pacemaker

pacemaker
Name	Pacemaker
Caption	A cardiac pacemaker implanted in the chest.
Specialty	Cardiology, Cardiac electrophysiology
Inventor	John Hopps, Rune Elmqvist, Wilson Greatbatch
First use	1958
Related	Implantable cardioverter-defibrillator, Cardiac resynchronization therapy

pacemaker. A pacemaker is a small, implantable medical device that uses electrical impulses to regulate the beating of the heart. Primarily used to treat bradycardia and other cardiac arrhythmias, it ensures the heart maintains an adequate rate and rhythm. Modern devices are highly programmable and can respond to the body's physiological demands.

History

The development of the pacemaker involved key contributions from multiple pioneers and institutions. Early external devices were pioneered by John Hopps in Canada and Paul Zoll in the United States. The first fully implantable pacemaker was created by Rune Elmqvist and surgeon Åke Senning, and implanted in Sweden in 1958. A critical breakthrough came from Wilson Greatbatch, who invented the long-lasting, implantable lithium-iodine battery. Subsequent decades saw miniaturization and the integration of advanced microprocessor technology, leading to today's sophisticated devices developed by companies like Medtronic, Boston Scientific, and Abbott Laboratories.

Medical uses

Pacemakers are indicated for a variety of cardiac rhythm disorders. The primary indication is symptomatic bradycardia, which can arise from sick sinus syndrome or atrioventricular block. They are also used to prevent tachycardia in conditions like long QT syndrome and to manage heart failure through cardiac resynchronization therapy. Devices may be prescribed following certain cardiac surgeries or ablation procedures that risk damaging the heart's conduction system. Decisions are guided by guidelines from the American College of Cardiology and the American Heart Association.

Types and components

Pacemakers are categorized by their chamber involvement: single-chamber, dual-chamber, and biventricular systems. The main components include a hermetically sealed titanium or stainless steel generator housing the battery and circuitry. One or more insulated leads, containing electrodes, are threaded through the venous system to contact the myocardium of the right atrium, right ventricle, or coronary sinus. Modern devices often include sensors for activity and minute ventilation to provide rate-responsive pacing. Magnetic resonance imaging conditional devices have special filtering to allow safer scanning.

Implantation procedure

Implantation is typically a minor surgical procedure performed under local anesthesia in a cardiac catheterization laboratory or operating room. Access is most commonly gained via the subclavian vein or cephalic vein in the pectoral region. Using fluoroscopy for guidance, the leads are advanced into the heart and secured. Their positions are tested for electrical parameters like threshold and impedance. The generator is then connected and placed in a subcutaneous pocket, often below the clavicle. The procedure is overseen by a cardiac electrophysiologist and a specialized team from the Mayo Clinic or similar centers.

Function and programming

Pacemakers function by sensing intrinsic cardiac electrical activity and delivering stimuli when the heart's own rate falls below a programmed lower limit. This is described by a standardized NBG Pacemaker Code. Programming is performed non-invasively using a radiofrequency programmer from the manufacturer. Parameters such as base rate, atrioventricular delay, and sensor settings can be adjusted. Advanced algorithms manage mode switching during atrial fibrillation and minimize unnecessary right ventricular pacing. Data on device performance and patient arrhythmia episodes are stored and can be transmitted remotely via transtelephonic monitoring systems.

Complications and considerations

While generally safe, pacemaker implantation carries risks including hematoma, pneumothorax, cardiac tamponade, and infection. Lead-related issues, such as dislodgement, fracture, or venous thrombosis, may occur. Long-term considerations include battery depletion, typically after 5-15 years, requiring generator replacement. Electromagnetic interference from sources like arc welding or metal detectors can temporarily affect function. Patients require regular follow-up at clinics like the Cleveland Clinic. End-of-life decisions regarding device deactivation involve ethics consultations, often referencing principles from the Hastings Center.

Category:Medical devices Category:Cardiology