes for delivering the stimulus are located on the chest wall.
SYN: SEE: transthoracic pacemaker
A cardiac arrhythmia in which the site of origin of the pacemaker stimulus shifts from one site to another, usually from the atrioventricular node to some other part of the atrium.
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